Model Output Discussion 12z 03/04/13

[Gibby]

Hi folks. Here is the evening report on the 12:00hrs outputs from GFS, UKMO, GEM, NAVGEM and ECM for tonight Friday April 19th 2013.

All models are in broad agreement on the weather pattern over the coming week or so. The current rise of pressure over the UK will ensure a dry 24-48hrs with some good sunny spells and light winds before a cold front moves SE over the UK with some rain reaching the SE late on Sunday. As the cold front clears the SE on Monday the South and East would turn largely dry in a light west flow while the NW stays cloudier with showers or rain at times. Pressure rises from the South again towards midweek with Southern Britain drawing a feed of warm Southerly winds from France bringing temperatures comfortably into the high teens and low 20'2 in the SE for a time. Through the second half of next week the warmth over and to the South is pushed away steadily South and East as a mid Atlantic anticyclone and low pressure combine to feed increasingly colder and more unsettled conditions down across the UK in time for next weekend.

GFS then shows a rather chilly spell with increasingly unsettled conditions developing from the North by next weekend with showers, heavy, thundery and wintry on Scottish hills plus unseasonably cold nights with frosts under any clearer skies. The rather cold and unsettled theme continues for all of the UK throughout the remainder of the run with plenty of days of heavy, thundery showers and bright Spring sunshine offsetting the chill at times.

The GFS Ensembles show a rather chilly and unsettled spell developing after a few warmer days in the middle of next week in the South. With time rainfall amounts across the UK increase indicative of low pressure moving slowly down from the north to affect all of Britain by next weekend.

The Jet Stream continues to flow largely over the UK from off the Atlantic with the flow buckling North around the Northern periphery of a mid Atlantic High pressure and diving South or SE to the West of Britain by next weekend.

UKMO tonight shows High pressure receding away Eastwards by Thursday with Low pressure gradually creeping down from the NW dislodging the warm and dry conditions from Southern England and dragging colder and more unsettled conditions down from the North in the following days.

GEM too shows the embryonic signs of change to cooler and more unsettled conditions following the expiry of it's run as the last frame shows High pressure positioning in mid Atlantic with lower uppers soon to move SE towards Scandinavia and the rest of NW Europe.

NAVGEM shows a cold pool dropping South over the UK by next weekend with an increasing risk of showers in rather colder conditions.

ECM finally shows as much as a 10C drop in temperature over Southern Britain between Wednesday and Friday as a cold Northerly flow develops behind a cold front pushing the warm sunny weather of the midweek spell South deep into Europe later in the week. The weekend looks distinctly cold and unsettled with heavy, thundery showers or longer spells of rain falling as snow on the Scottish mountains with the risk of frost overnight becoming a real threat again.. By the start of the new week Low pressure lies close to Eastern England with a cold and very showery start to the new week with temperatures well below average everywhere.
 
In Summary there is some stark contrasts to be felt over the UK over the coming week or two, especially in the South. Through the first few days of next week the South will become increasingly warm and sunny with 20-21C possible midweek and maybe higher in the SE. Later in the week the weather will turn markedly as a cold front sweeps the warm air away South and replaces it with very chilly and windy conditions with frequent showers of rain, hail and thunder with snow over the Scottish hills and mountains. With Northern blocking yet again becoming established it could be a long road out of a chilly and unsettled start to May.

[bluearmy]

apart from the odd couple of warm days, spring certainly seems unwilling to take residence in 2013. the extended ens have pointed at this week 2 cold trough for a while now. There remains the slim chance that the trough could retrogress further west to allow the uk to sit on the less cold side but this looks the less likely scenario for the time being.

[weather_it_will]

Through the first few days of next week the South will become increasingly warm and sunny with 20-21C possible midweek and maybe higher in the SE.

I can't see anywhere in the UK reaching 21°C next week based on on the ECM & GFS 12z.

In reality 16-18°C is probably more likely at best on Wednesday, with the highest temperatures in the smog of London.

Edited April 19, 2013 by Deep Freeze

[damianslaw]

UKMO, ECM and GFS very similiar this evening, indeed even beyond the reliable timeframe of 144 hours, all are suggesting an evolution to much cooler conditions as we see a mid atlantic ridge and a cool northerly flow establishing itself to end the month.

 

The next few days should bring plenty of sunshine for all and for the south and east quite warm conditions by the middle of next week thanks to a feed of warm uppers off the continent, whilst the north and west will see more average temperatures thanks to the feed of air being off the atlantic.

 

Late April - early May is often a period when we see marked switcharounds, southerlies are often replaced by cold northerlies and vice versa in a short time span thanks to the atlantic being at its quietest in mid spring, so no suprise to see the charts offering a switch to much cooler northerly airstream. Thus for the north in particular proper spring warmth still looks a long way away - gosh its been a long cold season for the northern half of the country....we've not endured such a delayed start Spring since at least 1996... lets hope we don't see a May like 1996!

[weather_it_will]

I can see the number "21" on this chart:

Congratulations, you posted a chart with some numbers on it.

Very good.

Can you apply some theory to this also?

The latest 18z GFS confirms a max of 16°C with a hint of 18°C possibly in central London areas.

[SP1986]

why don't you post much in the winter? i think it would be more your scene.

Of course, we'll have to wade through the posts about "locked in" cold before that can happen.

 

I don't like cold! (read my whole posts with at least some lucidity!)

 

As I don't have time for unnecessary cold ramping really, i also don't have time for mild rampers who attack others posts..

 

This week, it's actually looking like a NW-SE split may occur within the milder weather, but it may actually end up feeling quite humid in the west despite the lower temperatures, particularly towards the 144 hour time range. In the south it looks rather pleasant with some warmth initially, as shown on the 18z. The signal for cold air flooding down the country is strong though, and I don't understand why this would be contested, afterall it's only what the models are showing. That said the 18z puts a run is without, initially, a strong Greenland High, which means such blocking by the ridging mid-Atlantic High may not last long if a link is established, so the high should topple if that is the case..  

[winterof79]

Not what i really wanted to see late April.

http://www.meteociel.fr/modeles/ecmwf/runs/2013041912/ECM0-192.GIF?19-0

http://modeles.meteociel.fr/modeles/gfs/runs/2013042000/gfsnh-1-180.png?0

 

Still,some pleasant warmth before the cool down.Seems like a cool easterly flow is setting up in the mid term, so the further west you are the better.http://www.wetterzentrale.de/pics/Rtavn2768.png backed up by the Met office update.Mid may expected to settle down.

[mushymanrob]

enjoy some very pleasant days before it inevitably turns cooler. what matters if it reaches 21c or 18c? its still very nice!

 

disagreement however over the nature of the cool off. the gfs as per usual trends towards a shorter less intense cool period. the ecm as per usual predicts a colder lengthier period. the anomaly charts suggest the ecm is closer to reality, if they firm up on this mornings charts. leaving the uk stuck in a lengthend trough between two large areas of high to our west and east.

 

could be quite cold, with hill snow and sharp overnight frosts at least for a while.

[Frosty.]

The 00z runs suggest a thundery breakdown for southern britain later next week as the cold air spreading down from the north hits the warm air coming up from the south, some big storms could result from this clash of airmasses before the cold air sweeps south to all areas and then it's sunshine and showers, wintry on hills with widespread frosts. The further outlook appears to show rather cold and unsettled conditions with showers and longer spells of rain with snow for northern hills and mountains and night frosts. There is a fine spell to look forward to before the above occurs, today looks sunny for many areas with temps around 13-14c but tonight will be cold with a touch of frost, tomorrow starts cold and sunny in the east/se but turning more unsettled for the north and west through the day and clouds increasing for the southeast by tomorrow afternoon. Monday is an improving day with temps similar to today, tuesday and wednesday look like being the warmest and sunniest days, especially further southeast with temps nudging into the 70's, mid 60's further north and west but low 50's for nw britain. Thurs/Fri is when the colder and more unsettled weather starts to push south and east and as pressure falls across the south, thundery downpours with torrential rain is possible in my view.

[Gibby]

Good morning. Here is the report from the midnight outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Saturday April 20th 2013.

All models show the pattern as of last night's output with a cold front moving SE across the British Isles reaching the SE of England later tomorrow. before that arrives a very decent day today is likely over England and Wales. behind the front a mix of sunshine and showers looks likely, these largely in the North with a lot of dry weather in the South where by midweek it becomes rather warm as High pressure transfers East to the South of the UK. Then later in the week the weather takes a stride downhill as High pressure in mid Atlantic drives a cold northerly flow South down over the UK with a showery and rather windy and cold end of the week and weekend lined up for most areas from Thursday.

GFS then shows FI being mostly influenced by an Easterly flow as the low slipping South over the UK later next week becomes cut off over the near Continent and plaguing Southern Britain with chilly winds and rain at times while High pressure to the North keeps more Northern areas dry and bright.

The GFS Ensembles show good support for both a warm up and a cool off in the weather over the coming week, the contrasts between these two events most felt in the South. After a largely dry start the weather shows signs of becoming more unsettled. A slow trend towards more average conditions is shown through the final third of the run.

The Jet Stream as last night shows a rising of the flow high over a mid Atlantic high later next week which then sees the flow returning South just West of the British Isles to Southern Europe then NE to Russia.

UKMO today shows cooler air and Low pressure slipping SE into the UK on Thursday, a process that will continue in the following days bringing an increased risk of showers by the weekend and rather colder conditions.

GEM has a chilly and unsettled end to it's run with Low pressure sliding SE across or just NE of the UK with a showery NW flow with disturbances giving longer spells of rain at times and snow over the Scottish mountains.

NAVGEM today shows Low pressure over Scandinavia late next week with High pressure over mid Atlantic sending cold and unstable NW or north winds down over the Uk with rain or showers for all, heavy at times and wintry on high ground in the North.

ECM today continues to look very disturbed beyond the middle of next week as Low pressure continues to sink South, on this run further West over the UK. It will make little difference at the surface with heavy showers or more prolonged rainfall at times in rather cold conditions.

In Summary the weather will divide into two halves over the coming week or so. After a Westerly flow with scattered showers following tomorrows rainy trough the weather will warm up over the South briefly midweek. Thereafter a cold plunge of air on the Eastern flank of a mid Atlantic High sweeps South over the UK with showers and bright intervals developing in considerably colder air in the South from that of earlier in the week. Longer term it still looks like a cold spell could greet May with the North perhaps seeing the best of the sunshine as an Easterly wind looks the long term likely outcome. This will mean rather chilly conditions with some further rain in the South at times while Eastern coasts could be jolly cold and raw with onshore winds from a very cold North Sea. The North and NW will see the best of any sunshine should this pattern prevail where it could feel rather warm in the afternoons. With synoptics as shown this morning we cannot unfortunately rule out the continued risk of frosts in places over the term of the output.

[johnholmes]

without posting any charts the 500mb anomaly charts remain consistent in the colder more northerly spell into early May.

[IDO]

As others have said, cross model agreement on the synoptics right out to D15. After a temporary ridge next week gives the south some milder temps, GFS and ECM still vary on details, the later more subdued, we see a mid-Atlantic ridge by D6-7, and we are on the colder side of the setup. D10 charts:

GFS 0z op: ECM Op:

There remains a differential between the extent of the cold uppers and position of the trough over the UK but very similar.Though the GEFS mean is more in line with the ECM op:

The GEFS highlight temps next week: I am not sure we will get much above seasonal highs from that, but should feel mild. The ECM 12z ensembles show lower temps for Tuesday/Wednesday in London: compared to GFS (op and mean). No sign from the mean of anything milder right out to D15 though a few members hinting at an improvement.

The precipitation members are well scattered on the ECM so the position of the trough and its associated lows still low confidence:

The north remains locked into a cool setup for the next 15 days+ and the anomaly charts highlight this:

D8-10:

Looking a medium term setup. So the odds of an early Summer this year are getting smaller.

Edited April 20, 2013 by i'm dreaming of...

[Summer Sun]

Looking at this mornings ensembles there is good agreement on a peak in temperatures around the 24th then we see a cool down before another rise in uppers from around May 3rd

 

 

Rainfall remains below average through-out as well

[Methuselah]

Looking at this mornings ensembles there is good agreement on a peak in temperatures around the 24th then we see a cool down before another rise in uppers from around May 3rd

 

 

Rainfall remains below average through-out as well

It looks like some very typical late April-early May weather, to me...HP to our west is hardly unheard-of at this time of year.

[bluearmy]

naefs now firming up on a developing ridge retrogressing from western russia into scandi through week 2 as the trough sinks sw. fits in with the meto extended of renewed easterly flow.

[Frosty.]

Next tuesday promises to be a fine and sunny day across central and southern britain on the Gfs 06z with high pressure in control across the southern half of the uk, temps of 17-19c and possibly 20-21c across the southeast, a very similar day to today, sunshine wise but several degrees warmer, wednesday promises to be similar but a degree or two warmer still.

[Frosty.]

After a warm and sunny day on wednesday, especially towards the southeast, thursday looks wet with heavy rain pushing east across southern britain with a risk of thunder in the heavier bursts before the rain clears away to the east later with showers then spreading down from the north although the showers won't really get going further south until friday when some heavy and thundery downpours can be expected, then even colder air spreading south into the weekend with arctic air spreading down into scotland, turning the showers wintry with snow on hills and frosts becoming widespread where skies clear overnight leaving icy patches.

[Frosty.]

The Gfs 06z in FI is not bad, we don't get a secondary cold surge to follow up next weekends cold snap and the 6z even teases us with the possibility of much warmer air over eastern europe being drawn our way, as it is, FI is rather unsettled but temps recover back to average after the cold blip which isn't even that cold for the south anyway, temps still just about make it to 10c in the south even with the uk under -5 T850 hPA, showers would be wintry on northern hills though and overnight slight frosts would occur for a little while but then further into FI becomes milder but cyclonic. The 6z ends with an increasingly warm settled pattern with temps recovering into the low to mid 60's f.

[Frosty.]

If the Ecm 00z verified, there would be a chance of thunder as a trough develops along the boundary of the colder unstable air to the north with the residual warmer air to the south of it, heavy showers with a risk of thunderstorms would break out as the active cold front slides southeast, followed by colder and showery weather for friday & the weekend with overnight frosts, the ecm 00z looks rather cooler than the gfs 6z in FI.

[johnholmes]

well two differing views on heavy showers/thunder above, can we resolve this?

go to

http://www.netweather.tv/secure/cgi-bin/premium.pl?action=cskew;sess=bc6944382aceb16058e7652734b52172

I have used Doncaster and looked at T+120 out to T+180 the furthest the current output on Net Wx for skew-t goes, and one can see how the upper air changes in that time, to become quite unstable to 18000ft by 27 April but fairly dry then, so showers in this area yes and perhaps heavy by the 27th where they occur, thunder ?. Those more expert on storms can come along and give their idea perhaps?

T+180 =27 April

Edited April 20, 2013 by johnholmes

[Methuselah]

It'll be 'resolved' as-and-when it either happens or doesn't happen; rather like those expectations concerning 'widespread convective snowfall' back in the winter...

[phil nw.]

Some interesting views on possible convection as the air mass changes on Thursday.

I am certainly no expert on these developments but i always thought that unless there`s a big undercut of colder air near the surface as the front moves through then all we would get is rain but no thunder.

Looking at GFS on NW extra for Thurs Midday the cold air comes through gradually with no sharp boundary

so as W09 explained quite low lapse rates at that time.

Certainly once the cold air becomes established then with the strong late April sun there`s every chance of some convectional activity in the days following i would think.

Of course some uncertainty on these fine details with some days to go but there could well be some interesting April showery weather once the UK comes under the influence of the upper trough towards next weekend.

Meanwhile some warm sunshine on offer through the next few days beyond tomorrow as the high moves across to the south of the UK.

Temperatures further south widely in the upper teens around mid-week before the much cooler conditions come through later.

[Frosty.]

It'll be 'resolved' as-and-when it either happens or doesn't happen; rather like those expectations concerning 'widespread convective snowfall' back in the winter...

spot on, nothing has been resolved unless he has jumped in a time machine. There is some uncertainty how the warm and settled spell in the south will end in my opinion, if a shallow trough forms on the boundary of the cold and warm upper air (as per ecm 00z) I believe that would spark some shower activity, and or at least increase the intensity of the rainfall along the cold front and given the time of year with the high sun which is already the equivelant of late august, showers which could be heavy and thundery would seem a reasonable possibility, or else it will just be a weakening frontal band of rain pushing into the residual but departing higher pressure and fragmenting to nothing, either way, it will be turning much cooler by friday and next weekend with a mixture of sunshine and showers which could be heavy and would be wintry on northern hills.

The met office update today goes for the rainband weakening as it pushes further southeast but nothing is resolved yet.

Edited April 20, 2013 by Frosty039

[nitro_deluxe]

At least there's plenty enough to keep tabs on 

[nitro_deluxe]

Only get out clause to the above.Things may change till then? next...

 

Enjoying the present clement weather to be honest, could be a bit chilly again overnight tonight for some.