Model Output Discussion - 23rd Jan - 12z onwards

[MR EXTREMES]

not overly concerned this morning certainly no blow torch sw flow showing.

and either we get better ridging like the gem which i might add i choaked on my tea what a beauty.

anyway gem is not a model of choice for me performance wise.

 

noticable thing is all the models show progress towards high pressure over the uk but what it also shows is that a rinse and repeat looks likely id say perhaps a week of high pressure still fresh and chilly but then a rerun of what we have been getting since after december so perhaps a return to polar air then arctic and maybe with strat forcings a pacific activity better chance of a block most likely to our north eas!

 

t the point id like to make is the lower heights to our south would be better to keep that risk of an ne or easterly flow if heights retrogress to scandi area.

so lets hope the lower heights stay dominant in europe to our south.

 

but i agree very swift breakdown showing but the signs where there on lastnights infact yesterdays runs.

so its no suprise we still have something to look forwards to hopefully i get to see a snowflake this year.

[Frosty.]

GEM 00z is an upgrade on the 12z last night, superb run choc full of wintry weather. I'm looking forward to the Arctic blast, the fax chart for noon Monday shows a clean and bitterly cold flow from the arctic..Nice :-)

[carinthian]

The GEM is a winter feast of epic proportions. Not out of the question but more than likely the extreme outcome. However, the GFS latest run reverts again and slows the Atlantic with blocking coming in the equation again later in the run. ECM could end up with a rinse and repeat of short mild Atlantic and quick return to cold. I still favour a blocking scenario to the East or Northeast in the longer term outlook towards Mid Month. Still the snow scenario beckons for the next 5 days for much of West Europe including the British Isles. Will have an update later this morning regarding our snow portal service information. Its outer perimeters may give some guidance for your part of the world.

C

[weather eater]

Unfortunately the GEM stands alone and if it comes off I may have to start believing in the super natural. However the changes from the big three happens really early into the run and it is similar to last night output, so maybe that gives it some credibility. Then again none of the big three have shown any sign of backing that evolution at any stage.  I want it to be right but I feel it's a wild goose chase, can anybody remember the last time it trumped the GFS, ECM and UKMO at 96-120hrs.

[Gibby]

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS

THE CURRENT GENERAL SITUATION A cold and windy WNW flow will continue across the UK over the next 24-48hrs with showery troughs of Low pressure moving SE across the UK at times.

MODELS-2 WEEK HEADLINE Becoming colder with snow showers or snow at times before becoming less cold and changeable again by next weekend.

THE JET STREAM ENSEMBLE FORECAST The Jet Stream Forecast shows a week long spell with a deep trough over NW Europe keeping the flow well South of the UK in NW winds. In week 2 the pattern flattens and weakens as the trend towards High pressure to the SW and perhaps NE makes for some sort of link and stalling any would be major attack from the Atlantic away from the NW.

GFS OPERATIONAL The GFS operational today continues to show Northerly winds blowing across the UK through the weekend and much of next week with a slow relaxation of conditions later as High pressure builds NE across the UK from off the Atlantic. In the meantime showers of sleet and snow will affect all Northern, Western and Eastern coasts with the risk of more prolonged sleet or snow in the West for a time early next week. From next weekend on conditions are shown to become more changeable with rain and showers at times, wintry on hills still under Low pressure disrupting from the NW over the UK for a time before Atlantic SW'lies are shown at the very end of the run.

THE GFS CONTROL The GFS control run is much the same in the sequence of events with a cold Northerly for a week before High pressure builds across the UK later with cold and frosty conditions for many with this pattern largely.

THE GFS CLUSTERS The GFS Clusters are are a real mix of options with the majority showing High pressure of some sort near the UK but no real agreement on positioning which of course is fundamental on conditions of air source across the UK. there are still some more unsettled options shown too including some disruption of Low pressure to the SW of the UK by 10% of options.

UKMO UKMO this morning continues to show the UK in a very cold Northerly flow well into the middle of next week and probably longer with unstable air and disturbances running down from the NW next week enhancing the risk of more widespread snowfall for the West for a time early next week before a High pressure ridge attached to a centre over the Atlantic moves slowly SE down across the UK by the end of the week with cold and frosty weather likely then but much less in the way of wintry precipitation.

THE FAX CHARTS The Fax Charts show a concoction of fronts embedded on cold air slipping South across the UK over the next 72-96 hours. Thereafter, Low pressure sliding South to the West of the UK could complicate things in the far West in an otherwise more straightforward and cold Northerly flow next week.

GEM GEM is the pick of the bunch for cold lovers this morning as it takes our cold spell into unchartered territory this Winter. The Northerly is still shown in place for the start of next week but on this run pressure builds to the NW and this then drifts across towards Scandinavia with North winds veering NE and maintaining their strength and continuing to carry snow showers across many Eastern and Northern areas and perhaps the South too with the far West looking brightest and driest later.

NAVGEM NAVGEM today keeps the cold going over the UK well into next week with snow showers in places but the flow is cut off later in the period for late next week as a High pressure ridge collapses SE over the UK.

ECM ECM this morning shows cold and unstable conditions through the next week with mostly Northerly winds and snow showers the likely scenario with the chance of more prolonged wintry precipitation for a time in the SW early next week and again more generally later before the cold finally looks like relaxing its grip at the end of the run at the expense of Atlantic WSW'lies.

ECM 10 DAY MEAN The 10 Day Mean this morning remains in nomansland but indicates a cold pool remaining over Europe while the UK lies on the Western periphery of this. High pressure over NE Europe is hinted at here and a quiet spell of weather for the UK is how I would deduce things likely to be at Day 10.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trend remains for much colder and windy weather through the next week. The longevity of the spell has remained about a week as there is still the desire from most output to bring a cessation of the cold Northerly feed and introduce something less cold from the West by next weekend.

MY THOUGHTS The models continue to handle the cold period well with just small scale features harder to pick up within the generally cold and wintry theme. The current cold weather will intensify come the weekend as a more direct flow from the North takes hold and replaces the wintry mix on the showers in the South until then. Northern areas as usual in Northerly set up's will see the biggest share of snowfall, disruptive at times over the hills. For other areas to join in this fun we have to await any small scale disturbances ruinning South or SE in the flow and one such feature looks like possibly affecting Western and SW Britain early next week and providing the air is cold enough could give some sizeable snow amounts over the hills. not all places will see snow and inland Central Britain may miss it entirely with just bright and cold weather with frosts by night. Then we have to look for the end of the spell which still looks likely to come from the West as a ridge of High pressure from our old friend the Azores high creeps across late next week. How significant this ridge is will determine events thereafter with a real mix of options shown with some keeping High pressure and cold and dry weather across the UK while others show milder air filtering in from the west by 10 days, notably ECM while GEM goes the other route in sending High pressure North of the UK and setting up a true Easterly wintry blast. Which is right will not be determined for some while yet with plenty of options likely to crop up in upcoming model runs before an eventual coming together of thoughts will probably arise by the end of the weekend.

Issued at 08:00 Wednesday January 28th 2015

[Frosty.]

The Azores high is no friend of mine, I'm happy to say the models are continuing to lengthen the cold spell, only a few days ago it looked like it would all by over by 0z Monday but that was premature, most of next week looks very cold with a risk of snow showers and with widespread hard frosts, especially over the many snow fields..The first nationwide spell of wintry weather for a few years.

[Weathizard]

18z flicked the op with the milder members:

 

Screen Shot 2015-01-29 at 05.10.11.png

 

But the 0z has reverted to the op back below:

 

Screen Shot 2015-01-29 at 06.23.44.png

 

But it's closer to the mean and there is a fair bit of support for it. In fact those ensembles are a slight improvement.

 

ECM is interesting at T120:

 

Screen Shot 2015-01-29 at 06.28.15.png

 

But there are problems with the uppers at the key time:

 

Screen Shot 2015-01-29 at 06.28.47.png

 

As with the last slider, the angle isn't great, nor the preceding temps. Colder air briefly is pulled in behind but that's after the bulk of the precipitation has passed.

 

All models are now pointing to a breakdown next week. It looks like it's just a question of when rather than if, and whether it's via a toppling high or straight back to the Atlantic. I'm favouring the latter from upstream signals and ensembles, but we'll see.

 

In the short term we should make the most of what we have. There are some marginal issues with the upper air temps leading to rain and sleet at lower levels especially in the south, particularly this weekend when it will actually be a little milder with temps close to average, but for those who see snow fall, and hopefully settle, enjoy it:    

A fair post. With regards to the ensembles there has been a big switch to cold overnight. Look how far the mean drops in medium term on the ensemble charts you posted and a large cluster of colder solutions.

[Jason M]

Unfortunately the GEM stands alone and if it comes off I may have to start believing in the super natural. However the changes from the big three happens really early into the run and it is similar to last night output, so maybe that gives it some credibility. Then again none of the big three have shown any sign of backing that evolution at any stage.  I want it to be right but I feel it's a wild goose chase, can anybody remember the last time it trumped the GFS, ECM and UKMO at 96-120hrs.

GEM does also have a decent degree of support within its ensembles. There is a lot of scatter but there is enough support for an easterly for it to be considered a coherent signal. Coupled with some support in the GEFS its well worth watching.

[EastAnglian]

If I understand this correctly the Ensemble members have modified starting conditions for each member of the set to promote divergence, is that correct? The main point I think being to promote a spread of solutions, if the spread is wide and varied then that provides doubt on the main model solution, but if the spread is tight and not very divergent then that implies that the operations solution is along the right lines. Not an expert but from what I have read in the last few years that seem to be to way these sets are analysed. Do the Ensemble set have the same alteration to each member in their starting conditions every run?

 

There are deterministic models and statistical models, again if I understand correctly the deterministic models are the operation models and they solve a set of fluid dynamic equations to predict surface flow and other conditions. However, I wondered if the statistical models have "a priori" information added in the form of historic outcomes for similar situations and they use a set of Earth Science equations to measure the deviation from the mean of any outcome. I am familiar with this type of model in the Earth Science area where the a priori knowledge is the "Ground truth in my terms" and is used to calculate the probability of an particular pixel belonging to a set of similar values. The main difference being that in the Earth Sciences satellite example the pixels are measurement of the spatial reflectance of an area on the ground measured in a particular wavelength from a geostationary satellite and in the weather model the pixel would be the value of a cell within a 3 dimensional matrix. Sorry for the questions I am trying to understand the basic working of the weather models in terms that I understand Earth Sciences satellite analysis.

Edited January 29, 2015 by EastAnglian

[Gibby]

Something from IF on the SW Regional Thread re the small Low slider early next week.

 

It's all still very marginal next week with developments Mon-Tues. An awkward rain v snow situation depending on track, scope of deepening and phasing with diurnal cycle. ECMWF-DET remains at the extreme end of solutions (offering disruptive snow W Mids/parts of W Country/S-Central England) but with discernable move of UKMO-GM towards the *broad* scheme of things; i.e. trend to pull the low centre a bit closer to SW UK. EC 00Z ENS continue to offer a fair range of solutions, including deeper centres running further to E; equally many are much less developmental. For now, we continue with a low (30%) PROB of something unfolding akin to EC DET outcome. Rest assured it's a key point for our attention into medium range, with constant re-assessment at Ops Centre. We will keep you fully updated via BBC forecasts but I do urge suitably cautious acceptance of hyperbole or any attempts (for now) at deterministic forecasts re snow/areas affected/etc etc. We are a way off getting to that level of forecast confidence or detail.

[mushymanrob]

i dont get it....

im uncertain why the tv people are downplaying snow chances for most of the uk when we have charts like this

 

 

surely theres huge potential there for alot of people to get snow, but the tv bbc forecasters are only talking about coastal areas exposed to the northerlies as getting any?...

[Nick F]

Hopefully most of the UK will catch some snow out of this cold spell and not just the favoured north and west as per last cold spell. But, alot of uncertainty with features moving south bringing a threat of more organised sleet/snow to areas away from the favoured N/NW.

 

Need I say, plenty of snow showers packing across western areas this morning, but some of these filtering east this afternoon too. But as early as tonight there is some uncertainty with regards to a trough/occlusion. 00z UKMO meso and GFS op shows a band of more organised sleet and snow, associated with this surface trough/occlusion, spreading south from Scotland tonight, across N England, Wales, The Midlands and arriving SE England/E Anglia by 6am. Strangely ECM and Euro4 keep and area of rain/sleet and hill snow moving south further west across Wales and SW England.

 

Slightly less cold tomorrow, so wintry showers falling mostly as rain/sleet away from higher ground. But winds veer northerly over the weekend, dragging much colder air down from the arctic regions. Wishbone effect the general rule, with nothern Scotland and north facing coasts elsewhere seeing the sleet/snow showers, drier inland, but can't rule out unforecast troughs/fronts in the flow bringing something further inland.

 

Monday though, models have been consistent in indicating a low moving out of NE Canada on Saturday moving over the top of the north Atlantic ridge and sliding SE toward the UK by Monday. However, the models differ with the track by several hundred miles. The jet stream driving this low's track arches over Greenland before diving south across EIRE and the Bay of Biscay/W France. Modelling lows and the upper up towards Greenland with more sparse data up here could lead to some difference by a few hundred miles in track which can make a big difference to the outcome over the UK. 00z ECM poses the highest risk with a track further east (and slower) than UKMO and GFS. ECM EPS mean looks further east too:

 

 

00z ECM postage stamps - control similar to the deter. at t+120 with low over the SW. Otherwise a spread between further west and further east solutions.

 

http://old.ecmwf.int/samples/d/inspect/teasers/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!120!pop!od!enfo!enplot!2015012900!!/

 

So will be interesting to see who comes out top with the track of this low ... I guess many in the south hope it will come off like ECM!

 

I echo others thoughts wrt to the models being to progressive in bringing in the Atlantic in FI, you can see on EC and GFS at t+160 the Azores high joining up with arctic HP towards Svalbard, and I can't imagine that will be flattened as quickly as the models suggest.

Edited January 29, 2015 by Nick F

[weather eater]

If I understand this correctly the Ensemble members have modified starting conditions for each member of the set to promote divergence, is that correct? The main point I think being to promote a spread of solutions, if the spread is wide and varied then that provides doubt on the main model solution, but if the spread is tight and not very divergent then that implies that the operations solution is along the right lines. Not an expert but from what I have read in the last few years that seem to be to way these sets are analysed. Do the Ensemble set have the same alteration to each member in their starting conditions every run?

 

There are deterministic models and statistical models, again if I understand correctly the deterministic models are the operation models and they solve a set of fluid dynamic equations to predict surface flow and other conditions. However, I wondered if the statistical models have "a priori" information added in the form of historic outcomes for similar situations and they use a set of Earth Science equations to measure the deviation from the mean of any outcome. I am familiar with this type of model in the Earth Science area where the a priori knowledge is the "Ground truth in my terms" and is used to calculate the probability of an particular pixel belonging to a set of similar values. The main difference being that in the Earth Sciences satellite example the pixels are measurement of the spatial reflectance of an area on the ground measured in a particular wavelength from a geostationary satellite and in the weather model the pixel would be the value of a cell within a 3 dimensional matrix. Sorry for the questions I am trying to understand the basic working of the weather models in terms that I understand Earth Sciences satellite analysis.

There is no historical data its pure climate science mathematics and yes I think the same set of starting conditions are run, remember these are global models so trying to work from historical data from all over the world would be next to impossible.

Edited January 29, 2015 by weather eater

[stratty]

i dont get it....

im uncertain why the tv people are downplaying snow chances for most of the uk when we have charts like this

 

brack2a.gif

 

surely theres huge potential there for alot of people to get snow, but the tv bbc forecasters are only talking about coastal areas exposed to the northerlies as getting any?...

.........pretty much nothing down the centre of the country from this as shown in latest forecasts and GFS 

[rich1]

i dont get it....

im uncertain why the tv people are downplaying snow chances for most of the uk when we have charts like this

 

brack2a.gif

 

surely theres huge potential there for alot of people to get snow, but the tv bbc forecasters are only talking about coastal areas exposed to the northerlies as getting any?...

Probably a mixture of uncertainty (have always found snow forecasting here to be a bit more nowcast, more so these days, bar vague statements. Warnings pop up later) and past experience with northerlies which tend to end up being quite dry by and large. This one looks a bit more disturbed than the usual type when you look at that chart but the end effect could be still relatively dry for places

Overnight models not bad at all for cold deep in to next week. Any release is going in to um bongo land where a mix of solutions are progged. Worth bearing in mind also the temps seen on the tv are max city temps. Day and night out of the towns you can subtract a couple of degrees, if not more. Don't see anything truly exceptional but in the north this could be a reasonable winter overall. Northern Ireland have done better than usual with all these northwesterly bursts. I strongly suspect and this is hinted at in paces that even if we do see a let up in a week or sos time, we will see another go at this pattern following on within a matter of a few days, and deeper in to February is usually not an active period in the Atlantic comparatively speaking so lots of interest I think going in to the back end of the winter period. Fine by me. Not seen too much heavy rain this winter which makes a nice change

[weather eater]

GEM does also have a decent degree of support within its ensembles. There is a lot of scatter but there is enough support for an easterly for it to be considered a coherent signal. Coupled with some support in the GEFS its well worth watching.

Well we can live in hope but some ensemble support doesn't mean much, there is support of other options as well, I would have a lot more faith in the GEM if it had some other operational support. Remember the operational is the models best guess, the ensembles are just a guidance for the operational they are not alternative forecasts as such.

Edited January 29, 2015 by weather eater

[warrenb]

I think the 6z may go easterly

[weather eater]

Incredibly difficult for the MO, small synoptic changes are making big differences in precipitation, will it won't it, amounts and type they will keep their cards close to their chest so as to give the best advice as soon as they are sure.

[Captain Shortwave]

GFS sinking the Euro trough very quickly allowing heights to begin to rise to our north east

Certainly a chance of backing the winds north east or even easterly later.

 

GFS interpretation of Mondays event, a little further east this time

[Hocus Pocus]

Incredibly difficult for the MO, small synoptic changes are making big differences in precipitation, will it won't it, amounts and type they will keep their cards close to their chest so as to give the best advice as soon as they are sure.

Indeed and the nature of showers means the difference between seeing precipitation and staying dry could be a matter of only a mile or two.

[Yarmy]

Come on, you can do it...

 

[weather eater]

_{Well the 06z is not the GEM but it's not a million miles away either, this evenings runs could be quite interesting to say the least.}

[southbank]

The 06z certainly making the call early next week v difficult to call as alluded too , looks like mET thinking is low 30% prob at wider snow South come Tuesday

[Weegaz]

.........pretty much nothing down the centre of the country from this as shown in latest forecasts and GFS 

 

 

Same sort of chart as Tuesday with large central belt getting nothing.

Edited January 29, 2015 by Weegaz

[chionomaniac]

.........pretty much nothing down the centre of the country from this as shown in latest forecasts and GFS 

Yes nothing at all.... The point is that precipitation wise nothing is certain so don't look too far or be selective in thye precip chart you use. - look at the band nr Manchester presently

Edited January 29, 2015 by chionomaniac