In Depth Model Discussion, Analysis and Summaries

[mushymanrob]

guys ... any signes yet of an end to this (awful) cold please?

[SteveB]

Yeah I was hoping for an update on ideas for what Spring has in store for us.

[BLAST FROM THE PAST]

guys ... any signes yet of an end to this (awful) cold please?

12th March approx, certainly midmonth...but not prolonged before becoming unsettled and cooler again. The jetstream may well be a headache for sometime yet.

BFTP

Edited February 24, 2010 by BLAST FROM THE PAST

[damianslaw]

12th March approx, certainly midmonth...but not prolonged before becoming unsettled and cooler again. The jetstream may well be a headache for sometime yet.

BFTP

I agree the jet stream is unlikely to swing northwards anytime soon, also this is not the time of year when you would expect it do so, if it was November then perhaps yes. The jet stream over the past 2-3 years has been very erratic and displaced on a much more southerly track for very long periods - remember summer 07 and 08, not sure if this is cyclical or just a blip, but the trend in recent years has definately been for a more southerly tracking jet.

[Don]

I agree the jet stream is unlikely to swing northwards anytime soon, also this is not the time of year when you would expect it do so, if it was November then perhaps yes. The jet stream over the past 2-3 years has been very erratic and displaced on a much more southerly track for very long periods - remember summer 07 and 08, not sure if this is cyclical or just a blip, but the trend in recent years has definately been for a more southerly tracking jet.

Interesting stuff. I see that over on TWO they are expecting the jet stream to return to its normal position by mid March, bringing much milder and Springlike weather to the UK, although they are expecting some colder weather at times in the meantime.

[cooling climate]

Sorry I thought this was technical model thread not the lets have a stab in the dark

or wild guess thread. This is a good thread with in depth posts from GP, John Holmes etc

but posts such as above with no detail or reasoning behind a prediction should not be allowed

in this thread. The title of the thread is quite clear.

I posted this in a couple of threads this morning and I think it would be relevent

in here plus with most of the convection in the tropical Pacific now just west of

south America this would support blocking further east I would have thought.

It would be good to here you thoughts GP.

Looking at these stratospheric charts it looks like I was wrong calling for this blocking

and potent cold spell some two weeks back.

The stratospheric charts below show that the warming in November did not really impact

upon us until some 6 weeks later and although we have felt the influence of high latitude

blocking during February the MMW over Svalbard and Scandinavia has not shown up (blocking)

in the models until now. Again this looks to be roughly six weeks since the warming

commenced that the blocking in the areas mentioned are now showing up in the models.

http://strat-www.met...t=temps&alert=1

http://strat-www.met...ot=town&alert=1

http://ds.data.jma.g...e/pole30_n.html

Due to the warming further norht than where the models show the block to form I would not be

surprised to see the block further north on future runs.

Another reason I was so far out with the downward propagation of the 30mb warming was that

I stupidly had it in my head that the 30mb level was lower than the 400k isentropic level.

This of course is completely wrong the 400k isentropic level is approximately 50,000ft where as

the 30mb level is approximately 70,000ft. Whoops.

Edited February 25, 2010 by cooling climate

[lorenzo]

AO projected to go positive for the first time in a while within the fortnight, blink and you'll miss it.

NAO still in a negative position but only just, weakening as March begins.

MJO Firmly in stage 7.

A good animation of the 500mb preceeding our current position -giving no indication of any blocking establishing?

Next fortnight seems pretty unsettled, I reckon Atlantic Lows may be the headline events..

[bluearmy]

AO projected to go positive for the first time in a while within the fortnight, blink and you'll miss it.

NAO still in a negative position but only just, weakening as March begins.

MJO Firmly in stage 7.

A good animation of the 500mb preceeding our current position -giving no indication of any blocking establishing?

Next fortnight seems pretty unsettled, I reckon Atlantic Lows may be the headline events..

very odd post Lorenzo - the forecast is completely different and becoming blocked within the reliable. certainly not atlantic driven.

interestingly, the AO was forecast to return to neutral within the next couple of weeks though NOAA cpc yesterday wrote that it would now stay negative. Chio expected the polar ridge to migrate towards siberia though it would seem to stay stuck close the pole for the foreseeable. the icleandic anomoly was shown stronger than the candian one on yesterdays 8/14 dayer. nice to think it will be the same ths evening.

[lorenzo]

Headline events in terms of intensity, interest and model watching blue army - not a long term prediction.

Am not citing a breakdown here just venturing that it seems to be where the majority of the energy is kicking up, agreed not Atlantic driven.

[johnholmes]

I'm not sure if this belongs in here mods as its not particularly technical-so delete if you wish as its already in my blog?

Update on my last thoughts

Well meteorology can and does change, at whatever time scale you try and forecast for.

This time in the longer term view-into mid March and its now got a definite suggestion of staying cold-how cold is open to question. Obviously its highly unlikely to be as cold as during mid winter. The average temperature for here is now almost .75C higher than mid January so everywhere starts with a higher base line temperature. Mid winter provided values 2 sometimes almost 3 degrees below the long term average, so will this give 2 or 3C below the early/mid March values?

I doubt it other than an occasional day but its still looking cold, or rather cold, with surface high pressure probably most likely located NW of the UK-how far west is of course important, too far and the jet would be able to develop north with the major trough well west of the UK. To me it looks like the upper ridge will be over or west of the UK which puts the country on the ‘cold’ side of the upper flow.

How unsettled is another question. Initially the idea of the high close by and fairly settled if rather cold into early March is perhaps a slightly higher bet than cold and unsettled but its close. With time I suspect the surface high and upper ridge will move further west and FOR A TIME the UK will be on the cold and unsettled side of the ridge. How long this might last with its prospects for snow as well as frost even for lower lying areas is impossible to give a reasonable idea yet-it is a possibility of at least 5-7 days I would think. Eventually though the flow off the Atlantic and with less cold indeed milder air flowing north must happen-betting? Say mid March onwards, probably by the third week for an overall rise in temperatures across most of the country.

[Glacier Point]

Since early February, the gobal circuation has become firmly and fundamentally shifted towards an El Nino base state.

All measures - the SOI, Angular Momentum and Global Wind Oscillation - all show a strong Nino signal. Tropical convection remains centred east of the Dateline despite some semblence of a trade wind increase in line with upper level vorticity waves. This is the clearest indication of the extratropics and tropics working together to add westerly wind anomalies to the general circulation. Leaving out the QBO signal, relative angular momentum is well, well above average with anomalies of +3 SD:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig1-21.90day.gif

Another important consideration is that the current hemispheric SSTA pattern outside of the tropics is strongly reinforcing the atmospheric signal, especially a distinct Atlantic Tripole:

http://weather.unisys.com/surface/sst_anom.html

All of these project onto a strong -NAO signal with the associated depressed jetsream going forward into March, probably sustaining for a substantive amount of the month given historical analogues guidance:

With the stratospheric profile signalling blocking into the next 30 days (weak polar vortex), there is very little to suggest any change to the overall pattern which broadly consists of below average pressure over Europe and the back end of a much below average winter across large parts of the Northern Hemisphere.

Tonight's GEM/GFS ensemble mean guidance continues to advertise the expected weather pattern with pressure higher over Iceland and southern Greenland, low heights over the Atlantic and the jet well to the south of the UK allowing below average temperatures and generally unsettled conditions, particularly to the southern and south-western parts of the UK.

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

[Rollo]

Thanks again Stewart for your latest update-your projections throughout the winter have been a revelation.

[BrickFielder]

If anyone is wondering why this thread has gone a bit quiet it is because many of the signals you expect to influence the weather at this time of year are not really present. Mostly I agree with what Stewart has suggested with some perhaps subtle differences.

Firstly the stratospheric vortex is very weak and seems likely to remain over northern asia. This gives us a somewhat weak signal for high pressure to build in our region.

One of the strong influences on our weather would appear to be the atlantic tripole of sea surface temperatures again as stewart mentions.

The correct atmospheric response to those sea temperatures at this time of year is as follows.

Stewart also quite rightly points out that global angular momentum is high which would normally indicate an el nino base state. I think this is where I might question the thinking having looked at the state of the MJO.

This shows that although there have been MJO events they really have not made it across central and eastern parts of the pacific. El nino events don't need thunderstorm activity to hold back the trade winds across the central pacific, but I would not suggest this is a typical MJO driven el nino. We know that the SOI has tanked recently and this appears to be related to tropical storms rather than the base el nino. In a way the southern hemisphere and the region between Africa and the western pacific is driving the global weather, which is unusual.

Sub surface temperatures in the central pacfic suggest that el nino may well make a bit of a reappearance at some point, but I am not sure it is a critical factor at the moment. Mountain torque is back on the rise so I expect global angular momentum to fall a little from here on in.

Key for me at the moment is the MJO forecasts which show a slow moving event decaying as we go into march. I should note that things have somewhat deviated from these forecast already, but the repsonse I think we hold for a while.

and the response to this would be.

Notice the high pressure north of the MJO event, which I think will force a battle between the pacific and the atlantic patterns. I expect a negative NAO to form while the AO will tend towards neutral, which by nature seems a rather unstable situation. For once I have a hunch that the atlantic might win, although once the reminants of the el nino emerge this might be overturned.

Short term I expect high pressure not too far from the UK, whilst longer term we need to watch for the complete decay of the stratospheric vortex, the changing jet stream wave lenghts and the emergence of the sub surface warm water in the pacific which will change the pattern.

[Eugene]

Thanks brickfielder, you say the atlantic winning yes towards the spring equinox you would expect the atlantic to awaken from its slumber, you are expecting a negative NAO with AO tending towards neutral so are you favouring HP retrogressing northwestwards and allowing the awakening atlantic to undercut the high and dive into france only really affecting southern england and keeping most of the UK cool to cold?

When you say which will change the pattern do you mean HP centred over northern UK or just to our north slipping into europe and allowing the atlantic in that way?

Would you expect a cool zonal or mild zonal flow if that was the case?

[BrickFielder]

Thanks brickfielder, you say the atlantic winning yes towards the spring equinox you would expect the atlantic to awaken from its slumber, you are expecting a negative NAO with AO tending towards neutral so are you favouring HP retrogressing northwestwards and allowing the awakening atlantic to undercut the high and dive into france only really affecting southern england and keeping most of the UK cool to cold?

When you say which will change the pattern do you mean HP centred over northern UK or just to our north slipping into europe and allowing the atlantic in that way?

Would you expect a cool zonal or mild zonal flow if that was the case?

For the next few weaks high near the UK and low pressure systems undercutting into france seems right although this will slowly begin to move northwards.

After that its a bit guess work. The lengthening wave lengths should move things eastwards, the breakdown of the stratospheric vortex will promote a blocked pattern especially to the north, but will also bring the pacific and el nino more into play. In the meantime the jetstream will begin to move north, although slowly in regions with remaining snow cover I expect a swifter move north in our vicinity. For me I think we get the atlantic weather for a month through April and May rather than later in the season like last year, leaving the door open for a warm summer period.

[Eugene]

Ok cheers for your reply :lol:

Yes warmer drier April/May periods tend to lead to cooler wetter summers so hopefully a wetter April/May period will promote a warmer drier summer than the past three summers :lol:

The atlantic dominating April/May isn't all bad news for April especially though as we can get some traditional April showery PM type northwesterly/westerly airstreams with warm sunny periods and convective showers with hail some wintriness and thunder

[Thundery wintry showers]

It will be interesting to see how this pans out- the suggestion of a sudden northward lurch of the jet might indicate scope for a switch-around sometime in the third week of March perhaps? I'm thinking in terms of possible northerlies and wintriness followed by a plume of southerlies and temperatures into the teens over much of the country- like the switch-around of mid March 2005.

Also thinking of the implications of a blocked pattern to the north but an Atlantic regime- possibly some scope for the odd brief cold/wintry incursion in there? Like Eugene I can also envisage a fair amount of polar maritime based convective potential arising from that scenario.

I don't think there is much of a relationship between warmer drier April/May periods and the following summer.

[mushymanrob]

I don't think there is much of a relationship between warmer drier April/May periods and the following summer.

spring 1983 = cool and wet, summer 1983 = hot and sunny

spring 1975 = cool and dry, summer 1975 = hot and sunny

spring 1990 = warm and dry, summer 1990 = hot and sunny

i agree, theres no correlation between spring weather and summer weather.

[johnholmes]

No one has ever been able to produce sufficient evidence to link any prior season to any subsequent one, not for temperature or precipitation. Had there been any then it would have featured in the major centres seasonal forecasts.

[Glacier Point]

Anyone for a below average March ? You bet.

Tropical convection is somewhat suppressed but generally the largest anomalies are centred east of the Dateline indicative of a mature El Nino base state.

http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html

East zonal mean wind anomalies are prevelent across 10N - 30N in most of the tropical Pacific indicative of a downward phase in angular momentum.

http://cimss.ssec.wisc.edu/tropic/real-time/wavetrak/winds/wavetrkP.html

However, thanks to our surge in westerly winds during February, which have drawn atmospheric support from coupled ocean-atmopshere dynamical processes, both total and relative angular momentum are still well above average. Notice how, despite easterly winds in the tropics, the atmosphere is still dominated by westerly intertia.

Mountain and frictional torques are helping to remove and add westerly winds and the whole set-up looks to have a stable look. MJO forecasts provide a useful insight into the overall direction of travel for the atmosphere. Ensemble forecasts weaken the MJO signal but the key thing to note is that the tropical wave signal is still centred in the western hemisphere and struggling to make a low angular momentum push towards phases 2,3,4.

http://www.cpc.ncep.noaa.gov/products/people/wd52qz/mjoindex/index/diagram_40days_forecastGFSOP_CFSOP_GEFS.gif

The Global Wind Oscillation is centred in phase 6 and the overall signal from the tropics and extratropics would tend to keep the GWO in phases 6-7-8, perhaps falling back a little over the next 10-15 days before our next westerly wind burst at the end of March (more blocking therefore in April) introduces further westerly inertia to the system.

Composites for these phase of the GWO are somwhat problematic as they offer unsatisfactory continuity between phases but using the MJO and GWO plots appears to suggest the following:

1) mean upper ridge centred to the north and west of the UK, becoming more centred towards Iceland and Greenland coinciding with phase 8;

2) mean upper trough for Scandinavia and much of Eurasia.

3) blocking high centred over the Canadian Arctic.

GWO phase 6:

GWO phase 7:

MJO phase 8:

This translates to a flow generally north and north west for the second half of the month, possibly easterly at time. This is a strong pointer I think towards a below average temperature regime to persist with rainfall generally below average.

[chionomaniac]

Anyone for a below average March ? You bet.

Composites for these phase of the GWO are somwhat problematic as they offer unsatisfactory continuity between phases but using the MJO and GWO plots appears to suggest the following:

1) mean upper ridge centred to the north and west of the UK, becoming more centred towards Iceland and Greenland coinciding with phase 8;

2) mean upper trough for Scandinavia and much of Eurasia.

Thanks for the update GP. I have been too busy recently to update the stratosphere thread but would suggest that indications from the 100 hPa level stratospherically strongly reinforce the above suggestion for days 7-10. My bet is for the current mid latitude high to back west then ridge north. Whether the PV weakens sufficiently to allow a full high latitude blocking event after this remains to be seen but it is good to see that GWO/MJO phases reinforce this idea.

c

[SteveB]

I wonder if anyone would be kind enough to give their thought on the coming months. I t would be interesting to hear what the state of the strat, AO,NAO is.

Purely from a selfish point of view, more interested in the end of May as that is when I am getting married.

Edited March 30, 2010 by SteveB

[The PIT]

I would like this to be a regular feature as it's very interesting and educational.

[johnholmes]

Yes its a great thread in the winter but it does take a lot of time and effort to produce the posts that you see from ch and GP.

One of the reasons I gave up on the detailed lrf work was the amount of time and effort it took once a week.

[The PIT]

Yes its a great thread in the winter but it does take a lot of time and effort to produce the posts that you see from ch and GP.

One of the reasons I gave up on the detailed lrf work was the amount of time and effort it took once a week.

Perhaps you could ask them nicely if they've got any ideas for the summer.