Summer 2006

[Glacier Point]

I won't pretend that any seasonal forecast is easy, but this year's Summer forecast presents particular challenges, one where any of the below, average or above average permutations are entirely possible.

The challenge is presented by a whole range of changing long term variables, and, we are forced to decide just how much what has been will influence the future. For example, the La Nina episode of the Winter has now effectively ended, the Pacific Decadal Oscillation which for the last few months has been positive now shows all the hallmarks of a negative phase for the majority but not all of the Pacific. Add to this the variability in the model outputs, and you get some sense of just how tricky putting up a call for the next three months is going to be.

In my preview post I examined a range of factors which I believed would have an influence on the winter.

http://www.netweather.tv/forum/index.php?s...ndpost&p=665782

Some of the factors have changed (most notably in the Pacific) so here is my assessment of what I believe will be a Summer shaped significantly by the large oceans of the northern hemisphere.

El Nino Southern Oscillation (ENSO)

ENSO is a well documented phenomenon which has a strong statistical relationship with the pressure, rainfall and temperature patterns over the Pacific Basin and beyond. There are many measures of this but I'm using the Multivariant El Nino Southern Oscillation Index (MEI).

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

http://www.cdc.noaa.gov/Correlation/mei.data

April's MEI value was -0.594 which is indicative of a weakish La Nina event. This represented a continuation of La Nina (negative MEI) back to October last year. However, looking at the current Sea Surface Temperature Anomaly (SSTA) plots, the equatorial Pacific SSTAs look to have entered (for the most part) ENSO neutral conditions.

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

This is borne out by the SSTA modelling with a consensus on neutral ENSO conditions now taking effect:

http://www.cpc.ncep.noaa.gov/products/pred...efing/sstaa.gif

http://www.met-office.gov.uk/research/seas...nino/index.html

http://www.cdc.noaa.gov/forecast1/for4entrgl.html

http://iri.columbia.edu/climate/ENSO/curre...fo/figure3.html

http://www.cpc.ncep.noaa.gov/products/anal...ino34SSTMon.gif

Although what has taken place over the last six months (La Nina), the latest assessment of the Pacific Basin indicates the atmospheric effects of this cold phase only to persist in the far western Pacific - and not anticipated to last for much longer.

There have been many comparable ENSO neutral condition Summer periods, and, whilst some there is some variability within these analogue years (1995 for example), the composite anomaly pattern for upper level anomalies looks like this (assuming average JJA values between -0.2 and +0.5):

Note the positive anomalies over the central Pacific, negative ones over the Hudson Bay area, weak positive anomalies in the central northern Atlantic and of course, the very negative anomalies over the UK. Whilst all composite anomaly patterns are to be treated with a certain amount of scepticism, this represents a large enough sample and strong correlation for negative heights over the UK to be taken seriously.

The Quasi-biennial Oscillation (QBO)

The QBO is regarded by some metreologists as a key measure of the strength and future guide to the behaviour of the Pacific Jet.

http://www.jisao.washington.edu/data_sets/qbo/

http://ugamp.nerc.ac.uk/hot/ajh/qbo.htm

http://www.cdc.noaa.gov/Correlation/qbo.data

We should now be familiar with this as the large negative (easterly) phase zonal wind was largely responsible for Europe falling just a little short of wintry expectation. Now the QBO is in a positive (westerly) phase (it broke positive in April with a value of +5).

One more look as the current SSTA plot shows a warm pool of surface waters in the central-western Pacific.

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

Crucially the warm waters extend to some depth in the west...

whilst plenty of cold anomalies to the north-western Pacific allied to colder than normal air spilling off a snow covered Asia will make for a strong thermal gradient in the western Pacific and a stronger jet.

As the QBO tends to change on 5 to 8 point values every month in a predictable biennial pattern, this means that we are likely to experience a moderate strength QBO this Summer, typically around +12 to + 16.

Whilst a rising westerly phase QBO is something of a scarcity for Summers (there have been approximately 10 in the last 58 years, the composite anomaly pattern is reasonably convincing towards the following pattern:

Once again, a similar pattern to ENSO neutral pattern arises - positive upper level anomalies over the central and north-eastern Pacific, negative anomalies over the Hudsons and a striking negative anomaly over the UK.

On the other hand, a strong West Pacific Jet may also be characterised by a positive phase West Pacific Oscillation. This teleconnects to troughing in the jest ream over the western USA and higher pressure over western Europe (a Bartlett High):

http://www.cdc.noaa.gov/people/gary.bates/tele/wpo.cmp.gif

Pacific Decadal Oscillation (PDO)

http://www.jisao.washington.edu/pdo/

http://jisao.washington.edu/pdo/PDO.latest

I'm just not sure how to read the PDO at the moment. The PDO has been in a positive state ever since August of 2002 although it has had a few flirtations with the odd negative month. However, the Pacific SSTA looks strikingly like a cool phase PDO, and has done so since late March early April:

http://weather.unisys.com/archive/sst/sst_anom-060319.gif

http://weather.unisys.com/archive/sst/sst_anom-060409.gif

http://weather.unisys.com/archive/sst/sst_anom-060507.gif

Note the cold water up and down the eastern Pacific and the warmer central western Pacific - a classic indicator of the cool phase PDO,

…..except that is apart from the strong cold anomalies around the seas of Japan and the Gulf of Alaska.

The SSTA forecasts pick up this cold eastern Pacific theme, albeit to varying degrees:

http://www.cpc.ncep.noaa.gov/products/anal...s/glbSSTSea.gif

http://iri.columbia.edu/forecast/sst/06/gl...JA_may2006.html

If we are to enter a brief -ve phase PDO, there may be some influences on the jet pattern over North America which would impact on the UK's Summer. However, I've seen lots of and often conflicting composite anomalies and analogue patterns for -ve PDOs, but I'm yet to be convinced. For what it's worth, here are the composite anomalies for the most negative PDO years and the linear regression for the seasonal mean:

If anything, I'm slightly inclined to the solution suggesting positive upper level anomalies over the central Pacific and guess what, that big blue (negative an height anomaly) blob over the UK. The other point to note is that the effects of the PDO tend to vary somewhat from month to month.

Atlantic Sea Surface Temperature Anomalies

The UKMET use a statistical forecast for Summer and Winter patterns based upon the SSTA of the northern Atlantic during the 6 previous months:

http://www.met-office.gov.uk/research/seas...background.html

The predictor pattern indicates well how positive SSTA influence long lived positive height anomalies and negative SSTAs help bring about negative anomalies in the upper level patterns.

Looking at the SSTA composite anomaly for the period January through to April, and the latest available seasonal product, the following are noticeable:

http://www.cdc.noaa.gov/map/images/sst/sst.anom.seasonal.gif

1) The warmth of the entire northern Atlantic, with the core of this warmth located to the western Atlantic region off Newfoundland.

2) The development of cold SSTAs down the eastern Atlantic in the last month.

3) The relatively less cold band across the sub-topical Atlantic and marginally cold anomalies now extending down to the Azores from the UK.

4) The warm tropical Atlantic.

This pattern is neither a perfect match with the cold or warm predictor pattern used by the UKMET, although the developments over the last month to six weeks (cold anomalies over the Azores and UK) incline this assessment towards the cooler pattern rather than the warmer one - if nothing else the prevailing SW wind will be cooler than normal just because of the long fetch of cold SSTA over which they have passed.

For the last couple of months, this pattern has been conducive to the lowering of pressure in the north Atlantic as low pressure systems coming off north America are forced to take a lower and lower track. This in turn helps promote height rises over Greenland, a de facto negative North Atlantic Oscillation (NAO).

http://www.met.rdg.ac.uk/cag/NAO/

http://en.wikipedia.org/wiki/North_Atlantic_Oscillation

http://www.jisao.washington.edu/data_sets/nao/

http://www.cdc.noaa.gov/Correlation/nao.data

http://www.cdc.noaa.gov/people/gary.bates/tele/nao.gif

Whilst the NAO is rarely in a prolonged -ve phase, the period from late February has been characterised by an unusual frequency of -ve NAO in the context of the last few years, no doubt aided by a strong tropical storm season last year.

Based on the assumption that SSTAs from the previous 1 to 6 months influence the summer patterns, a weakly -ve NAO is a high probability based upon the SSTA alone although other factors such as the Arctic Oscillation and jet patterns exert their own influence on Atlantic pressure patterns.

A composite pattern for the top -ve NAO summers looks something like this:

Note the very strong indication of negative height anomalies over the NE of North America and those over NW Europe, plus the strong positive anomalies across the Polar region.

Another aspect of the northern / central Atlantic SSTA, particularly that showing now:

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

.. is the couplet of cold and warm anomalies in the sub-topical region. This will continue to exert a strong influence for the sub-topical jet to remain active and displaced well to the south of its normal latitude, as it has done so since February. This will in itself increase the chances of continued height rises over Greenland (as shown by the -ve NAO composite anomaly) and increase the chances of the polar jet stream straddling the UK.

Polar Cell

This Winter was really characterised by a noticeably larger but slightly displaced polar cell. Warm waters in the Pacific and perhaps the effects of the approaching solar minima helped to shift the parcel of cold air towards the eastern half of the northern hemisphere across Eurasia. This is still in evidence today, look at the relative positioning of the cooler air:

One of the pieces of analysis arising out of the winter forecast was the possible long term influence of forced global warming in promoting a warmer pole leading to greater probability of blocking and a negative Arctic Oscillation (AO). The theory suggests that increased surface temperatures will warm the atmosphere over time, eventually affecting the upper levels of the troposphere and eventually the stratosphere.

Right now the temperature profile of the polar region looks like this:

http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif

….. note the influence of surface temperatures up to around the 200 hPa level - high enough to influence the hemispheric circulation. Looking once again at the SSTA analysis over the last few months, the most striking aspect is the warmth of the polar region which is likely to increase the chances of a -ve AO for at least one of the summer months.

http://www.cpc.ncep.noaa.gov/products/prec...ent.ascii.table

It should be noted however that statistically the three Summer months are most likely to be AO neutral although June is when a +ve AO is most likely to materialise and August a -ve AO.

All of this translates to an increased probability of the polar cell remaining intact through the Summer, and occupying a greater area thereby working against the migration northwards of the high pressure cells.

Incidentally, the ITCZ has shown a variable pattern exceeding its normal position in some longitudes and falling below in others (possibly reflecting long term changes in global weather patterns and likely to lead to increased variability in extra-tropical weather patterns):

http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/west.gif

http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/east.gif

The below average mean positioning off the African Coast might signal a stronger sub-tropical high shifting the mean position of the Azores High further east towards SW Spain and northwards to the mid-Atlantic.

Tropical Storm activity

This Summer, the key ingredients for another active Atlantic tropical storm season are in place. A warm tropical east Atlantic and a westerly phase QBO leading to reduced wind shear will see a string of low pressure systems circulating from the Gulf Coast up the eastern Seaboard from mid Summer onwards.

The positioning of the polar jet stream at this point will be crucial in determining where these depressions go. If the jet is positioned close to the UK, then there is the potential for large rainfall totals and some sublime warm days before each big depression makes its way across the Atlantic.

Model outputs

If there were to be a broad consensus in the modelling, it would for a cool June followed a warming trend into July and August however the major long range models have been jumping around a lot recently whilst there are significant differences in the programming of pressure patterns over North America which could dramatically alter the resulting flow over the UK.

The UKMET's output contains a health warning as it is likely to be slightly at odds with their statistical model. This suggests a generally warm Summer brought about by low pressure to our west in the eastern Atlantic. For North America, a weak ridge over the western 'States is forecast with lows over Alaska and noticeable blocking over Eastern Canada which teleconnects very nicely with the idea of an Azores Low type scenario and its consequent warmth.

http://www.met-office.gov.uk/research/seas...terce_cat2.html

http://www.met-office.gov.uk/research/seas...terce_cat2.html

The lastest CFS output supports the lows over Alaska and blocking over Canada which must teleconnect to fine weather over the UK. Noticeably this is only for June with July and August programmed to have much cooler conditions as the blocking forecast over Canada recedes.

http://www.cpc.ncep.noaa.gov/products/peop...s/glbT2mSea.gif

The ECPC output has probably been the most variable although it appears to have settled over a solution which warm lovers will most be looking forward to with a cool Alaska, deep troughing over the central 'States and as a result, high pressure over Eastern Canada and warmth over the UK and western Europe - another fine example of the teleconnection between ridging over eastern North America and Europe.

http://ecpc.ucsd.edu/projects/GSM_home_dat....ano_global.gif

In common with most , models, the IRI output has altered somewhat in the last month, shifting to an above average temperature Summer with average rainfall amounts. This is a somewhat puzzling forecast as it programmes warmth for Alaska and the western USA, a weak trough over the central US and ridging into Newfoundland. This is not entirely plausible as high pressure over Alaska normally relates to low pressure over NE Canada and Newfoundland.

http://iri.columbia.edu/climate/forecast/n...6_Eur_temp.html

http://iri.columbia.edu/climate/forecast/n...06_Eur_pcp.html

http://iri.columbia.edu/climate/forecast/n...6_NAm_temp.html

The German Climate Model (Roeder) programmes the western US and Alaskan ridge during June resulting in a downstream mi-Atlantic ridge and cool, unsettled start to the Summer. However, during July and August it turns this situation around with a large trough developing across the western US and as a result a downstream ridge up the eastern US and the consequent ridging over Scandinavia which would give very warm conditions for the UK.

http://www.climaprog.de/website0506004.htm

http://www.climaprog.de/website0506005.htm

http://www.climaprog.de/website0506006.htm

The latest Soil Moisture Model (USA only) predicts a suppressed ridge over Alaska and the western / southern central States with equal chances for the remainder. This would tend to endorse the CFS output for July and August but not June, with no major probability of warmth over the NE States and as a result, no increased probability for warmth over the UK.

http://www.cpc.ncep.noaa.gov/products/pred.../off01_temp.gif

Looking at the combined suite of North American forecast tools, a range of outcomes are predicted indicating low confidence in model outputs and patterns over the crucial areas of Alaska, NE Canada and Newfoundland:

http://web1.cdc.noaa.gov/cgi-bin/seasonal/...od=all&lag=lag1

Jetstream patterns

Amongst all this uncertainty, I think there are two very probable features of this Summer related to the relative strength and amplitude of the jet streams.

The Northern Atlantic has since the winter shown a distinct trend for prolonged phases of meridional and weak jet flow, due in no small part to the arrangement of warm SSTA over cold SSTA thereby reversing the normal polarity which favours a stronger jet by weakening the thermal gradient. At the same time and related to this is the relative strength of the sub-topical jet which is most probably related to the approaching solar minima and strength of the polar cell.

More recently, the SSTA over the Pacific have really begun to favour an amplified and split jet pattern with the warm waters over the central / western Pacific and cold anomalies up and down the eastern Pacific.

Looking at the current SSTA and the forecasts over the next month or two, the situation is likely to remain quite similar. In other words, an amplified jet pattern where the sub-tropical jet is much stronger than usual is quite likely. This would make an Azores High ridging NE towards the UK quite unlikely for any prolonged period. This should not in itself rule out high pressure though as the Summer of '95 testifies where a break away High managed to sit over the UK.

This stated, there is I think a high probability of the formation of a recurring mid-Atlantic ridge as the Azores High is 'sucked' north west towards the Greenland High, which in turn will collapse as a result of the evolution of the east Pacific trough and ridging over the 'States.

It's also worthwhile looking at the West Pacific Jet and its likely behaviour downstream. With warm water at depth in the western central Pacific, plenty of cold water to its north (aided by an increased snow cover in east Siberia) and cold water programmed to the east, the Pacific Jet is likely to be quite strong in the west (with a QBO value averaging around 12-15) but I foresee a marked difference between the west and east Pacific.

When this jet hit's the colder waters of the east, it is likely to do two things. First, a slowing jet buckles and will likely split with a ridge pushed northwards into Alaska (Soil Moisture and IRI Models agree this), and a deep trough pushed southwards into the sub-topical belt.

This will lead to a downstream ridge over the western half of the US (some models push this westwards) and a consequent trough over the eastern US, in other words, similar to the present pattern with a mid-Atlantic ridge and trough digging into western Europe. The key questions are where and how pronounced any troughing of the Pacific Jet are going to be.

Summer Forecast

Tricky call. Right of wrong, I'm sure I'll learn a great deal from this forecast.

With a number of potentially conflicting signals, the key to unlocking this Summer's forecast will be to nail the factor that will emerge and have the single greatest influence. If the winter forecasts taught us anything, we must look at those factors which are significant enough as far upwind as possible.

This is the West Pacific Jet and a signal for a +ve phase West Pacific Oscillation which favours the union of the displaced Azores and Bartlett Highs to sustain a very warm, moist SW'ly flow over the UK, as the UKMET's seasonal numerical model predicts.

These two factors must be weighed up against; an ENSO neutral signal with a strong statistical relationship with poor Summers over the UK; a +ve QBO (but limited sample) indicating unsettled conditions; a -ve PDO generally suggesting a large ridge over the USA and cool conditions for the UK; a -ve NAO; a greater probability of -ve AO conditions and great uncertainty over the behaviour of the SSTA and jet stream over the NE Pacific.

On this basis, the probability of an average or below average Summer must be the call.

I have little doubt that the QBO and SSTA of the western Pacific will bring about a reasonably strong west Pacific Jet. This will sustain an amplified jet stream and troughing in the eastern Pacific setting up a recurring cool and showery theme throughout the Summer.

I suspect we will see a mean ridge over the western / central Atlantic and a weak downstream trough over NW Europe supporting showers and long spells of unsettled conditions, becoming more established through July. June already looks very cool and unsettled to start, and, with most modelling agreeing on this, there is an increased probability that we will arrive at the end of June with an uninspiring month in the bank. I am a firm believer that Summer patterns are usually apparent at the end of June so this largely reaffirms my belief in a pretty average outlook. I respect the German Climate Model but I just can't sign up to a dramatic turnaround in the Pacific and Atlantic pressure patterns following a dodgy June.

The warmth of the Atlantic and tendency for the displaced Azores High to throw ridges north and east (but not traditionally NE as we benefit) will I think serve to mitigate slightly these negative factors so I would view quite long phases of fairly slack pressure (with some beefy shower activity) alongside the more prevalent low pressure and intermittent ridges collapsing over the UK. If we get a little sunshine during the slack pressure periods and between the showery interludes, the 'feel' of the weather won't be too bad.

Given these factors, I think the chances of record breaking warmth are slim. We may well struggle to get values many times over 30 C. The best of the weather traditionally found in these types of regimes occurs around late July and this when I'll plump for the most prolonged settled spell whilst we may get some shorter pleasant spells ties into storm development over the eastern US before they make their way steadily across the Atlantic.

As the trough over the eastern Pacific collapses and re-sets, I would anticipate brief spells of ridging off the mid-Atlantic orientated ridge throughout the Summer before it collapses and low pressure re-establishes over the UK.

Reading this you might think I'm painting a picture of a well below average Summer, but it's worth bearing in mind that an average Summer is not great in this country where we've become accustomed to some very glorious recent years' weather. Compare the ENSO neutral composite anomaly for 500 hPa geopotential height and temperatures

- very low height anomalies look bad but only translate to 0.5 C below normal.

To put some verification on this, I would view the Summer as being between average and 0.5 C below average. Although the recent deluge reminds us just how much rain can fall in unsettled periods (as do the memories of 2000 and 2001), I'll forecast average amounts of rain due to some quieter spells of weather and showery nature precipitation in general most heavily influenced by the Atlantic SSTA although there is much less probability attached to this aspect of the forecast.

To put some perspective on the probabilities, I rate the forecast's chances as:

Average to 0.5 below average: 65%

much lower temperatures 20%

much warmer than forecast 15%

The key weakness to the forecast are the difficulties in predicting the pattern over Alaska and the Pacific NW and the downstream impacts on pressure anomalies over NE Canada. A sustained spell of Stratospheric cooling such as that observed in April would completely derail this forecast and probably require revision - good news for sun worshippers if this were to happen.

Edited May 24, 2006 by Glacier Point

[Dawlish]

Thanks Glacier. Such interesting info. Again, a highly educated and knowledgeable attempt at a long-range forecast, which comes to exactly the opposite conclusion to the warm and drier forecast on the other thread.

Long-term forecasting has a long way to go!

[John Cox]

Hi GP,

Even if your forecast does not come off this has been a great education lesson.

Thanks.

[PersianPaladin]

Bloody hell GP.

I'm surprised that your not a senior member of the forecast team. That was a really in-depth and insightful post. Wow.

:lol:

[Bottesford]

Crikey that's a big read! Will need to go through that later when I have more time.

From my skim it certainly doesn't look positive for the kind of summer we all want & hope for. You are also against the numerous other forecasts around (although Meto are still on the fence) so we're still completely unsure as to what we'll get. We are well overdue a rubbish summer now. We got the 'average' winter so maybe it is time for an 'average' summer... :lol:

[kold weather]

As the others have said, a truely stunning post every bit able to match Steve M's attempt.

I suppose the pattern your thinking about is a similar one to the one we've been having and the type that the models are predicting for the next 2 weeks, spells of unsettled weather, with some northerlies as well as the odd settled period.

As you say the jet stream will be key this year, much more so then last year was. Looking at the probablities for TS/hurricane landfalls in the summer, it does seem the east coast is at risk which seems to indicate a trough over central regions and a fairly strong Berumda high which will send TC northwards into the jet stream which then opens up possiblities to both warmer and colder weather depending exactly where the jet lies.

Stunning stuff, and I agree with PP, you really should be a forecaster, though thats upto others!!!!

[Stuart]

Not a bad summer forecast at all it must took you a long time to do it :lol:

Edited May 24, 2006 by Stuart H

[SMU]

A Great Summer Forecast matey-

Covering All aspects- Im at work & will have to have a more comprehensive read when People arent looking over My shoulder....

Anyway, with posts like that it shows how far we/us/all things.... have advanced even in such a short period of time...

Whether the actual forecast comes off is still a mystery, however one thing is very true-

Our basic assumption that due to continual global warming, the lower level forcing of the Troposphere & cyclical variabililty of the Stratosphere is & will lead to dramatic Climatological changes that in Some regions may not be reversabal...

The most noticable for us being the Higher amplificational patterns in particularly the Winter with a displaced polar cell....

The sad part though is that eventually the polar cell may not be cold enough to support anything Wintry South of 50N.....

Best regards & congrats once again....

Steve

[Nick F]

Great read GP -well explained, definately learnt some stuff that I haven't really take in before from your analysis.

Certainly a difficult call it seems given the conflicting views given by the various models and teleconnections.

[acbrixton]

Hi GP,

Even if your forecast does not come off this has been a great education lesson.

Thanks.

John, yes well put!

GP many thyanks for the time and care put into this. I will have to read it all quite a few times I think...

Regards

ACB

[MP-R]

One of the, if not the most interesting read I've read on this forum since last Summer. The forecast doesn't look that bad either. Thanks for such a detailed description of the next few months to come. You manage to keep it really neatly set out - a skill I fail at.

Well done! :lol:

[Anti-Mild]

Blimey GP, that's one hell of a forecast! Your forecast puts me in mind of the summers of my youth in Scotland in the mid 80's :lol: !

[The PIT]

Now thats how a good example on how to post.

Technical yet with an easy to follow summery at the end.

Wonder how it'll spin out in the end.

[Joneseye]

I can't add much more to the comments already posted. Other than it took me 50 minutes to read.. can't imagine how long it took to type!

[Polar Continental]

Thanks for that GP,

Yes a great read and really educational, a post I will need to read a few times to really absorb.

As I have said earlier, if this summer produces some fine summer weather that’s great, not to hot, so I hope your forecast is accurate, and I hope some improvement over the last week lol, although I think this type of summer weather suits TM down to the ground. :lol:

Regards

Paul

[phil nw.]

Hi G.P.,

I just wish to add my thanks and admiration for your detailed and knowlegable post.It must have took a lot of research and i `m sure everyone who has read it appreciates the effort you have made .

[Methuselah]

Not a lot I can I add, GP... :lol:

But thanks for all the time and effort spent; a wonderfully educational read!

[Glacier Point]

Thanks all for your comments. If once you've had chance to read through the forecast and have a query, I'll be happy to oblige if I can.

GP

[Terminal Moraine]

That must have taken a hell of a long time to put together, G.P.

It's not only an interesting read of epic proportions which I haven't fully digested as yet, it also says things I want to hear, like cool and showery.

Cold and wet would have been better of course but I musn't be selfish.

I'm taking plenty of flak at this end for revelling in the current weather.

I'll now return to your post for another 20 minutes.

T.M

[summer blizzard]

The key weakness to the forecast are the difficulties in predicting the pattern over Alaska and the Pacific NW and the downstream impacts on pressure anomalies over NE Canada. A sustained spell of Stratospheric cooling such as that observed in April would completely derail this forecast and probably require revision - good news for sun worshippers if this were to happen.

Glacier Point, congratulations, it was a very well done forecast, bravo.

Glacier Point, i notice you are going for a ridge over Alaska, and highlight this as one of your biggest weaknesses, however during April, there was a mean low over Alaska and according to the latest GFS output, that trough is still there, as you belive in patterns, i would of thought that you would have gone for a Alucien Low with more chance of high pressure in that region during the second half of the summer.

[Glacier Point]

Glacier Point, congratulations, it was a very well done forecast, bravo.

Glacier Point, i notice you are going for a ridge over Alaska, and highlight this as one of your biggest weaknesses, however during April, there was a mean low over Alaska and according to the latest GFS output, that trough is still there, as you belive in patterns, i would of thought that you would have gone for a Alucien Low with more chance of high pressure in that region during the second half of the summer.

very true SB, there was a large negative height anomaly in the area during April, fuelled I think by a big Stratospheric cooling event,

http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif

....which helped set up the warm April and early part of May experienced.

My reasonings for mean positive anomalies during the Summer in the area are the stronger -ve SSTA further west off Siberia and the large +ve SSTA mid Pacific likely to enduce a dowsntream ridge over this area, and the slight differential in the SSTA of the eastern Pacific likely to result in neutral or even weakly -ve East Pacific Oscillation values which teleconnects to this pattern.

GP

[Glacier Point]

UKMET's model has just updated and now shows average temperature probabilities and wetter than average rainfall:

http://www.met-office.gov.uk/research/seas...terce_cat2.html

with the most cool month likely to be June. ECPC's forecast now also goes for cool June.

I'll be fascinated how the METO place their Summer forecast given latest model output and their statistical method which must show a similar or even below average probability given the SSTA March - June pattern now in evidence:

http://weather.unisys.com/archive/sst/sst_anom-060312.gif

http://weather.unisys.com/archive/sst/sst_anom-060416.gif

http://weather.unisys.com/archive/sst/sst_anom-060514.gif

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

http://www.cdc.noaa.gov/map/images/sst/sst.anom.month.gif

... which is somewhat opposite of their predictor pattern for residual SSTA.

When they release the forecast, what's the betting the words 'average' and 'unsettled at times' appear ?

GP

[Bottesford]

Interesting stuff GP- not quite what we want to hear however! An average & damp summer is just not as nice as warm & dry! Good for water supplies though I guess...

Edit: Although looking in more detail at the Europe map still gives the east a warmer than average result. Spain looks much cooler this year though!

http://www.met-office.gov.uk/research/seas...prob_public.gif

Thing is with these plots is they change radically every month. Here's April's release for the same period:

http://www.met-office.gov.uk/research/seas...prob_public.gif

Only thing I can summerise from this and all the forecasts I've read is a cool, dampish June with a nice July & August. A lot of contrasting opinions around.

Edited May 27, 2006 by Bottesford

[The PIT]

Translating means they haven't a clue.

[Glacier Point]

Busted Forecast

One third the way through the summer and although the near outlook looks a little less settled, June was an exceptionally warm month and it would take the remainder of the summer to be well below average to bring my LRF back on track - something that is not going to happen.

So I'm calling it bust for the UK and Western Europe. The Northern American forecast remains remarkably good and still valid with the west coast ridge - east coast trough very much in evidence.

We will have to wait until September to provide the full analysis but the key features so far would appear to have been:

1) a very big positive spike in the Artic Oscillation - note the extent of the negative 500 hPa and MSLP anomalies across the polar region;

2) the absence of a strong Azores High pressure, if anything weakly -ve anomalies in this area indicative of a displaced high;

3) the strong positive pressure anomalies in the NW Atlantic; and of course,

4) the positive pressure and temperature anomalies over the UK and NW Europe.

In fairness to my initial thoughts, a June +ve AO was the identified weak spot and this has driven the NAO positive.

http://www.cpc.ncep.noaa.gov/products/prec...nnections.shtml

This has built the heat over Europe to such an extent that it will now take a lot of shifting.

The key error at the moment looks like the wrong placement of the mid-Atlantic ridge - so far it has been a lot further west in line with that warm sea surface temperature anomaly off Newfoundland, and of course the AO.

Looking to the remainder of the summer, a more neutral or even slightly negative summer AO is statistically most likely to occur during August, but I wouldn't bet against the continuation of the strong trend so far. Also the SSTA in the eastern Atlantic if anything look to me to indicate a more amplified trough increasing the probability of extreme warmth into August.

GP