Model Output Discussion - September Onwards

[summer blizzard]

C

I think that the retrogression will not be that high and hold but get toppled out eventually.

BFTP

It's likely that we will see a big cool down in the sence that we get the cool uppers however high pressure is likely to stay very close and as such it will remain fairly dry (the cold front will likely have nothing on it either).

Looking at the 0z model outputs, GEM does not have a breakdown at all while both ECWMF and GFS have the breakdown at day 10.

The message from the models is that the breakdown will come, but only when they stop pushing it back.

[SP1986]

I notice the GFS is going for a cooler scenario on Tuesday this is most noticeable in Northern England where the GFS originally forecast 22C but is now going for 18-19C. Most likely the GFS has underestimated the temperatures (as is normal in these situations), unless cloud cover is an issue. If it is the issue, cloud cover could plague some western areas the first few days (up until say Wednesday or Thursday), limiting temperature heights, relative to what the setup would suggest..

[summer blizzard]

I notice the GFS is going for a cooler scenario on Tuesday this is most noticeable in Northern England where the GFS originally forecast 22C but is now going for 18-19C. Most likely the GFS has this completely wrong, unless cloud cover is an issue. If it is the issue, cloud cover could plague some western areas the first few days (up until say Wednesday or Thursday), limiting temperature heights.

The main core of the 'hot' spell was always likely to be wednesday-friday away from the south east.

[chionomaniac]

C

I think that the retrogression will not be that high and hold but get toppled out eventually.

BFTP

Me too, that is the form horse as I consider energy in the northern arm of the jet stream too high and lacking amplitude.

[roys]

any one know how long this warm spell is goning to last

[Radiating Dendrite]

any one know how long this warm spell is goning to last

Around 6 days.

It should start to cool down from Sunday onwards.

[SP1986]

The main core of the 'hot' spell was always likely to be wednesday-friday away from the south east.

Tuesday was initially suggested with 23C too, so I'd say it was originally Tuesday-Sunday. (Friday?)

[Thundery wintry showers]

We currently have a polar maritime incursion across central and northern Britain, and the real warmth will get underway for many of us tomorrow as the very warm south to south-westerly flow starts up. Tomorrow looks like having a NW-SE split, but the "SE" part of the split will already be pretty widespread judging by the model outputs, with only the north and west of Scotland, Ireland and perhaps parts of NW England seeing much in the way of rain and/or persistent cloud. Elsewhere we can expect the sun to break through pretty widely.

Wednesday-Friday look like being unusually warm almost everywhere- highs of 23-26C are likely to be widespread. There will be some mixing out of the warmest air from the SE resulting in 850hPa values just short of 15C, so I don't think it will be quite as hot as the 1st October 1985 in most areas, but it won't be far short.

[Summer Sun]

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

A Gorgeous chart, this would be a very warm start to October question is how long could that hang on it could take some shifting.

[summer blizzard]

GFS12z is out and has the breakdown complete at day 9 but then resets the pattern until day 15.

[Gibby]

Hi Folks. Here's my take on the 12zs tonight. Due to the universal agreement between the models tonight for the reliable period I'll talk in general model terms and point out the differences as we move forward.

Tuesday 27th-Sunday 2nd All Models

A very warm spell is on the way and we may all share in it to a greater or lesser degree. Between tomorrow and Sunday the models show High pressure to the east of the UK with a warm Southerly flow developing over all areas. Away from the far NW of Scotland and the NW of Northern Ireland where cloud amounts may remain rather large with a little rain at times the rest of the UK will enjoy warm then very warm conditions with sunny skies by day and mist and fog patches overnight, clearing quickly each morning.

GFS from next Sunday shows the Southerly flow weakening as a slacker SW flow develops over the UK. This though is only temporary as High pressure is shown to position itself close to the south for a while before Atlantic depressions eventually break through in the last days of the run. So weatherwise a slow fall off in temperature from next Sunday with temperatures still above normal though in the south. Later as the rain and wind develop temperatures would be back to the seasonal normal.

ECM is very similar by developing a West or SW flow gradually from the North in the first two days of next week. Changes would be slow but a slow downward trend in temperatures would occur as more cloud becomes evident over all our skies as the Atlantic begins to take influence. By the middle of next week a cold front is shown to move steadily SE over all parts bringing much cooler and fresher conditions and a band of rain on the leading edge of the drop in temperatures.

Towards the end of the run things become distinctly chilly with winds turning Northerly for a while and temperatures falling below normal by day and the first widespread frosts of the season looking possible with some showers in the North and East, perhaps wintry on Scottish mountains for a while.

There is something for most on tonights outputs as the models struggle to determine where we go from the very warm weather this week. UKMO on its 144hr chart looks rock solid in continuing very warm conditions well into next week. GFS changes High pressure areas with one to the South being dominant next week meaning a fall in temperatures but still above average for many before Autumn weather returns by the end of the run. ECM illustrates how precarious the heat of this week is at this time of year by developing High pressure to the West next week opening the door for a short cold blast from the North which would be a serious shock to the system for most of us as temperatures fall to below normal levels and give a risk of frost at night.

[SP1986]

GFS 18z attempts to break this one down much earlier than recent runs, on that basis we can probably consign it to the bin, until tomorrow runs. It looks a little suspect anyway as it alters the air feed direction to a SSW'ly which seems a little unlikely.

FI with a it's intense high pressure scenario looks equally as shady.

[snowlover2009]

GFS 18z attempts to break this one down much earlier than recent runs, on that basis we can probably consign it to the bin, until tomorrow runs. It looks a little suspect anyway as it alters the air feed direction to a SSW'ly which seems a little unlikely.

FI with a it's intense high pressure scenario looks equally as shady.

I thought this too, however the high in FI is much cooler than the one this week thankfully. I can imagine night time fog and frost being a possibility. The cold to the north of us at the end is such a tease...

[summer blizzard]

GFS 18z attempts to break this one down much earlier than recent runs, on that basis we can probably consign it to the bin, until tomorrow runs. It looks a little suspect anyway as it alters the air feed direction to a SSW'ly which seems a little unlikely.

FI with a it's intense high pressure scenario looks equally as shady.

GFS18z was quite similar to the GFS12z in that it had a semi-breakdown bringing cool uppers but not losing the high pressure before resetting and then breaking down completely late on. ECWMF has the breakdown complete at day 9.

[mushymanrob]

well ..... if the 00z gfs becomes reality the summer forecast looks like being right....only late! a succession of re-setting high providing us with a pattern to die for in summer. this last 12 months or so seems to have repeated some extremes from history... december the coldest for 30 years, the summer the coolest for 18 years, this warm spell is on track to be the warmest for 26 years (for the end of sept/early oct ) .. i thinkl though the overriding theme from the gfs and ecm is the lack of precipitation, which is still needed in the east (at least)

[Alex]

After almost giving up on heat this year and then out of the blue this! Incredible!

GFS keeps it generally warm through the entire run with uppers averaging between 10-15c however it seems it could be an outlier as the only member to do this, most others have a breakdown of some sorts from Tuesday. Precipitation is low though right through.

[Gibby]

Good morning. Here is the morning look at the 00zs from the big three.

GFS shows High pressure to the east of Britain and a warm Southerly flow across all areas between today and Sunday. Daytimes would be warm or very warm with sunny conditions by day and mild, misty nights. By Sunday Low pressure gets close to the SW briefly, close enough to inject more cloud into the mix. tempering temperatures a little. Then as we move into next week High pressurere-establishes itself first to the South and then to the East once more keeping temperatures well above normal with dry and sunny weather for most areas, more especially to the East and South. At the very end of the run pressure falls with more unsettled conditions shown with rain at times and cooler temperatures.

The GFS 00z Ensembles show the operational run described above was a marked warm outlier with most models going for much cooler conditions from about the 4th.

UKMO today also shows High pressure to the East of Britain with warm Southerly winds blowing and sunny conditions throughout this week and the weekend though as the end of the weekend approaches and we move into next week cooler, but still dry conditions look like moving slowly down from the North as westerly winds develop in the North. The far NW will for the most part miss out on the brightest and warmest of the weather under more cloud and breeze.

The Fax Charts show a Southerly airflow over the UK with High pressure to the East and all troughs held well west of Britain affecting only the far NW at times.

ECM this morning also continues the fine and very warm theme this week with Sunday the day we transfer to steadily less warm conditions as winds pick up from the West and NW delivering more cloud and rain in the North and East. By the end of the run things have become much cooler, especially to the North and East with a NW flow although elsewhere a lot of dry weather persists as High pressure remains close to SW Britain.

It looks like Sunday is the day when we commence a steady fall off in temperatures. Nevertheless, the weather from then continues to look far from unsettled with dry and warm weather continuing as per GFS operational or becoming more noticeably cooler with winds from the West or NW and a little rain from ECM. It should be noted though that the GFS operational was a marked outlier this morning being right on the top of the pack from the 6th-12th.

[No Balls Like Snow Balls]

Looking at the ensembles of the past couple of days it looks as though things will be decidedly average/slightly above temp wise for the forseeable future after this very warm spell this week. Nothing to suggest anything significantely colder, YET!!.

[nick sussex]

Looks like the ECM has been over amplifying the jet in its recent runs and has now gone for a flatter scenario. In terms of the possible record October heat for the UK . The current record is 29.4c.

I think theres a good chance this could be broken on Saturday. Given the heat building over France and some even warmer uppers heading north.

Here its currently just over 30c which even for here is very good this late into September, generally this set up brings max temps close to or over 40c in the middle of summer so its really the perfect set up for the UK given that southerly flow.

I think around Thursday we should have a much better idea of whether that UK record is under threat.

Edited September 27, 2011 by nick sussex

[January Snowstorm]

Great to see you back Nick, welcome!

Looks like Ireland will lose out in most of the heat

[Radiating Dendrite]

Great to see you back Nick, welcome!

Looks like Ireland will lose out in most of the heat

Yeo, great to have Nick back!

Had not even contempated breaking the record.

I have still not broken 30c here this year. Would be mental if the warmest temperature of the year for me was in October!!

[Stormyking]

Yeo, great to have Nick back!

Had not even contempated breaking the record.

I have still not broken 30c here this year. Would be mental if the warmest temperature of the year for me was in October!!

Going by the look of the charts, it wouldnt be far off to be honest

Imagine these charts in Mid summer would be amazing and proper hot

[Radiating Dendrite]

Going by the look of the charts, it wouldnt be far off to be honest

Imagine these charts in Mid summer would be amazing and proper hot

I still don't think it will happen.

I imagine I will max out at around 26-27c.

I am too far away from the London UHI and it always seems to be slightly cooler in the North Downs.

Edited September 27, 2011 by Radiating Dendrite

[Bottesford]

Remember this is model discussion - we already have a thread for discussing the warm spell.

[Radiating Dendrite]

Remember this is model discussion - we already have a thread for discussing the warm spell.

Sorry..............did not mean to stray off.

The models are certainly showing a fantastic period of weather coming up!

The GFS is keen to keep a high close by in one way or another with a warm start to October most likely, which could carry on into the middle of the month.

Looks like the dryness will also continue.

Edited September 27, 2011 by Radiating Dendrite