JH and a look into the period from T+144, usually

[J10]

(Mon 3 Mar)

(Tue 4 Mar)

(Wed 5 Mar)

Far more agreement now between the models, although the GFS still goes for bigger heights across Greenland.

There is still a slight difference, by Wednesday with GFS pushing the low further south than the GFS and UKMO, possibly allowing a NW feed back in, The Ensembles Average goes for more of this as some of these go for the potent northerly as shown on previous GFS control runs.

[johnholmes]

no update tonight or tomorrow(tomorrow I'll be busy doing the outlook on the forecast thread for Extra) but I'll be monitoring the situation and will do an update probably late on Monday evening.

[johnholmes]

sorry update not done again tonight as promised, will do it sometime tomorrow as been away all day

even had some snow when I got back tonight, well moderate sleet!

[johnholmes]

As a general rule I think it might help objectivity if I did this just a couple of times per week rather than every evening. It is no bad thing to step back a little and see how events appear to be progressing.

Whenever possible I will try and do this each Tuesday and Friday evening using a mix of 00z 12z output each time (but having looked at most runs when time permits, and making notes over the intervening days). This means I can drop into the NOAA discussions and their latest charts and the same data base is then used every time. The same with outputs from GFS along with ECMWF and the UK Met O at the far end of their output range(T+144). Charts used routinely are North Atlantic/Europe/N American and northern hemisphere.

The NOAA data includes comments on most of the most bandied around acronyms, AO, NAO, MJO, El Nino, La Nina etc and an explanation of most of these can be found below.

If you lose this list then go here

http://www.netweather.tv/forum/index.php?showtopic=46150

and they will be there all the time to bookmark or make your own list from them.

AO=

http://booty.org.uk/booty.weather/FAQ/AF.h...cticOscillation

NAO=

http://booty.org.uk/booty.weather/FAQ/2B.htm#2B.10

MJO=

http://www.cpc.ncep.noaa.gov/products/prec...k/MJO/mjo.shtml

EL Nino/La Nina=

http://booty.org.uk/booty.weather/metinfo/ENSO_ref.htm

http://www.pmel.noaa.gov/tao/elnino/la-nina-story.html

also this=

http://www.pmel.noaa.gov/tao/elnino/wwv/

more reading here

http://www.cru.uea.ac.uk/tiempo/floor2/data/soi.htm

or

http://booty.org.uk/booty.weather/FAQ/2B.htm#2B.12

and more!

http://www.pmel.noaa.gov/tao/elnino/nino-home.html

as you can see its very very complex and I have to confess much of this I have only the most basic understanding of them.

For some first class comments about them and how they link into longer term attempts at forecasting the GP or Brick are well read on these topics. Read their regular inputs quoting the above factors.

recent inputs by GP are here

http://www.netweather.tv/forum/index.php?a...sult_type=posts

So the next full update will be this evening.

[BrickFielder]

I have added a new topic to talk about the MJO , Rossby and Kelvin waves in the advanced discussion area of the learners forum.Here I have tried to explain some of my thoughts on how the MJO works what it is ,given a brief overview of rossby and kelvin waves along with clear diagrams of how MJO Phases affect the global weather patterns. Anyone who wants to contribute please do so and hopefully we can all learn and see what John is talking about. Click below to link to the MJO discussion.

MJO, Rossby and Kelvin waves

[johnholmes]

tks for that Brick

yes for many of us its very much a learning area

[johnholmes]

Update for Tuesday evening 04 March 2008

This is what my summation said a few days ago

There are two possible variations out to mid March in my view.

1) The upper ridge remains over Greenland or the Atlantic surface high is sufficiently far north to give a cold or rather cold flow north of west.

2) If the above does not hold(and the recent post from GP, link here,

http://www.netweather.tv/forum/index.php?a...sult_type=posts

suggests that it will, but if it does not then a milder westerly or even south west flow would be in place by mid month.

That would be after a mostly below average to cold spell for the 7 days or so from about Monday of next week.

Cold using Met O terminology is 4 to 5C below the expected temperatures for early March

Overall I would sum up the guidance on Sunday 17 February as good. (always assuming the talked of colder weather does arrive as most centres are predicting!)

So what has happened in that time?

Let’s do it the opposite way round to the usual?

What do NOAA say and show over the past 24 hours?

This is what they wrote this morning

PREFERENCE TOWARD THE 00Z CANADIAN WITH THE EAST COAST SYSTEM...

CONSENSUS THAT IS WEAKER THAN THE GFS WITH THE WEAK SFC REFLECTION

OF UPSTREAM PACIFIC SHRTWVS CROSSING THE CONUS... AND UNCERTAINTY

WITH SPECIFICS OF THE SYSTEM NEARING THE WEST COAST BY EARLY NEXT

WEEK... FAVOR USING THE CANADIAN... BLENDED WITH ITS CLOSE COUSIN

THE 00Z ECMWF MEAN... FOR THE INITIAL BASIS OF THE DAYS 3-7 FCST.

DAYS 3-5 FRI-SUN UTILIZE AND EVEN CANADIAN/EC MEAN BLEND TO TONE

DOWN THE CANADIANS EXCESSIVELY STRONG HIGHS... WITH A FURTHER

SHIFT TOWARD THE EC MEAN DAYS 6-7 MON-TUE TO ACCOUNT FOR TYPICALLY

INCREASED UNCERTAINTY AT THAT TIME FRAME.

and I would imagine the last two 500mb anomaly charts going out to day 15 or so were also on their minds, see below

For our neck of the woods the first one shows a –ve anomaly between Iceland and the UK with any =ve signal being fairly well south over Atlantic; 09-13 March

the second chart (not shown) has a –ve anomaly more to our north east with the +ve sign a little more north but with a bit more indication of the flow possibly being more north of west, for 11-17 March

Neither the 12z GFS nor the 00z ECMWF seem to buy that idea with either having the surface high close by or even south east of the country.

If we look a little closer at the reasons, yesterday evening that NOAA gave for their thoughts and take a look at the weightings they gave to the two charts what do we find?

TODAYS OFFICIAL 500-HPA BLEND CONSISTS OF 25 PERCENT OF TODAY'S 0Z GFS ENSEMBLE

MEAN CENTERED ON DAY 8...25 PERCENT OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED ON

DAY 8...25 PERCENT OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 8...15

PERCENT OF TODAY'S CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8...AND 10 PERCENT OF

TODAY'S EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 7.

They further on give their view of confidence in this, 2 on a scale of 1 to 5. There are times when they mark confidence for this time period at 4, so they are not too confident of the evolution. Not that there is any clear indication as to what they think more likely to happen, at least not directly.

So is GFS and ECMWF in their T+240 ideas (around 14 March) a better guide to what we may expect?

I have to say this far out I really have no idea.

We have two comments from GP and Brick recently which may shed some light on how they think Tropospheric events will impact that possibly GFS and ECMWF do not have in their calculations yet.

GP=

http://www.netweather.tv/forum/index.php?a...sult_type=posts

Essentially, he says

That means strong ingredients in place for a large Pacific anticyclone and significant Rossby Wave Dispersal setting up a series of NH sub-arctic ridges. Going on previous form, this will manifest itself over Scandinavia in our neck of the woods but the PV has shifted somewhat and I'd punt a little further west towards Iceland-Orkney-Norway triangle.

Whilst Brick again today=

posted in the March Forecast thread finished with this

That means strong ingredients in place for a large Pacific anticyclone and significant Rossby Wave Dispersal setting up a series of NH sub-arctic ridges. Going on previous form, this will manifest itself over Scandinavia in our neck of the woods but the PV has shifted somewhat and I'd punt a little further west towards Iceland-Orkney-Norway triangle.

So yet again I suspect we wait to see what actually transpires.

In a simple man’s language(mine) looking at GFS and as far as ECMWF goes then post T+168 I would punt for a coldish Polar Maritime start with high pressure settling near the UK and possibly milder air coming up its western flank into the UK. Beyond about T+240 then POSSIBLY an attempt, not that different from either GP or Brick’s ideas, for a colder set up developing with that colder air coming from the north east rather than the north or north west. This would be into about the end of the second week, from about 15-16 March on behind a 500mb trough with surface low moving into the continent with high pressure building behind it.

Very very long shot and please give your views.

I will monitor this period and update twice a week as suggested in an earlier post.

also my thanks to GP and Brick for their inputs in other threads which I hope they don't mind me quoting!

[bluearmy]

reading the prose from NOAA re the 14 day 500mb output, i'd say things are the most uncertain i've seen for a long time John -

A SHORTWAVE DIGGING SOUTHEASTWARD FROM THE PACIFIC NORTHWEST SHOULD BE ACCOMPANIED BY COOL AND WET CONDITIONS. IT IS VERY DIFFICULT, AT BEST, TO CONFIDENTLY PREDICT ANY OTHER ANOMALIES ACROSS THE CONUS AND MUCH OF ALASKA. CONTINUITY WITH THE OFFICIAL 6-10 DAY FORECAST, AND KNOWLEDGE GLEANED FROM RECENT ERRORS WERE USED IN ADDITION TO THE USUAL TOOLS, TO MAKE THIS WEEK 2 FORECAST. IT IS HOPED THAT TOMORROWS MODEL GUIDANCE AND SURFACE TOOLS WILL BE BETTER ABLE TO RESOLVE THE MEAN TEMPERATURE AND PRECIPITATION PATTERNS FOR THE WEEK 2 PERIOD.

[johnholmes]

yes, in the relatively short time this year in fact, I've been regularly looking, I don't recall them being so uncertain

Edited March 4, 2008 by johnholmes

[johnholmes]

Update on Friday evening 7 March 2008

This is what I posted on Tuesday

In a simple man’s language(mine) looking at GFS and as far as ECMWF goes then post T+168 I would punt for a coldish Polar Maritime start with high pressure settling near the UK and possibly milder air coming up its western flank into the UK. Beyond about T+240 then POSSIBLY an attempt, not that different from either GP or Brick’s ideas, for a colder set up developing with that colder air coming from the north east rather than the north or north west. This would be into about the end of the second week, from about 15-16 March on behind a 500mb trough with surface low moving into the continent with high pressure building behind it.

A brief summary/update would be yes it still looks along those lines, a spell of several days in the cold category.

Taking it in more detail to try and explain that summary

NOAA for one day, only one I think, did seem to suggest that no blocking would occur to the north, be it west or north east. But only on one day. They have since gone more and more down the road of +ve pressure areas to the north west of the UK and -ve pressure areas to our east/northeast or south east. They have also upped their confidence in this scenario to ‘high’ 3 or 4 out of the 5 they allocate to each chart right out to 21 March.

This below is the one for tonight for 15-21 March, the one for the earlier period 13-17 had already got similar areas of +ve and –nve 500 mb anomalies.

Their assessment of La Nina is this, the most recent issued in late February

continue

to indicate a moderate-to-strong La Niña through March 2008, and a weaker La Niña through

April-May-June 2008

In spite of this they appear to believe that some sort of block or lack of movement across the Atlantic is going to occur as we move towards the start of the 3rd week in March.

As one would expect their model, GFS, does mirror this, and has done almost constantly for nearly a week, possibly longer. Interestingly, ECMWF seems to be doing something similar. (NOTE ECMWF was ‘offline’ from Tuesday until today, but both days it had a similar idea to GFS, not the same, but of stopping the flow of depressions across the Atlantic of the past days.

So we have 3 sources if you like, if we call GFS and NOAA two! All 3 indicate much the same idea and have been doing so for, well over a week, I think two weeks, not constantly, but more often than not. Their indications gave us the start of the colder spell, end February-early March, 10-14 days before it happened. Coupled with the data supplied by GP and also Brick, that makes 4 sourse, regarding events in the Stratosphere impacting some time later on the Troposphere, and their times agreeing with the end of Feb-early March and latterly for the middle onwards of March, then I think we are seeing more and more evidence to support my initial summary.

As always we will not know for certain until mid month, beyond say 15-17th, and no doubt there will be changes before then.

What we cannot do, this far ahead, is look at individual charts and expect that/them to occur. They are indicating a trend and its that we are looking for.

The most probable evolution to me is that pressure will rise in mid Atlantic/Greenland/Iceland linking with a northward extension of the Atlantic/Azores high. This will allow pretty cold air, for the time of the year, to reach the UK. I also think it may well be a 5-7 day event.

Pick holes as you wish, its only my ideas.

[mountain shadow]

I for one have been pretty scathing about GFS this winter, but really has been very consistent in picking up this pattern change to something much colder. The ECM appears to be on board and the furthest out UKMO stalls the trigger low in mid atlantic.

Given the El Nina forecast I would hypothesis that IF the Greenland block does materialise then it will last at least 14 days if not longer.

Cannot argue with your thoughts John, I wish I understood the mechanisms whish cause the low to stall mid-atlantic with subsequent pressure rises as well as yourself.

Edited March 7, 2008 by mountain shadow

[mcweather]

Thank you John

I always appreciate your professional thoughts especially when peering into abyss that is FI.

[johnholmes]

the words first

I'll put the charts in as soon as I've had a breather

Update on Tuesday evening 11 March 2008

This will be a very full linking of as many variables from as many sources as possible so be prepared for a longish but I think interesting read. At the end I will make my assessment but it may well be faulty and/or at variance with yours.

When I began this section of the lrf I took Monday 17 March as about the time to expect a 'start date' if there was going to a combination from both the Stratosphere and Troposphere such that a cold spell with northern blocking would develop.

Apologies to our site owner but most of the charts will be GFS/ECMWF not off Net Wx.

We are now within what is sometimes called a reasonably reliable time frame for seeing trends develop.

The chart for Monday 17 March at 12z by GFS is below. It has shown quite similar but certainly not identical charts for the past 8 or 9 days. It goes along with what you will see further on from NOAA whose 500mb +/- anomaly charts have been showing a likely build of pressure to the north west for the same period.

First though let us look at ECMWF for the same date/time as it now goes out well within that date.

Nowhere near identical but not that different. Its also within the UK Met O chart which shows

again not that far different from the other two.

Now for the 500mb NOAA chart over that time period

It certainly appears to suggest, and its chart for even further ahead also suggests, that a ridge is probable in the Greenland area with a flow then into the UK from a colder source than recently.

Let us have a look then at the two charts for T+240 hours, GFS first then ECMWF

The low has moved from well west of Iceland.

ECMWF again not the same but showing many similarities. Chief being the marked 500mb ridge in the Greenland area from the Atlantic high.

So there seems to be quite a lot of evidence to suggest that a colder flow from the north west seems likely to begin to develop by the end of this weekend and could last right over the Easter period. This idea of a colder blocked set up fits with the prediction given by GP some time ago.

So is it watertight? Of course not. So let us look at why.

The first and perhaps fairly obvious item on the T+240 charts is that the surface high is NOT a full blown Greenland high, just an extension of the Atlantic high towards an area where surface pressure could be expected to rise with the 500mb ridge being there. As per the NOAA charts and also, although I've not shown them from ECMWF outputs.

But read below some of the items that may negate this development.

NOAA and La Nina along with comments about the MJO

NOAA also continue to predict that La Nina will continue moderate perhaps strong at first through Spring.

This is their comment about the MJO

VARIOUS MODEL FORECASTS ARE GENERALLY INDICATING THAT THE CURRENT MJO WILL STRENGTHEN AND BEGIN PROPAGATING DURING EARLY MARCH, POTENTIALLY REACHING A LOCATION THAT WOULD HELP TO REINFORCE THE EXPECTED LA NINA SIGNAL.(excuse the capitals it's the way NOA write) and this comment in their latest release about impacts way upstream, indeed, hemispherical impactsVALID 12Z SAT MAR 15 2008 - 12Z TUE MAR 18 2008

AN ADDITIONAL WRINKLE NOT YETVISIBLE IN THE VARIOUS MODEL SOLUTIONS IS WHETHER OR NOT THE DEEPVORTICES IN NORTHERN CANADA AND THE NORTHEAST PACIFIC MIGHTINTERACT /FUJIWARA/ IN SUCH A WAY TO SWEEP THE PACIFIC VORTEXEASTWARD...BREAKING DOWN THE CANADIAN PORTION OF THE RIDGE WHICHWOULD ALSO FAVOR MORE PROGRESSION.

So with just those comments there obviously is a lot to overcome if the blocking being predicted for the Greenland area is to happen, at any rate for any length of time beyond early next week.

My assessment:

In spite of the last paragraphs I believe that a more north westerly and colder flow than recently will be in place by early next week, possibly before the end of the weekend.

I also believe it is more than even probability that it will last into the Easter holiday period.

I'm not predicting thick snowfalls and ice days but certainly below normal temperatures for the country. Frost at times at night, snow for some, especially with even modest elevation.

Normal temperatures in the third week of March range from about 8.5C in the north to around 11C in the south west, night time values 2 to 5 or so. These are figures from this site

http://www.metoffice.gov.uk/climate/uk/ave...2000/index.html

the Met O definition for below average or rather cold to cold can also be found by searching the same site.

I hope you enjoyed reading and do please make any CONSTRUCTIVE comments you feel appropriate. Once again I have to say its a new learning area for me.

I do hope to continue it through the year so for those not interested in cold it may show up, well in advance, Spanish plumes, hot spells, very wet periods, I simply don't know.

Edited March 12, 2008 by johnholmes

[Thundery wintry showers]

It seems to have messed up the averages link somehow- here it is:

http://www.metoffice.gov.uk/climate/uk/ave...2000/index.html

Good posts btw, it's very interesting and informative to get the informed views of an ex-MetO forecaster. I'll be interested to see how it all pans out, but have to agree that a spell of below average temperature looks odds-on from the current evidence.

[smich]

Thanks John, what a breath of fresh air! Threads like yours help me keep the faith in the forum when the so called "Model Analysis" threads are wandering off topic.

Another variable I would add to your analysis are the AO and NAO ensembles, which are looking quite favourable. (Although I don't necessarily think they are the holy grail some describe - the height rises implied might not verify in the perfect position for the UK!)

Below average temps for the remainder of the month may not please some if there isn't widespread snow, but a below average CET for the month overall would be a rare in it's own right!

smich

[johnholmes]

cheers Ian and tks smitch I did actually look at them and then forgot to add them as I was still searching for the blocking data, and as you say they are favourable, just two more to add to that equation, although from what I read about blocking about a week ago that may come down on the other side.

charts now included will put correct link from Ian in shortly = done

Edited March 11, 2008 by johnholmes

[dallas]

cheers Ian and tks smitch I did actually look at them and then forgot to add them as I was still searching for the blocking data, and as you say they are favourable, just two more to add to that equation, although from what I read about blocking about a week ago that may come down on the other side.

charts now included will put correct link from Ian in shortly = done

Cheers for all that JH, was out last night and was keen to read it this morning, lets hope we overcome those two barriers as I would not mind seeing a cold Easter. Do you beleive this would be the last glimpse of cold weather for now?

[BrickFielder]

The stratospheric vortex looks shifted out towards asia for next week. The vortex also tends to shift towards russia during spring but this looks like a stronger move. I am linking this to an MJO event (currently quite strong in phase 1)which should pick up momentum and for a period disrupt the jetstream across the Pacific.

ECMWF forecast tropopause level vorticity patterns show a lack of vorticity in our area (dark blue on the chart below) which is often an indicator of higher pressure.

We should note the GFS partterns differ somewhat although the 5wave anomaly patterns are suggesting a strong signal for atlantic high pressure.

5Wave Anomaly Chart.

I guess when we see that rare high pressure to the north out in F.I. our pulses start to quicken.

It really is a little too far out to be certain and there are even inter model uncertainties a close as Saturday , but the prospect is there tantilisingly close. The reality of course is that during March temperatures and conditions are unlikely to coincide to give any sort of substantial snow fall.

[johnholmes]

Update Friday evening 14 March

Time for another look at how various centres/models/comments fit or don't fit over the past 2 weeks or so.

No its not cast iron at all and it may still not pan out as my understanding of the overall guidance has been for around two weeks but let us try and have an objective look.

On Monday 4th March I posted this as a summary of the evidence of that evening and the previous 3-4 days.

'In a simple man's language(mine) looking at GFS and as far as ECMWF goes then post T+168 I would punt for a coldish Polar Maritime start with high pressure settling near the UK and possibly milder air coming up its western flank into the UK. Beyond about T+240 then POSSIBLY an attempt, not that different from either GP or Brick's ideas, for a colder set up developing with that colder air coming from the north east rather than the north or north west. This would be into about the end of the second week, from about 15-16 March on behind a 500mb trough with surface low moving into the continent with high pressure building behind it.'

added this evening for clarification only T+240 on 04/03=14/03

This post from GP even earlier being just one reason for my post above.

date/time 2005 29/02 from GP, part of his text at post no 148

'with temperature anomalies extending downwards to the 200 hPa layer already. Add another two weeks onto this and we are very likely to see blocking at high latitudes.

Mid Atlantic ridge + fragmented polar vortex = Greenland High. I wish it were that simple, but this is where I'm looking week 2, for potential at least.'

So the indications from various sources, NOAA, ECMWF/GFS 500mb charts, GFS T+384 downwards and inputs like that above from GP have pointed to events sometime from this weekend onwards bringing less mild/rather cold air from the north, varying between nw and ne.

If we look at various 12z outputs by GFS for Monday 17/3 they are far from the same except they almost all have shown some kind of flow from between n of west and east of n shall we say!

T+144

and the one from today

and this one from NOAA on 7 March was not the first to suggest large +'ve anomalies to the north west by 15-21 March. The first time this really showed was, I think, around 3rd March.

Looking at the 12z GFS for today and is that showing?

One would have to say, maybe, but not too solid a looking rise at this particular time.

In summary then, signs not totally conclusive I would say, but sufficient each time I've updated to suggest that less mild/rather cold air would be in place from about the 17th.

Then turning to the Easter weekend. Once again without filling up page after page(anyone wants copies I have them of GFS/ECMWF ensembles and NOAA) the evidence has slowly mounted that, with a temporary hiccup as what some call a 'trigger low' crossing west to east, a similar weather pattern, as predicted by the NOAA anomaly charts along with the posts from GP(also Brick) that, in spite of La Nina remaining moderate to strong for the Spring, that a colder interlude of several days was going to occur over the UK-say 17-24/26 March.

We will again have to wait and see but I remain convinced that a spell of below or even rather cold-cold weather is about to start and will last, with minor temporary hiccups, for 7-10 days.

Below is this evenings comments from NOAA about model reliability and their weightings along with the 500mb +/- anomaly chart for the period mentioned above.

THE MODELS AGREE FAIRLY WELL THAT RIDGES WILL BE LOCATED OVER THE CENTRAL NORTH ATLANTIC EXTENDING TO OVER GREENLAND,

and their weighting and comments on the models for the period over Easter(out to 28/03)

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS AVERAGE, 3 ON A SCALE OF 1 TO 5, DUE TO GOOD AGREEMENT AMONG THE GFS NSEMBLE SOLUTIONS, OFFSET BY RELATIVELY POOR AGREEMENT AMONG THE OPERATIONAL PROGS.

Days 8-14.

The ensemble spread for the 8-14 day time period is relatively low. The general pattern consists of a ridge west over the Bering Strait, a broad trough over the eastern Pacific, a ridge over the western CONUS, a trough over the eastern US and a ridge southeast of Greenland. There are a few extreme outliers, but overall most members capture this pattern with some differences in amplitude.

this is the web site to read their text and look at their charts for this period

http://www.cpc.ncep.noaa.gov/products/pred...mbles_brief.php

and the 500mb anomaly chart for the period over Easter.

the +ve area s and se of Greenland is noticeably reduced from the one valid to 24 March but it is still there.

GFS for 28 March shows this today at T+336

So do I start to look for lrf that shows up prospects of warmth or is it still cold? We wait to see.

As to the meat on the bones, how cold, any frosts, where will it snow etc, then I would refer you to the first class 96 hour model thread with Paul B nope he is here already! the 3x weekly text forecast by the forecasters, along with updates on the Front Page from Paul M and watch for any Watches/Alerts. Of course if you prefer the model discussion then enjoy that.

I will monitor how this pans out and show this after the event along with an update on Monday and again Friday next week. Beyond that and its then trying to use this rather sketchy method to search for any warm spells or prolonged wet ones.

Edited March 14, 2008 by johnholmes

[johnholmes]

Update issued Tuesday evening 18 March

This will start with events predicted after T+144, after the Easter weekend.

For that prediction go to here to the excellent daily situation report from Paul B here;

http://www.netweather.tv/forum/index.php?showtopic=46459

which will do the count down from now(Tuesday)T+72(Thursday) to T+96 and cover the Easter weekend.

A quick summation would be from all the data I've been able to gather from various sources out to T+384(3rd April) would be that overall the colder flow seems likely to continue, possibly even beyond T+384. Yes there may well be temporary swings to a more reasonable temperature regime but in the main colder rather than milder for the time of year.

To the detail

First looking at the 3 main models and comparing.

T+144

All have a northerly with a build of pressure to the north west of Iceland.

By T+240 ECMWF and GFS show a rather different chart, even at 500mb. ECMWF favours what seems a rather fanciful idea of a surface block from north Russia all the way across to Greenland with an easterly setting in and low 500mb heights way south of the UK. GFS has what looks to be a more realistic assessment with a surface high west of the UK and a n'ly flow but with low pressure between nw Iceland and Greenland with the coldest air over Europe(presumably from the airmass we had/look like having over the Easter period.

By later in the run GFS(the only one available this far out) has a 500mb ridge south west of the country out to almost the USA with cold air flowing roughly from a direction north of west with a series of lows crossing the country and then ese into Europe.

Different patterns from them both but the end result is a flow from north of west still giving an 850mb temperature regime mostly below zero C for northern areas, sometimes sub -5C, with temporary increases for the south to near +5C.

The ECMWF and GFS 500mb anomaly charts have, over the past few days been fairly consistent although a little different from one another. ECMWF favouring a more blocked looking suggestion than GFS. This ties in with charts and comments I'll show from NOAA.

The 500mb for today is below, and is perhaps a fair indication of the differences they have shown over the past few days.

There has been no forecaster input over the weekend from NOAA so, although the 500mb anomaly charts come out I prefer to wait until we can read what they say.

First the early morning comment(done every day by the way) and illustrating their difficulties in trying to decide which way to jump both in the next day or so and further ahead.

518 AM EDT TUE MAR 18 2008

VALID 12Z SAT MAR 22 2008 - 12Z TUE MAR 25 2008

THE 00Z GLOBAL MODELS PRESENT A WIDE ARRAY OF SOLUTIONS FOR THE

MEDIUM RANGE PERIOD FROM COAST TO COAST...WITH TRENDING ADDING AN

ADDITIONAL CHALLENGE FOR PINPOINTING THE EVOLUTION OF INDIVIDUAL

SYSTEMS. STILL...TWO OF THE MORE RELIABLE MODELS...THE ECMWF AND

UKMET...SEEM TO HAVE BROKEN AWAY FROM THE PACK WITH THEIR HANDLING

OF THE INTERACTION OF STREAMS OVER THE EASTERN UNITED STATES DAYS

5 AND 6...AND TOOK THEIR CUE FOR THE PRELIMINARY FRONTS AND

PRESSURES MANUAL FORECAST. THE GFS AND ITS ENSEMBLE MEAN KEEP

HIGH PRESSURE IN CONTROL OVER THE EAST DURING THE SECOND HALF OF

THE PERIOD...WHILE THE ECMWF...GEM GLOBAL...AND UKMET INDICATE

SIGNIFICANT CYCLOGENESIS. THE GEM IS THE FASTEST TO SPIN

UP...WITH A LATE SEASON SNOWSTORM INDICATED FOR PORTIONS OF THE

MID ATLANTIC REGION LATE DAY 4 INTO EARLY DAY 5. THE ECMWF AND

UKMET WAIT UNTIL THE FOLLOWING DAY TO COMBINE ENERGY IN THE

NORTHERN AND SOUTHERN STREAMS OVER THE EASTERN STATES...WITH A

MORE CLIMATOLOGICAL LOCATION ACROSS THE GREAT LAKES AND THE

INTERIOR NORTHEAST FOR THE WINTER PRECIPITATION IMPLIED ON THEIR

SOLUTIONS. THE GFS SOLUTION HAS NOT BEEN RELIABLE DURING THE PAST

DAY OR SO...TRENDING MORE AND MORE SUPPRESSED WITH ANY STORM OVER

THE EAST VERSUS WHAT WELL AMOUNTS TO A WESTWARD...DEVELOPED TREND

ON THE OTHER MODELS. THIS RUN OF THE ECMWF DOES HANDLE THE ENERGY

COMING OFF THE PACIFIC DIFFERENTLY THAN ITS PREVIOUS VERSIONS AS

WELL...BUT WITH NO ECMWF ENSEMBLE DATA AVAILABLE FOR THIS MODEL

CYCLE AS OF THE TIME OF THIS FORECAST...COULD NOT HEDGE ONE WAY OR

ANOTHER FROM ITS DETERMINISTIC SOLUTION WITHOUT JEOPARDIZING THE

INTEGRITY OF THE FLOW WITH THE INCORPORATION OF A DISPARATE SET OF

MASS FIELDS.

Later in the day after time to see more data and perhaps have a rethink this is what they posted

1000 AM EDT TUE MAR 18 2008

VALID 12Z SAT MAR 22 2008 - 12Z TUE MAR 25 2008

UPDATED PRELIM DISCUSSION...

THE PRELIM FCST IS REVISED TO INCORPORATE A NEARLY EVEN BLEND OF

THE 00Z ECMWF/00Z EC ENSEMBLE MEAN AND 12Z/17 ECMWF. TELECONNECTIONS RELATIVE TO FAIRLY STRONG POSITIVE ANOMALY CENTERS OVER THE NRN ATLANTIC/NWRN PACIFIC AND NEGATIVE ANOMALY CENTER OVER THE NERN PACIFIC

So they seem to be content with the idea of +ve anomalies in the northern Atlantic. A subtle change from late last week when the area was 'near Greenland'.

Their 500mb charts are below

24-28 March

and the on for 26 March-1 April(!!)

Both continue, after a bit of a question end of last week, with the +ve anomalies to the north west of the UK.

Other input

GP posted this earlier this evening and may have a fuller report soon.

With strong easterly trades in evidence over the western-central Pacific and the MJO showing signs of westward movement, allied to continued tropospheric impact from the recent upper warmings, I can see the 12z ECM as a big hint on the way forward from here:

....continued -AO conditions with shifting emphasis of the sub Arctic (-NAO) ridge towards Scandinavia late March into April.

and this just now, the link

http://www.netweather.tv/forum/index.php?s...p;#entry1216632

if it does not drop on to GP's post its No 154 on page 10 of the current model thread(time 2030)

and looking at other sources, chiefly from NOAA regarding La Nina(no change from their 29 February assessment and none due until 31 March)=moderate to strong through spring.

NAO/AO are predicted to go negative end of the month/early April.

To sum up

The odds are on a colder rather than a milder end period to March and similar into early April. The general flow being from the northern half of the North Atlantic, a mainly north of west flow. If GFS is near the mark for end of the month/early April, and other data suggests it may well be, then Atlantic depressions running across the country at times and ese into the continent. Thus some milder air ahead of them then back to a colder source. The ECMWF idea at T+240 is interesting to say the least. IF it verifies(I'll do a check around its verification date) then it may be even colder but at the moment I would favour the GFS version.

update is scheduled for Good Friday evening

Edited March 18, 2008 by johnholmes

[mcweather]

Thank you for that John whether its gfs or ecm that comes off ( personally I,d prefer the ecm) it certainly not going to be warm. Could we be seeing a carbon copy from 50 years back when March ( warmest of the century)/early april 57 was very warm ( a la 2007) only to be followed 12 months later by a very cold 2nd half of March and early April with substantial snowfall in places. Even the south!!

[stratty]

thanks again john

[johnholmes]

Update on Good Friday 21 March 2008

Well what has happened since the last update on Tuesday?

NOAA, or rather GFS, tried to create a large snowstorm that promised to cause some upset over the Atlantic for several days and perhaps knock the then long term forecasts. It seems to have been downgraded with time and hence its overall impact on the major troughs and ridges in the upper atmosphere will be less than at first thought. Much of the time NOAA do seem to prefer the outputs from ECMWF from other models. One of our posters from the States also commented on this. Quite often the charts they prepare show a ‘mix’ of % amounts from various models and ensembles.

The overall impression I get is that it seems unlikely that I’m going to be reporting a probable change to much milder/warm weather for the UK for some time to come.

As a summary I would post this

Cold rather than mild well into April. Certainly times when south in particular but not exlusively will have a milder flow from south of west. Hoever, the predominant direction looks like being west to north west. There is some basis for believeing that a more north to north east flow may take over in early April but by no means conclusive.

A very different start to last April anyway.

Putting a bit more detail on it, and I’ve covered the possible hiccup that might have occurred if the USA ‘storm’ had developed as much as it first appeared likely. The NOAA outputs continue to suggest some +ve anomalies in the 500mb flow over the Atlantic in the Greenland area and the chart below shows this.

issued last evening – the weekend sees these charts issued but they have no human input into them, so not unlike the Met O model charts compared to their Fax version, thus I don’t show them over weekends. As commented this is the one from Thursday evening

valid out to 3 April. Less marked +ve but its still there. The charts below show their idea of the 500mb ensembles, again less marked but still there on the 5520m chart, obviously some divergence amongst the ensemble members at that range. The latest one(not ashown) does suggest that the 500mb flow is going to be much flatter, I’ll monitor that as it would make an effect on the temperatures for the UK.

The GFS/ECMWF version is below, but its only for T+168-T+240

For the time scale, out to T+240 they both show the +ve values in the Greenland area, albeit rather different values and patterns

Over the past 3 days GFS has varied somewhat in its LRF output, that is beyond T+144 and so has ECMWF out to its limit that we see, T+240. This may be due to the projected snow storm over the ne of the USA, but I’m not sure. Latterly GFS in its distant time scale is going back to the idea of cold rather than mild and flow from north of west not south of west to the end of its run. Interesingly it has on a couple of occasions toyed with the idea of the surface pressure rise occurring north east not north west of the country.

This is something that GP has shown or rather suggested in his latest post, read it here

http://www.netweather.tv/forum/index.php?s...p;#entry1218375

just summarising his last paragraph, and he posts,

‘Both operational GFS and ECM have begun to pick up these developments in the extended outlook. Thereafter, I think it not unreasonable to think that the next evolution to be for any Scandinavian ridge to retrogress into the North Atlantic, especially if the MJO wave manages to progress through phases 6-8. All of which boils down to a cool to cold Spring outlook with average levels of precipitation but feeling a total contrast to this time last year.’

Finally this from NOAA in their update regarding La Nina for the States

PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK

NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD

830 AM EDT THU MAR 20 2008

30-DAY OUTLOOK DISCUSSION FOR APRIL 2008

STRONG LA NINA CONDITIONS CONTINUE THROUGHOUT THE TROPICAL PACIFIC AND WILL CONTINUE TO FORM THE UNDERLYING BASIS FOR THIS MONTHLY FORECAST.

So again we have slightly different versions from different areas. Overall though I feel its leaning towards cold rather than mild into about the start of the second week in April(as far as this lrf goes). So my initial summary above is I think a correct summation of things look from the different sources this evening.

next update is due Tuesday evening 25 March

[mcweather]

Many thanks John.

I have thought that some of the GFS members were far to progressive. Even when our Easter event is over I don't think this will be the last of the cold or snow for that matter. I think there will probably be one more major shot possibly as late as mid April. Just a feeling I get from the models and 40 odd years of weather watching.

[johnholmes]

cheers MC, yes its a fairly consistent signal from all data sources that cold not mild is the word for much of the time for 2weeks plus. Beyond who knows!