LRF or attempting them

[Terminal Moraine]

Very interesting, as always, John. It looks as though GFS is dealing with the first of these tropical storms on the 06z run looking at the projected charts around the 29th of this month.

Something I will be following with almost fanatical zeal over the next few days/weeks.

[johnholmes]

No 27 issued 21 August for the period 31 August – 10 September 2009

General comment

Partly through being on holiday and partly due to continuing pc problems I've not been able to keep as close an eye as usual on the various parameters I use.

Tropics

ENSO update 20 August

The full is below

http://iri.columbia..../technical.html

Some comments from it

'As of mid-August 2009, SSTs are above-average across much of the equatorial Pacific, indicative of weak El Niño conditions.

…' The emergence of weak El Niño conditions during June, July and August is often, but not always, followed by continued El Niño conditions of at least weak, if not greater, magnitude for the remainder of the calendar year and often into the initial months of the next calendar year.

.. For the current Aug-Sep-Oct season, nearly all (96%) are predicting El Niño conditions, and 4% predict ENSO-neutral conditions.

For December into February, all 16 models give either El Nino or neutral ENSO.

'… An alternative way to assess the probabilities of the three possible ENSO conditions is to use the mean of the forecasts of all models, and to construct a standard error function cantered on that mean.

… This method shows probabilities for El Niño at 80-95% for Aug-Sep-Oct and Sep-Oct-Nov, holding at about 80% throughout the rest of 2009, and then declining to near 50% during boreal spring 2010.'

AO over the past 7 days

As the two graphs show there has been some changes in the prediction of where the AO is going to be come early September.

NAO over the past 7 days

This has changed from a prediction, in the main, of above zero, to almost all now showing below zero.

NOAA comments over the past 7 days

They have mostly been reasonably happy, marking 3/5 for the whole 6-14 day period. They have had doubts about the models they use at that time frame though on how 'flat' or meridional the upper flow is going to be over N America.

NOAA 500 mb anomaly charts over the past 7 days

13 for 21-27 August and 20 for 28 August – 3 September

Obviously there are changes in the periods shown but the pattern is pretty much the same for the UK area with the deep upper low remaining over or very slightly west of the UK and a general westerly flow at 500mb.

EC-GFS 500mb anomaly charts over the past 7 days

On the left that issued on 14 for 24 August and on the right that from today (21) for 31 August

The pattern predicted through the week seems quite realistic and consistent.

EC and GFS T+240 charts over the past 7 days

See my notes at the start so these are not included this week.

But the 6 day 'scores' for the main models are in the link below

http://www.emc.ncep..../html/acz6.html

In general EC has, as usual, outscored the other models, although the Canadian one did far better over a 2-3 day period in the past week. By last evening (Thursday) NOAA were already tending to disbelieve the Canadian model again.

Summary

Most of the data shown above shows a mobile westerly upper flow. Nothing suggests any sign of prolonged settled weather into the start of the period. Quite what effect any further Tropical storms becoming involved with the Atlantic is impossible to predict, or even IF any will do so. Thus the probability of any settled spell, at this time, seems less likely rather than more likely into the period end.

Forecast for period 31 August – 10 September 2009

Cautionary note again!

Remember that none of the synoptic style charts; NOAA 500mb anomaly being the furthest, go beyond the beginning of the period. Only the Tropics, AO and NAO guidance data is in that time scale.

A start with unsettled as the theme and around normal to a touch below for the temperatures with only the SE corner likely to be much above at times. Rain or showers at times for all, especially the further NW you are in the UK. Quite windy in exposed western and northern areas as lows track near NW Scotland at times. In the far outlook then there is a prospect of a ridge developing in mid Atlantic and edging east, just how far east is too early to say.

It could all go wrong IF any major tropical storm gets into the Atlantic but its impossible in my view to predict what may happen with those this far ahead.

Edited August 21, 2009 by johnholmes

[Rob]

i'm guessing that i live in the best place weatherwise at the moment!

[johnholmes]

No 28 issued 28 August for period 7-17 September 2009

Tropics

Nothing from NOAA on the ENSO position since the last update on 20 August.

The latest NOAA update on 24 August

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) remain +0.5 to +1.5 above-average across much of the equatorial Pacific Ocean.

•Current observations and dynamical model forecasts indicate El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

AO over the past 7 days

There have been 3 days when the AO update has not been issued. Overall the idea of a peak at +1 or +2 then a dip towards zero has been a feature through the week.

NAO over the past 7 days

No matter which link I use nor can I find anything on the NAO since 2 August. However the general trend has shown a fall with the last one suggesting a rise above zero. This is the only one that suggests this happening.

NOAA comments over the past 7 days

They have been less than happy with their outputs over the week. Rarely giving even the 6-10 day charts more than 2/5.

They comment on the wide spread from various models although their own 500mb anomaly charts seem reasonably consistent over the whole area to me. I suspect the Tropics is much to blame. None of the models seem very sure of things in this period when tropical storms are more likely than at any other period.

The link to the 6 day 500mb prediction for the northern hemisphere is below

http://www.emc.ncep..../html/acz6.html

It shows that UK Met is having a pretty variable time with GFS actually being ahead of it most days and the usual ECMWF standard much of the time-ahead of the others, but not by much.

NOAA 500 mb anomaly charts over the past 7 days

These have shown the upper trough staying close by or even over the UK through their forecast period, (the start of mine). In that time the value of the 500mb contours is dropped by about 6DM over central UK. The 500mb flow is slightly more zonal than before with the trough near the UK less obvious than at the start. The flow is also fairly strong. I have just looked at that issued this evening, Friday) and its very different from anything before it. The –ve area is south of Greenland with a small +ve area SW of the UK, with some slight rise in contour heights over the country!

20 Aug for 28 Aug-3 September 27 Aug for 4-10 September

EC-GFS 500mb anomaly charts over the past 7 days

They have both gone along rather different lines to the NOAA 500mb charts. For much of the week each has extended the trough west of the UK further south thus causing the 500mb flow to be from south of west, NOAA show it as almost westerly. Both have also built the upper ridge over Europe, EC more than GFS. However the final chart today (Thursday) does show more of a westerly.

Their last charts are valid for 7 September, the day this lrf starts.

21 for 31 Aug 28 Aug for 7 September

EC and GFS T+240 charts over the past 7 days

Differences on some days but tending overall to favour low rather than high pressure as the dominant factor for the UK area.

Fri 12z issue 21 Aug for 31 Aug

The 30mb temperature curve continues its journey close to the expected average.

Summary

The NOAA synoptic charts show a different idea at 500mb to those from ECMWF and GFS, albeit NOAA are for 3-5 days later. The NOAA chart now shows a different set up this evening so I'm not sure what to make of it. No wonder NOAA are awarding such low marks to the models. NOAA has shown little trust in any of the model outputs. The AO and NAO updates have been less than regular. ENSO suggests little is changing at the moment in the Tropics.

Forecast for period 7-17 September 2009

With AO and NAO issues being sporadic over the period, NOAA charts suddenly showing a different scenario, ECMWF and GFS also changing over the past day or so, its one of the least clear outlooks I've had in a long time.

I think it's a case of deciding, for the start of the period, which synoptic guidance to follow, NOAA or the ECMWF/GFS version. By the end of the check ECMWF and GFS were reverting back to the idea of a mainly westerly flow so the weight of evidence points to the unsettled weather continuing. Again the NW-SE split. With high pressure never likely to be that far from southernmost areas then the SE quarter is going to have a better start to autumn than further north. Just where the surface high is going to be is difficult to decide, probably over Europe at times. Fairly disturbed Atlantic type weather dominating, for most of the time, the further north west you are. At least one active depression giving strong winds, if not gales, for exposed western and NW'ern parts, possibly the remains of an ex hurricane. Overall temperatures averaging just above normal in the SE, with some warm days, to near or just below in the NW. No sign of any really deep cold air penetrating to the far north in this forecast. But probably the odd night with at least a ground frost for northern areas.

Less confidence in this than usual.

Edited August 28, 2009 by johnholmes

[johnholmes]

No 29 issued 7 September for the period 17-27 September 2009

Tropics

The 30 day issue from NWS-31 August

30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2009

A WEAK EL NINO PERSISTED DURING AUGUST, WITH MONTHLY SEA SURFACE TEMPERATURE

(SST) DEPARTURES RANGING FROM +0.5C TO +1.5C ACROSS THE EQUATORIAL PACIFIC

OCEAN. SOME INCREASE IN SST ANOMALIES WAS EVIDENT AT THE END OF THE MONTH.

ALSO, CONVECTION WAS GENERALLY SUPPRESSED DURING THE MONTH OVER INDONESIA.

HOWEVER, IMPACTS ACROSS THE UNITED STATES FROM EL NINO ARE TYPICALLY WEAK

DURING SEPTEMBER, SO ENSO COMPOSITES WERE NOT CONSIDERED FOR THIS FORECAST.

There has been no ENSO update since 20 August from IRI

but this is the NOAA update on 31 August

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) remain +0.5 to +1.5 above-average across much of the equatorial Pacific Ocean.

•Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

Other indications from the Tropics suggest that ridge rather than trough conditions are likely in the UK area but with mixed signals about just where that trough may settle.

AO over the past 7 days

It picked out correctly the sharp rise and is now suggesting a fall, albeit with some uncertainty.

NAO over the past 7 days

In spite of a couple of days when this was not updating, hence the gap in the black line, it has generally suggested a rise in its more reliable time frame. At the end it is now suggesting perhaps a fall but its pretty uncertain by how much.

NOAA comments over the past 7 days

NOAA, again this week, remain unhappy with the overall model guidance for their area of concern.

Never marking higher than 3/5 and much of the time 2/5.

It might be an idea to see how their check of the 500mb models for the northern hemisphere is looking. Below is a copy of that for the 6 day period. A rather variable performance by them all, with ECMWF, until the end being just about the best of a not too inspiring bunch.

See comments in the summary.

NOAA 500 mb anomaly charts over the past 7 days

From its chart on 27 August for 4-10 September with a continuation of the strongish westerly 500mb flow it has, fairly consistently, over the past 7 days not only dropped that idea but brought in a largish +ve are east of the UK. The overall effect is to push the 500mb trough west and, not so much latterly, but to back the flow into the UK to a more SW'ly direction. Another effect is to raise the height at 500mb over the country by about 12DM. This is quite a large rise if you compare changes over any 7 day period previously. Even prior to the warmth of mid/late June, the contours only rose by about 9DM. Again see the comments section.

on 27 August for 4-10 September 3 for 11-17 September

EC-GFS 500mb anomaly charts over the past 7 days

They both showed a similar idea to the NOAA charts at first, a strongish 500mb mainly westerly flow into the UK. Much again as NOAA they both abandoned that idea and switched to +ve rises over/near the UK. Latterly there is a difference between ECMWF and GFS. Both persist with the +ve area but they have differing ideas on its position, crucial to what temperature levels might be and possibly also the overall weather pattern. ECMWF has this occurring to south and south east of the UK whilst GFS shows it more over and west of the UK. This gives a 500mb flow north of west rather than the ECMWF version of south of west. Again see the summary. That said, the one issued today, shows GFS very similar with ECMWF having shifted its 500mb ridge over/almost west of the UK.

28 Aug for 7 September 3 for 13 September

EC and GFS T+240 charts over the past 7 days

The overall trend from both models over the 7days has been similar. To create a chart with more emphasis on ridging across the Atlantic into NE Europe than for some time. The ECMWF for tonight has gone off this idea with a marked upper trough moving into the area where its had an upper ridge for the past several days. GFS is still showing more ridge than trough but with a possible break down on its way from the NW.

The 30mb temperature curve

Has shown a wish to cling to the average line as it starts its winter descent.

Summary

A lot to ponder over from above. Most of what I call the non synoptic influences, Tropics, AO and NAO seem to suggest less Atlantic activity to me. The synoptic longer term guidance, NOAA at 8-14 days taking us to the start of this forecast period, suggests ridge not trough in the upper pattern as the main feature. This seems to be supported, on a shorter time scale, by the ECMWF/GFS 500mb anomaly charts. Even the T+240 ECMWF and GFS have tended towards that solution.

There remains, at this time of the year, the Tropical storm 'pebble' to drop in the pond. Will there be one? I have read nothing anywhere which suggests that we get more than about 7-10 days warning of this occurring. Please correct me if I am wrong and point me to a link? There are two on the NOAA charts at the moment, one just leaving Africa and another east of the Gulf of Mexico. However neither is looking like disturbing the 14 day or so synoptic Atlantic pattern from what I've already discussed.

Forecast for period 17-27 September 2009

So an anticyclonic start with some 'summery' type weather for most central and southern areas. Even further north much less unsettled than currently but likely to start to see further systems near enough to make conditions less settled than further south.

Beyond that and its a question it seems, aside from the Tropical storm issue, of which high cell will be the dominant one-Euro or Azores/Atlantic. Probably the latter in my view with some suggestion that an upper trough may work round its northern flank to gradually spread more disturbed and autumnal type weather south in the latter part of the forecast period with that high pressure belt retreating WSW.

Edited September 4, 2009 by johnholmes

[bluearmy]

looking at the FI trends, i fear your assessment in the longer term is correct JH. and it may well be sooner rather than later.

[johnholmes]

the lrf will either be issued very late this evening or tomorrow-continuing pc problems or rather issues with soft ware since new hard disk put in

[johnholmes]

No 30 issued 11 September for the period 21—1 October 2009

Tropics

Nil IRI update since 20 August so far as I can see (anyone got a link that shows a later one – yes please?)

ENSO update on 8 September

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) remain +0.5 to +1.5 above-average across much of the equatorial Pacific Ocean.

•Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

AO over the past 7 days

It accurately predicted the fall at the start from 3 September and now suggests, first a further fall then a rise to above zero.

NAO over the past 7 days

This has gone for a rise, although later efforts suggest this is less certain before it tends to fall again.

NOAA comments over the past 7 days

They have had a variable week with the models. On Monday, after a variable few days, they gave 3/5 and 4/5 out to 14 days but today its back to 2/5 for both 6-10 and 8-14 day model watching.

NOAA 500 mb anomaly charts over the past 7 days

For much of the northern hemisphere the pattern suggested has been fairly consistent. The +ve area over/east of the UK has been moved to just SW of the country through the week. The 500mb flow into the UK is perhaps a touch more westerly at the end of this week than the beginning. There is a fall of about 6DM predicted to occur.

3 for 11-17 September 11 for 19-25

EC-GFS 500mb anomaly charts over the past 7 days

Over the period they started, see lhs, with a flow south of west and +ve areas over and east of the country. This continued for several days with an actual cut off high at 500mb showing over the country, more so on the EC with an upper low in the Iberia area. This has slowly been changed to the position you see on the rhs (for 21 September). This shows little sign of any +ve area around the UK with both showing the major feature as the upper low in the Greenland area as the main feature. Both have dropped contour heights over the UK but with the 500mb flow more south than north of west. EC more so than GFS. GFS also has a minor +ve area to the SW as well as the +ve area both show over Scandinavia.

EC and GFS T+240 charts over the past 7 days

They both started for Monday 14 September with ridging being the more dominant and with dissimilar shaped upper troughs north of the country. By the issue for Sunday 20 September the upper trough was now dominant. This more so with EC than GFS which holds the ridge idea much more so than EC does.

The 30mb temperature curve

This continues to show about the average for this time of the year, no noticeable departures.

Summary

Both sets of synoptic hemisphere charts suggest a flow at upper levels from around west (NOAA) or south of west (ECMWF/GFS). Remember the NOAA version is for several days after the EC/GFS issue. El Nino is expected to strengthen although this is unlikely to be having much if any impact at this time scale. Other Tropical forcings seem to suggest the possibility of high pressure being around, although its position seems rather uncertain. If this is so then the NOAA charts are a bit at odds with it. Possibly it is suggestive of a change through the forecast period. We have to remember it is still the hurricane season and there is often little more than 7-10 days warning of one getting into the Atlantic, way before the issue of any lrf. This one, being written on Saturday 12 September does not start until 21 September.

Forecast for period 21 September – 1 October

Starting off with the oft commented on NW-SE split. High pressure never that far away from the south with low pressure never far away from the NW. So a typical split with disturbed weather at times for all but less frequent and less marked the further south one lives in the UK. Probably one fairly active system with gales and heavy rain for the NW and affecting even the far south but with less vigour. Otherwise reasonably settled for much of the time in the far south with daytime temperatures at or above normal but with coolish nights at times and some mist or fog probable on one or two nights. Further north then near normal temperatures and occasionally below with a small risk of the odd night with air frost.

Late in the period then the settled weather for the far south does seem likely to extend further north. The mechanism for this probably the surface high to the south or southwest trying to ridge further NE, maybe a ridge into Scandinavia?

Edited September 14, 2009 by johnholmes

[NorthNorfolkWeather]

Thanks John,

Interesting how this NW/SE split is so persistent this year, in my neck of the woods we need the rain, as has been attested to on other topics, so roll on Autumn

[johnholmes]

No 31 issued 18 September for the period 28 September-8 October 2009

Tropics

The ENSO update from NOAA on 14 September

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) remain +0.5 to +1.5ºC above-average across much of the equatorial Pacific Ocean.

•Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

AO over the past 7 days

The signal seems a bit more definite towards the end (assuming it is reliable-and this is not that clear at this range), of a trend down, possibly even below the zero line.

NAO over the past 7 days

The trend here seems to be for it to stay above the zero line throughout.

NOAA comments over the past 7 days

This week they seem happier with the model outputs, along the line of 3 or 4/5 most days. A slightly meridional flow for the states is their idea.

NOAA 500 mb anomaly charts over the past 7 days

The +ve area just SSW of the UK has been moved to a position in mid Atlantic with the 500mb flow, as a consequence showing a more westerly flow, almost north of west in fact, with little change showing in the height values.

EC-GFS 500mb anomaly charts over the past 7 days

The Thursday issue by ECMWF put a ridge where it had a trough the day before so it does not exactly inspire confidence in its evolution. GFS seems rather more sequential in its day to day runs. This fact is borne out to some extent by the 6 day model accuracy which NOAA run. This shows GFS tending to outperform EC over a 6 day period. Of course we have no data to show the comparison at 10 days.

EC and GFS T+240 charts over the past 7 days

Again in these comparisons GFS has been more consistent than EC has. Both now suggest at T+240 (Sunday 27 September) that high pressure will be dominant.

The 30mb temperature curve

This continues on or about the average for this time of the year

Summary

Ridging from west of the UK appears to be the most likely outcome from somewhat mixed signals from the data this week.

Forecast for period 28 September – 8 October

The weather is likely to start quiet and dry for almost everywhere. With high pressure probably tending to be just SW later, drifting to be east possibly SE for a time sunshine amounts will depend on the track and moisture the high brings along. Reasonable temperatures by day with coldish nights if skies clear with inland mist or fog patches for a time on those morning following clear skies overnight.

Once again all it needs is an active tropical storm/hurricane to upset even this far ahead.

Beyond about the first week in October and I suspect that we will, ex-hurricane or not, see a more active Atlantic. Probabilities I would say are about 70/30 in favour of that. So not definite. That would give yet another NW-SE split I suspect. More wind and rain the further north one is.

once again no charts-sorry-in a rush as of on holiday 4am tomorrow

No updates until Friday 2 October.

[damianslaw]

Interesting reading as always, from your analysis, the outlook doesn't look like conjuring anything interesting synoptic wise for some time, with very quiet weather in the main lasting into early October and then a return of the NW/SE split, if so, lets hope the NW/SE split doesn't equal mild tropical maritime air variety, I am on holiday for 2 weeks in the south west from 9 Oct.. the thought of an atlantic onslaught on south west trajectory depresses me, would much rather the quiet weather continue into said period, but its inevitable that it will break down, as we head into true autumn this is what you would expect, would much rather a north westerly airsteam set in, but always difficult to get a sustained spell of north westerly airstream it seems nowadays.

[johnholmes]

the next lrf covering the period 12-22 October is done but I'll post it in the morning after having slept on it so to speak!

[Glacier Point]

Extended range tools are suggesting a quite strong +H5 anomaly (ridge) centred somewhere close to the southern UK/Europe. However, as ever with these mid latitude ridges, the exact placement is going to make a big difference in terms of both weather implications and follow-on evolutions.

The Global Wind Oscillation is showing a response to tropical forcing over the last ten days with poleward fluxing of mean westerly zonal wind anomalies. Tendency in relative angular momentum is sharply up and this has driven the GWO into phase 4:

http://www.cdc.noaa....d.sig.90day.gif

http://www.cdc.noaa....gcm/gwo_40d.gif

With further additions of westerly wind flow to come, this should continue a quasi-stationary phase 4 migrating phase 5 type orbit.

Composites for these phases indicate that the model guidance may have the position of the mean ridge too far south:

GWO phase 4:-

GWO phase 5:-

Both operational 00z ECM and GEM 03/10/09 are hinting at a northward correction of the position of the high, bringing a sniff of an easterly at first then possibly northerly evolving north-westerly to become more unsettled according to the composites.

[damianslaw]

I'm liking very much your thoughts for mid October from a personal perspective, I will be holidaying in the south west for much of the period, I'll be a happy man if high pressure is the dominant force. the atlantic can wait until late October before it really kicks into gear.

The evolution seems very plausible, I don't foresee a particularly active atlantic for a while yet, high pressure will never be too far away from the south, so a fairly settled spell is on the cards away from the north west as we head in to the middle of the month.

Interesting reading about future predictions with El Nino, it is beginning to look like it may not be as strong in the coming months as first expected, hence caution I feel for anyone calling a particularly wet and mild winter.

[johnholmes]

No 32 issued 2 October for period 12-22 October

Tropics

ENSO update from IRI on 17 September

The most recent weekly SST anomaly in the NINO3.4 region is 0.9 C, indicating weak-to-moderate El Niño conditions in the tropical Pacific. What is the outlook for the ENSO status going forward? Wind anomalies along the equator in the western Pacific are currently westerly, but in the central and eastern portions of the basin winds remain more random. These westerly wind anomalies can create more downwelling Kelvin waves that could enhance the strength of the current El Niño conditions. The spatial pattern of SST anomalies remains fairly unstructured, however, which is not favourable for encouraging a strong atmospheric response that would lead to substantial air-sea coupling of the type observed in strong El Niño events. It is possible that well timed, but independent, intra-seasonal variability in the atmosphere could provide such a kick to the ocean, but such variability is largely beyond the scope of current ENSO prediction models.

And this

Presently, the models and observations taken together indicate probabilities of about 89% for maintaining El Niño conditions and about 10% for dissipation to ENSO-neutral conditions for the Sep-Oct-Nov season in progress. Going forward, probabilities for El Niño stay near 85% for the remaining 3-month periods in 2009, decreasing to approximately 50% by early 2010, and falling to climatological probabilities of 25% by mid-2010. Probabilities for La Niña conditions are predicted to be negligible, not rising to above 10% until the middle of boreal spring 2010.

And from NOAA on 28 September

El Niño is present across the equatorial Pacific Ocean.

Sea surface temperatures (SST) were at least 1.0ºC above-average across much of the central and east-central equatorial Pacific.

Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

There appears to me to be a bit of a discrepancy between IRI and NOAA outlooks through this coming winter for El Nino

AO over the past 7 days

The first chart is the last one I saw before going away for a week. So I thought it would be interesting to compare with the first one on return, on the right? Some semblance with the predicted rise but it was greater than predicted it seems to me?

Then to the one below which is the latest available (there are no AO or NAO charts since 29 September for some reason). It shows the predicted fall with some variation thereafter on what follows. The overall trend seems to support the idea of AO being either ve or nearly so.

NAO over the past 7 days

The same with NAO, before the holiday and after for the first two charts. Again the rise was greater than initially predicted with quite a fall then suggested.

It was followed by an expected rise with some tailing off, less marked on the 29th chart than earlier ones showed, to just above the zero line.

NOAA comments over the past 7 days

First their monthly outlook, the first paragraph only

30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2009

A WEAK EL NINO CONTINUES ACROSS THE EQUATORIAL PACIFIC OCEAN WITH MONTHLY SEA SURFACE TEMPERATURE (SST) DEPARTURES REMAINING AT LEAST 1.0C ABOVE AVERAGE ACROSS MUCH OF THE CENTRAL AND EAST-CENTRAL EQUATORIAL PACIFIC. THE LATEST NINO4, NINO3.4, AND NINO3 REGIONAL SST INDICES ARE +0.8C, +0.8C, AND +0.7C

RESPECTIVELY WITH VERY SLIGHT DECREASES DURING THE LAST TWO WEEKS INDICATED. THERE REMAINS A RESERVOIR OF ABOVE AVERAGE SUBSURFACE OCEANIC HEAT CONTENT ANOMALIES AND THE PATTERN OF ANOMALOUS TROPICAL CONVECTION AND LOW- AND UPPER-LEVEL WINDS ARE CONSISTENT WITH EL NINO. ABOVE AVERAGE SSTS CONTINUE ALONG THE NORTH COAST OF ALASKA AND HAVE RECENTLY DEVELOPED ALONG THE NORTHERN

PORTIONS OF THE US WEST COAST.

The link is http://www.cpc.ncep....day/fxus07.html

With regard to the model scores over the past week or so, as is usual ECMWF outscores all, UK Met having a rather variable week.

Their own model assessment has been around 3 or 4/5 on most days, 4 more often for the 6-10 day and 3 for the 8-14 day outlook for the states. Going for some progression of the flow over their area as the 8-14 day outlook below suggests.

Monday and give 4/5 for 6-10 days and 3/5 for 8-14 days

DURING THE WEEK TWO PERIOD, THE 500-HPA CIRCULATION IS EXPECTED TO SHIFT SLIGHTLY TO THE EAST, COMPARED TO THE 6-10 DAY PERIOD. THE 00Z GFS AND CANADIAN ENSEMBLE MEANS ARE VERY SIMILAR, WITH AN UPPER-LEVEL TROUGH FORECAST JUST WEST OF ALASKA, UPPER-LEVEL RIDGES OVER THE WEST COAST AND SOUTHEAST US, AND UPPER-LEVEL TROUGHS OVER THE SOUTHWEST AND THE NORTHEAST/GREAT LAKES.

NOAA 500 mb anomaly charts over the past 7 days

Once more showing the last charts before being away and the first after. The trough over/near the UK was sharpened a little and the +ve area shifted further west, otherwise quite similar through the period forecast of 23 September to 10 October. Not shown here but on my master data file is a comparison of what the 500mb flow actually looked like. It showed the +ve area, in the form of a surface high, to be further east than shown. Between it and the states a marked upper and surface trough had developed which the models had not predicted.

15 for 23-29 26 Sept for 4-10 Oct

Since the chart on the right, subsequent ones have kept a pretty similar flow pattern with the +ve area near the states totally cleared and the 500mb flow into the UK more westerly once more.

29 sept for 7-13 oct 1 for 9-15 oct

The right hand chart shows an upper ridge starting to build over the UK with the flow backing somewhat again along with a +ve area just SW of the country. This seems a feasible follow on from previous charts.

EC-GFS 500mb anomaly charts over the past 7 days

No charts issued 00z 2 October

Again the chart from mid September into late September on the left and the right shows the late September issue for early October. Gone is the +ve area around the UK and in its place a deepish trough. The latest one for 1 October covering out to 11 October and they show different emphasis between EC and GFS. EC has more of a suggestion of a mid Atlantic upper ridge than GFS with a more N of W flow over the UK than GFS has.

EC and GFS T+240 charts over the past 7 days

The first charts show their ideas for late September, that is a ridge over the UK! Not far from what we actually had either.

Over the past week and there has not been a terrific consistency either from run to run for each model or in comparison to one another. However, below are their offerings for this evening (Friday) and they both have a fairly marked upper ridge with surface high pressure dominating our weather. Not quite the same but quite a similarity in the upper 'wave' pattern on both charts, that is trough-ridge-trough of a sort!

The 30mb temperature curve

This continues close to the average line.

Summary

Quite a lot of data tonight from the Tropics with updates from IRI and NOAA along with a 30 day NOAA outlook into the usual data available. How to sum it all up? The items to do with El Nino obviously have little impact on this range but that of the AO and NAO do. On balance they seem to suggest less mobility than we are perhaps going to have in the short term. The 500mb patterns from NOAA, CMWF and GFS (shorter term for these two) does also seem to suggest less activity on the Atlantic, at least for southern areas.

Forecast for period 12-22 October

After a fair amount of activity over the next 3-10 days (5-12 October approximately) then I would suggest a quieter autumnal spell of weather with, yet again, something of a NW-SE split. Southern areas being mainly anticyclonic with the usual weather types associated with this-mainly dry with just an occasional foray into southern areas by weather systems. Further north then less settled with the most unsettled, probably, through most of this period, in the NW. Here disturbances seem likely with surface and upper ridges staying fairly well south thus allowing systems to track towards the usual area between Iceland and NW Scotland. Probably no major storms though.

well at least you have some charts-still unable after various ideas to post into my own post but at least there are some charts available-sorry not time to re-do and add the rest

Edited October 4, 2009 by johnholmes

[johnholmes]

I'll post the update tomorrow-done but too tired to spend time posting with charts

[johnholmes]

No 33 issued 9 October for period 19-29 October

Tropics

ENSO update from IRI on 17 September; nothing since

NOAA update on 5 October

And is much as the past few comments from them-going for El Nino to strengthen but not saying by how much. The IRI update last month appeared not to make too much of any strength for this feature.

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) were at least 1.0ºC above-average across much of the central and east-central equatorial Pacific.

•Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

AO over the past 7 days

The fall pretty well predicted on the 5th but earlier at the end of September; an example of its relative accuracy at 7 days but being less successful further out.

NAO over the past 7 days

The fall and rise predicted in late September was well predicted as the later one shows. It remains to be seen how accurate is the rise it shows.

NOAA comments over the past 7 days

They have been reasonably happy with the models and how its handled the polar outbreak for North America. However, today they highlight the variability of the GFS operational runs over the past 24 hours.

From 4/5 earlier this week its now 3/5 for the 6-14 day outlook for their area.

The NOAA model check shows a general improvement from late September for all the models until a few days ago, then GFS started to decline as did UK met. Its staged something of a recovery unlike GFS. Meanwhile ECMWF, for the 6 day check shown, yet again outscores them all throughout.

NOAA 500 mb anomaly charts over the past 7 days

The +ve anomaly predicted over/just SW of the UK for mid October has been shown to decline over the week as the right hand chart shows. Whilst the 500mb flow into the UK is a touch more westerly than shown for a week earlier.

EC-GFS 500mb anomaly charts over the past 7 days

These both tended to build an upper ridge, in about the same place as NOAA (again remember these charts are for a day or so before the NOAA charts usually). They have continued with this idea as you can see from the chart on the right.

EC and GFS T+240 charts over the past 7 days

Both have shown a tendency for anticyclonic weather over and near the country. However, although the surface high is still in evidence the upper trough is shown to be turning into the major player by T+240 from Friday(Monday 19 October)

The 30mb temperature curve

This continues to stay quite close to the expected average at this time of year.

Summary

Most output suggests that high pressure may well be the major factor at the start of the forecast period. Both the AO and NAO are predicting that they will go +ve by the start of the period. NOAA data shows that ECMWF has remained more constant than the other models. Its T+240 chart shows it a shade more anticyclonic than the GFS version. However, it does suggest that the upper trough in mid Atlantic looks like playing a part, at least for a time.

Forecast for period 19-29 October

I would suggest many parts will be fairly settled and quiet to start the forecast, fairly typical autumn style-some sunshine but with fog around late evening into the morning, and possibly slow to clear from some places. A touch of frost, probably chiefly ground. Then for, I suggest a few days, more unsettled, especially for the NW, perhaps a gale but probably not a severe one with overall temperatures lower. For the south less settled but with less rain than further north. Beyond the middle of the period then it would seem that a return, especially for the south, to anticyclonic conditions if the favourite with the north less settled at times.

[johnholmes]

No 34 issued 16 October for period 26 October-4 November

Tropics

The latest RIR ENSO update on 15 October-the link is below

http://iri.columbia..../technical.html

In general they appear to be saying there are mixed signals for the level of El Nino through the winter period- this is their summation at the end

The IRI's probabilistic ENSO forecast takes into account the indications of this set of models, the outcome of the standard error approach described above, and additional factors such as the very latest observations that may have developed after the initialization times of some of the models. It indicates a 90% probability for El Niño conditions in the Oct-Nov-Dec season in progress, slowly decreasing to near 85% for Jan-Feb-Mar 2010 and decreasing rapidly thereafter, crossing 50% for Mar-Apr-May.

Overall, to me they seem to favour not much, if any, strengthening of El Nino through the winter, either early or later.

This is the NOAA latest assessment on 13 October-

•El Niño is present across the equatorial Pacific Ocean.

•Sea surface temperatures (SST) were at least 1.0ºC above-average across much of the central and east-central equatorial Pacific.

•Based on current observations and dynamical model forecasts, El Niño is expected to strengthen and last through Northern Hemisphere winter 2009-10.

AO over the past 7 days

As usual the 7 day prediction is looking spot on for the rise in levels. It now, in the realistic time frame, seems to be suggesting first a drop then a rise after this. In the far distance even another fall.

Remember that beyond day 10 its far from reliable-see the link below for how it performs

http://www.cpc.ncep....ex/ao.sprd2.gif

NAO over the past 7 days

This also is pretty reliable 7-10 days ahead so the rise looks 'on' with probably some fall beyond that towards –ve values as a probability.

NOAA comments over the past 7 days

Thur=3 for 6-10 days and 3 for 8-14 with them expecting

DURING THE WEEK TWO PERIOD, THE GFS ENSEMBLE MEAN SOLUTIONS DEPICT A STRONGER TROUGH OVER THE EASTERN CONUS THAN THE CANADIAN ENSEMBLE. THE GFS PATTERN IS PREFERRED DUE TO CONSISTENCY WITH THE PRIOR RUNS AND WITH THE 8-10 DAY ECMWF MEAN PERIOD FROM LAST NIGHTS 00Z RUN. THERE IS REASONABLY GOOD AGREEMENT ON AN AMPLIFIED TROUGH DOMINATING EASTERN NORTH AMERICA IN THE MEAN. TO THE WEST, RIDGING IS FORECAST NEAR THE WEST COAST AND CONTINUED TROUGHING OVER THE GULF OF ALASKA NORTHWARD INTO WESTERN ALASKA.

In terms of the model performance levels then this link shows their latest 6 day levels

http://www.emc.ncep..../html/acz6.html

Variable performances from them all-as GFS and UK Met rise so ECMWF falls-although ECMWF has a better overall score, probably due to its very long term performance.

NOAA 500 mb anomaly charts over the past 7 days

The +ve area mainly east of Svalbard has been shown to grow through the week. Meantime over the UK and west into North America any +ve has been deleted in favour of a 'neutral' level with a –ve area over the UK. The overall 500mb flow into the UK is predicted to be just south of west as the major trough swings in. This may be partly due to the marked upper ridge shown to be developing NE of the UK (see the comment about +ve east of Svalbard).

EC-GFS 500mb anomaly charts over the past 7 days

The chart before the one shown on the left had both been showing large +ve signs in the UK area. This was quickly replaced by the upper trough swinging east with –ve then showing just west of the UK. A large +ve area has developed through the week, initially over west and north Russia but now edging further west towards Svalbard, even further NW into the north of Greenland and right across towards NE Russia. The whole of the previous comments are pretty much valid for both models.

EC and GFS T+240 charts over the past 7 days

They each started with some sign of an upper trough developing in the Atlantic with pressure high to its south and east of the UK. As we have seen they both deal rather differently in mid week with the surface low created by this upper trough. Well illustrated by the charts issued on Thursday. Both still have a marked upper trough over/west of the UK with surface pressure high to its SW and also to the east of the UK. This area is shown NE of the country on ECMWF but east on GFS! Tonight's' version shows them both with an upper trough to the west of the UK and high pressure to its WSW, EC keeps the high to the NE and GFS still more to the east.

The 30mb temperature curve

This has very recently shown the first suggestion of a rise--the question is will it continue?

Summary

Most indicators appear to be suggesting blocking rather than much mobility. AO and NAO have this, NOAA 500mb charts show the blocking to the NE of the UK as does ECMWF T+240 with GFS more to the east than NE. On their 500mb anomaly charts they each show the +ve anomaly to the NE.

Forecast for period 26 October-4 November

Based on the above it has to be mostly anti-cyclonic for the start with the probability that it may well, see the AO and NAO, be mainly thus through most of the period, at least for the more eastern areas of the country. Current trends suggest the surface high to the NE of the UK with an upper trough to the SW or west. The 500mb flow being predicted across the Atlantic looks quite mobile so it may end up with something of a battle between the upper ridge and surface high NE or E of the country and the upper trough with surface lows trying to swing in from the W or SW.

The overall weather pattern would then suggest more of a west-east split with the west being more prone to incursions from the Atlantic, perhaps the SW rather more than the NW. Winds could well be a feature in the west at times. Further east then less precipitation and wind although there will be occasions when the Atlantic takes over temporarily. Temperatures lower in the east than the west. Frost could well feature fairly often but snow probably below average even for the higher ground.

[Glacier Point]

The 30mb temperature curve

This has very recently shown the first suggestion of a rise--the question is will it continue?

Stratospheric ozone over the last weeK:

10/10/09:

16/10/09:

http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/gif_files/sbuv17_ll_latest.gif

With 30mb temperatures correlated to ozone concentration, the change in ozone is being reflected in temperatures, over both hemispheres. I suspect that the overall circulation is starting to reflect an El Nino character, particularly with the MJO and GWO becoming coupled (finally). Phase space composites for the GWO and MJO both signal Atlantic trough and blocking to the NE Atlantic / Siberian sector and this is the way the ozone concentrations are going.

[johnholmes]

thanks Stewart

[johnholmes]

No 35 issued 23 October for period 2-12 November

Tropics

No update of course from IRI but from NOAA in which they simply repeat what their updates have said over several weeks, 'El-Nino is expected to strengthen and last through the northern hemisphere winter 2009-2010'.

This is an extract from the IRI from 15 October

It indicates a 90% probability for El Niño conditions in the Oct-Nov-Dec season in progress, slowly decreasing to near 85% for Jan-Feb-Mar 2010 and decreasing rapidly thereafter, crossing 50% for Mar-Apr-May.

And my comment

Overall, to me they seem to favour not much, if any, strengthening of El Nino through the winter, either early or later.

AO over the past 7 days

It started with a distinctly below zero line look. Out to its issue on 22 October when it showed, as it does for 23 October a very large increase in most of the ensembles.

NAO over the past 7 days

This has, as it often does, tended to mirror the AO but nothing like as dramaticically. From mixed signals regarding rises and falls it now shows more of its members going for a rise.

NOAA comments over the past 7 days

They started with fairish content with the models but have gone down to marking 6-14 days, on Thursday, at only 2/5.

Their overall expectation of the major upper flow is generally as given below for the States/Canada

THERE IS LESS AGREEMENT FROM MOST OF THE GFS-BASED AND CANADIAN ENSEMBLE GUIDANCE TODAY AS COMPARED TO THE PAST COUPLE OF DAYS ON THE EXPECTED 500-HPA HEIGHT PATTERN DURING THE 8-14 DAY PERIOD. THE PATTERN FOR MUCH OF THE WEEK HAS FEATURED TROUGHING OVER EASTERN NORTH AMERICA, A BROAD RIDGE ACROSS THE WESTERN CONUS, AND A TROUGH OVER ALASKA.

They have continued for around 10 days accepting the trough over the east and a ridge to the west.

The stats shown below indicate variable performance from the models with EC generally well ahead throughout.

http://www.emc.ncep..../html/acz6.html

NOAA 500 mb anomaly charts over the past 7 days

The major ridge feature suggested by the +ve areas eastern Greenland into northern Russia have largely persisted but latterly the main +ve area is shown migrating south to be off the Norwegian coast in the last issue (Thursday). The upper trough has been pushed back west through the week, and again lies over the eastern part of N America.

EC-GFS 500mb anomaly charts over the past 7 days

The +ve area ENE of the UK got 'lost' somewhat through the week but they both have it back today with the marked trough

EC and GFS T+240 charts over the past 7 days

Both started with the upper trough west of the Uk and an upper ridge with its surface high to the east. GFS has been the more persistent about the Euro high than EC

Tonight (Friday) both are back to the trough west of the UK and a ridge/high to the east. This time its EC which makes more of the ridge, having it more to the NE. Remember that there is almost a weeks difference between the first two charts and the last two. So that must be borne in mind when looking at the more realistic outcome.

The 30mb temperature curve

This is now back to about the normal curve after a brief excursion above the normal line.

Summary

Much as last week most of the drivers suggest blocking rather than mobility. Crucial will be the exact position of both the trough (to the west) and the ridge (to the east). How much, if any, mobility will there be?

Forecast for period 2-12 November

Starting fairly settled for most areas, perhaps less so for the far NW. Some sunshine once lowland mist/fog thins out. Winds look like being mostly from a southerly point so frost is probably going to be below average much of the time. A small chance of winds more off the ESE would give a risk of frosts but about 35% I would think.

The rather less settled weather for the NW seems likely to spread further south in the latter part of the period. There is little to suggest any major storm but that does not preclude one developing in that latter part. Rainfall totals about normal in the north below for the south. Snow seems unlikely apart from possibly the mountain tops as cold fronts move across parts of Scotland. Perhaps a higher risk later in the period with temperatures tending to fall in the north.

[johnholmes]

No 36 issued 30 October for period 10-20 November

Tropics

Nothing new issued from any centre since the last lrf.

AO over the past 7 days

From a quite –ve value it early on predicted a rapid rise into relatively high +ve values. Latterly it has decided to reverse this and take the value well above zero again.

NAO over the past 7 days

It predicted a steady rise back into +ve territory but has over the past 2-3 days, (29 Oct is the latest available-it always now seems 1 day behind the AO output), started to show some tendency to fall again.

NOAA comments over the past 7 days

They have generally marked the 6 out to 14 days for their area at 3/5

Much of the time they have been happy with a generally zonal flow across them.

The link below shows the overall model output; the dramatic fall by GFS has only just shown and I'm not sure if its real; nothing by NOAA suggests its had such a rapid fall from grace!

However, both UK and the Canadian mirror similar drops in accuracy, with ECM

http://www.emc.ncep..../html/acz6.html

NOAA 500 mb anomaly charts over the past 7 days

Overall the flattish flow across much of the area seen, Pacific into Europe is and has been about the main feature. In terms of +ve, then the area in the far north, usually NE-N-NW of Svalbard has shown the main +ve area. The latest shows this to be NE of that island. The –ve areas are now suggested to be south of Alaska and south of Greenland.

EC-GFS 500mb anomaly charts over the past 7 days

Some changes for sure, from the initial idea of an upper ridge east of UK with deep trough to the west on both, then both flattening the flow. Now they both have gone back to their original idea, of a week ago, for a block idea east of the country and a deep trough west of it.

The +ve area ENE of the UK got 'lost' somewhat through the week but they both have it back today with the marked trough

EC and GFS T+240 charts over the past 7 days

Through the 7 days, to me, GFS seems to have been rather more consistent than ECMWF, that in spite of how NOAA have them marked for their 6 day progs at 500mb.

Both started out with a largish 500mb trough west of the UK, EC more anti with GFS tending to show more cyclonic type weather. GFS has tended to switch from one to the other with GFS rather more consistent with its idea of cyclonic being the major weather pattern. Latterly EC has taken up this. The final chart from GFS does look like one of its' overcooked' lows.

The 30mb temperature curve

It has shown a tendency over the past days to move from below average to above. Its currently showing a climb above normal as shown below. Funnily enough not that different from about the same time as last year.

Summary

Rather mixed signals it seems to me, some suggesting anticyclonic, some cyclonic. Its certainly cyclonic at the moment but that is 11 days from when this forecast is due to start so it is obviously of little help.

Forecast for period 10-20 November

Taking up the summary and the variability in the AO. Its unusual for it to be so variable and I wonder if the first signs of a positive 30mb temperature are causing some twitches with it?

Overall I will go for a short anticyclonic spell soon turning more mobile as several Atlantic systems come across on quite a strong westerly flow. Possibly one fairly severe storm. As usual the north and west are likely to be worst affected. Rainfall amounts through the unsettled spell, around the average with temperatures fluctuating either side of that. Possibly cold enough in the Polar Maritime behind the lows for some mountain snow in Scotland. Frosts probably about or just below average for most parts.

The run in to the end of the period is finely balanced, or so it seems to me. I tend to favour the mobility being pushed somewhat further south as the northern block starts to have some effect. Just whether it will be NW, N or NE is impossible to say, perhaps favouring the N-NW quadrant. Hopefully it will seem a bit clearer in a week's time.

[johnholmes]

No 37 issued 6 November for period 16-26 November (issued Thursday 5th)

Tropics

Nothing from IRI since its 15 October update-see earlier lrf’s for the text and link.

Also nothing new in the routine update by NOAA

CPC monthly outlook issued 30 October, link below, with except from it below that.

http://www.cpc.ncep.noaa.gov/products/predictions/30day/fxus07.html

WHILE THE CLIMATE SIGNALS OF THE CURRENT EL NINO ARE EXPECTED TO HAVE SOME

IMPACT ON US TEMPERATURES AND PRECIPITATION DURING NOVEMBER, DYNAMICAL GUIDANCE

FOR THE FIRST 15 DAYS OF NOVEMBER ARE THE MOST IMPORTANT SOURCE OF INFORMATION

FOR THE ZERO LEAD UPDATE. THE EXPECTED NEAR ZONAL FLOW PATTERN OVER THE CONUS

FOR THE BEGINNING OF NOVEMBER

AO over the past 7 days

For AO and NAO there is nothing later issued than 3 November:

The predicted sharp rise did occur as can be seen in that issued 2 November. It did predict an equally sharp rise after the fall during the week but seems to have modified both latterly with a pretty indeterminate looking set of ensembles towards the end.

NAO over the past 7 days

Its rise was also well predicted from late October for early November. The prediction of a fall then a tendency to rise is continued, values hovering around zero.

NOAA comments over the past 7 days

They mark the 8-14 day period at only 2/5 with the comment below-previously they were more confident in the evolution shown by the models.

ARE IN

AGREEMENT IN MAINTAINING A STRONG NORTH PACIFIC JET THROUGH THE ALEUTIANS INTO THE GULF OF ALASKA DURING THE 8-14 DAY PERIOD. HOWEVER, THERE IS SOME DISAGREEMENT ON THE FORECAST OVER THE CONUS AMONG ENSEMBLE MEANS AND HIGH-RESOLUTION MODEL SOLUTIONS WITH MOST RECENT MODEL SOLUTIONS INDICATING A PROGRESSION OF A TROUGH OVER THE CONUS DURING THE 8-14 DAY PERIOD. THIS PROGRESSION RESULTS IN LOWERING OF 500 HPA HEIGHTS OVER THE EASTERN US AND RISING HEIGHTS OVER THE WEST RELATIVE TO THE PREDICTED FLOW PATTERN FOR 6-10 DAY PERIOD.

NOAA 500 mb anomaly charts over the past 7 days

The polar vortex has been moved ne with the +ve area also to its ne now extending into Greenland and ne n America as well as south into uk;trough off w coast us sharper flow into uk a touch back from w than it was

EC-GFS 500mb anomaly charts over the past 7 days

The overall pattern has been kept fairly similar through from last week. A strongish westerly across most of the Atlantic into a trough over/west of the UK. Then a building ridge to the east or NE. Some variations but along those lines with both models and its still a similar evolution on both the models in the last run shown. The initial idea of linking the ridge across the pole has gone. Both show the major polar vortex to be in about the same place, well north of Alaska.

EC and GFS T+240 charts over the past 7 days

As in most cases there are considerable differences but both have kept the major upper trough, but with differing ideas on its location and orientation, west of the UK with the upper ridge well east and ENE out over Russia. Various shorter wave features, troughs and ridges have been the main differences in how each model has dealt with these.

The 30mb temperature curve

Side by side 2009 on left 2008 on right at the same time

Summary

Not a great deal to be said beyond what I’ve posted above under the various headings. Regarding the final comment last week in the forecast section, ‘Hopefully it will seem a bit clearer in a week’s time.’-I have to say its not really any clearer!

Forecast for period 16-26 November

Its looking like a bit of an east-west split at the start with high pressure holding on east of the country. Weather systems coming across the Atlantic then largely shearing away north east. So western and north western parts more unsettled than further east. Temperature levels hovering around normal values. Some frost and fog in parts of the east and south east those days when the Atlantic has not got a system close by the country.

Further ahead and there are signs, no more than that of more definite blocking taking place over areas north of the UK, from far NW across to far NE. I really am unsure how this will pan out so it has to be left for another week when I’ll be having to take the lrf into the start of winter proper, meaning early December.

My apologies for no charts this week but this is being done in a bit of a rush Friday morning.

[johnholmes]

the latest one is almost ready but it will be tomorrow morning before I can get round to issuing it.

[johnholmes]

No 38 issued 13 November for period 23 November-2 December

Tropics

Nothing new from any centre- The NOAA 9 November update maintains the same-ENSO continuing to strengthen and last '..through at least the Northern Hemisphere winter 2009-10.'

AO over the past 7 days

There were no updates from 3-11 November for either AO or NAO.

The major change is that it now makes less of its fall and seems more set on a rise late in the period.

NAO over the past 7 days

Its projected fall still appears to be partly followed by something of a rise with some of the ensembles-a fairly wide spread as is often the case for the end period, but the majority at or below zero.

NOAA comments over the past 7 days

The issue from NOAA on Friday 13 November gave 3/5 over the period 6-14 days but the 8-14 commented as below.

8-14 DAY OUTLOOK FOR NOV 21 - 27 2009

FOR WEEK 2 THE GFS SUPERENSEMBLE AND CANADIAN ENSEMBLE MEANS SHOW A CLEAR PROGRESSION OF THE EXPECTED CIRCULATION PATTERN FROM THEIR RESPECTIVE FORECASTS COMPARED WITH THE 6-10 DAY PERIOD. THE GFS-BASED ENSEMBLES ARE MORE AMPLIFIED COMPARED TO THE CANADIAN ENSEMBLES. THE OPERATIONAL 0Z AND 6Z GFS ARE SIMILAR TO THE GFS-BASED ENSEMBLES ALTHOUGH THE OPERATIONAL RUNS ARE MORE AMPLIFIED.

Latest model 6 day checks show all falling in accuracy with UK Met still in the lead; EC and GFS are both about the same as each other latterly.

NOAA 500 mb anomaly charts over the past 7 days

The Polar vortex is now predicted to be just north of Alaska. One of its major changes has been the development of a +ve area over eastern North America and its movement east. If this does happen then the two would tend to suggest a change in flow-with it starting to become more meridional across the area shown. Another +ve area is shown SSE of the UK.

EC-GFS 500mb anomaly charts over the past 7 days

There appears to be some suggestion of changes showing on both models. The flow from Japan into the western states is about zonal and pretty strong. Past the Rockies and there are signs of the flow buckling-not surprising considering the flow into the Rockies.

EC and GFS T+240 charts over the past 7 days

The marked upper trough, such a feature over the Atlantic for some time now remains. What they both seem to be trying to show is a build of pressure in the far west. This is not that different an idea, albeit some days later, to the NOAA 500mb anomaly charts.

The 30mb temperature curve

The rise is still happening, its certainly much bigger than anything we saw in mid November last year. On this basis one MIGHT be tempted to call for a cold spell some 18-25 days down the line from now. However, it needs confirmation from other sources-have we got it? See summary.

Summary

Indications of the AO turning +ve and the NAO towards ve along with the 500mb anomaly charts, NOAA, ECMWF and GFS all showing some indication of a change of flow over the States with the word meridional appearing in my view. The 30mb basic temperature curve, one not really used by the purists but to me it is an indication of the Stratospheric events, shows the largest rise at this time of the year over the past 3 years.

What does this mean?

Forecast for period 23 November 2 December

Carrying on from the summary-where do the above signals leave us?

The start of the period is very likely to be a general surface flow from the SW, with the upper trough anchored west of the country as it has been for some time. Unsettled with rain or showers, above average temperatures and strong winds from time to time. Possibly one major storm in the first part.

Taking a look into the second half and I suspect we should begin to see signs of a fairly marked change. To me most of the pointers are suggesting a more meridional flow developing. Its hard to say just which side of that flow the UK will be. I'll stick my neck out and say on the cold side with some form of blocking to the NW of the UK being the main driver for our basic weather in the latter part. Its far too early for any detail but obviously that would mean much lower temperatures. So more on that next week.

Edited November 16, 2009 by johnholmes