Model Output Discussion 1200 hrs 30/09/14

[phil nw.]

A new thread ready for the next set of model runs due soon.

 

A change from the  dry and warm golden days of this September is now getting closer just as we start the new month.

 

A look at the 06z GFS charts illustrate the approach of the cooler and unsettled weather coming south east at the weekend.

 

The cold front bringing a band of rain and much fresher and windier conditions to all of the UK by the start of next week.

Will this change be a short term development or a more protracted unsettled period?

 

Please continue discussions below,as usual please remain on topic and a reminder there is the Model ramp/moan thread or the Winter hopes thread for more subjective discussions.

 

Thanks all.

 

 

[phil nw.]

Just a heads up from our forecaster Nick F-copied from his post in the locked thread.

 

quote:

 

"My second look, synoptically, for the next 14 days ahead - the general synopsis is for increasingly unsettled conditions for early October, as upper troughing and low pressure systems to the NW move in across the UK into next week:

 

http://www.netweathe...ryid=6186;sess=

 

Will try and do this outlook twice week now, time and work permitting, with updates in between."

                                                                                                                                                              unquote.  

 

[knocker]

The progress of the colder air from the NW

 

[phil nw.]

It looks quite an active cold front too Knocker.

A pretty steep temperature gradient with the GFS showing a possible wave development along it across the north.

 

 

some slight adjustment to detail still possible at this range but parts of Scotland in particular could see some quite heavy rain and blustery conditions as it comes through.

Another view of the change to the wave pattern- we can see our wedge of warmth disappearing east along with our current Summer like conditions

 

It's been good while it's lasted but the other face of Autumn is on it's way at the end of the week.

 

 

 

 

[SteveB]

Well the change to unsettled and cooler weather is still there on the GFS tonight, affecting all from Monday onwards

 

 

Turning very unsettled later in FI, but temps recovering in the South

 

[Frosty.]

Tonight's GEFS 12z mean shows proper autumn finally arriving after the extended summery weather of the last 4 weeks, becoming increasingly unsettled, windier and cooler / colder during the outlook, the transition from settled & warm to unsettled and much colder occurs during next weekend behind an active cold front sweeping SE, the front looks like intensifying late friday and into saturday with a prolonged spell of heavy rain followed by brighter but colder weather with scattered showers especially across the northwest of the uk, the southeast takes longest to turn unsettled and is then first to see an improvement later next week as the PFJ is pushed north again due to pressure rising across the near continent allowing brighter, drier and milder weather to spread across the southeastern ¼  or ½ of england..actually the 12z mean is pretty much in line with the latest met office update with signs of a northwest / southeast split eventually with the nw staying generally unsettled and cooler throughout.

 

Following the warmest and driest september across parts of southern uk since records began in 1910, much of the first ½ of october looks unsettled with temperatures around average but feeling chilly at times, especially in the stronger winds and persistent rain. In any quieter interludes there is likely to be a risk of slight frosts and thick fog but generally too much breeze and cloud for that to be a widespread problem.

Edited September 30, 2014 by Frosty.

[ANYWEATHER]

The start of October looks dramatically different from a month ago ,and across the Nation ,folks will feel a Big shock. Well into the stupid hours of the model output ,some really wild and often cold weather looks likely......

[Summer Sun]

Looking pretty unsettled from Saturday some rain at times and often windy

 

 

Right at the end ECM shows pressure just starting to rise in the SE so a bit more settled here remaining unsettled the further north you go

 

[Frosty.]

Tonight's Ecm 12z op run shows a sharp contrast on saturday (T+96 Hours) between the departing warm uppers across the SE and the much cooler atlantic air sweeping in from the NW behind an active cold front, an area of strong S'ly winds ahead of the cold front and the front will probably be held up as a wave feature forms along it across southern ireland and then runs NE as an intensified feature so a good soaking as that band of heavy rain spreads southeastwards on saturday. Then the ecm shows lots of chopping and changing of airmasses on a daily basis between milder and cooler. So a massive change on the way, this run shows low pressure becoming locked over the uk sandwiched between the scandi high to the NE and high pressure in the atlantic to the SW, really nowhere for the low to go except eventually fill in situ and drift slowly north with signs of something drier, brighter and a little warmer by the end of the run spreading into the south / southeast but the northwest of the uk is likely to bear the brunt of this upcoming disturbed spell.

[knocker]

The anomalies tonight showing a weakening of the ridge western Atlantic with the trough still situated in the area of the UK although the ECM has a slightly different orientation. Doesn't appear to portend a very active Atlantic with a still weakish meridional jet but it does allow for low pressure systems in the eastern part of the Atlantic which would indicate periods of unsettled weather and about average temps for the UK. Furthe afield this pattern seems set to continue with a fairly slack HP area in the western Atlantic.

 

[bryan629]

Im really surprised that no one has picked up on this little feature that has been showing up on the GEM for the past couple of runs, 

 

Ok its way out into FI but its been there for a few days now, GFS and ECM dont have the tropical storm 

 

 

Just to give a little credence to this model it was the first one to pick up on the signal we are about to see. 

 

IF this were to verify, and engage the low dropping out of western Greenland... well who knows ?

[Geordiesnow]

although there is going to be a pattern change, I don't think its going to be a quick process, yes there is going to be an active cold front pushing through but then we are in clearer and sunnier weather again and there is hints that pressure may even briefly rise to an extent across the South. Maybe into next week is when the change will fully arrive but its too far out to know for sure. 

 

Some interesting variation coming up, looking forward to hopefully experiencing a cold crisp morning on Thursday when heading to work and Saturday into sunday could be quite chilly also. 

[knocker]

The ECM this morning showing the cold front. Pity I haven't a dew point chart.

Edited October 1, 2014 by knocker

[knocker]

Not too clever next week either but hey, a brief hot spot for the SE

Edited October 1, 2014 by knocker

[IDO]

For the SE the model runs have been improving with respect to rainfall totals. The GFS was another decent step this morning. The cold front on Saturday and the LP on Monday look the main bands of rain, otherwise the SE escapes the washout. Totals for the next 8 days according to GFS 0z:

 

 

So close to average amounts here but slightly above for the Midlands and very wet for the NW.

 

Though the three main models by D9 model the trough/LP differently re location:

 

ECM:   GFS  GEM: 

 

All models agree that there is no pending Atlantic zonal assault and by D10 there is still slow development of the UK trough. The GEFS after D10 show lots of possibilities mostly with a less settled theme, but no trend towards the Atlantic taking over. I notice that the UKMO (yesterday's update for OND) expects the Atlantic to break through late October and continue through December) so the GFS FI ties in with this.

[Gibby]

HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY WEDNESDAY OCTOBER 1ST 2014.

 

NEXT UPDATE THURSDAY OCTOBER 2ND 08:00

 

THE CURRENT GENERAL SITUATION. Weak cold fronts will move SE across the British Isles today and tomorrow becoming slow moving across the South.

 

MODELS-2 WEEK HEADLINE  Continuing largely benign this week with a lot of cloud and a little rain at times especially in the NW. Becoming more unsettled and cooler for all later with more widespread rain at times.

 

THE JET STREAM ENSEMBLE FORECAST The Jet Stream currently flowing NE to the NW of Britain is soon to change it's orientation and position to lie close to Southern England over the weekend and next week flowing in a more Easterly direction and wavering slightly North and South of this position under a cyclonic pattern.

 

GFS The GFS operational this morning shows High pressure close to SE Britain finally giving way to less settled weather from the NW in a few days time. By early next week a deep Low will of moved down from the NW and this brings wind and rain to all at times next week in much cooler air. The model run then continues very unsettled and sometimes windy weather from renewed and slow moving Low pressure over the UK moving in from the West by the end of the run.

 

THE GFS ENSEMBLES. The GFS Ensembles support the operational well this morning with the general message of Low pressure becoming dominant across the UK with spells of wind, rain and showers for all, heavy at times commencing from the weekend. There is jsut a weakening of the pattern shown right at the extremity of the run with pressure slowly rising across the UK from the South.

 

UKMO UKMO this morning shows a deep Low pressure area having slipped SE across the UK to lie over the heart of England by next Tuesday with troughs and strong winds circulating it bringing spells of rain and showers to all in temperatures conssiderably lower than of late.

 

THE FAX CHARTS  The Fax Charts show weak cold fronts dissipating near Southern England over the next 36 hours with High pressure close by while a new surge of Atlantic energy in the shape of an active cold front moves in across the NW by Saturday and moves erratically SE to give all areas some heavy rain for a time before a temporary ridge moves across the South late in the weekend as pressure falls markedly to the NW by day 5.

 

GEM The GEM operational brings deteriorating conditions from the NW too by the weekend with next week looking decidedly unsettled as Low pressure becomes slow moving across the UK with rain and showers at times in cool conditions. By the end of the run a Southerly element to the airflow could lift temperatures somewhat later especially towards the East.

 

NAVGEM NAVGEM today is very similar to all other output setting the UK up to be home to a slow moving Low pressure next week with rain and wind at times for all in temperatures returning to average if not rather below at times in strong breezes.

 

ECM The ECM operational maintains the basic theme of all other output in bringing a deep Low down towards and probably over the UK next week with rain and wind at times for. With the thrust of Low pressure slightly further West it does hold the chance that temperatures would be quite mild at times across the SE with a Southerly fetch for much of the time but overall it would feel much less warm than recently.

 

NOTABLE TREND CHANGES FROM PREVIOUS RUNS There is no change in the trend towards much more cyclonic based weather holding firm across the UK for all of the output term this morning.

 

MY THOUGHTS  All models are once more very supportive of a change to a much more seasonal pattern of weather developing from the weekend across the UK. The change is well marked to occur from a cold front crossing SE on Saturday and introducing much cooler air with sunshine and showers following a band of heavy rain SE. Low pressure slipping down behind across the UK will enhance showers to longer spells of rain at times for all next week and with an air source from a point well North it will feel distinctly chilly when compared to what we have felt of late. In the longer term there is little evidence of any release from this pattern quickly with all models promoting pressure being relatively low and slow changing from this position once it arrives with further spells of rain and showers likely right through Week 2 with just the slightest hint that pressure may rise slowly from the South in 10-14 days time pushing the Jet flow back North slightly and bringing the most wind and rain back towards the North and West with longer drier spells then possible towards the South and East. This is a long way out though and should be treated only as a 'chance' of occurring at this range.

[No Balls Like Snow Balls]

After the initial cool down over the weekend it does look like temps could recover a little from mid next week (in the South anyway)

still remaining unsettled though.

Very chilly for parts of the North early next week.

All areas seeing some rain for the 48 hours from Fri 12z to Sun 12z, although the SE not seeing much at all. Worst of the rain in the NW.

Becoming wet again on Monday.

Edited October 1, 2014 by No Balls Like Snow Balls

[johnholmes]

The anomaly charts, well the 3 I use, all point to the same idea byt this weekend and then out to day 15 or so, unsettled with an upper low over or close by the UK and the air sourced through much of that time (this is at 500mb) from the Gt Lakes area, so a big difference being felt by all. This especially so regarding temperature levels for the southern half of the UK compared to the past several weeks. How much rain is as always far more uncertain and has to be left to no further out that 72h for a general idea and closer to 24h for a more accurate idea on location and amounts.

links to the 3 anomaly charts

EC-GFS

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

NOAA

http://www.cpc.noaa.gov/products/predictions/814day/500mb.php

for interest how close the various models are over the northern hemisphere at 500mb at day 6

http://www.emc.ncep.noaa.gov/gmb/STATS/html/new_acz6.html

for all the stick it gets at times, UKMO in the lead recently even beating EC.

[No Balls Like Snow Balls]

Big difference in temp for 3pm Friday and 3pm Saturday.

SE just about managing to hold onto some warmth.

Edited October 1, 2014 by No Balls Like Snow Balls

[SteveB]

Things look very disturbed from next week onwards with the complete opposite to what we've just had

 

Instead of looking for a wet day, we will be looking for a dry day over the next couple of weeks.

 

 

There will be drier day's,  & temps look around average throughout.

 

I don't mind this in Autumn, as long as it doesn't carry on through to Spring next year

Edited October 1, 2014 by SteveB

[Cheshire Freeze]

GFS 12z ups the ante even further RE gradient on that cold front for Friday night. Looks like it could be a nasty feature..

 

 

 

Torrential rain, thunder and isolated tornadoes a possibility if it was to transpire like that.

Edited October 1, 2014 by CreweCold

[Mapantz]

GFS 12z ups the ante even further RE gradient on that cold front for Friday night. Looks like it could be a nasty feature..

 

 

 

Torrential rain, thunder and isolated tornadoes a possibility if it was to transpire like that.

 

 

It shows up nicely on the 700hPa vorticity charts, i imagine it could be a tight squall line with positive vorticity advection that strong, covering a large area.

 

[Mokidugway]

Certainly be a shock to the system , but at last some interesting weather !!!!...

[IDO]

The GFS trend is to make this weekend's LP system a transient feature lasting about 3 days before it retreats back north as the Azores pushes back in. So D5: 

 

 and by D8 moving away :  D10 higher pressure back in: 

 

Out in FI we have the return of HP:  The control is on the same wavelength (D10): 

 

GEM looking like it's struggling with the situation but again it's on the same page now by moving lower heights to the NE. The cool Scandi trough is looking less likely now and again no sign of a zonal flow.

 

D10 GEM

 

CFS October mean:   The CFS Daily 06z run has high pressure in charge till at least mid November ending:

 

 That is unusual so some signal(s) leading CFS that way.

 

The AO looks like it is showing  just a short negative run so that may enable the higher pressure to push north again: 

 

So signs now showing up that this may be a brief trough and though less settled than September (obviously!), the south looking like it may not be too bad after mid-week. However a few more runs needed to see if this trend matures and tonights NOAA 8-14 day should indicate if this is trending as last nights had a strong surface low anomaly (80) centered over S Ireland.

[draztik]

Clearly the latest GEFS update hasn't read the memo about this being brief, especially for the West!