Model Output Discussion October 2012

[I remember Atlantic 252]

Quite a settled FI tonight from GFS

Would prefer your FI than tinybill's, only 0ct, and I live away from Scottish hills

Edited October 6, 2012 by chionomaniac
Removed repeated charts

[Methuselah]

F2's looking good too. Hope it's not an 'outlier'?

[IDO]

Summer Sun, I suspect the GFS 12z op run is one of the milder options. Looking at the 12z GEFS (control):

http://www.meteociel...&mode=0&carte=1

This certainly appears to be a continuation of the colder theme. Its two weeks away and there is plenty of differences in the GFS clusters by late next week, so could go either way. Though HP for 4-6 days looks a good bet, that is after the trough for later next week (Thursday-Sunday...ish).

Autumnal in the short term.

Just checked and the Op run is at the top end, as far as Air Pressure goes. However the GEFS Control run is a ludicrous cold outlier!!! So take no notice of that.

http://cdn.nwstatic....prmslLondon.png

Edited October 6, 2012 by i'm dreaming of...

[Gibby]

Good evening. Here is the latest look at the 12z review of GFS, UKMO and ECM.

All models indicate the current weak but significant High pressure holds on close to Eastern Britain over the next 2-3 days. Further Southwest shows a weakening low pressure area move towards the SW of England bringing cloud and rain into the area from Monday. This pattern continues through the first half of the week with a SW/NE split in the weather over the UK. Just after midweek a change begins to take shape as winds freshen from the South as a cold front nudges in from the West. Rain would reach the West at some point through Thursday.

GFS then shows the trough moving in through Thursday/Friday and developing a Low pressure centre near SE England. A chilly and unsettled weather pattern develops over the South while the NW of Scotland seems the best bet for dry if rather chilly weather. Through FI tonight the pattern is High pressure based with an axis stretching across the UK. A lot of cloud would evolve with some overcast and misty, rather cold days before the High pressure slips South at the end of the run opening the door to the Atlantic.

The GFS Ensembles show the operational as a cold outlier in its second half tonight in the South. Most members prefer a more normal temperature gradient close to the long term mean. There is plenty of spread in the members though with the pivotal point being around the 13th indicating uncertainty in what happens after the late week Low pressure. rain at times is possible almost anytime though the next three to four days look dry in the North.

The Jet Stream continues its splitting process with the Northern arm moving over Scotland while the Southern arm descends over France. later on the Southern arm weakens further with the Northern arm becoming dominant later next week.

UKMO for midday on Friday shows Low pressure South of Iceland with a trough clearing Eastern England. A fresher and cool NW flow develops. Rain would clear the East soon with a showery WNW flow following on behind.

ECM shows Low pressure transferring from a position South of Iceland Eastwards to the North of Scotland. Later in the run Low pressure drives SE across Britain enhancing the unsettled theme with rain at times for all in rather cool air at the surface. towards the end of the run a High pressure ridge moves East over Britain with a fine and chilly day or so before the next trough arrives from the West.

In Summary the weather continues to look very changeable over the coming few weeks. There doesn't look like being much exciting weather with plenty of cloud and dampness early on in the SW with fine mid Autumn conditions in North-eastern areas. There are mixed messages from beyond next weekend with the most likely outcome being a changeable one though GFS and ECM show different ways of interpreting that theme.

[syed2878]

Evening people.

PRELIMINARY EXTENDED FORECAST DISCUSSION.

VALID 12Z WED OCT 10 2012 - 12Z SAT OCT 13 2012

　

DAYS 3-5...MEDIUM RANGE ECMWF/GFS GUIDANCE AND THEIR ENSEMBLE

SOLUTIONS WERE REASONABLY ALIGNED WITH THE UNDERCUTTING OF THE

UPPER RIDGE/REX BLOCK PATTERN ALONG THE WEST COAST OF NORTH

AMERICAN. AND DOWNSTREAM...THE LARGE-SCALE MEAN TROUGH OVER

EASTERN NORTH AMERICA WILL LIKEWISE MOVE SLOWLY EASTWARD WITH

TIME. THE EASTWARD PROGRESSION THE MEAN TROUGH THROUGH EASTERN

CANADA WILL BE PREDICATED ON THE SMALL-SCALE TIMING/DETAILS

EMBEDDED IN THE UNDERCUTTING ENERGY TRACKING THROUGH THE

INTERMOUNTAIN WEST...CENTRAL HIGH PLAINS AND EJECTING

EAST-NORTHEASTWARD THROUGH THE UPPER MIDWEST.

BEYOND DAY 5...THE MEDIUM RANGE GUIDANCE USED A 50/50 BLEND OF THE

00Z ECMWF/GEFS MEANS AS THE PATTERN TRENDS AWAY FROM THE REX

BLOCK/UPPER RIDGE ALONG THE WEST COAST OF NORTH AMERICA. THE BLEND

HANDLES DIFFERENCES INHERENT IN THE 6/00Z OPERATIONAL GFS/ECMWF

RUNS FROM THE 4 CORNERS EASTWARD INTO THE MISSOURI VALLEY AND

GREAT LAKES.

VOJTESAK.

Last Updated: 958 AM EDT SAT OCT 06 2012.

http://www.hpc.ncep....epd/preepd.html

[Gibby]

Good morning. Here's my morning look at the 00zs.

All models show the weather becoming more unsettled in the South over the coming few days as a weakening Low pressure moves gently East into Southern Britain. The North will remain under an equally weak Anticyclone with fine and chilly weather continuing until midweek. Soon after, most likely Thursday winds freshen from the South with a cold front sweeping all the gloom and merk away from the South as well as the fine weather further to the NE to be replaced by a band of rain crossing East somewhen through the day.

GFS then shows the weather becoming very unsettled as we move into next weekend with a complex Low pressure area drifting SE over britain and away into Europe. Thereafter, pressure builds slowly from the NW and High pressure drifts towards Scandinavia with a ridge extending SW through Britain. After the rain from the low to the SE clears away the weather would become dry but benign with a lot of cloud and cool conditions in light winds. Some bright or sunny conditions would develop by day though but equally these would translate into areas of fog and frost if they occur overnight.

The GFS Ensembles show a sharp dip in the South on the 12th then remain at or lower than the long term mean. rain at times is shown throughout. In the North the current dry weather gives way at the same time as the cool off in uppers occur in the South reversing what is a rise in uppers until then for Scotland to levels close to the long term mean thereafter. The operational was a colder option in the South later.

The Jet Stream shows a split flow with one arm travelling over France and one over scotland. This continues for a while. Later the flow becomes diffuse around our shores with much disorientation and break up.

UKMO for midnight on Saturday shows a ridge of high pressure over britain at the surface though an upper trough is still present. Despite a lot of dry weather the odd outbreak of rain could still occur in near normal temperatures.

ECM prefers a continuation of the Atlantic based changeable conditions with the run ending in a deep Low to the NW sending rain bearing fronts east in fresh winds from the SW in normal temperature values for all.

In Summary the weather looks changeable this morning. All areas look like seeing rain at times although there is a gulf once more between the longer term output of GFS and ECM though the differences are solely reached by the failure of ECM to develop the Scandi High at all.

[latitude]

Evening people.

PRELIMINARY EXTENDED FORECAST DISCUSSION.

VALID 12Z WED OCT 10 2012 - 12Z SAT OCT 13 2012

　

DAYS 3-5...MEDIUM RANGE ECMWF/GFS GUIDANCE AND THEIR ENSEMBLE

SOLUTIONS WERE REASONABLY ALIGNED WITH THE UNDERCUTTING OF THE

UPPER RIDGE/REX BLOCK PATTERN ALONG THE WEST COAST OF NORTH

AMERICAN. AND DOWNSTREAM...THE LARGE-SCALE MEAN TROUGH OVER

EASTERN NORTH AMERICA WILL LIKEWISE MOVE SLOWLY EASTWARD WITH

TIME. THE EASTWARD PROGRESSION THE MEAN TROUGH THROUGH EASTERN

CANADA WILL BE PREDICATED ON THE SMALL-SCALE TIMING/DETAILS

EMBEDDED IN THE UNDERCUTTING ENERGY TRACKING THROUGH THE

INTERMOUNTAIN WEST...CENTRAL HIGH PLAINS AND EJECTING

EAST-NORTHEASTWARD THROUGH THE UPPER MIDWEST.

BEYOND DAY 5...THE MEDIUM RANGE GUIDANCE USED A 50/50 BLEND OF THE

00Z ECMWF/GEFS MEANS AS THE PATTERN TRENDS AWAY FROM THE REX

BLOCK/UPPER RIDGE ALONG THE WEST COAST OF NORTH AMERICA. THE BLEND

HANDLES DIFFERENCES INHERENT IN THE 6/00Z OPERATIONAL GFS/ECMWF

RUNS FROM THE 4 CORNERS EASTWARD INTO THE MISSOURI VALLEY AND

GREAT LAKES.

VOJTESAK.

Last Updated: 958 AM EDT SAT OCT 06 2012.

http://www.hpc.ncep....epd/preepd.html

These updates you keep posting are meaningless to most of us without some sort of laymans explanation of what they are saying.

[latitude]

i just seen deep f1 if that happens this place could go into melt down for late oct

Some sort of NW/Westerly pattern there. Better if it was a Scandi High bringing an easterly surely?

[bluearmy]

These updates you keep posting are meaningless to most of us without some sort of laymans explanation of what they are saying.

they tend to say that a blend of the output is going to be used beyond day 5 . They are useful when they indicate that a particular op run is unsupported and therefore 'binned' by the forecaster. at this time of year when nothing of particular interest is happening, they are not very relevant. However, come winter, they will contain many bits of info that nick Sussex will seize upon to bolster his thoughts!

[Summer Sun]

Quite a settled run in FI again from GFS

Temps are nothing special but nothing cold thanks to high pressure keeping us settled

[reef]

Quite a settled run in FI again from GFS

Temps are nothing special but nothing cold thanks to high pressure keeping us settled

High pressure doesnt always equal good weather on the ground. Those charts would give overcast, dull weather with occasional drizzle and temperatures changing little by day or night. The North Sea is still warm at this time of the year and the upper air isnt shown as particularly cold, its a recipe for cloud.

[Frosty.]

The models have firmed up on an unsettled and cool spell from next thursday until early the following week but at least the next 3 days are looking fine for many but cold overnight with a touch of frost and some fog but tomorrow does look cloudier across southern britain, especially the southwest with some patchy rain but then tues/wed look sunnier. Thursday is the main day of change as low pressure moves in from the west but friday may actually be a fairly sunny but breezy day once the rain clears away eastwards. After an unsettled weekend the gfs and ecm go in very different directions, the gfs 00z ens mean is going with an anticyclonic further outlook for the whole of the uk but the ecm 00z mean is showing a continuation of the unsettled westerly pattern. I find it surprising because it's usually the ecm which handles blocking such as the scandi high better than the gfs from my experience yet it's the gfs showing it this time instead of the usual zonal atlantic patterns.

Edited October 7, 2012 by Frosty039

[IDO]

The models have firmed up on an unsettled and cool spell from next thursday until early the following week but at least the next 3 days are looking fine for many but cold overnight with a touch of frost and some fog but tomorrow does look cloudier across southern britain, especially the southwest with some patchy rain but then tues/wed look sunnier. Thursday is the main day of change as low pressure moves in from the northwest. After the unsettled spell the gfs and ecm go in very different directions, the gfs 00z mean is going with an anticyclonic further outlook for the whole of the uk but the ecm 00z mean is showing a continuation of the unsettled westerly pattern. I find it surprising because it's usually the ecm which handles blocking such as the scandi high better than the gfs from my experience yet it's the gfs showing it this time instead of the usual zonal atlantic patterns.

https://twitter.com/...865989144023040

I dont think there is a lot of confidence from any model beyond T144.

For example GFS clusters (0z) has a 45% chance of LP in charge by the end of FI:

http://www.weatheron...=0&WMO=&PERIOD=

The 0z GFS op run is clearly an outlier near the end of FI, favoring higher heights than most members:

http://cdn.nwstatic....erdeenshire.png

The 06z op run goes a different route (LP in charge):

http://nwstatic.co.u...2715d78dc46b96;

I think the next seven days are showing relatively high confidence; three days of HP for most and four days of trough influenced. Interestingly the temps remain constant on most graphs for the whole period, so the HP is not necessarily milder (both below average temps). The cut off low that GFS maintains may be the synoptic that influences the following seven days (or not).

Edited October 7, 2012 by i'm dreaming of...

[TonyH]

I am not expecting a settled outlook:

http://forum.netweather.tv/blog/309/entry-4483-weather-guide-monday-8th-to-sunday-14th-october-2012/

[Summer Sun]

GFS has support for its idea of a pressure rise mid month

Matt Hugo has tweeted the following

Interestingly the ECMWF 32 day forecast from Fri supports the GFS with a signal for higher pressure between the 15th and the 21st... hmmm

Edited October 7, 2012 by Summer Sun

[Chris K]

GFS has support for its idea of a pressure rise mid month

Matt Hugo has tweeted the following

I wouldn't call it support because at the same time he also mentions the fact that there is model uncertainty...

"Distinct split longer term between the GFS and ECM ensembles, the latter far more unsettled, the former building high pressure by mid-month"

"The divergence evident here: http://www.wetterzentrale.de/pics/Reem2401.gif… |http://www.wetterzentrale.de/pics/Rz500m10.gif… - Hmm, tricky, I'm with the ECM ensembles..."

Anyone can cherry pick information to show what they prefer...but it doesn't help people trying to learn or understand the model outputs, including myself, if posts are biased.

Edited October 7, 2012 by Chris K

[bluearmy]

He isn't showing a reference for a particular type. He shows the variation on offer. He states that the 32 dayer shows support for the gefs option but he feels that th ECM ens are in the right area if he has to choose an option. Being a pro forecaster, matt does have to pick an option.

[johnholmes]

I wouldn't call it support because at the same time he also mentions the fact that there is model uncertainty...

"Distinct split longer term between the GFS and ECM ensembles, the latter far more unsettled, the former building high pressure by mid-month"

"The divergence evident here: http://www.wetterzentrale.de/pics/Reem2401.gif… |http://www.wetterzentrale.de/pics/Rz500m10.gif… - Hmm, tricky, I'm with the ECM ensembles..."

Anyone can cherry pick information to show what they prefer...but it doesn't help people trying to learn or understand the model outputs, if posts are biased.

I do so agree with you.

Cherry pick, pick any chart you like to post but it does really confuse newcomers if you do not explain how likely the chart you show is compared to other charts in the same run or the last output by the same model for the same date/time.

I do get a lot of e mails from relative newcomers asking what is going on.

just a request - please?

[Geordiesnow]

Finding the model output slightly interesting at the moment, not really for a cold POV nor really for the weather over the UK but the Northern Hemisphere pressure patterns looks quite interesting with the models hinting at blocking to develop towards our North East, the cold pools heading into Canada and what looks like an NAO developing over the Arctic for a brief time at least. Be interesting how the models play around with all these factors in the next week or so.

As for the UK, it does seem for a stronger agreement of the Atlantic slowly breaking through the high pressure that has became more stubborn than forecasts suggested but looking forward to the sunny days and cold nights, which is what Autumn should be about really and not just mild, wet and windy weather.

[Methuselah]

Another note to all newcomers:

People who wish to see a cold, snowy winter (and that would include yours truly) tend to cherry-pick outputs that are suggestive of that outcome. It's only human nature, to do that, but don't let our enthusiasm (for this-or-that particular forecast-chart) lead you 'up the garden path'...

[Cloud 10]

If we take a look at the ensemble mean charts for +10 days time from the ECM,GEM and GEFS

it would seem that the gefs is the odd man out with its fairly settled outlook.

ecm. gem.

gefs.

The ecm and gem are fairly similar so the balance

of probability seems to favour cool and unsettled conditions as we head for mid-October.

The mean height comparisons between GFS and ECM are very different,especially for the UK

so using the ensemble means is probably the best we can do.

ECMWF/GFS DAY 8-10 MEAN 500MB HEIGHT COMPARISON

[AWD]

GFS 12z has certainly backed away from its previous medium - long range scenario of a more settled outlook now.

GFS now going for rather unsettled conditions persisting with rain for all, becoming very unsettled in FI. The only settled weather coming from very brief ridges between fronts crossing the UK.

Nothing mild on this run, with temps distinctly autumnal throughout. Frost would be possible on some nights, with wintriness on Scottish high ground.

An average October outlook, if not slightly cooler, something we haven't had recently.

Edited October 7, 2012 by AWD

[ICETAB]

ECM 12z T144 looks nice for northern blocking!

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2012100712/ECH1-168.GIF?07-06

The best model in town suddenly not feeling the love for the atlantic..... ( as expected )

S

[IDO]

http://www.wetterzentrale.de/pics/Recm1441.gif

As above post.