Model Output Discussion - The final stretch to Christmas

[gottolovethisweather]

Updated warning.

 

 

There is a 90% probability of severe cold weather/icy conditions/heavy snow between 1500 on Friday and 1200 on Wednesday in parts of England. This weather could increase the health risks to vulnerable patients and disrupt the delivery of services. Please refer to the national Cold Weather Plan and your Trust's emergency plan for appropriate preventive action.

 

 

Nuff said

 

That's good to know   , the Pros are finally coming around to my thoughts from ten days ago where I said the following.

 

"Moreover the NH view and a certain level of consistency inter and intra operational runs now, lead me to believe the final week will be the coldest of the Winter so far with snow potential increasing ever so slowly. The greatest need for patience will be required IMBY and especially for parts of Southern England. however, even here, there will be an increasing likelihood of proper cold wintry weather during the festive break."

 

When one dedicates time and effort to view the data and charts and listen to the hints from the more professional members, each and every one of us with a bit of knowledge can pick up on the forecast trends. Intriguingly, I don't advocate picking out isolated charts at t+300 hours or a similar timeframe and taking them as gospel but if the above verifies, it does show a broader signal of the weather can be picked up. 

 

Once again, whilst I'm at risk of hyping up my own posts over other respected members in here  , I said the following some eight days ago 

 

"All in all, a far removed weather pattern from last Christmas and its horrid Winter and any further confidence in the forecast will continue to grow, once other runs back up and perhaps play catch up nearer the date. I have a feeling the Countryfile forecast will be the mostly hotly anticipated forecast of the year. My current bet (not having one as I've punted on the darts) is that there is a very small chance of snow up North on Christmas Day but a much greater chance of more widespread snow as we head nearer the turn of the year." 

 

Again, the broader European aspect of the general weather pattern, albeit with the UK positioned on the periphery remains unaltered. We are entering a pattern change to colder much more seasonal Temperatures and frosty nights at last.

 

Finally, the ten day forecast produced by gottolovethisweather on the 21st December remains on target too.

 

https://forum.netweather.tv/topic/82046-model-output-discussion-the-run-in-to-christmas/?p=3093572

 

The game-changing low has arrived, so has Boxing Day and so too has the snow, sleet and rain. Enjoy the cold spell upcoming guys n gals.

Edited December 26, 2014 by gottolovethisweather

[Jason M]

GEFS out beyond 300 hours now. I can report only one brief sighting of the lesser spotted HLB, but sadly I must report it was quickly deceased (another sinker).

 

http://www.meteociel.fr/modeles/gefs_cartes.php?code=18&ech=336&mode=0&carte=0

 

Overall, no change. Low pressure to the north, high pressure to the south. Looking through the various options there may be enough amplification down the line for a very brief northerly but that's about it. Given the number of runs and ensemble runs through a day, its remarkable that we haven't really seen even a hint of any real eye candy. Its a poor pattern really, and one that may have legs for some time. Assuming the current high sinks (almost certain, but worth waiting until this evening as still a few details to resolve around 72 hours).

 

Hope people manage to break their snow drought today :smiliz19: . The snow shields are still set to 100% IMBY I suspect.

[johnholmes]

looking at the latest charts and using its current movements since 00z and the isollobars (rate of fall per 3 hours) it still looks like into the Bristol Channel area and into the English Channel about the IOW. As to snow then the update from Met is spot on I think (who am I to make such remarks!) as intensity will be a major factor in where the snow falls, rain for many at low level (in the area threatened) to start turning to snow if the intensity is sufficient. Usually 2mm or more per hour will do it but it might need 4-6mm rainfall rate to achieve it the lower down you are. High ground above about 200m, 600ft or so should get several cm's, maybe 5cm and 10cm+ is possible for even higher up. Think of TM for this and look for his report in the weather today perhaps?

Those Derbyshire web cams should show snow for a good many places tomorrow morning once it gets lighter, along with other in the Midlands area and hills further south. Some will be lucky even on quite low ground further south, again much depends on the intensity. check, if you do not have your own weather station for T and Td, the lower they are better chance you have. Lots of other checks you can do, see the 'how to forecast snow' Guide but enjoy it folks.

Well it's very simple.... The location for the forecasted temps. ....

I am going to assume he's talking city centre temps and southern locations

 

sorry forgive me who and exactly where are you then I can help-sorry if I seem to be not helping I do genuinely want to.

[MR EXTREMES]

Any chance of back edge snow for the South as it won't lay still be nice to do some lamppost watching ????

[Biggin]

In Derby or the south coast?

My local for cast is +1 +2 after today....... neither 4 or 6. But then I don't know where those temps are for

Location in profile would help.

Edited December 26, 2014 by Biggin

[terrier]

Hope everyone had a great xmas day. Now looking at the gfs this morning looks like we will see temps struggle this coming week. Before atlantic try's and makes inroads into next weekend but a lot of weather to get through before then. Looks like Wales and the Midlands could see some substantial snow tonight. But away from these areas more in the way of ice and frosts.

[Neilsouth]

 

 

Once the low clears, risk of some wintry showers for eastern England tomorrow, turning increasingly to snow I should think, by Saturday night, these sleet and snow showers perhaps keeping going across Kent and Sussex on Sunday morning before easing. Otherwise, Sunday's looking fairly dry.

 

 

Hi Nick F, Merry Christmas to you

 

No sign of snow showers on the latest national forecast re:SE Saturday-Sunday. What time are you expecting these to filter in? Any models to show this?

 

Thank you

[IDO]

Looking at the updated JMA week 3-4 it is also going with the GEFS with a Canadian PV lobe firing up the jet and sending low heights across the N Atlantic to the UK with 850s favouring the west for a PM flow:

 

 

The Euro heights are never far to the east but with the mean also showing a clear Alaskan Ridge retrogression of those heights will be difficult as the PV > Block.

 

The GFS 06z has total contrast re the 10hpa in the strat when the P is compared to the Op:

 

 

A few days needed to see how we go with the strat I suspect.

[snow mad]

The infamous snow event from February 6 1996, just by looking at those 850's some would think how on earth did that produce some remarkable snow totals especially in the nw, even the Channel Islands saw significant snow from this and see how close they are to the 0c 850 temperature.

 

SLP

 

archives-1996-2-6-0-0.png

 

850 Temperature

 

archives-1996-2-6-0-2.pngyes

 

The key was that the actual flow into the UK was from the se.

 

For those old enough to remember this event and who lived in London at the time like myself this event is etched in the memory as the snow ground to a halt just to the west of London!

yes Nick this was a great event that wasn't supposed to have been as bad! The Orwell bridge became blocked due to lorries unable to get up it so had to spend many an hour crawling through ipswich to get home. Only to find drifts of snow nearly blocking the road to get home was a classic surprise event

[Nick L]

For more general chat about today's snow potential, please use this thread:

 

https://forum.netweather.tv/topic/82113-boxing-day-snow-event-thoughts-and-reports/

 

Thanks.

[Catacol]

The infamous snow event from February 6 1996, just by looking at those 850's some would think how on earth did that produce some remarkable snow totals especially in the nw, even the Channel Islands saw significant snow from this and see how close they are to the 0c 850 temperature.

 

SLP

 

archives-1996-2-6-0-0.png

 

850 Temperature

 

archives-1996-2-6-0-2.png

 

The key was that the actual flow into the UK was from the se.

 

For those old enough to remember this event and who lived in London at the time like myself this event is etched in the memory as the snow ground to a halt just to the west of London!

Yep - that week is etched into my memory as one of the most remarkable in my weather life. South Dorset forecast was for rain and indeed in Weymouth and Poole it was only rain. But around Dorchester we got 6 inches of snow that shut the area down completely AND it stayed all week long as further snow arrived throughout the week.

Quite remarkable and showed how marginal events can deliver the best results!!

[IDO]

Updated warning.

 

Current alert level: Level 3 - Cold Weather Action

Issued at: 1034 on Fri 26 Dec 2014

 

There is a 90% probability of severe cold weather/icy conditions/heavy snow between 1500 on Friday and 1200 on Wednesday in parts of England. This weather could increase the health risks to vulnerable patients and disrupt the delivery of services. Please refer to the national Cold Weather Plan and your Trust's emergency plan for appropriate preventive action.

 

Low pressure, tracking southeastwards over central and southern England later Boxing Day and overnight into Saturday 27th, is expected to give a period of sleet and snow across the Midlands, some northern parts of East Anglia and southern parts of both NW England and Yorks and Humberside. Some significant snow accumulations are possible, especially on higher ground. Strong winds will develop in places for a time, exacerbating the chill. As the low clears away southeastwards, cold air will move south across the whole of England giving a risk of wintry showers and icy conditions across England for the rest of Saturday. Sunday to Tuesday, high pressure brings lighter winds but with widespread night frosts and freezing fog patches which may linger well into the day in places

 

Nuff said

 

 

Yes hard to believe that the Met are ramping the prospects for the next few days. Bordering on calling a National Emergency: http://www.metoffice.gov.uk/public/weather/cold-weather-alert/#?tab=coldWeatherAlert  

 

A passing low with some back edge snow. Some cold days over the next five and its like the sequel to "The Day After Tomorrow". The Derby temp forecast (in that Cold Weather Alert zone):

 

 Cold...but extreme? Just December fare surely

 

If the strat does split what sort of headlines are we going to get from the Met.

 

Some sort of perspective would be sensible. I thought they wouldn't go the Madden/Express hyperbole route but these new severe weather warnings are really out there. 

[Barry12]

Yes IDO, it's going to be cold and wintry over the next few days. Which is rather confusing, since the day 10-16 mean charts you posted didn't show this at all?

 

Edited December 26, 2014 by Barry95

[Bristawl Si]

Have to agree IDO re the warnings.

We're now part of an extremely risk averse society.

Verging on the pathetic really.

[gottolovethisweather]

Yes hard to believe that the Met are ramping the prospects for the next few days. Bordering on calling a National Emergency: http://www.metoffice.gov.uk/public/weather/cold-weather-alert/#?tab=coldWeatherAlert  

 

A passing low with some back edge snow. Some cold days over the next five and its like the sequel to "The Day After Tomorrow". The Derby temp forecast (in that Cold Weather Alert zone):

 

 

 

Yes but as a public facing partly government owned organisation, I think they have a responsibility to keep the general public informed. Of course, we could all simply rely on the Daily papers to find out what the future holds and trust their "Day After Tomorrow" headlines time and time again.  :smiliz64: All of which fail to materialise.

 

Back on topic, I may be looking at a daytime Maximum of 3.6c should things continue as they are and that is newsworthy in itself given the 10 day charts predicted for Southern England would have suggested something nearer average or milder. I'm starting to get a few drops of rain now but with the luck, our attention and yours too (given your location) will be brought to the back edge of the passing low for snow chances.

Edited December 26, 2014 by gottolovethisweather

[gottolovethisweather]

Have to agree IDO re the warnings.

We're now part of an extremely risk averse society.

Verging on the pathetic really.

 

Think the elderly, infirm and very young might be in a "need to know basis" though.

 

Anyway, end of discussion from me on this here, other threads for such talk are available.

Edited December 26, 2014 by gottolovethisweather

[IDO]

Yes IDO, it's going to be cold and wintry over the next few days. Which is rather confusing, since the day 10-16 mean charts you posted didn't show this at all?

 

 

The GEFS picked this cold spell out over a week ago and although specific temps at that range are difficult to pin down I think they picked the cool down very well:

 

From 20th: 

 

[fergieweather]

Hi folks, not wishing to be a pedant, but I think some folk might be confusing/misinterpreting the nature of 'evaporative cooling' effect that is critical today. It's not a process of dragging-down parcels of cold air etc from aloft (e.g. as we see in convective downdrafts of thunderstorms etc). The process today is one of extracting latent heat as a result of snow melting (as it falls)... this in turn lowers the Wet Bulb Freezing Level (WBFL) as a result of the evaporative cooling, allowing snow to penetrate progressively lower than might otherwise have been the case. Now, in today's set-up, the reason why this process is so important centres upon a cold pool of air - formed by the evaporative cooling effect - which will form just ahead of the low centre, aided by upper forcing giving higher PPN rates (and thus higher rate of evaporative cooling). This cold pool, sitting at the boundary layer, then gets entrained within the flow to the north of the low centre and as it advects to wrap-around westward later today/this evening above the low, it will create conditions where snowfall could turn heavy and readily get down to lower levels. However, the amount of settling is hard to judge: in many areas, snow may readily melt on paved surfaces, but either way, the ice hazard that will follow by early Saturday is a key point of concern.

 

There's a more detailed discussion of evaporative cooling, WBFL's etc on the blog I wrote way back in 2010 - http://www.bbc.co.uk/blogs/legacy/weather/ianfergusson/2010/01/youve-guessed-it-more-snow-exp.shtml

Edited December 26, 2014 by fergieweather

[frosty ground]

The GEFS picked this cold spell out over a week ago and although specific temps at that range are difficult to pin down I think they picked the cool down very well:

 

From 20th: graphe6_1000_306_141___Londres.gif

 

Just a point a week isn't ten days..... your mean charts missed this cold spell which is why realise get on them for surface conditions is not recommended IMHO

[nick sussex]

Have to agree IDO re the warnings.

We're now part of an extremely risk averse society.

Verging on the pathetic really.

What would you rather they do? They can't win either way, they have to urge on the side of caution otherwise they will get lambasted especially by the media. As Ian F has just mentioned the snow could turn heavy but its one of those marginal situations where the heaviness of the precip will make a lot of difference.

[Bristawl Si]

What would you rather they do? They can't win either way, they have to urge on the side of caution otherwise they will get lambasted especially by the media. As Ian F has just mentioned the snow could turn heavy but its one of those marginal situations where the heaviness of the precip will make a lot of difference.

I think the bigger question is what they'd do if we had a really severe blizzard situ approaching for large parts of the UK - then i could understand it.

My reference to risk averse is uncanny, in that i'm quite averse to public funded organisations anyway! Nanny state and all that.

[fergieweather]

Yes hard to believe that the Met are ramping the prospects for the next few days. Bordering on calling a National Emergency: http://www.metoffice.gov.uk/public/weather/cold-weather-alert/#?tab=coldWeatherAlert  

 

A passing low with some back edge snow. Some cold days over the next five and its like the sequel to "The Day After Tomorrow". The Derby temp forecast (in that Cold Weather Alert zone):

 

graphe6_0000_271_85___.gif  Cold...but extreme? Just December fare surely

 

If the strat does split what sort of headlines are we going to get from the Met.

 

Some sort of perspective would be sensible. I thought they wouldn't go the Madden/Express hyperbole route but these new severe weather warnings are really out there. 

 

 

Sorry, but that's very ill-informed. What has been issued is a health alert for cold weather (these are done in conjunction with health professionals) - NOT a 'severe weather warning' within the scope of what comes from NSWWS.  Statistics show very starkly how mortality rates of certain elderly/vulnerable people rise sharply when certain temperature thresholds are reached - be these for cold or indeed hot weather. The alert is to focus attention amongst carers and others, who then operate a pre-determined mode to ensure greater viligance for vulnerable groups. The alert is only issued when the forecast shows certain threshold temperatures will be attained/sustained for a certain period (like heat alerts in summer) and in this case, it's exemplified by the fact that the period from Sat through to Tues is expected to be the coldest of 2014 on the basis of overnight minima.

 

Yellow Alerts re snow later today-tonight were issued solely because of the potential impacts on people travelling, due to the time of year. These alerts/warnings are issued on an impacts-based matrix of assessment, not on the amount of snow/rain as a sole deciding metric (as used to be the case). Thus, the fact that it's 26-27 Dec, with many people on the roads, was a critical factor. That seems wholly reasonable in my books.

 

Hope this explains.

 

(As for SSW's and UKMO, they have issued press releases in the past when these are forecast and imminent. For example, in Jan 2013. So, a measured approach to communicate something many people don't know about... but certainly no 'smoke and mirrors'. As it happens, there's no current need to issue any such communication and as of now, no conclusive signals any will be required, looking further ahead)

[pyrotech]

I think the bigger question is what they'd do if we had a really severe blizzard situ approaching for large parts of the UK - then i could understand it.

My reference to risk averse is uncanny, in that i'm quite averse to public funded organisations anyway! Nanny state and all that.

there are two warnings out

one by public health England for severe cold this is given when met office suggest temperatures day and night remain below a preset level for preset time. This gives a huge danger for public who are vulnerable. 

So this warning is correct.

then severe weather

We have rain and snow coming through today and for some this will be heavy and of the snow variety.

So people out doing their boxing day bargain shopping will be at risk in some areas of having disruption.

Then we have ice following

 

Not severe for us lot on here watching tv or on internet from our armchairs

Try telling that to someone stuck in their car on a remote moor trying to get home.

These warnings are preparation

Too many experts on here that give their forecast and if wrong slip back under the covers with no consequences.

Met office have a duty of care and can not hide, much harder to be in limelight like that.

 

Why don't we work on predicting the models rather than criticise the arguably best Meteorological organisation today.

 

sorry i see Ian has answered these posts whilst i was writing this one

Edited December 26, 2014 by pyrotech

[Mark Parsons]

Sorry, but that's very ill-informed. What has been issued is a health alert for cold weather (these are done in conjunction with health professionals) - NOT a 'severe weather warning' within the scope of what comes from NSWWS.  Statistics show very starkly how mortality rates of certain elderly/vulnerable people rise sharply when certain temperature thresholds are reached - be these for cold or indeed hot weather. The alert is to focus attention amongst carers and others, who then operate a pre-determined mode to ensure greater viligance for vulnerable groups. The alert is only issued when the forecast shows certain threshold temperatures will be attained/sustained for a certain period (like heat alerts in summer) and in this case, it's exemplified by the fact that the period from Sat through to Tues is expected to be the coldest of 2014 on the basis of overnight minima.

 

Yellow Alerts re snow later today-tonight were issued solely because of the potential impacts on people travelling, due to the time of year. These alerts/warnings are issued on an impacts-based matrix of assessment, not on the amount of snow/rain as a sole deciding metric (as used to be the case). Thus, the fact that it's 26-27 Dec, with many people on the roads, was a critical factor. That seems wholly reasonable in my books.

 

Hope this explains.

 

(As for SSW's and UKMO, they have issued press releases in the past when these are forecast and imminent. For example, in Jan 2013. So, a measured approach to communicate something many people don't know about... but certainly no 'smoke and mirrors'. As it happens, there's no current need to issue any such communication and as of now, no conclusive signals any will be required, looking further ahead)

All very reasonable and obvious to those who read carefully the meto website and listen to the likes of you Ian, cheers.

[dragan]

Looking further ahead, the encroaching Atlantic bumping into cold air will surely produce some snow?? I would say, after that most models are going for atlantic dominated weather. Id also imagine, the northwest would be first to feel the milder air.