LRF or attempting them

[johnholmes]

No 18 issued 6 June for 15-25 June

Tropics

This is the end of May summary for the month ahead from NOAA, obviously for the USA area but worth a read, link below

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

This extract may have implications for this area

AN AVERAGE OF CFS AND CANADIAN MODELS FOR DAYS 8-14 INDICATES THE LIKELY PRESENCE OF UNUSUALLY HIGH 500 HPA HEIGHTS OVER THE GULF OF ALASKA, WITH POSTIVE HEIGHT ANOMALIES ALSO EXTENDING ACROSS ALASKA AND THE ARCTIC OCEAN TO NORTHEASTERN SECTIONS OF SIBERIA AND ACROSS THE POLE TO THE DAVIS STRAIT AND GREENLAND.

and the ENSO update from NOAA on 1 June

•ENSO-neutral conditions are present in the equatorial Pacific Ocean.

•SSTs have been increasing with warmer-than-average conditions across much of the equatorial Pacific Ocean.

•Based on recent trends in the observations and model forecasts, ENSO-neutral conditions are expected to continue into the Northern Hemisphere Summer.

AO

This has consistently shown a predicted rise at about the same date with a tendency to level off, or even dip a little at the end.

NAO

NAO has been less consistent this week compared to the AO-and I have no idea why this is so. Initially, as the first plot shows predicting a drop, with some ensembles against that. The last one carries on from the last two with a general rise being predicted which mirrors to some extent the AO forecast. Remember though they are not necessarily meaning the same thing.

NOAA comments

Throughout the week they have marked the models overall around 3/5 for the 6-14 day periods.

NOAA 500 mb anomaly charts

The trend here has been to develop a –ve area west of the UK which has the effect of backing the upper flow more SW'ly. It also seems to want to make a +ve area east of the UK.

1st for 9-15 June 5 June for 13-19 June

EC-GFS 500mb anomaly charts

31 for 10 June and 4 June for 14 June

EC has fairly consistently gone with the idea of an upper low SW of the UK with a consequent flow from the SW, along with an increasing sign of a +ve area east of the UK.

Not a million miles from the comment I made above about the NOAA output. Remember though the EC/GFS set are for, at the latest 14 June, the NOAA versions are for several days from about the same date.

GFS was about the same in terms of the 500mb flow although it had a cut off low to the SW rather than a trough. Its latest has changed to a flatter westerly with the trough mostly NW of the UK but still with a +ve area developing to the east of the UK.

ECMWF and GFS T+240 charts

EC charts on the left

They have each followed their own idea of how things will develop and end up with different weather patterns. EC favours an anticyclonic one and GFS a cyclonic pattern. Neither fit all that well with their circumpolar equivalent!

Summary

Once again we have different signals from different parts of the jigsaw-not at all unusual. Most consensus, to me, does suggest an upper level flow into the UK from south of west. Also for surface pressure, coupled with the upper air, to show signs of building over Europe rather than northern parts of the Atlantic or even further north. As mentioned above though the T+240 outputs are not that supportive of this.

Forecast for period 15-25 June

I would plump for the anticyclonic type of weather with a surface flow from south of west over the country. It may well show a NW-SE split for much of the period. More settled drier and warmer in the south and south east. More unsettled for the NW. Here further rain or showers at times with about average temperatures. Further south more settled less rain and temperatures generally above normal and possibly into the very warm category at times. Just how long this weather pattern is to last is difficult to say. At some point the upper trough must swing east even if only temporarily which would give more unsettled and thundery type weather for the south for a time. Overall though I think the pattern I've suggested for the start is going to be more dominant say 65-35 over the period.

No lrf on 12 June as away-next one will be issued on 19 June for 29 June-9 July

Edited June 6, 2009 by johnholmes

[PB22]

Thanks John, a top quality read as always.

[johnholmes]

tks Paul-now to add in the charts at last

No 19 issued Friday 19 June for 29 June to 9 July

Tropics

See the comment below regarding the GWO

Latest ENSO update on 15 June

•ENSO-neutral conditions are present in the equatorial Pacific Ocean.

•Equatorial SSTs are warmer-than-average across much of the Pacific Ocean.

•Current observations and dynamical model forecasts indicate conditions are favourable for a transition from ENSO-neutral conditions to El Niño conditions during June-August 2009.

the link below is the IRI update on 18 June

http://iri.columbia.edu/climate/ENSO/curre.../technical.html

well worth reading it all but just one para is shown below

Presently, the models indicate probabilities of about 56% for developing El Niño conditions, and about 43% for ENSO-neutral conditions for the Jun-Jul-Aug season in progress. Going forward, probabilities for El Niño increase to 60 to 65% for the remaining 3-month periods in 2009, decreasing toward the end of the year and falling below 50% by northern spring 2010. Probabilities for La Niña conditions are predicted to be negligible through the remainder of 2009.

AO

Its interesting to see, on the first prog where the AO was forecast to be around 16 June and compare it to where it actually was? Quite a difference with the peak at zero occurring long before the first predict suggested. Quite what implication that has for its latest prediction, 17 June, I am not sure. Through the week it has trended much the same as the 19th shows.

NAO

The NAO similarly reached zero earlier than the chart on 11th predicted, so the same caveat probably applies to that. Still more suggestion of a fall late on rather than a rise, after a couple of days showing a more uncertain end.

The 30mb temperature line is hovering just above the normal over the past few days, perhaps that is some indication of it. Also remembering the posts about the GWO and it being in phase 8/7 and apparently 'stalling'. I am no expert on these things but perhaps GP (Stewart) or someone else might like to comment on this part of the lrf?

NOAA comments

They started out quite happy with their own neck of the woods as depicted by the chart on the left (see the NOAA 500mb charts below). However, largely due to uncertainty about where and how marked the two troughs shown on the first chart will be by day 14 their confidence has fallen.

An indication of how the models have performed over the past few weeks can be seen below.

On the 5 day all have taken a bit of a nose dive with ECMWF below that of GFS and UK Met, at 5 days the better of the big 3. Day 6 checks still show UK Met leading but both ECMWF and GFS recovering to near their score.

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

NOAA 500 mb anomaly charts

The 500mb pattern has shown no major change throughout the week with troughs over both east and west coasts of America. They also show an indication of the main 500mb trough for us being just a little west of the UK. Again its shape changes a little from run to run. The main area of +ve has also moved from SE of Greenland to between Iceland and the UK. There is also, on the latest version out to 2 July a –ve area developing close to the Azores.

EC-GFS 500mb anomaly charts

Both have generally gone along with the idea of a +ve area developing near, or just east of the UK, although GFS did tend less towards this than the ECMWF version. GFS preferring to have a build more to the SW and a flatter 500mb flow, that is, until the Thursday issue when it picked up the ECMWF pattern. ECMWF has continued with a reasonably sequential idea of the ridge tending (the +ve area that is) to edge further N or NE. Both have a cut off low around 40N which was in mid Atlantic; and is now somewhat nearer to the UK (19 June issue for 29th), especially on the GFS model.

T+240 charts for ECMWF and GFS (on right); usually 12z

They both have indicated that higher surface rather than lower surface pressure is the most favoured option over the past 5-7 days. Not totally alike either with one another or there own day by day assessment but similar. Both do appear to favour the idea of the surface high moving to a position to the NE of the UK, or did, I should say, as ECMWF, in particular seems, latterly, to favour its position to the west of the UK.

General note

Please be aware that the GFS/Euro circumpolar and T+240 charts do only extend to the first day of this forecast. This is the case on each lrf. The NOAA version does extend into the beginning but not by much.

Summary

At first glance most data, from whatever source, seems to suggest that anticyclonic rather than cyclonic weather is most likely near/over the UK to start the period. I have a hunch its not that straightforward and suspect by about the start that the 500mb upper trough will be coming into (if not already) in prominence. Thereafter then with some kind of blocking evident then the 500mb trough is probably going to return to west of the Uk with the upper ridge north of the UK, perhaps eventually NE of the UK.

Forecast for period 29 June – 9 July

If not then soon rather unsettled, probably thundery for a time; well above average temperatures in places, especially the south, but with a fair amount of rain developing, generally of a showery/thundery nature. Much of it for the south and west but not exclusively.

Beyond the first few days then expect high pressure to begin to dominate again. Its location is quite open to doubt, but somewhere north of the UK rather than south. Its position is obviously crucial as to whether it is a 'dry' high or one which allows weak disturbances to run around its northern flank. My punt would be for the former at first and becoming the latter later. So a lot of cloud from the high at first with the driest and sunniest weather for the SW. becoming mostly dry everywhere with spells of sunshine for most and temperatures mostly above normal throughout; near/around away from the SW at first. Probably well above normal in some southern areas before the end of the period, perhaps approaching hot. Eastern coasts may be affected on a few days by North Sea low cloud/mist in the second part of the forecast.

Edited June 20, 2009 by johnholmes

[johnholmes]

No 20 issued 26 June for 6-16 July

Tropics

Looking at the MJO I would read it as there not being much change to our current conditions in the major synoptic pattern?

The only update since the last lrf is the NOAA one of 22 June in which they say

•ENSO-neutral conditions are present in the equatorial Pacific Ocean.

•Warmer-than-average SSTs are increasing across much of the equatorial Pacific Ocean.

•Current observations and dynamical model forecasts indicate conditions are favourable for a transition from ENSO-neutral conditions to El Niño conditions during June-August 2009.

AO

This has been consistent through the week, predicting the decrease and then the increase so perhaps its prediction of this continuing to near zero by period end is near the truth?

NAO

It has not been too certain in the trend although it has favoured an overall fall through the past 7 days.

NOAA comments

Out as far as their issue on Thursday it was not a full endorsement of the various models, usually allotting 3/5 to the 6-10 day and between 3 and 2 to the 8-14 day period.

As can be seen in their charts below the idea of a trough off the west and east coasts shown on the 23 June prediction is not that different on Thursday. It also keeps the 500mb trough west of the UK with indications of –ve heights to the SW and +ve heights well to the NW. This would support the idea, with a not strong flow at 500mb across the Atlantic off little sign of any reawakening of the Atlantic into early/mid July. A 500mb flow south of west also suggests warmer rather than cooler weather for much of the country?

NOAA 500 mb anomaly charts

23 June for 3-7 July 25 June for 3-9 July

EC-GFS 500mb anomaly charts

The evolution of both ECMWF and GFS through the 7 days seems reasonably consistent with the NOAA charts, (remember they are for several days earlier though), with an upper trough to the SW of the UK. +ve height anomalies have been a bit more variable; GFS favouring much of the time it to be +ve to the E or NE. ECMWF being less sure of this. When we get to the T+240 outputs this shows again.

For 20 June for 30 June 26 June for 6 July

ECMWF and GFS T+240 charts (usually 12z)

For much of the past week GFS has shown a more consistent story. Just a quick probably rather inaccurate summary first

GFS has shown LP to the west of the UK on 6 out of 6 checks done; ECMWF has shown 4 highs to the west and 2 days with lows to the west.

It might be an idea (I've not looked this week so have no idea until I call it up) what the scoring is for the models for day 6 over the last week or so; link below

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

Well, according to it EC has outscored GFS over that time, which I find a touch surprising, whilst UK Met has recently taken a dive below GFS. So mixed signals from this link.

Issued Mon 22 June for Thur 2 July; ECMWF on the left

Fri 26 June for Mon 6 July

Summary

Mixed signals from some others more consistent sums up the models and other outputs.

Forecast for period for 6-16 July

It would seem highly likely that heat and slack winds with thundery potential is how we are going to start the period. Highish dewpoints at times will give some patchy sea mist/fog around whichever coast has onshore winds-too light to be sure what the main direction will be.

Soon after the start then a portion of the 500mb trough is going to move ENE, relaxing as it does. This should cause a more unsettled spell with cooler weather for the more southern areas. Beyond that and I can see the high re asserting itself with largely dry weather returning although with nothing like the same heat during this forecast period. As to where the surface high sets up shop is open to a fair spread. I think initially its going to be west of the UK, north or south? That again is open to question. There is little sign, so far, of sea temperatures in the Azores area rising much so I'd punt for NW of the UK. By the end of the period this may be trying to link back into another ridge to the east of the UK.

All in all summer is far from over-just a temporary hiccup at the start of this period.

sorry the EC/GFS charts are overlaid on the NOAA

Edited June 26, 2009 by johnholmes

[johnholmes]

No 21 issued 3 July for 13-23 July

Tropics

CTC monthly output

30-DAY OUTLOOK DISCUSSION FOR JULY 2009

SEA SURFACE TEMPERATURE (SST) ANOMALIES ALONG THE EQUATOR IN THE CENTRAL PACIFIC OCEAN CURRENTLY AVERAGE AROUND 0.5C ABOVE ZERO FROM ABOUT 160E TO THE SOUTH AMERICAN COAST. THERE IS A RESERVOIR OF

MODERATELY (1 TO 2 AND LOCALLY 3 CENTIGRADE DEGREES ABOVE AVERAGE) WARM WATER BENEATH THE SURFACE ALONG THE EQUATOR, SLOPING UPWARD FROM A DEPTH OF ABOUT 150 METERS AT 160E, TO VERY NEAR THE SURFACE AT THE SOUTH AMERICAN COAST. PRESENTLY WESTERLY WIND ANOMALIES IN THE WESTERN PACIFIC MAY ENHANCE WHAT APPEARS TO BE AN EL NINO IN THE MAKING. ENSO-NEUTRAL OR BORDERLINE WARM CONDITIONS ARE EXPECTED IN JULY. ENSO COMPOSITES ARE NOT USED FOR JULY.

NOAA summary 29 June

•A transition from ENSO-neutral to El Niño conditions is occurring in the equatorial Pacific Ocean.

•Positive SST departures continue to increase across much of the equatorial Pacific Ocean.

•Current observations and dynamical model forecasts indicate conditions are favourable for a transition from ENSO-neutral conditions to El Niño conditions during June-August 2009.

There has been no ENSO (IRI) update since the last one on 18 June

AO

It has been pretty consistent in predicting a rise towards the zero line but with the usual variations between ensembles, perhaps rather more so over the last day or so?

NAO

This looks reasonably accurate at first so perhaps its latter stages are also a reasonable forecast of likely events?

NOAA comments

They have mostly marked, for their area, the models at 4/5 (6-10 days) and 3/5 for the 8-14 day charts. Accepting that in the latter stages the flow is likely to retrogress and amplify a little in the period.

Their model checks on Sun for 6 days ahead recently showed EC back in the lead followed by UK Met then Canadian ahead of GFS. By Thursday ECMWF was showing the lead although not by much from either GFS or UK Met.

link below

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

NOAA 500 mb anomaly charts

Their chart from a week ago valid for 3-9 July is on the left with their chart issued Thursday 2 July for 10-16 July on the right.

It shows a more westerly flow at 500mb than we have had for some time. It does appear consistent on the charts through the past week or so. Certainly the flow is shown more amplified over North America. The 570DM line is show south of the UK whereas it has been over the country. This seems to imply a less warm, possibly more unsettled spell through the period shown by the NOAA charts.

EC-GFS 500mb anomaly charts

These also show contour heights tending to fall over the UK with both models and for the flow at 500mb to be from N of W. Once more remember the last chart is for 12 July, the day before this forecast starts and before the last chart shown for the NOAA version.

ECMWF and GFS T+240 charts

They have, as is often the case, been rather different at times. EC ( for 2 July started with a ridge with GFS showing a much more accurate idea of what we now have, low approaching from the west). They have both been a bit variable in their output since. Favouring in turn, high or low pressure. I would not want to try and give any view on which seems the more accurate or most consistent with itself! There has been a tendency, at times, with them both, to suggest some kind of northern blocking. But its position has changed too much to get any real idea on a trend from either.

Summary

Overall the input from different sources favours a less warm and probably rather unsettled spell with the main flow coming off the Atlantic but not an active one.

Forecast for period 13-23 July

So I would suggest a rather cool and somewhat unsettled spell with a NW-SE split in terms of more unsettled and cooler in the NW than the SE-not unusual for much of the year, but that is how it shows as likely to be for this period. For the start at least. How long this lasts is open to doubt at the moment. The longer term guides (teleconnections) do seem, about on balance, to favour the probability of another dry and very warm spell before the end of July. At the moment I'll leave it at that until the next update on 10 July when I hope a clearer signal will be there.

Edited July 3, 2009 by johnholmes

[johnholmes]

No 22 issued on 10 July for 20-30 July

Tropics

Only the NOAA update is new, issued on 6 July

•A transition from ENSO-neutral to El Niño conditions is occurring in the equatorial Pacific Ocean.

•Positive SST departures continue to increase across much of the equatorial Pacific Ocean.

•Current observations and dynamical model forecasts indicate a transition from ENSO-neutral conditions to El Niño conditions is in progress.

AO

Over the week it has consistently shown an anticipated rise by late July to near the zero level.

NAO

This has indicated some fall for a time, now rather more marked, before a rise, consistently predicted, for late July to near zero.

NOAA comments

They have remained quite happy with the model outputs scoring 4/5 throughout the week for 6-10 days and 8-14 days.

8-14 DAY OUTLOOK FOR JUL 18 - 24 2009

THE 500-HPA CIRCULATION PREDICTED FOR THE 8-14 DAY PERIOD IS QUITE SIMILAR TO THE EXPECTED PATTERN FOR THE 6-10 DAY PERIOD. THE MODEL SOLUTIONS OF THEVARIOUS GFS AND CANADIAN ENSEMBLES REMAIN VERY CONSISTENT WITH ONE ANOTHER IN THEIR PREDICTION OF A PERSISTENT TROUGH OVER THE EASTERN U.S., A TROUGH OFF THE WEST COAST, AND A RIDGE OVER THE NORTHERN AND CENTRAL ROCKY MOUNTAINS. THE TROUGHS NEAR BOTH THE WEST AND EAST COASTS FILL SLIGHTLY BETWEEN THE TWO PERIODS, BUT REMAIN IN SIMILAR POSITIONS.

NOAA 500 mb anomaly charts

Through the past week the 8-14 day outlook has attempted to suggest some backing of the flow SW/W of the Uk but has slowly dropped this in favour of a more westerly 500mb pattern across the Atlantic into the UK. The height values having remained about the same. Its +ve height anomalies NE of Greenland have been moved to NW of Greenland in that time. The –ve area W/SW of the UK having been increased in size in that time.

2 for 10-16 July on 9 for 17-23 July

EC-GFS 500mb anomaly charts

ECMWF started the period suggesting a low SW of the UK and has gradually changed it to a more westerly flow with a 500mb shallow low WNW of the country.

GFS also followed this idea and it too has taken the stance much as shown by the EC model.

Both show some suggestion of a +ve area developing over eastern Europe.

on left=2 July for 12 July and on right=10 for 20 July

ECMWF and GFS T+240 charts

They have at times been rather different, (this is quite often the case), but much of the time showing similar charts. The general theme being one of surface low pressure being more dominant than high pressure. Low pressure off to the west with some indication of high pressure way WNW or away to the WSW on many of the charts.

Looking at the NOAA checks on the models recently and it shows ECMWF and UK Met, for the past few days, mainly way ahead of GFS; see the link below, for outputs for 6 days. Up to the beginning of July then all 3 were much the same.

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

Summary

Most pointers are towards an upper flow being mainly westerly with little sign of major blocking over Europe or a marked upper trough west or at least just west of the UK through this period.

Forecast for period 20-30 July

This is what I posted in the final comment on the last lrf

'The longer term guides (teleconnections) do seem, about on balance, to favour the probability of another dry and very warm spell before the end of July. At the moment I'll leave it at that until the next update on 10 July when I hope a clearer signal will be there.'

To me there seems little sign of that this Friday.

I would suggest a rather unsettled spell with temperatures hovering around the average for late July, as usually is the case, the warmer values in the south and east. Here there are going to be a few more days above, possibly into the warm and perhaps a couple of days below in the period. Quite breezy at times as lows affect areas of the west and north especially. But these weather systems crossing all parts so some rain at times in the south and east. A small chance, say 30%, of perhaps one giving a brief warmer thundery flow before cooler Polar Maritime or returning PM air comes back in.

Edited July 10, 2009 by johnholmes

[La Bise]

Cheers John, you just ruined my week of hiking at the end of July in the UK. Right, flights to Switzerland.... :lol:

[johnholmes]

I shall be flying East Midlands-Geneva 7th August for 5 days walking in the Wengen/Jungfrau region.

Not that it will guarantee good weather-last year 2 good, 1 poor and 1 mixed out there!

[mushymanrob]

Forecast for period 20-30 July

This is what I posted in the final comment on the last lrf

'The longer term guides (teleconnections) do seem, about on balance, to favour the probability of another dry and very warm spell before the end of July. At the moment I'll leave it at that until the next update on 10 July when I hope a clearer signal will be there.'

To me there seems little sign of that this Friday.

I would suggest a rather unsettled spell with temperatures hovering around the average for late July, as usually is the case, the warmer values in the south and east. Here there are going to be a few more days above, possibly into the warm and perhaps a couple of days below in the period. Quite breezy at times as lows affect areas of the west and north especially. But these weather systems crossing all parts so some rain at times in the south and east. A small chance, say 30%, of perhaps one giving a brief warmer thundery flow before cooler Polar Maritime or returning PM air comes back in.

gutted :lol: , thanks anyway john, i hope you are wrong!

[johnholmes]

have to say I rather hope so

[William of Walworth]

How things change

Earlier hopes of July ending with a warmer, summery, more settled spell seem to be right out of the window for the moment ....

[johnholmes]

No 23 issued 17 July for the period 27 July to 6 August

Tropics

The only additional input from any of the centres is the NOAA update on 12 July which said;

•El Niño conditions are present across the equatorial Pacific Ocean.

•Positive sea surface temperature (SST) departures continue to increase across much of the equatorial Pacific Ocean.

•Current observations and dynamical model forecasts indicate El Niño conditions will continue to develop and are expected to last through Northern Hemisphere Winter 2009-10

AO over the past 7 days

It dropped the dip for a time but its back again and kept the rise towards zero, and about the same spread.

NAO over the past 7 days

The ‘dip’ has been just about made into two with a late rise above the zero line seemingly more definite on the last output.

NOAA comments over the past 7 days

mainly 3 or 4/5 through the week.

Looking at the NOAA model check and UK Met is about or a touch below GFS which is below the Canadian (not often its almost up to EC) with ECMWF just leading but not by much

NOAA 500 mb anomaly charts over the past 7 days

The area of +ve anomaly over the far north of North America into Greenland has been kept through the week with some extension south off the eastern seaboard. The –ve area near/over the UK and north north east has extended a little although the actual 500mb vortex near Svalbard has filled slightly. The trough just west of the UK from this has sharpened slightly making the 500mb flow more south of west rather than straight west into the UK. Some slight indication of a +ve area over Europe (south) but no marked change in that.

9 for 17-23 July and on right 16 for 24-30July

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

There have been some differences through the week between the two models regarding the positioning, size, depth/height of the main 500mb ridges and troughs.

EC has ended up suggesting a more SW flow than does GFS. Both show a +ve area for North America (similar to the NOAA version). Over Europe EC has the larger +ve signature. GFS also shows a more westerly 500mb flow again than ECMWF.

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

Of the two GFS has been the more consistent with its idea of a build to the NW as the trough and its low over the UK move east. EC dropped the idea altogether but has since brought it back (Thursday)

The 30mb temperature curve shows it a bit above the normal but tending slightly downwards.

Summary

Most model outputs both synoptic and others appear to suggest that it’s a flow at upper levels from north of west rather than south of west for this period. A surface flow from a similar point with a possibility of a more ridge type weather pattern settling over the country by the end of the period.

NB:-remember that the latest synoptic type chart finishes 30 July.

Forecast for period 27 July to 6 August

There now seems little to support the previous, diminishing idea as it was of the last 2 LRF’s. That is of a return of warmer weather by the month end. I would go 80/20% against that. A rather cool and at times unsettled spell seems the most likely. Perhaps one relatively active weather system but with the Atlantic through the period rather more evident than for some time. Some warmer settled days in the south east and fewer of these the further north west you go in the UK. Towards the end of the period then there is likely to be a more settled spell of weather developing with high pressure dominating. Initially this seems likely to be from a point WNW of the UK but could ultimately settle somewhere between ENE and ESE of the country.

apologies the charts will be added when I return Sunday evening

[johnholmes]

No 23 issued 17 July for the period 27 July to 6 August

Tropics

The only additional input from any of the centres is the NOAA update on 12 July which said;

El Niño conditions are present across the equatorial Pacific Ocean.

Positive sea surface temperature (SST) departures continue to increase across much of the equatorial Pacific Ocean.

Current observations and dynamical model forecasts indicate El Niño conditions will continue to develop and are expected to last through Northern Hemisphere Winter 2009-10

AO over the past 7 days

It dropped the dip for a time but its back again and kept the rise towards zero, and about the same spread.

NAO over the past 7 days

The 'dip' has been just about made into two with a late rise above the zero line seemingly more definite on the last output.

NOAA comments over the past 7 days

mainly 3 or 4/5 through the week.

Looking at the NOAA model check and UK Met is about or a touch below GFS which is below the Canadian (not often its almost up to EC) with ECMWF just leading but not by much

NOAA 500 mb anomaly charts over the past 7 days

The area of +ve anomaly over the far north of North America into Greenland has been kept through the week with some extension south off the eastern seaboard. The ve area near/over the UK and north north east has extended a little although the actual 500mb vortex near Svalbard has filled slightly. The trough just west of the UK from this has sharpened slightly making the 500mb flow more south of west rather than straight west into the UK. Some slight indication of a +ve area over Europe (south) but no marked change in that.

9 for 17-23 July and on right 16 for 24-30July

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

There have been some differences through the week between the two models regarding the positioning, size, depth/height of the main 500mb ridges and troughs.

EC has ended up suggesting a more SW flow than does GFS. Both show a +ve area for North America (similar to the NOAA version). Over Europe EC has the larger +ve signature. GFS also shows a more westerly 500mb flow again than ECMWF.

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

Of the two GFS has been the more consistent with its idea of a build to the NW as the trough and its low over the UK move east. EC dropped the idea altogether but has since brought it back (Thursday)

The 30mb temperature curve shows it a bit above the normal but tending slightly downwards.

Summary

Most model outputs both synoptic and others appear to suggest that it's a flow at upper levels from north of west rather than south of west for this period. A surface flow from a similar point with a possibility of a more ridge type weather pattern settling over the country by the end of the period.

NB:-remember that the latest synoptic type chart finishes 30 July.

Forecast for period 27 July to 6 August

There now seems little to support the previous, diminishing idea as it was of the last 2 LRF's. That is of a return of warmer weather by the month end. I would go 80/20% against that. A rather cool and at times unsettled spell seems the most likely. Perhaps one relatively active weather system but with the Atlantic through the period rather more evident than for some time. Some warmer settled days in the south east and fewer of these the further north west you go in the UK. Towards the end of the period then there is likely to be a more settled spell of weather developing with high pressure dominating. Initially this seems likely to be from a point WNW of the UK but could ultimately settle somewhere between ENE and ESE of the country.

Edited July 20, 2009 by johnholmes

[johnholmes]

No 24 issued 24 July for the period 3-13 August

Tropics

The IRI update issued 16 July link is below

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

Its main points were

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

'July is largely past the so-called "predictability barrier" of boreal spring, typically making ENSO predictions easier than several months ago for forecasts going through boreal spring. The emergence of weak El Nino conditions during June and July is often, but not always, followed by continued El Nino 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. The existence of positive sea temperature anomalies below the surface in the eastern tropical Pacific is conducive to El Niño development, as the warmer than average waters at depth (reflected by a positive thermo cline depth anomaly), currently strongest at longitudes of 100-130W, are poised to rise to the surface in response to the easterly low-level Trade winds.'

'Presently, the models indicate probabilities of about 82% for maintaining El Niño conditions, and about 17% for dissipation to ENSO-neutral conditions for the Jul-Aug-Sep season in progress. Going forward, probabilities for El Niño stay near 80% for the remaining 3-month periods in 2009, decreasing to approximately 75% by early 2010, and falling below 50% by boreal spring 2010. Probabilities for La Niña conditions are predicted to be negligible, not rising to above 10% until the middle of boreal spring 2010.'

AO over the past 7 days

Initially it predicted quite a rise but soon dropped this idea for the type of curve shown on the right.

NAO over the past 7 days

It also predicted quite a marked rise (see left) but has opted over the past few days for the type of graph seen on the right.

NOAA comments over the past 7 days

They have remained very happy with the model outputs throughout this week awarding 4/5 every day for the 6-10 and 8-14 day progs. Below is their summation as of Thursday (23/07)

6-10 DAY OUTLOOK FOR JUL 29 - AUG 02, 2009

THE NORTH AMERICAN LONGWAVE PATTERN REMAINS VERY AMPLIFIED FOR THIS TIME OF YEAR WITH THE MAIN DIFFERENCE FROM YESTERDAY A SLIGHT WESTWARD SHIFT IN THE OVERALL PATTERN. THE MODEL GUIDANCE FOR THE 500-HPA HEIGHT PATTERN DURING UPCOMING 6-10 DAY PERIOD REMAINS IN GOOD AGREEMENT AND INDICATES A DEEP TROUGH NEAR THE ALEUTIANS, AN AMPLIFIED RIDGE STRETCHING ACROSS WESTERN NORTH AMERICA TO EASTERN ALASKA, AND A DEEP TROUGH ACROSS THE CENTRAL US.

8-14 DAY OUTLOOK FOR JUL 31 - AUG 06, 2009

THE OVERALL LONGWAVE 500-HPA PATTERN INDICATED FOR THE 6-10 DAY PERIOD IS EXPECTED TO PERSIST DURING THIS FORECAST PERIOD. THE MAIN DIFFERENCES ARE A SLIGHT DEAMPLIFICATION OF THE OVERALL PATTERN - ESPECIALLY ACROSS THE CONUS -AND A MINOR SHIFT EASTWARD OF THE MEAN 500-HPA EAST-CENTRAL US TROUGH.

NOAA 500mb anomaly charts

They have shown the development of the –ve area w to sw of the UK and the main upper trough to move south to be close/over the country as shown on the right.

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

The two models have not been that different over the last 7 days. Generally indicating a flow either w or just s of wet for the UK. Neither have really made overmuch of any building upper ridge east of us. EC has been more bullish with the +ve area well north of the UK (USA into the Arctic area) than has GFS.

17 for 27 july 24 Jul for 3 Aug

It is worth noting that over the last 2-3 weeks the 500mb heights have slowly fallen in our area, by about 6-10DM.

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

The charts have tended at first glance to be rather different on some days but overall much in common but with the expected variations.

Starting with HP to the west as the cold upper trough moves east. By the end of the period both had brought another upper trough in with its attendant surface low.

I thought as an addition I'll put the Extra/GFS msl-jet chart for T+240 on as well. I can then see how well it compares with the actual data.

The 30mb temperature curve

This is just about on the normal curve.

Summary

Most of the output does seem to 'fit' together for the upper air and therefore its probably not too far out for the surface. All suggest to me that unsettled rather than settled is the main pattern for the period of the forecast.

Forecast for period 3-16 August

The synoptic charts all suggest, as far as they go, (remember the furthest only goes to the beginning of this forecast), a fairly mobile Atlantic at 500mb, and also the jet displaying characteristics more fitted to mid winter than mid summer. As an aside I have no idea why its taken up this stance since early July, I don't believe that the Tropics really hold the answer, but anyone have any ideas?

As to the weather then its unsettled more than settled, much as we are seeing today (24 July) I suspect. So little need to add the detail on that. At least one active depression I would imagine. There seems little sign yet of any major change occurring in this period. What may happen is that the high pressure in the Atlantic could move more towards the UK with it settling over or even perhaps a shade east of the country. That would seem to be only likely about the end of the period.

as usual charts will follow as time allows

Edited July 24, 2009 by johnholmes

[Gavin P]

Thanks John

Looks like continuing very mixed indeed.

Why has to jet taken up residence in such an unusually southerly position again? I wonder if the extended solar minimum is having an effect?

Edited July 24, 2009 by Gavin P

[damianslaw]

Another good read always and each week I am slowly beginning to understand more and more of your technical comments being a complete amateur.

Its not looking good is it... no pattern change as far out as mid August, think the curtains are closing in now on this summer being recorded anything other than average at best.

[pottyprof]

Fantastic work as always John..

Much appreciated..

[summer blizzard]

Indeed, it is very difficult to work out why we are seeing such a southerly Jet track, however my theory is that it is a combination of an easterly QBO encouraging negative AO conditions, and an El Nino keeping the Azores High weak.

[johnholmes]

I have done it but would prefer to sleep on it and see if I feel the same in the morning-tough choice this week-more than usually.

I will post it Saturday morning.

[NorthNorfolkWeather]

Indeed, it is very difficult to work out why we are seeing such a southerly Jet track, however my theory is that it is a combination of an easterly QBO encouraging negative AO conditions, and an El Nino keeping the Azores High weak.

Arghhh, another TLA I don't know (or my brain has seized up) what's QBO?

[johnholmes]

No 25 issued 31 July for 10-20 August

Tropics

The only 'new' item in this area is the NOAA update on 27 July; and the final sentence will obviously be noted by the cold winter lovers!

•El Niño conditions are 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 conditions will continue to intensify and are expected to last through Northern Hemisphere winter 2009-10.

AO

After a forecast of a rise then a drop it has now gone much more towards a rise, although the one this evening (on the right) is perhaps a touch too high based on evolution over the past 7 days.

NAO over the past 7 days

This has tended to show an increase but with quite a spread at times; its idea of a fall at the end is something new on the output for today.

NOAA comments over the past 7 days

Their main comments have been directed at the differences from the models in the Alaska area, otherwise they seem happy enough with their output for their area.

On Tuesday they said:-THE HIGH-LATITUDE RIDGING DEPICTED OVER NORTHEAST CANADA AND GREENLAND IS WELL SUPPORTED BY NEARLY ALL MODELS.

8-14 says, much as yesterday re this trough and again 4/5

THE OPERATIONAL 00Z AND 06Z GFS RUNS CONTINUE TO PREDICT, FOR THE SECOND DAY IN A ROW, A DEEP UPPER-LEVEL TROUGH OVER THE ARCTIC OCEAN WHICH EXTENDS SOUTHWARD ACROSS MOST OF ALASKA.

By Friday THE FAIRLY INTENSE ARCTIC OCEAN VORTEX IS EXPECTED TO REMAIN ON THE ASIAN SIDE OF THE BASIN.

NOAA 500mb anomaly charts

Taking the NOAA comments as acceptable for their area then the area of concern for UK/Europe is the position of the 500mb trough in this area and is there any build of pressure to our east.

Consistently over the past week the NOAA 8-14 day charts have shown the trough sticking around in about the same longitude through the period, although the orientation has changed. The direction of 500mb flow predicted stays either west or even a touch north of west. A –ve area has been progged to be over/NE of the UK with a +ve area to the west of the country.

23 Jul for 31 Jul-6 Aug 31 Jul for 8-14 Aug

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

Their output has been quite interesting. Both, to a degree, disagreed with the NOAA version and moved that trough west, from near the meridian to about 20W as the one on the right shows. However, this morning they both changed their minds and went back to the idea of it in about the same place as the NOAA charts had kept it all week. That said they do show the 500mb flow more south of west than NOAA.

The one valid for 9 August is on the right

I thought as an addition I'll put the Extra/GFS msl-jet chart for T+240 on as well. I can then see how well it compares with the actual data. As you can see the jet is very much with us.

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

The Euro model has been fairly consistent showing surface low pressure near/over the UK with high pressure showing through the 7 days both over Europe and out in the Atlantic.

GFS has, this week, been the more variable of the two, alternating between trough and ridge. Tonight it shows a not too different idea from EC, so perhaps there is some confidence in the outlook at T+240?

The 30mb temperature curve

This is just about on the normal curve.

Summary

I find there to be rather conflicting suggestions of the flow at upper levels. Will it be north of west or south of west? Where will the upper trough be during the period 10-20 August? On these two major factors rests the probable weather pattern for the UK.

Forecast for period 10-20 August

Given what I've written in the summary it's a tough choice. Like most I would like a bit of 'real summer' so trying to be unbiased is very difficult.

I think there is more evidence against a summery spell than for it to be honest. On a betting basis maybe at 60/40.

On this basis I would go for a cooler than average start and unsettled with still a decent flow at upper levels across the Atlantic. Rain or showers at times for all especially so for the north west and also breezy at times as lows track near or even across the UK. During the period then things will calm down with high pressure beginning to have more effect. It will be perhaps a two way development. Higher pressure than for some weeks in the Azores area ridging east with signs of the European high also developing. Temperatures tending to rise from the SE corner with only the more NW'ern areas not benefiting. Less in the way of wind and rain for most as well. As to how warm then best to leave for another week as also about whether any thundery developments may occur.

Edited August 1, 2009 by johnholmes

[Methuselah]

Thanks John. An interesting read as usual.

[johnholmes]

If anyone is interested, as part of the increasing use of videos on NW, the link below will give an insight into how a previous lrf was prepared and what the two checks on it revealed.

In time I would hope that about 1 in 4 of the lrf's would be available on video as well as in text and charts as above.

http://www.netweather.tv/index.cgi?action=community-video;sess=

[johnholmes]

No 26 issued Thursday 6 August for period 16-26 August

Tropical input

NOAA update on 3 August

•El Niño conditions are 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 conditions will continue to intensify and are expected to last through Northern Hemisphere winter 2009-10

No ENSO update expected until mid month-please read lrf for the one issued 16July

In brief it anticipated El-Nino and said in the final paragraph

It indicates a 82% probability for El Niño conditions in the Jul-Aug-Sep season in progress, remaining near 80% through Dec-Jan-Feb 2009/10 and decreasing rapidly after the first few months of 2010.

It made no mention of intensity.

Other

CPC monthly outlook in USA area

30-DAY OUTLOOK DISCUSSION FOR AUGUST 2009

EL NINO CONDITIONS CONTINUE ACROSS THE EQUATORIAL PACIFIC OCEAN WITH WEEKLY

AVERAGE SEA SURFACE TEMPERATURE (SST) ANOMALIES BETWEEN +0.5 AND +1.5 DEGREES

CELSIUS ©. DURING THE LAST MONTH CONVECTION HAS BEEN ENHANCED NEAR 180W

LONGITUDE WHILE LOW LEVEL WESTERLY WIND ANOMALIES HAVE BEEN OBSERVED JUST TO

THE WEST OF THIS AREA ALONG THE EQUATOR.

AO

It has shown a continula idea of increasing values above zero; not quite as much as the first prediction.

NAO over the past 7 days

It too continues to show values rising to above zero with perhaps a slight suggestion of a fall towards the end.

NOAA comments over the past 7 days

They have been none too impressed throughout the week with marks usually 3/5 and this evening down to 2/5 for the 8-14 day in their main area of interest.

NOAA 500mb anomaly charts

Through the week it showed the +ve area migrating eastwards so that it is now expected to be into the west/SW by the second into the third week of August. Less pronounced in terms of +ve anomaly and still far enough south for the flow to be, at 500mb, from north of west.

9-14 and on the right 14-20 August

The link below is to the running check NOAA do on the models scoring in the N Hemisphere

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

Briefly it shows EC leading with the other 3, UK, GFS and Canadian interchanging for second position.

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

The marked 500mb trough has been predicted over the 7 days to be replaced by a ridge WSW of the UK. The latest chart shows this continues; the 500mb flow is from the WNW, especially on the GFS version.

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

They both had low pressure dominant in their prediction for Monday 10 August whilst the overall idea from them both, now at T+96, is for the low to be somewhat less noticeable and the ridge rather more so.

Subsequently EC has still got this at its T+192 but GFS has opted for high pressure. By T+240 today EC is now ‘pro’ low and GFS is ‘pro’ high!

So little real continuity for anyone there. The EC version does fit better with both of their N Hemisphere predictions for T+240 and also that from NOAA over a similar period.

And the jet at 12Z on Saturday 1 August for T+240 and T+384 as well

It remains to be seen how that fits with the actual pattern on those dates. Neither really fits with the 500mb anomaly charts from any of the 3 centres it has to be said.

The 30mb temperature curve

It continues to trundle just a touch above its average for this time of the year.

Summary

The immediate synoptic guidance, the T+240 is mixed. GFS and its msl-jet idea (from 1 August) are at variance with the hemisphere 500mb charts from all 3 centres. Otherwise the synoptic advice, as opposed to further out (-ENSO-AO-NAO) is along similar lines from each source.

Forecast for period 16-26 August

The T+240 from GFS is not too reliable this week in my view. I rarely give it more than a slight weighting anyway and EC is often the one, as shown almost every month on the NOAA checks, to outperform GFS at 6 days.

So the forecast today leans heavily on the 500mb outputs from all 3 centres for an idea of how the period may start.

Almost certainly with high surface pressure west of the UK, probably between 50 and 55N. This means more settled the further south one is but with possible weak weather systems affecting some in the east or at least the north east. As time goes on I feel that this area of upper ridging will tend to shift a bit further east which will bring most of the country under its influence. To me it would seem more likely that an upper ridge will end up a little east of the UK with any marked upper trough well east of it. The next one to the west is probably going to take 7-10 days to move into the UK area. So a settled and increasingly warmer spell through the period but with a threat of a breakdown, possibly thundery towards the end of the period.

I’ll have another quick look at it in about 8 day’s time.

No full update though; I’m away until then, so the next full update will be Friday 28 August for 6-16 September. Autumn already!

my apologies but due to time constraints there will be no charts in this issue.

[johnholmes]

I said I would have another look at this period when I got back from holiday. Forecast for period 16-26 August

It’s a very different ‘picture’ that most inputs are now showing.

Be it in the Tropics, and its longer term effects, NOAA anomaly charts and those from ECMWF and GFS, all show unsettled as the theme rather than settled well into this forecast period. There will be some drier and warmer spells in the SE of the UK but overall it’s a picture of unsettled weather with weather systems passing fairly close to the NW of the UK, giving bursts of rain and strong winds at times for that quarter, and for weakening frontal systems to make their way into southernmost counties at times. The start of the period coinciding with a thundery break-down with the hotter and humid air soon moved away east of the country.

High pressure may be tantalisingly close at times, both SW and NE of the country. However, I rather feel that neither will be close enough for much of the time to have more than a transitory effect on most parts of the country. The SE quarter, as mentioned above, being the most likely to benefit at times.

Remember also when looking at the two major models, ECMWF and GFS, certainly post T+144/168, at this time of year, the probability of tropical storms occurring. Both models have problems initialising these systems, so don't expect too much from them at the longer time scales in terms of accuracy nor of continuity. Of course they can be amazingly accurate so we just have to keep a very careful watch on their outputs.