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Model Output Discussion - 23rd Jan - 12z onwards


Paul

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Posted
  • Location: Reigate Hill
  • Weather Preferences: Anything
  • Location: Reigate Hill

with the moderator hat firmly off, I have to say it does get very frustrating trying to decipher the 'bigger picture' of future events when members are squabbling over what constitutes the parameters of 'marginal uppers' (god, how I hate that phrase!)

 

first of all, they are not 'uppers', they are temperatures at the 850 hpa or millibar boundary which is normally around 1.5km in the atmosphere, and in terms of the vertical extent of our atmosphere, is hardly 'upper'

 

 

 

Hi

 

I think most people use the term "upper" to differentiate from the surface temps. So when someone mentions the "uppers" they know you are talking about the 850s rather than 2m temps. In the trop they are the most important temp guidance as they can correlate directly with the surface temps. What would you say is upper then? I have always thought that upper air maps are mainly 850 mb, 700 mb, 500 mb and 200 mb. they are all at different heights but they are all part of the upper air. So I do not really understand why 850s are not uppers?

 

Why are uppers important? Because the colder they are the proportionally increase in any precipitation being snow. Ruling out any other variables, uppers of -6c in the UK will give  better than 50% chance of snow at sea level. It is a rough guide and why many posters use them at D5 plus; usually our best guide at that range. The rest of the variables become more prevalent as we enter nearer T0. So I do not think that is deserving of any criticism. Snow is the hardest weather to forecast so if we can get colder uppers all the better. Bearing in mind the 850-1000 thickness' is the best for predicting snow (lowest part of atmosphere) it does quantify the importance of the 850s?

 

You add that 850s can vary for snow at different upper temps. That is also the case with thickness'. In the UK snow is seen from 519 to 535 dam depending on location, snow cover, etc. So to say that uppers are not helpful would be also to say that thickness' are also unhelpful. It is a useful guide and I don't see any problem for members to use them as a rough guide. Remember the UKMO put up an apology a few days ago for poor forecasting of snow in Wales when a Warning went up a few hours before heavy snow (up to 4 inches) was predicted and it eventually only rained. So if the experts fail at that range then maybe they deserve some flack but us amateurs using the uppers as a guide to probability at D5 plus is rather unfair. 

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Posted
  • Location: st albans
  • Location: st albans

Bad update on the AO. Going firmly high positive territory as we head towards second week of Feb. The state of the AO will have a huge bearing on whether this upcoming cold will be a cold snap or a cold spell. We need tomorrows update to bring the forecasted AO down into negative territory as we head towards week 2 of Feb.

Very few forecasts recently have taken the AO negative for any length of time. I agree that if it's right, we won't maintain a split vortex in the right place. However, a pos AO does not preclude cold conditions for nw Europe.

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Posted
  • Location: Darlington
  • Weather Preferences: heavy convective snow showers, blizzards, 30C sunshine
  • Location: Darlington

CC you made a post 3 days ago posting a 144 chart with some strong words starting there was only one to go from there and it is mild.... 3 days later do you still feel the same? Clearly the models have picked up a new signal and we are looking at a decent cold period of weather with plenty of time for even more improvements.what is also encouraging is that some of the tweets from our met office contacts are dropping increasing less subtle hints that we are in for a noteworthy snap.. Reckon we might see "since 2010 "bounded around soon..

Well TSNWK i certainly wasnt the only one going for mild three or four days ago some of our most respected members were too. Obviously it is looking colder than it was three days ago on the models i however don't think it will be a memorable spell of wintry weather or even that notable to be honest. Take this chart for example http://www.wetterzentrale.de/pics/Rtavn1202.gif!! Very marginal for those who don't have elevation, this chart a day later even more marginal if you ask me Rtavn1442.gif  I know things will change at that distance but it is coming within the semi reliable now and in my opinion those upper air temps will not improve much. A day later at 168 still marginal Rtavn1682.gif   And for those members who talk about wet bulb this and SST's that if we get an easterly with -10 850's it will snow even down to sea level no marginality at all no finger nail biting or nashing of teeth about it. There just seems to be far too much atlantic air mixed up with it all for my liking and after our recent let down I for one am not getting my hopes up. Also a little IMBYISM in my posts I concede as NE england will get nothing from westerlies and most likely the northerly afterwards if that ever happens!!

Edited by Continental Climate
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Posted
  • Location: HANDSWORTH BIRMINGHAM B21. 130MASL. 427FT.
  • Weather Preferences: WINTERS WITH HEAVY DISRUPTIVE SNOWFALL AVRAGE SPRING HOT SUMMERS.
  • Location: HANDSWORTH BIRMINGHAM B21. 130MASL. 427FT.

With all due respect guys this cold snap is not going to be what some are ramping up yes some of us will see some significant snow i've no dout. as for the met earlly yellow warnings it's for mainly for the favoured places I really can't see any ware from midlands south will see anything note werthey. Here's the met's outlook from the coming Friday.  Outlook for Friday 30 Jan 2015 to Sunday 8 Feb 2015:

Sunny spells and blustery wintry showers Friday, the latter primarily affecting northern and western parts with snow across hills and to low levels in the north. It will likely turn even colder through the weekend with sleet and snow showers, frequent across northern parts, with overnight frost and ice. Strong northerly winds, with gales in places, will accentuate the cold with a significant wind chill. The best of the drier, brighter conditions will be in the south. These conditions may well last into the first week of February, but there are signs of more changeable weather by the end of the forecast period. By then, spells of wind and rain would mean that temperatures may return to nearer normal and the likelihood of snow, frost and ice would be lower.  Mods please remove if needs be thank you. I just thought i post this so when the goods don't meterialise then no toys will get chocked out of the prams.

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Posted
  • Location: Billinge, Lancashire
  • Location: Billinge, Lancashire

The set up from Wednesday (according to the Meto) of cold N/NW winds tend to deliver some good events for low lying parts of NW England

 

Indeed, the North West is certain;y the "sweet spot" for Wednesday night/Thursday.

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Posted
  • Location: st albans
  • Location: st albans

Indeed and remembering IF saying possible NAO going negative mid Feb il be interested to see the update on the NAO which seems to be more of a driver to whether we see colder conditions than the AO

Remembering that it's not a driver but merely a measure of the likely pressure pattern which is taken from whichever model you want to use.

a very broad brush approach to predictions but statistically significant.

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Posted
  • Location: Sunderland
  • Weather Preferences: Hot Summer, Snowy winter and thunderstorms all year round!
  • Location: Sunderland

Hi

 

I think most people use the term "upper" to differentiate from the surface temps. So when someone mentions the "uppers" they know you are talking about the 850s rather than 2m temps. In the trop they are the most important temp guidance as they can correlate directly with the surface temps. What would you say is upper then? I have always thought that upper air maps are mainly 850 mb, 700 mb, 500 mb and 200 mb. they are all at different heights but they are all part of the upper air. So I do not really understand why 850s are not uppers?

 

Why are uppers important? Because the colder they are the proportionally increase in any precipitation being snow. Ruling out any other variables, uppers of -6c in the UK will give  better than 50% chance of snow at sea level. It is a rough guide and why many posters use them at D5 plus; usually our best guide at that range. The rest of the variables become more prevalent as we enter nearer T0. So I do not think that is deserving of any criticism. Snow is the hardest weather to forecast so if we can get colder uppers all the better. Bearing in mind the 850-1000 thickness' is the best for predicting snow (lowest part of atmosphere) it does quantify the importance of the 850s?

 

You add that 850s can vary for snow at different upper temps. That is also the case with thickness'. In the UK snow is seen from 519 to 535 dam depending on location, snow cover, etc. So to say that uppers are not helpful would be also to say that thickness' are also unhelpful. It is a useful guide and I don't see any problem for members to use them as a rough guide. Remember the UKMO put up an apology a few days ago for poor forecasting of snow in Wales when a Warning went up a few hours before heavy snow (up to 4 inches) was predicted and it eventually only rained. So if the experts fail at that range then maybe they deserve some flack but us amateurs using the uppers as a guide to probability at D5 plus is rather unfair.

I just hate the phrase....you'd be more accurate calling them 'lowers'....lol

I must take you to task though as you infer that I think t850's are unhelpful or unimportant....where did I mention that?......I didn't, I simply stated that t850's are just one of many parameters used to forecast snow and aren't necessarily the most important

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Posted
  • Location: Consett, Co Durham 270m asl
  • Weather Preferences: Atlantic Storms, Snow, Snow and more Snow!!
  • Location: Consett, Co Durham 270m asl

Well TSNWK i certainly wasnt the only one going for mild three or four days ago some of our most respected members were too. Obviously it is looking colder than it was three days ago on the models i however don't think it will be a memorable spell of wintry weather or even that notable to be honest. Take this chart for example http://www.wetterzentrale.de/pics/Rtavn1202.gif!! Very marginal for those who don't have elevation, this chart a day later even more marginal if you ask me Rtavn1442.gif  I know things will change at that distance but it is coming within the semi reliable now and in my opinion those upper air temps will not improve much. A day later at 168 still marginal Rtavn1682.gif   And for those members who talk about wet bulb this and SST's that if we get an easterly with -10 850's it will snow even down to sea level no marginality at all no finger nail biting or nashing of teeth about it. There just seems to be far too much atlantic air mixed up with it all for my liking and after our recent let down I for one am not getting my hopes up. Also a little IMBYISM in my posts I concede as NE england will get nothing from westerlies and most likely the northerly afterwards if that ever happens!!

Not always the case, we had several centimetres of snow last week which is still lingering now over the fields. It's impossible to say at this time exactly when and where snow will fall and I'm sure little feautures will pop up at short notice this coming week or hopefully two.

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Posted
  • Location: Rotherhithe, 5.8M ASL
  • Location: Rotherhithe, 5.8M ASL

^^GFS should not be taken in isolation...I'd much rather have the ECM/UKMO on board. Who knows what MOGREPS is punting for but whatever the scenario, it all points to cold, nothing can be argued there.

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Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth

Been too busy to post recently but watching with interest. Just 4 days ago, it looked like nothing special till February but now snow could be back on the cards in just 3 days time. You just can't take your eyes off the charts can you!

Just to add one extra variable in - the time of year. I've seen one snowfall in Hampshire from this kind of set-up - about 20 years ago - in the last week of January. Winter cold generally seems to peak over the next two weeks (last of Jan, first of Feb). This factor can tip the balance in a marginal between rain and snow. I must say, I feel there's going to be flakes for all this week.

Beyond that, I feel the ECM is best case scenario for the northerly - holding a northerly with that profile looks precarious, downgrades likely unless a north or eastern block somehow emerges - that's not to say I don't think there will be another 3/4 day wintery window from Saturday onwards.

Edited by rjbw
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Posted
  • Location: Boar's Hill, Oxon
  • Weather Preferences: Interesting weather
  • Location: Boar's Hill, Oxon

It actually did look quite promising a couple of weeks ago but some of us didn't say anything back then as it would have been shouted down as being far too far in the future to happen. It is not unusual for February to be cold and snowy! This is what I hope will happen!

post-22381-0-43259400-1422197912_thumb.j

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Posted
  • Location: North East Cotswolds, 232m, 761feet ASL
  • Location: North East Cotswolds, 232m, 761feet ASL

I'm hoping the METO models are more in line with the ECM, looking at that again it could be a 10'day event...with occasional ice days especially inland and north

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Been too busy to post recently but watching with interest. Just 4 days ago, it looked like nothing special till February but now snow could be back on the cards in just 3 days time. You just can't take your eyes off the charts can you!

Just to add one extra variable in - the time of year. I've seen one snowfall in Hampshire from this kind of set-up - about 20 years ago - in the last week of January. Winter cold generally seems to peak over the next two weeks (last of Jan, first of Feb). This factor can tip the balance in a marginal between rain and snow. I must say, I feel there's going to be flakes for all this week.

Beyond that, I feel the ECM is best case scenario for the northerly - holding a northerly with that profile looks precarious, downgrades likely unless a north or eastern block somehow emerges - that's not to say I don't think there will be another 3/4 day wintery window from Saturday onwards.

 

 

Yeah it seems this winter has had plenty of interest with short milder snaps interspersed with regular cold spells, many times people have written off cold on the charts yet before you know it another cold spell is progged.

Edited by Eugene
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Posted
  • Location: Penrith Cumbria
  • Weather Preferences: Cold, snowy winters and warm sunny summers
  • Location: Penrith Cumbria

Indeed, the North West is certain;y the "sweet spot" for Wednesday night/Thursday.

Hmmm, they said that last week and at over 400feet I could only manage 1cms, hopefully, this time will be different.

Andy

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Posted
  • Location: Manchester
  • Weather Preferences: Sunny and warm in the Summer, cold and snowy in the winter, simples!
  • Location: Manchester

Northern and Western regions look the place to be Wednesday night through Thursday - I am very confident of seeing snow falling for my region for example and accumulations even to low levels quite possible but anywhere with a some height in the NW will undoubtedly have good snow cover by Thursday night IMO.

There is no question of marginal conditions for me during this initial blast .

Much harder to say how far South and East any snow line will push initially so these regions less likely to benefit from the initial cold blast. 

From later Thursday the cold air begins to get mixed out with less cold air circulating around the trough, this could lead to showers turning more to rain/sleet and a likely thaw of any lying snow in low lying areas for a while but it depends on the behaviour of the trough. UKMO would have little mixing with a longer fetch of cold arctic air while GFS has plenty of mixing with its rounded trough just circulating the original cold air and slowly mixing it out. ECM is somewhere in between. 

As the weekend progresses the trough should slowly pull away East dragging in colder air once more and though there may well be less ppn around it also quite possible there will be  embedded features in the flow that the models won't yet pick up on and here more Eastern and Southern areas would be in the game too. There will certainly be snow showers for the NE at least.

Early next week could be very cold across the UK and the coldest period of this spell with penetrating frost and scattered snow showers but we are getting a little far out for forecasts here.

I would say the general synoptic is guaranteed and all areas will be below average for at least 5 days from Thursday so plenty to be happy about, especially for those in the North but I would like to see GFS move away from its complex rounded trough as that will likely result in a slushy wintry mix before colder weather digs back in.

Edited by Mucka
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Posted
  • Location: NR Worthing SE Coast
  • Location: NR Worthing SE Coast

with the moderator hat firmly off, I have to say it does get very frustrating trying to decipher the 'bigger picture' of future events when members are squabbling over what constitutes the parameters of 'marginal uppers' (god, how I hate that phrase!)

 

first of all, they are not 'uppers', they are temperatures at the 850 hpa or millibar boundary which is normally around 1.5km in the atmosphere, and in terms of the vertical extent of our atmosphere, is hardly 'upper'

 

secondly, why are members getting so hung up on T850 temperatures relating to snowfall possibilities anyway?.....It's just one of several parameters that the weather afficienado looks at, and IMHO, it certainly isn't the most important.

 

IMO for surface snowfall, the key parameters are surface dewpoint, wet bulb temperatures (and the accompanying wet bulb freezing level) and the thicknesses between the 500hpa and 1000hpa boundaries and especially the 850-1000hpa thickness values........In theory you can have snowfall with T850's hovering around 0c providing a cold pool is in place, and their are low thickness values and low humidity (wet bulb/dewpoints) even if surface tmeperatures are above freezing.....flipping the coin, it is quite feasible to have T850's of lower than -5c, but with high thickness values (thickness represents the amount of atmosphere between to fixed pressure boundaries expressed in dameters) ppn will fall as rain/sleet as the ppn has more atmosphere to fall through and is therefore subject to to increasing temperatures for an increased time before reaching the surface....

 

Sorry to waffle on, but the gist is, don't get too sucked in to T850 charts on the output, or rather, look at the other parameters (heights, WBFL, dew points) in conjuction......

 

 

...and lastly, if in doubt, have a look at John Holmes excellent snowfall guide in the learning area of the forum, and I'm going to shut up now, and get back to lurking......lol

well it snowed here on south coast last week so why people think uppers not cold enough this time
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Posted
  • Location: Worcestershire/Warwickshire/North Oxfordshire
  • Location: Worcestershire/Warwickshire/North Oxfordshire

It actually did look quite promising a couple of weeks ago but some of us didn't say anything back then as it would have been shouted down as being far too far in the future to happen. It is not unusual for February to be cold and snowy! This is what I hope will happen!

 

post-22381-0-43259400-1422197912.jpg

I know it's an old chart you posted, but it's a poor one also if you want snow, unless you are over 200m asl.

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Posted
  • Location: Derbyshire Peak District South Pennines Middleton & Smerrill Tops 305m (1001ft) asl.
  • Location: Derbyshire Peak District South Pennines Middleton & Smerrill Tops 305m (1001ft) asl.

Please can we keep IMBY posts to the regional threads, Its far far to early to predict snow potential up until 24hr..

Thanks PM.

Edited by Polar Maritime
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Posted
  • Location: Manchester
  • Weather Preferences: Sunny and warm in the Summer, cold and snowy in the winter, simples!
  • Location: Manchester

GFS really starting to wind me up - I know, I know, but it is.

 

gfs-1-114.png?12

 

UKMO still preferable and further East. T96

 

UN96-21.GIFgfsnh-0-96.png

Edited by Mucka
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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m

Interesting and wintry but very MARGINAL out to 126h

 

Rtavn1262.gif

Rtavn12617.gif

 

I think a lot of rain/sleet and wet snow in many low lying areas. But an absolute snowfest for those above 200m (Obviously were the precipitation falls.)

 

 

Wednesday evening ~ through to thursday main window for low lying snow, after that can't see much apart from transient snowfalls that turn slushy within 24 hours.

Edited by Harsh Climate
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Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth

Anyway on to the 12zs, still plenty of snow showers possibly in western areas Weds/Thurs, not much getting east. Just waiting for the latest on the northerly...

Edited by Polar Maritime
To move discussion on..
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Posted
  • Location: North East Cotswolds, 232m, 761feet ASL
  • Location: North East Cotswolds, 232m, 761feet ASL

GFS miles away from other mods with regards a straight Northerly next weekend...strange, but hopefully not true.

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Posted
  • Location: Eshaness, Shetland Islands
  • Weather Preferences: Cool and Stormy
  • Location: Eshaness, Shetland Islands

GFS, very marginal away from high ground. Similar to last week, where with just a bit of elevation, there could be accumulating snow. Very little in the south and west.

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