Model Output Discussion - 23rd Jan - 12z onwards

[Nick L]

Dewpointwatch update (number of GFS frames above freezing for South Midlands area between Wednesday 3pm and Sunday 9pm:

 

25/1/06z - 10

25/1/12z - 1

25/1/18z - 2

26/1/00z - 7

26/1/06z - 12

26/1/12z - 9

26/1/18z - 4

27/1/00z - 7

 

Less favourable period for snowfall remains on Friday and Saturday's has been enlarged again.

 

Before that, dewpoints look OK Thursday evening:

ukpaneltemp2015012700z.png

 

but NMM isn't having any of it:

nmmuk-1-68-0a.png

 

The air becomes less cold later on Thursday and Friday making lowland snow unlikely for many areas. It's not until Saturday night until decent cold air returns.

[Continental Climate]

Slightly better ridging north on the 06z 

This may prolong our cold for a few hours or a day at the most but it will eventually topple and I believe after that a settled few days with a cold high settling over us to prolong our snow cover (if you have any) then a rinse and reload. If the high does settle over us can the more knowledgeable tell me whether it will be a freezing fog high?

Edited January 27, 2015 by Continental Climate

[Ali1977]

Could be some hard frosts in the high pressure at day 9.

[carinthian]

Good day to all. Just seen the latest GFS (06hrs run ) not sure what to make of it post 300 hours , fires up the Atlantic jet and progs it all over the place. Think this will change again on later runs today .

 C

[bluearmy]

Morning, we can only look in wonder at the historic nor'easter blizzard unfolding across the NE USA where some parts there are forecast upward to 30 inches or 2 1/2 feet of snow

Historic in the sense that it's a complete bust ?? An epic fail all round.

The day isn't done yet Dave but it certainly seems that NYC will not get more than a foot of snow though further east and northeast, it looks like the crazy totals may verify.

Given that everyone will concentrate on New York itself, this will be seen as a good call by the new Gfs which progged less precip for the city.

[Yarmy]

I think many here would sell a kidney for the kind of complete bust NYC is getting. 

 

06z shifts the mid-Atlantic ridge westwards slightly and prolongs the Northerly flow. A step towards the UKMO perhaps.  

 

0z T144 GFS

 

06z T138 GFS

[The Enforcer]

The air becomes less cold later on Thursday and Friday making lowland snow unlikely for many areas. It's not until Saturday night until decent cold air returns.

At Thurs 9pm, if 06z GFS shows 850's around -4C, with dew points at or below freezing and with a low DAM value and no interference from daylight, what's stopping the snow?

[shaky]

At Thurs 9pm, if 06z GFS shows 850's around -4C, with dew points at or below freezing and with a low DAM value and no interference from daylight, what's stopping the snow?

totally agree with you!! it gets very complicated around Friday but i would not be surprised if preciptation stays as snow in some parts especially the east!!

[Nick L]

At Thurs 9pm, if 06z GFS shows 850's around -4C, with dew points at or below freezing and with a low DAM value and no interference from daylight, what's stopping the snow?

 

850 wet bulb potential temperatures are several degrees above freezing as we head into Thursday night, ideally you want these to be at freezing or below. Although the fact it is night-time will help as the precip moves southwards, and in any heavier bursts snow is certainly possible.

[summer blizzard]

6z is much more progressive in FI with the pressure build shunted quickly east.

[Troubleatmill]

850 wet bulb potential temperatures are several degrees above freezing as we head into Thursday night, ideally you want these to be at freezing or below. Although the fact it is night-time will help as the precip moves southwards, and in any heavier bursts snow is certainly possible.

I would of thought Thursday night looks great for your location with dews well below and wet bulb zero somewhere between 100 and 200 on the gfs, elsewhere further north they are both on the climb, friday for all looks a bit naff though ....before dropping again

[Man With Beard]

I wouldn't take the blindest bit of notice of the mean runs at T216. The bits which matter for our little islands are all over the place.

 

At a first glance, the GFS/ECM T216 means look solid:

 

 

But the spreads show that they have no handle on what the High Pressure in the Atlantic is going to do:

 

 

Interestingly the op runs both favour a slightly extended period of blocking in the North Atlantic:

 

 

 

Verdict: I agree there's probably a flattening of the pattern coming up, but the impact on the UK (i.e. ending the cold) could be anywhere between next Wednesday and next weekend. And there's still a chance the Atlantic ridge will combine with the Canada low(s) to do something peculiar.

Edited January 27, 2015 by rjbw

[Frosty.]

I like these charts from the 6z which show snow showers piling in from the NW during tomorrow, even the southwest eventually gets peppered by snow showers. This will be a very potent polar maritime blast, the best so far this winter. Even colder by the weekend as pm is mixed out but soon replaced by an increasingly strong Arctic maritime blast which will last for most of next week, when you think back to yesterday, the 0z output terminated the arctic flow by the end of next weekend but now we have an extra 48-72 hours and who knows, maybe a little longer..This is what coldies, especially in the south, have been hoping for and it's almost here..enjoy

Edited January 27, 2015 by Frosty.

[GrangemouthBairn]

Wow, you would never realise the most exciting weather of the winter was upon us. No posts in 3 hours! Although I suppose there is a big gap between the GFS 6z and the 12z model runs. Cold Wednesday and Thursday, slightly less cold Friday and early Saturday then colder again from late Saturday onwards seems to be the summary of the models. Only debate is how long the second blast lasts.

Its most likely that next Wednesday/Thursday the high will topple in giving a couple of sunny, cold days then the Atlantic moving over the top and sinking the high back to the Azores but the most likely scenarios don't always happen and I certainly hope it doesn't in this case. Having said that a near 7 day cold spell isn't that bad, especially compared with last year, having just come off the back of a cold spell which lasted just under a week

Edited January 27, 2015 by GrangemouthBairn

[Man With Beard]

I like these charts from the 6z which show snow showers piling in from the NW during tomorrow, even the southwest eventually gets peppered by snow showers. This will be a very potent polar maritime blast, the best so far this winter. Even colder by the weekend as pm is mixed out but soon replaced by an increasingly strong Arctic maritime blast which will last for most of next week, when you think back to yesterday, the 0z output terminated the arctic flow by the end of next weekend but now we have an extra 48-72 hours and who knows, maybe a little longer..This is what coldies, especially in the south, have been hoping for and it's almost here..enjoy

 

Just to add my thoughts .- Some truth in Frosy's observations, when you've been snow-starved for 2 years even a flake will do!

 

But my thoughts are - Beware. I think the next week is going to get very IMBY. I see this going one of two ways, and I think they are equally possible! 

 

Possibility 1: A straight N/NWly blast, the odd trough racing through N-S. In this scenario, coastal areas could see quite a lot of shower activity. This scenario will mean high snow amounts in northern and western areas (Dartmoor could be cut-off in the SW), possibly some places near the east coast too. Most central and southern areas will get the odd dusting as the troughs move through, but no big accumulations.

 

Possibility 2: Late-developing lows develop around Iceland and slide SE-wards as secondary lows around the main low out to the east. The models may not be showing this idea yet, but I think the situation is ripe for it. This, I believe, is the best chance of heavy snowfall in central/eastern areas - and possibly even on N/W facing coasts as the wind temporarily could switch to S/E. In this scenario, the chances are that a warm sector will be embedded in the low. This puts anywhere towards the SW at risk of receiving rain, whilst 50 miles to the north or east, heavy snow. Of course, the track of such a low makes all the difference - conceivably, it could track west meaning the SW get the snow and central/eastern areas stay dry - on the other hand, slightly more east and the rain area moves east with it.

 

So interesting times ahead - but one thing I think will transpire - it's going to be a snowy weekend for some, but probably not all. You have been warned!

[sorepaw1]

Wow, you would never realise the most exciting weather of the winter was upon us. No posts in 3 hours! Although I suppose there is a big gap between the GFS 6z and the 12z model runs. Cold Wednesday and Thursday, slightly less cold Friday and early Saturday then colder again from late Saturday onwards seems to be the summary of the models. Only debate is how long the second blast lasts.

I think people now are just waiting till tomorrow,and waiting the 12z and 18z, even the bbc aren't going beyond Thursday in there forecasts locally to me, it looks like blindfolded darts imo in the forecast, it's goi to be cold windy and snowy it's just where when and how much ,Im struggling to be honest ,and so are the professionals, things to me seem very up in the air the 12z will be different to the 06z, Nina ridge for the bbc seems very clear on the week ahead weather.

Edited January 27, 2015 by sorepaw1

[legritter]

Good afternoon ,Hello hello ,very quiet on here ,well the fun and games will kick off tomorrow ,and we already have had a fair set of charts .but as is usual in this sort of synoptic set up we are kept waiting and waiting ,simply when we get the cold air in then the features that will bring any snow will start to develope in the cold air over warm seas so if you are getting worried each day could bring a surprise or two .Looking at the charts today i think more of an interest later in the weekend ,5/6 days away so with a bit of luck i,d say all to play for .I do suspect a lack of interest of some posters as the posts the last couple of hours as been minimal .i,m pretty sure many of us will see some snow but remember its a very now cast situation in this set up with even the professionals holding fire untill all available and updated raw data comes in .remember we are talking arctic sourced air for probably a weekor so loads of possibilitys ,Its realy Fax chart territory ,Forget some of the hype around and concentrate on our regular posters and enjoy what arrives after tomorrow ,cheers gang   

[Mucka]

I like these charts from the 6z which show snow showers piling in from the NW during tomorrow, even the southwest eventually gets peppered by snow showers. This will be a very potent polar maritime blast, the best so far this winter. Even colder by the weekend as pm is mixed out but soon replaced by an increasingly strong Arctic maritime blast which will last for most of next week, when you think back to yesterday, the 0z output terminated the arctic flow by the end of next weekend but now we have an extra 48-72 hours and who knows, maybe a little longer..This is what coldies, especially in the south, have been hoping for and it's almost here..enjoy

 

Unfortunately very much at odds with higher resolution euro4 which has accumulations reserved for the far North and a dusting for Midlands and NE England.

n

 

 

I think the fact we are getting warm sectors from the N and NE in the heart of Winter says it all about hard it is to get a decent wintry synoptic for the UK.

 

I thought UKMO and GFS 00z were quite good as far as prospects of extending the cold go but the ECM and GFS 06z then went the other way. The GFS 06z was poor for me overall and the ensembles were the worse set yet as far as mixing out the cold air Fri/Sat goes with mean lifting to around -3c for my area where previously it has been -5c.

Hoping for better this afternoon, keeping the trough further East and a stronger ridge the sort of trough disruption SE on offer on the GFS 00z pushing heights to our N/NE.

 

GFS 12z keeps the trough a little further East so that is a plus but we could do with not having the low phase with the shortwave as with 06z,

 

Edited January 27, 2015 by Mucka

[The Enforcer]

850 wet bulb potential temperatures are several degrees above freezing as we head into Thursday night, ideally you want these to be at freezing or below. Although the fact it is night-time will help as the precip moves southwards, and in any heavier bursts snow is certainly possible.

Thanks - I now have a new nemesis in the form of WBFL. Here's another question - why in this situation is the WBFL so out of kilter with the other main variables, which are otherwise conducive to snow?

Edited January 27, 2015 by The Enforcer

[Mucka]

Typical, GFS moves the trough back East a little so of course UKMO goes the opposite way. T

Meanwhile, the models seem to be developing that shortwave more and more - there was much more separation between it and the next low previous runs. If they phase it will likely help flatten the ridge

 

Edited January 27, 2015 by Mucka

[Paul]

A few posts have been moved over into the model banter thread this pm as they're not discussing the models - please post over there if you want to have a moan/ramp about the current setup rather than using this thread.

 

https://forum.netweather.tv/topic/81281-model-banter-moans-and-ramps-autumnwinter-201415/

[Mucka]

We can't be disappointed with the UKMO 144 chart, the ridge surviving shortwave dramas.

 

[shaky]

Very good output so far for continuation of cold!! Both gfs and ukmo disrupt the low at 144 hours on the southwestern tip of greenland! !

[mulzy]

UKMO not bad at all - reasonable amplification

 

[Eugene]

UKMO not bad at all - reasonable amplification

 

 

 

Yes UKMO 12Z  T+144hrs better than GFS 12Z  T+144hrs tonight, UKMO doesn't develop the shortwave near greenland like GFS does, lengthier cold spell likely on UKMO.