Model Output Discussion - Spring 5th March Onwards 6z--->

[Gibby]

I have to say that I know you guys are only reporting on what the models churn out.

However but surely this type of scenario has been progged so many times and every time its no where near as bad/cold by the time it gets here.

Also for the south east and east coast dwellers it may not be any colder after the last few days of fresh easterlies, I know today/tomorrow much warmer here but its been dam perishing.

Yes I agree with your sentiments that near the coast and especially the East coast it has been very chilly. Hardly surprising considering the North sea is only 8-9C and with an onshore wind it has felt cold. Inland though the afternoons have felt like early Summer at times but my valley location here has given me some very unwanted morning frosts at -1.7C yesterday with a 20C temperature range by early afternoon as temps reached nearly 19C.

 

You are also right that things are often watered down by the models nearer the time though I think with a lot of cross model support currently suggests there will be a distinct chill in the air for all at times next week and some interesting cloudscapes as cold air aloft mixes with the strong April sunshine with a cocktail of ingredients in the heavy showers through the afternoons.

 

It's worth noting that snow can fall in Spring with temperatures as high as 8C normally in the form of soft hail or graupel as the dewpoint and temperatures range is much greater in cold polar Spring air, something many of us may witness at some point next week.

Edited April 21, 2015 by Gibby

[Summer Sun]

Turning unsettled from Friday but GFS again isn't showing much rainfall over the 10 day period for most of England, Wales, central and south Scotland

 

t144

 

 

Day 10 and some areas by this time still haven't got 10mm of rain

 

[karlos1983]

such a shame we couldn't see this sort of output in Jan/Feb. Not idealistic for late April. Be interesting though that's for sure

[Hairy Celt]

Some great charts showing up now for action weather fans like myself. Its a huge turn around coming up after a fairly non descript few weeks. Will be interesting to see just how cool/cold a northerly flow will be.

 

                                                     

 

 

 

The GFS 12z is actualy fairly well supported within the ensembles, it isnt an outlier or extreme solution:

 

gefstemp204.jpg

 

Temps just 5 or 6c on the 28th here for South Yorkshire, amazing really. After that then struggling to get into double figures for the rest of the run!

 

 

Its as if we get transported to another planet on the 24th, from flat line to big rain spikes:

 

gefsrain204.jpg

 

You are on a different planet in Yorkshire

Edited April 21, 2015 by Hairy Celt

[Tamara]

Synoptically, not for all but for many, the current outlook would have been much more appealing a few months back.

 

However, again not for all but for many, occurring as it is in late April the pattern change underway at the end of this week represents something much less enticing and a large contrast to the quiet and settled seasonal conditions that we have been used to

 

The reasoning behind the change from a meteorological perspective is a very interesting one however - it also helps give perspective to the winter pattern just past of 14/15, whilst at the same time explains the background to the pattern change about to get underway

 

Atmospheric Angular Momentum (AAM), effectively measures the turning force of the atmosphere relative to the Earth’s rotation  - and earth/atmosphere frictional torques and mountain torques are a gauge of this. AAM therefore provides us with a guide as to how the jet stream may behave and an indication of overall pressure pattern configurations across the hemisphere

 

The whole winter was characterised by a dominant La Nina state to the atmosphere, decoupled from the very weak El Nino Pacific Ocean signal. This manifested itself in a predominantly low Atmospheric Angular Momentum state with warm water pooling over the West Pacific which locks MJO forcing into this region due to the highly organised convective activity that results from such warm water pooling

 

This gave rise to the highly amplified jet patterns Stateside which lead to the sharp contrasts in weather conditions across the US from east to west - with the deep cold over the NE states giving rise to the temperature gradients downstream over the Atlantic that in turn helped fuel the jet stream and locked in our persistent westerlies

 

As winter started to turn into spring, we have seen the first developing signals to suggest a more dominant lead from the El Nino oceanic signal to come through 2015, with the atmosphere, so far, providing a weak (but steadily increasing) response.

 

Such a response has manifested itself in a phase of (relatively) higher AAM tendency which favours more blocked weather patterns across the UK and Europe and hence a good clue to the persistence of settled weather patterns and generally fine conditions dominating  - and only punctuated (in relative terms) by brief more unsettled spells

 

We also have to factor in seasonal changes to the stratosphere. Despite an attempted SSW in the middle of the winter, assisted by a background -QBO to encourage troposphere > stratosphere Rossby wave breaking, the unfavourable Pacific Nina-esque low AAM state negated any possible potential benefits of cold blocking developing for the UK and Europe

 

However, on-going, is a Final Warming of the stratosphere as the winter-time polar vortex disintegrates completely and summer-time stratospheric reverse polarity (easterlies) takes over

 

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/temps.gif

 

 

This leads us up to date, and the upcoming pattern change 

 

AAM is on the verge of plunging once more - with the Global Wind Oscillation (GWO) having orbited through an extremely large amplitude Phase 8/1 and consequently very strong negative frictional and mountain torques (US Rockies) now occuring. In tandem with the rapid changes happening in the polar stratosphere, we have to combine this with the ying-yang effects of the atmospheric state and the fall-out from a very strong -MT - as described.

 

 

As twin forcings, they together represent a highly vigorous NH amplification wave - with quite high impact weather conditions set to occur either side of the amplification

 

http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png

 

An interesting and somewhat contradictory aspect of this, is that whilst -AAM states are often associated with South-eastern U.S. ridge development and downstream strength in the Azores High (the latter such as seen influencing our weather patterns here throughout the last winter) the rapid warming of the stratosphere is ejecting the remains of the decimated vortex towards Siberia, and is leaving an emerging high-latitude blocked pattern over the North Pole and Greenland

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015042100/ECH1-144.GIF?21-12

 

This is set to provide us with a completely different weather pattern for us in the UK than was witnessed under low AAM and as seen in our winter. The transitory cold spells we saw then were manifestations of -MT which temporarily amplified the Atlantic westerlies as the Pacific pattern cyclically retrogressed

 

However, wave activity through the stratosphere was not sufficient to break the stranglehold of the vortex, and combined with the tropical Nina response of enhanced sub tropical ridging (Azores High in our 'locality') amplification of the jet stream across the Atlantic was restricted, muted, and cut short in time span - with no proper sustained -AO mechanism in place our side of the NH

 

This time though, we are seeing the effects of large scale high latitude blocking through stratospheric FW - augmented even further by the rippling effect of GWO induced Rossby wave action (MT) across the US - further amplifying and exacerbating the meridional pattern in sequence

 

With the El Nino ocean signal gathering strength however, this could conceivably be the final -AAM push of the year. Often such last pushes are the biggest - and this one certainly looks likely to be exactly that. The amplified push of arctic air southwards looks set to give as a period dominated by a cold trough and heights over Greenland and the Atlantic

 

Wrong time, wrong place as stated earlier

 

But, as reasoned, taken from a seasonal longer term prospective, the atmosphere/ocean signal is looking increasingly favourable for warm blocking patterns for the UK and Europe - much as El Nino type summers often provide

[knocker]

And if it's of any interest Michael Ventrice had ths to say in his blog last week.

 

Atmospheric Angular Momentum to drop this week; The Driving Mechanism and Future Implications this Summer

[Frosty.]

We are racing towards a major pattern change, most of April has been warm and anticyclonic across the south of the UK, not so further north but we will all soon be into a cyclonic pattern with low pressure domination. The Gfs 6z shows the UK being plunged into an unseasonably cold spell with arctic maritime air digging south bringing frequent showers of rain, hail, sleet and snow with thunder and lightening too, also, bouts of strong winds and persistent rain with snow on hills and damaging night frosts, however, there will be pleasant sunny spells but when the showers arrive, temps would drop like a brick. For fans of action packed weather, your cup will runneth over from the end of this week until possibly well into early may.

Edited April 21, 2015 by Frosty.

[Frosty.]

Well just as I was saying a major pattern change is on the way, along comes the Gfs 12z which shows high pressure building from the south next week cutting off the arctic blast prematurely, indeed, this run shows a pleasantly warm Saturday for most of southern / eastern England with the SE corner warm on Sunday too, further north the arctic air does flood south with wintry showers but it doesn't develop like it did on the 6z, the south starts to warm up again and become fine, this wasn't in the script..lol

[Smiler1709]

And as fast as the cold, rain and wind appears, the gfs wants to send it packing. Fingers crossed this cooler spell is a blip and we can continue on with this great spring weather.

[Summer Sun]

Well just as I was saying a major pattern change is on the way, along comes the Gfs 12z which shows high pressure building from the south next week cutting off the arctic blast prematurely, indeed, this run shows a pleasantly warm Saturday for most of southern / eastern England with the SE corner warm on Sunday too, further north the arctic air does flood south with wintry showers but it doesn't develop like it did on the 6z, the south starts to warm up again and become fine, this wasn't in the script..lol

 

Now this is coming into a more reliable timeframe its going to be interesting hows its handled turning cooler for sure but will the models start and water it down like in winter?

 

UKMO has a ridge of high pressure just to our south west on Monday a cooler flow to start the week but how long for will depend on where the high ends up

 

[Skullzrulerz]

So it seems that a cool/cold northerly blast is set to happen around the weekend as acroding to the last few runs of the models (GFS,ECM And so on)

However the latest GFS has seem to stop the northerly in it's tracks around Northern England even through the Main event will be up in Scotland and part's of England the uk will be having a cool down for a while when higher pressure strikes back later on.

 

But this is only "ONE" run on "ONE" Model which is the GFS ( 12z ) even through the UKMO does somewhat support the idea it's best to take this one step and a time due to how complex it may be.

 

I won't put hopes up for a cold blast from the north but not a hot wave from the south west or where ever it may be so I'm sticking to just a sightly cooler period and some unsettled rain and wind.

 

Take it one day at a time folks since the models always change in detail ( Minor or Major ).

[Frosty.]

Now this is coming into a more reliable timeframe its going to be interesting hows its handled turning cooler for sure but will the models start and water it down like in winter?

UKMO has a ridge of high pressure just to our south west on Monday a cooler flow to start the week but how long for will depend on where the high ends up

The GEFS 12z mean shows support for watering down the cold blast next week, similar to the op with weak height rises from the s/sw cutting off the arctic incursion before it even establishes in the south. the arctic blast could turn into a non event.

Edited April 21, 2015 by Frosty.

[knocker]

The futility of looking too far ahead on individual runs.

Charts weatherbell

Edited April 21, 2015 by knocker

[Winter Cold]

ECM tonight keeps the faith with a deep trough to the NE dragging in those cold 850s for a few days:

 

 

 

 

   

[Frosty.]

The Ecm 12z shows an unseasonably cold spell next week with arctic maritime air flooding south across all areas with sunny spells and a wintry mix of showers, some heavy with hail and thunder and some sharp night frosts, snow would be a possibility in the heaviest showers since temperatures would drop like a brick during showers but especially on northern hills, pressure rises from the west towards T+240 with increasingly fine conditions.

Edited April 21, 2015 by Frosty.

[damianslaw]

Strong synergy between the models today, all going for a significant change come Friday as heights break down squeezed out by low pressure from the SW, sending heights packing to Greenland for the first time this year..

 

End result an unsettled cool spell for all, cold in the north for the time of year with very supressed temperatures. A cold wind will accentuate the general cold feel.

 

GFS playing around with heights quickly building back to the SW, but with strong heights to the NW, the trough has to drop somewhere and its home most likely the UK, so I would treat it with caution this evening. ECM showing a stubborn trough over and just to the east of the country next week.

 

This time next week no doubt many will be complaining about the weather in contrast to today which has been fantastic here.

[Frosty.]

In my opinion, tonight's Ecm 12z ensemble mean looks about as wintry as you can get in late April / early may. A strong Arctic airflow bringing frequent wintry showers with hail and thunder and icy frosty nights. I think it's still game on for an unseasonably cold blast next week with snow on hills and to lower levels in the heaviest showers but with sunny spells too.

[bluearmy]

Just a note that the 12z op ECM follows the parallel ECM 00z late in the run with the ridge drifting across.

[Smiler1709]

Bets on the ECM backtracking tomorrow and resting this silly idea of bringing in a cool blast. All winter we had some banging charts on offer at T92 hours yet 99% of them disappeared when a model picked up a new trend. The gfs has picked a new one up this afternoon and I think it's a safe bet that come next week, it may be cooler and abit wetter but none of this wintry blast cobblers.

[Polar Maritime]

The GFS & ECMWF this morning continues the cool/cold unsettled theme, With a band of rain with chances of Snow to modest levels Midlands North, As a front sinks South over the UK by Sunday dragging in much colder air from the North, With most of the UK under single digit minima by then. The 29th again shows -10 850's touching Scotland.. A very mobile pattern coming up, With small changes making big differences for the surface in these set-ups, So a very interesting period coming up for the Models and how they handle the detail.  

 

Edited April 22, 2015 by Polar Maritime

[Frosty.]

but none of this wintry blast cobblers.

0z models showing a wintry blast, I expect we could see some quite spectacular skies as showers build in an Arctic flow...Bring it on!!

[Frosty.]

Wintry blast on the way, look at these early morning minimum temps on the Gfs 0z.. Brrrrrrrrr

[Captain Shortwave]

I have to be honest, I am struggling to see anything out of the ordinary here, the ECM has just come out and frankly the -4C isotherm barely makes it into the southern half of the UK with the -6C isotherm struggling to get into Scotland. Chilly nights yes but again frost isn't unusual, in fact there have been some frosty nights this week.

A lot of unsettled weather from Friday onwards, though again in the south it takes until Monday for cooler air to reach these areas. Before then temperatures will hit the high teens or even scrape to around 20C. Beyond that, single figures in the north, but low teens in the south.

Edited April 22, 2015 by Captain shortwave

[bluearmy]

I have to be honest, I am struggling to see anything out of the ordinary here, the ECM has just come out and frankly the -4C isotherm barely makes it into the southern half of the UK with the -6C isotherm struggling to get into Scotland. Chilly nights yes but again frost isn't unusual, in fact there have been some frosty nights this week.

A lot of unsettled weather from Friday onwards, though again in the south it takes until Monday for cooler air to reach these areas. Before then temperatures will hit the high teens or even scrape to around 20C. Beyond that, single figures in the north, but low teens in the south.

That ECM op at day 8 isn't far from a wintry sypnotic bliss for the north of the UK. Even at this time of year, I wouldn't discount decent snowfall on the Pennines and Peak District if that were to verify. hopefully this colder blast will be a precursor to a settled warm may and beyond.

[Gibby]

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS ISSUED AT 08:00 ON WEDNESDAY APRIL 22ND 2015.

 

THE CURRENT GENERAL SITUATION High pressure will slowly decline across Northern Britain tomorrow.

 

http://www.wetterzentrale.de/pics/Rtavn001.gif 

 

MODELS-2 WEEK HEADLINE Becoming unsettled and rather cold with bright spells and showers, heavy and wintry on hills. Local night frosts still likely.

 

THE GFS JET STREAM ENSEMBLE FORECAST The Northern arm of the jet continues to weaken, the axis of which slips slowy South across the UK over the weekend. The Southern arm over Spain and Portugal strengthens and amalgamates with the remains of the Northern arm and blows generally West to East in a position to the South of the UK later in the period. 

 

http://www.netweather.tv/index.cgi?action=jetstream 

 

GFS OPERATIONAL The GFS Operational this morning shows High pressure declining over the coming days with Low pressure edging up from the SW deepening as it does and centreing to the NE of Britain bringing rain or showers this weekend. Then by early next week a cold and showery NW flow takes control for much of the week before a ridge crossing East brings a dry if chilly spell towards next weekend ahead of a return to wind and rain at times at the end of the period.

 

http://www.wetterzentrale.de/pics/Rtavn1441.gif

 

http://www.wetterzentrale.de/pics/Rtavn3841.gif 

 

THE GFS CONTROL The theme of the GFS Control run is very similar with no return to the current fine and warm weather once it's replaced by unsettled and often rather chilly conditions from this weekend until the end of the period. It too shows a short drier interlude in the middle of the period as something of a ridge crosses over from the West.

 

THE GFS CLUSTERS The GFS clusters today have firmed up somewhat on changeable and unsettled weather across the UK two weeks from now with rain at times and with winds from between SW and NW. Only 15% of members this morning show High pressure instead lying over the UK in two weeks time.

 

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cpre&HH=372&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=

 

UKMO UKMO shows High pressure declining and being replaced by cyclonic conditions at the weekend with outbreaks of rain or heavy showers for all in cooler conditions overall as Low pressure settles to the North and NE of Britain early next week.

 

http://www.wetterzentrale.de/pics/Rukm1441.gif 

 

THE FAX CHARTS The Fax Charts show a concoction of troughs under falling pressure moving slowly NE then SE across the UK over the weekend and start to next week as High pressure dissolves away over Friday. Mild SW winds at the beginning of the weekend will be replaced by colder North or NW winds early next week.

 

http://www.weathercharts.org/ukmomslp.htm#t120.

 

GEM GEM this morning shows a very chilly week next week as the weekend of transition sees the current fine and pleasant conditions replaced by rain and showers from Friday. The showers could turn wintry over the hills next week as winds threaten to turn into a cyclonic NE'ly later across the South.

 

http://www.wetterzentrale.de/pics/Rgem2401.gif 

 

NAVGEM NAVGEM also shows colder air moving down from the NW at the weekend with sunshine and showers likely for most of next week for all areas but with some continuing bright or sunny intervals at times especially over the South.

 

http://www.wetterzentrale.de/pics/Rnvg1681.gif.

 

ECM ECM this morning keeps cold and unsettled weather going through next week once established with a source of air well North of the UK fuelling sunshine and showers, wintry on hills especially but not exclusively over the North. Through the week and on this morning's run some longer spells of rain could occur especially across the South at times and if things evolve as shown the Low in the channel on the 30th could even produce a little snow on it's Northern flank as it crosses East into Europe.

 

http://www.wetterzentrale.de/pics/Recm2401.gif

 

ECM 10 DAY MEAN(12z) The ECM 10 Day Mean Chart  from last night maintains the unsettled look to things with a daisy chain of Low pressure from across the Atlantic through the British Isles and East into Europe with rain at times for all.

 

http://www.wetterzentrale.de/pics/Reem2401.gif 

 

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trends this morning remain focused towards colder and more unsettled weather across the British Isles lasting for quite some time.

 

31 DAY HISTORICAL VERIFICATION STATS FOR GFS, UKM & ECM The current verification statistics for the past 31 days shows ECM leading the way at 3 days with 97.4 pts followed by UKM at 96.8 pts and GFS at 96.1. At 5 days ECM  continues to lead the field at 88.9 pts over UKMO at 88.3 pts and GFS at 85.6. At 8 days ECM remains the leader with 62.5 pts over GFS's 57.5 pts. Then at Day 10 ECM retains superiority at 44.8 pts over GFS at 40.6. 

 

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day3_PMSL_MSL_G2NHX.png 

 

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day5_PMSL_MSL_G2NHX.png

 

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day8_PMSL_MSL_G2NHX.png

 

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day10_PMSL_MSL_G2NHX.prig

 

 

MY THOUGHTS We are growing ever closer to a change in the weather pattern across the UK as High pressure which has ruled events over the UK for the last few weeks becomes a thing of the past as Low pressure moving up from the SW amalgamates with troughs moving SE from the NW to form a complex Low pressure area just to the North and NE of the UK for much of next week. First changes will be felt on Friday as cloud and some showers move NE across the UK over the weekend. At this stage temperatures will remain respectable in the light SW flow but by Sunday over the North and all areas next week cold NW winds will flood down across the UK from an air source within the Arctic bringing a mix of sunshine and strong convective showers each day with hail, thunder, sleet and snow all possible for many. If winds fall light at night and as daytime showers die out some unwelcome frosts look likely for gardeners and growers to be wary of. Complications could also come from small depressions or troughs enhancing showers to longer spells of rain in places at times and though nearly May the ECM small disturbance shown for around the 30th could produce some leading and back edge snowfall as it runs into the cold air across the UK. This of course cannot be taken as anything other than potential at the moment and will most likely be removed from subsequent runs so don't take this as gospel at the moment. Then looking further out still we have to ask ourselves how long will this rather cold and unsettled period last? Well looking at Northern hemispheric pressure patterns for the next few weeks and a little longer with pressure becoming High over Greenland and the Arctic the cold northerly bias to the winds in our part of Europe could well last into May with further bands of rain and showers affecting all areas at times but being May I'm sure that some compensatory warm sunny spells between the showers will offset the overall feel of some days but I cannot rule out the risk of frost at anytime yet for the next few weeks at least. 

 

Next update from 08:00 Thursday April 23rd 2015