Summer Forecast.....

[SMU]

Afternoon All-

This is the second Seasonal forecast I have Issued & covers the Period June to the End of August.

Having been reasonably happy with Winters effort I am this time covering a similar theme in the outlook.

Also I have taken into Consideration the Seasonal effetcs of the SST's this year & the associated teleconnections However I know my colleague Glacier Point is preparing a more in depth view of these & it would be unfair to present a lot of material that he is going to be using ( needless to say my informed forecast is based around the same thing & therefor we 'should' come out with a similar type post)

What I wont be doing is making the same mistake as before- which is forecasting anomalies Month by Month- In my humble opinion the details & conclusions to be made covering a seasonal forecast cannot be drilled down that far-

This is where the MET office proved quite successful covering Winter- they just used 2 base parameters & stuck to them- these being-

1) Temperature departure from the Norm ( & a comparison against a historic year)

2) Rainfall departure from the Norm

So in my Summary at the end I will use these 2 variables to measure the forecast with an estimated Summer E&W CET as well-

I suppose before we get to any nitty gritty we need to know what the breakdown of the norm is & a good starting point is what controls our weather during the Summer Months-

Firstly knowing the EXPECTED location of the Polar front is Key-

It should circum-navigate the 60N line - This is the boundary between the Polar cell & Ferrell cell and where this boundary sets up is Crucial-

One further note to this in which many woodbe forecasters over look is the type of high pressures that develop are correlated to the type of flow pattern being observed along the boundary between these cells.

In a 'Typical' year with a West-East flow being fairly un-inhibited the High pressures that develop are flat in Nature & ridge East- A good example of this would be the Bermuda/Azores high ridging along the Lattitude.

However in years where the Polar cell is persistent ( Another expression of this is seeing a negative AO) we often see large ungulations along the polar front- These years often ones with LOW sunspot activity see the uniform path of the path of the PF somewhat disturbed and providing large regions of exceptional static weather-

In these instances High pressure Cells are rather circular & Ridge North South rather than east west. These also known as highly blocked/Meridional flows.

Now were aware of the starting point of any summer we need to gather our thoughts in respect to the proposed positioning of our High pressure belts- Again it must be emphasised that the difference between the Polar front locale of 60N as opposed to 50N is the difference between a potential hot Summer & Cold unsettled one-

And the evidence we should use is the Cycle of Patterns/Feedbacks as we approach Summer- this is because with any entry to a season ESPECIALLY at the start the type of pattern that is feeding back is likely to be sustained at least for the first portion ( this is the same as Winter- get into a cold pattern at the start & this can repeat throughout)

However before we do that lets just remind ourselves of the 3/4 major high pressure players in Summer ( The reason I write 3/4 is because the Scandi High creates almost the Same type flow as the Bartlett in Summer )

The greenland High-

This feature 'Should' NOT be a player in the Summers weather, this is because as the polar front gradually retreats North during Late Spring & Early Summer the Jet stream should Naturally pass through the Greenland region keeping pressure there generally LOW-

If this doesnt occur & the polar cell stays strong the jet Stream will be Squeezed further South towards the 50N line-

Heres what you DONT want to see in JUNE....

http://www.wetterzentrale.de/archive/ra/19...00119910603.gif

http://www.wetterzentrale.de/archive/ra/19...00119910614.gif

Final June 91 E&W CET was 11.7C thats 1.8C below the 61/90 Norm - This was attributed to Greenland blocking pushing the Jet south of the Uk or allowing it to Straddle, 1987 was very similar as well-

The Azores high-

This is a feature that is often touted as the most important thing to a Summer- but its a Misconception really- Unless the jet is riding at 60N or above then its often unhelpful-

http://www.wetterzentrale.de/archive/ra/19...00119830703.gif

http://www.wetterzentrale.de/archive/ra/19...00119830721.gif

http://www.wetterzentrale.de/archive/ra/19...00119830729.gif

Final July 83 E&W CET 18.6C thats 3.2C above the 61/90 Norm.

This was the azores high at its best- with perpetual ridges being thrown East towards Scandi..... What a month.

The problem I have the azores high this year is that the flow patterns, AO behaviour & Sunspot activity are not at all condusive to that type of set up-

Also with the azores high often comes tropical air which is more often than not suturated ( VERY high humidity levels) which means we all feel uncomfortable....

The AZORES high on its own is NOT a prerequisite for a Good summer....

Finally The Scandi/ European High-

In my opinion the best Summer the UK has had is the much vounted 1976, I 'Think' It was the last offical drought & it gave us brits a taste of what continental air/weather was all about-

The best type of high is the one that drags ANY heat of a DRY origin, this can come via spain or indeed the heart of europe-

1976 was punctuated by this type of flow- August more Particularly...

http://www.wetterzentrale.de/archive/ra/19...00119760702.gif

http://www.wetterzentrale.de/archive/ra/19...00119760810.gif

http://www.wetterzentrale.de/archive/ra/19...00119760814.gif

http://www.wetterzentrale.de/archive/ra/19...00119760821.gif

http://www.wetterzentrale.de/archive/ra/19...00119760825.gif

The Final SUMMER 76 E&W CET was 16.86 thats 2.14C above normal- ( beating 1995)....

So we now in place an idea of the 3 Key players for the Summer-

Here would be my forecast & headlines on the 3 months June through August-

The headline I suppose of the bat would be that record 'BREAKING' heat this year may be a little out of reach- the early indicators of substantial early heat building from a deep & stable Azores high are not in evidence so my first headline would be-

No 100F recorded this Summer in the UK-

With the recent patterns I have seen in the global atmospheric patterns the jet stream is Anything but strong so....-

Flow Patterns are set to be MERIDIONAL throughout the Summer NOT ZONAL ( this is after a transitory phase at the start of Summer)

The correlation I make with Meridional flows is that Frontal rainfall events become fewer & further between so-

Reduced frequency of frontal rainfall across the UK ESPECIALLY FOR THE NORTH & NORTH WEST

The Jet stream activity looks to be awfully slow so we are in for lots of Split jets which will be good for us especially in the second portion of Summer-

Split jet running ABOVE 60N & south of 45N Should allow for the UK to sit in the dry slot-

In terms of MSLP Anomalies the headlines are-

Greenland Higher than ususal-

Azores Lower than usual

Central & Northern Europe Substantually greater than Normal especially for the second half-

To put a comment & some figures on The 2 base parameters which I mentioned at the start are as follows-

Temperature

This Summer will be punctuated by a Slow first third in terms of building Warmth & by a polar front that is making its migratory journey later than ususal-

However the remaining thirds should see this late start overturned by a VERY settled Period with consistent warmth/heat rather than Stiffling Heat-

The estimated E&W CET is 15.9C which is 1.2C ABOVE the E&W seasonal average-

comparison year- 1997 ( SUMMER ONLY)

Rainfall

This Summer im afraid looks like being another dry affair- The word arid does spring to Mind- but not quite....

The domination especialy in the second portion of the European high will see perpetual splitting of the jet & minimal frontal incursions-

The Estimated E&W rainfall is 60% of the season average

( A word on rainfall - Whilst the OVERALL pattern looks dry from a frontal point of view I am expecting increased incidence of Convective type rainfall to occur which could disproportionate local accumulations-)

Anyway I think that just about covers things...

Best regards

Steve :blink:

Edited May 16, 2006 by Steve Murr

[Bottesford]

Fantastic read there Steve - very interesting indeed! Warm & Dry being the headline it seems which ties up with a number of forecasts I've seen around (inc Met Office seasonal forecast).

I think we could all agree that sounds a great summer - persistant warmth, but without so much of the sticky heatwaves. And dry which, of course, is what you want in summer (well barring the need for some juicy storms!).

Hope you're correct with your forecast and thanks again for a great read!

[BLAST FROM THE PAST]

Steve

Great post with very good reasoning and generally I pretty much fully agree ie slow start. no record breaking heat, overall warmer than average, stable and warm latter part. I must admit the particular cold building/remaining over Greenland leads me to feel that the GHP IS likely to be a main feature for the 1st half of summer which will account for poor start. Oh and for the latter part of summer particular thunderstorm activity first half of August and a stonker September :blink:

BFTP

Edited May 16, 2006 by BLAST FROM THE PAST

[Glacier Point]

Nice work Steve.

The current modelling essentially throws up two scenarios - one of which you've gone for with a ridge (possibly influenced by the feedback from last year's drought) over western Europe and Scandinavia.

The other places the axis of the ridge further east with western Europe maintained in a cool unsettled trough.

Both are indicative of a highly amplified pattern and the key for me at this stage is calling where this pattern will start and where the 1st signficant trough will be ?

At present, I'm minded to go for a trough in the eastern Pacific and large ridge over the western and central USA placing the downstream ridges over the mid-Atlantic and the Russia, however I was looking at some composite anomaly analysis for weak La Nina fading to neutral by June suggesting the reverse.

I think an amplifed jet pattern is however the safe assumption at present, wherever the ridges ocurr.

Once again, nice forecast, let's hope it pans out.

GP

[SMU]

Nice work Steve.

The current modelling essentially throws up two scenarios - one of which you've gone for with a ridge (possibly influenced by the feedback from last year's drought) over western Europe and Scandinavia.

The other places the axis of the ridge further east with western Europe maintained in a cool unsettled trough.

Both are indicative of a highly amplified pattern and the key for me at this stage is calling where this pattern will start and where the 1st signficant trough will be ?

At present, I'm minded to go for a trough in the eastern Pacific and large ridge over the western and central USA placing the downstream ridges over the mid-Atlantic and the Russia, however I was looking at some composite anomaly analysis for weak La Nina fading to neutral by June suggesting the reverse.

I think an amplifed jet pattern is however the safe assumption at present, wherever the ridges ocurr.

Once again, nice forecast, let's hope it pans out.

GP

Cheers All-

GP when you posting your forecast??? Holding out for that last bit of data..???

S

[Glacier Point]

Hope to have it out by next week - I need to check the reanalysis on La Nina and cold anomalies in the eastern Pacific. A cool phase PDO ??

Edited May 16, 2006 by Glacier Point

[SMU]

Hope to have it out by next week - I need to check the reanalysis on La Nina and cold anomalies in the eastern Pacific. A cool phase PDO ??

I think the PDO came out at +5 for April- Plus the QBO is now Westerly - Oh for it to stay like that for Winter....

S

[Nick F]

Thanks Steve for your thoughts :blink: . Kind of in line with Ian Brown's summer forecast on a slow start for warmth/settled conditions maybe in June but the summer progressively becoming more settled, and as a whole, producing below average rainfall and a preponderance to convective rather than frontal rainfall during the summer - and therefore large local variations in rainfall.

[SMU]

Thanks Steve for your thoughts :blink: . Kind of in line with Ian Brown's summer forecast on a slow start for warmth/settled conditions maybe in June but the summer progressively becoming more settled, and as a whole, producing below average rainfall and a preponderance to convective rather than frontal rainfall during the summer - and therefore large local variations in rainfall.

Cheers Nick-

I deliberatly didnt read either ians or the METO's until I produced mine- that way I can say hand on heart it was what I forecast-

Glad to see were all on a similar wavelength..........

S

[Mammatus]

Very enjoyable and informative read Steve. All I hope for is that June 24th is sunny, dry, calm and comfortably warm as I get married on this day

Mammatus

P.s. Could someone kindly explain what 'PDO' & 'QBO' stand for.... Thanks :blink: I'm still learning...........with a long way to go

Edited May 16, 2006 by Mammatus

[SMU]

Very enjoyable and informative read Steve. All I hope for is that June 24th is sunny, dry, calm and comfortably warm as I get married on this day

Mammatus

P.s. Could someone kindly explain what 'PDO' & 'QBO' stand for.... Thanks :blink: I'm still learning...........with a long way to go

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

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

[acbrixton]

Steve many thanks for the reasoned and lucid forecast. Will be interesting to see how things pan out.

Regards

ACB

[kold weather]

Most intresting read Steve, and I do agree with quite a lot of your forecast, including the jet stream and its amplified set-up which I rekcon could be a round for a while yet...

For what its worth, what do you think about ex-hurricane tracks this year, because these can bring in a lot of warmth from the tropics regions.

I also agree with your slow warming-up idea, and actually I've gone for quite a hot August, with a purely estimated CET at 18c, though I think high amounts of cloud from convective systems overnight will probably be a lot to do with that high CE...IE 2004, which had several ex-hurricanes bring thier goods over from the USA.

It's those ex-hurricanes that may end up making August quite a wet month IF they re-curve at the right point.

[Dave J]

Cheers Steve for putting the summer forecast together.

Sounds great- Convective storms, prolonged warmth and no exceptional heatwaves. Great stuff! :blink:

[thestixx]

this is my first and possibly last post but as a regular reader of your posts on here and TWO I must say another thoroughly enjoyable read! Thanks Steve, thanks very much!!!

[John Cox]

great post Steve,

One question. Is your forecast, as i would probably do if I were you, for the south of the UK, or GB in general?

We here in Ireland can have quiet different weather, cool showery with north westerlies while the south east of the UK can have hot and sunny weather.

Edited May 16, 2006 by John Cox

[SMU]

great post Steve,

One question. Is your forecast, as i would probably do if I were you, for the south of the UK, or GB in general?

We here in Ireland can have quiet different weather, cool showery with north westerlies while the south east of the UK can have hot and sunny weather.

Hi John-

It was mainly for England & Wales.....

With Ireland its important that the jet goes as far north as Possible so the atlantic activity is swept up towards iceland-

FWIW I think after June you will be Ok Especially if you can pick up those SSE winds......

Best regards John...

Steve

[John Cox]

Thanks Steve,

I know us guys/gals here in Ireland are in a minority on nw and I do appreciate that forecast..

I hope it comes off and knowing you (and gp) you will not be too far off the mark. :blink:

this is my first and possibly last post but as a regular reader of your posts on here and TWO I must say another thoroughly enjoyable read! Thanks Steve, thanks very much!!!

Hi Thestixx,

Welcome to NW.

Why the last.

Stay around and have some fun.

[Polar Continental]

Thanks Steve,

Very interesting, in-depth and informative forecast, normal summer warmth will do nicely for me, thankfully / hopefully no ridiculous egg frying heat waves this year. :lol:

Regards

Paul

[STEVE M]

Yes a very imformative read, thanks Steve. That chart for June 1991 looks quite similiar to some of today's charts by comparison.

But here's hoping we see an improvement later on in the summer in July and August. Something tells me we are going to have an unsettled June this year, it's just the way the charts are looking at the moment, I don't see much of an improvement in the near future including early June at least. Things may improve through June, but I just can't see any drastic improvement all that quickly, not at least until mid-June. Although I hope I'm wrong.

But anyway, good luck with the forecast Steve :lol:

[Bottesford]

Yes a very imformative read, thanks Steve. That chart for June 1991 looks quite similiar to some of today's charts by comparison.

But here's hoping we see an improvement later on in the summer in July and August. Something tells me we are going to have an unsettled June this year, it's just the way the charts are looking at the moment, I don't see much of an improvement in the near future including early June at least. Things may improve through June, but I just can't see any drastic improvement all that quickly, not at least until mid-June. Although I hope I'm wrong.

But anyway, good luck with the forecast Steve :lol:

Just how summers were often like - warm spell in May sometime then the 'European summer monsoon' in June with things finally settling/warming late June/into July. Last year was annoying in the sense we had all the heat/settled conditions in June leaving the rest of summer fairly bland - nothing too warm or exciting (well until autumn when it just didn't cool off!).

[STEVE M]

Just how summers were often like - warm spell in May sometime then the 'European summer monsoon' in June with things finally settling/warming late June/into July. Last year was annoying in the sense we had all the heat/settled conditions in June leaving the rest of summer fairly bland - nothing too warm or exciting (well until autumn when it just didn't cool off!).

Yes last summer was very annoying. The start of the summer, mainly in June, did have some of the trademarks of being a great summer as well, but it turned out to be something of a disapointment in the end with close to average temps and rainfall in July and August, not the summer that I had hoped for myself.

But this summer does sound much more like a classic summer in terms of timing. It sounds as though, looking at Steve's forecast, we will be getting the best of our summer weather in the peak summer period being July and August, which is ideal for sun lovers and for those who love a good thunderstorm or two, lol.

Hardly a re-run of 1976 or 1995 perhaps, but this summer could be the most impressive summer in recent years if Steve's forecast comes off, which I think will.

Edited May 17, 2006 by STEVE M

[SP1986]

I'm actually very divided here, I think this year will be alot wetter than previous, but already it's proved warmth is building up. A warm and wet summer, I think a summer similar to last, or 2004 is more likely than anything, certainly no 2003/1995 coming, some people may be rather disappointed in that respect. It would be very unusual not to get temperatures above 30C in some parts this summer though. So I would personally call for a thundery, warmish but certainly wet summer - as we've seen this year, patterns aren't easily shifted so I expect an extension of our current wet/dry/wet phases.

[Glacier Point]

Hi Steve

How soon will we have indication as to if the QBO will stay westerly beyond the summer? I ask for 'obvious' reasons!!

Tamara

Positive phases last between 8 and 12 months on average. It 'broke positive in April, so this one should be with us for ..........[salivation smilie]

GP

[summer blizzard]

Personally, while my preliminary summer forecast makes for a rubbish June with a CET of 12.6C and hot July with a CET of 18C so far, i find the current weather pattern encouraging, as the european monsoon generally occurs during June lasting for a month, the fact that it has come two weeks earlier means that we could see more settled weather likely during the second half of June, so that the CET comes around average folowed by a hot July and August which i think a few people are suggesting.

On the other hand, if you believe the weather patterns in May occur again during the summer, then the fact that we have seen a warm spell lasting twenty days and the cool spell lasting around ten days is very encouraging.