Model Output Discussion

[Kentish Kiwi]

Hi steve, you beat me to it!

I must say, the way this runs panning out, the high just gets pushed back further NW, during wednesday night into thursday the easterly trys to push in, succeeds down south, kind of fails with me just staying on the SE most edge of the HP, then within a few hour it gets shunted away and the flood gates open, mean for the SE -12, with the mean i would say -11 for me, i would not be surprised if these 850 pools get colder!

Lovely run, truely lovely.

The GFS seems quite confident in relatively frequent showers for the early part of this week (ie Monday afternoon into Tuesday) along the East Coast and into the South-East, which it shows will definitley be of snow (I know how difficult and unreliable such a forecast is). Does this seem likely to enventuate and is it supported by other models in regards to the frequency/type of precipitation, for instance the NAE or NMM (I think those are the correct abbreviations)?

Regards,

KK

[Lewis]

The GFS seems quite confident in relatively frequent showers for the early part of this week (ie Monday afternoon into Tuesday) along the East Coast and into the South-East, which it shows will definitley be of snow (I know how difficult and unreliable such a forecast is). Does this seem likely to enventuate and is it supported by other models in regards to the frequency/type of precipitation, for instance the NAE or NMM (I think those are the correct abbreviations)?

Regards,

KK

Hello Kiwi,

They will certainly be snow showers falling tomorrow afternoon and Tuesday, during tomorrow a little more marginal the closer to the coast you are, as at first the flow is rather slack, so mixing will occur, more wintry of nature on/near the coast with a tendancy to fall as sleet/snow further inland. To be honest i cannot see it been mainly of rain, at coasts it will be more hail,sleet,snow mix.

I'll take a look at the NMM model for the 18z in about an hours time, it should have updated by then. The NAE was upgrading the precipitation tomorrow in terms of intensity and precipitation type (mainly of snow for areas inland).

And your spot on with your abbreviations

[greatgable]

looks to me as tho the high pressure is sinking south and by friday will be a lot further south an anticipated

[BLAST FROM THE PAST]

looks to me as tho the high pressure is sinking south and by friday will be a lot further south an anticipated

Nope, completely wrong. ALL the background signals are for retrograde.

I actually preferred the 12z to the 18z due to the evolution and easterly draw rather than the earlier Scandi trough bringing NNE'lies...but its gonna get cold to very cold either way.

Would like to see the jet not to be quite as far south as it is.....less action but I suppose guarantess the cold more. I am very pleased with how the solar signals regarding the jetstream and blocking patterns have verified so well this winter following on from a decent last winter.

BFTP

[Kentish Kiwi]

Hello Kiwi,

They will certainly be snow showers falling tomorrow afternoon and Tuesday, during tomorrow a little more marginal the closer to the coast you are, as at first the flow is rather slack, so mixing will occur, more wintry of nature on/near the coast with a tendancy to fall as sleet/snow further inland. To be honest i cannot see it been mainly of rain, at coasts it will be more hail,sleet,snow mix.

I'll take a look at the NMM model for the 18z in about an hours time, it should have updated by then. The NAE was upgrading the precipitation tomorrow in terms of intensity and precipitation type (mainly of snow for areas inland).

And your spot on with your abbreviations

Thanks SFL

Ironically I'm now experiencing a pretty heavy fine hail/sleet shower, which I suppose bodes well for tomorrow/Tuesday as colder air moves in. I'm particularly looking at snow potential for the early part of the week as I fly off to Barbados for ten days on Thursday morning and would be gutted if I didn't get to see anything from this promising cold spell, although sadly it seems as though its almost certain I'll miss out on the most potent cold which looks likely to move in late Thursday/Friday/Saturday.

Will appreciate that update in regards to the NMM, am I right in thinking many regard it very highly when looking at foreasting snocw in the close time frame?

KK.

[Bobby]

Better 18z than the 12z GFS but not as good as ECM. Going in right direction though. I'd always back the ECM in these situations anyway.

[Thundery wintry showers]

Yes, it is probably stating the obvious but with temperatures above 0c during the day there

will be thawing of any lying snow whether it be January or in this case February. To combat a

slightly stronger sun compared to January the temperatures need to be at freezing to +1c at

best to ensure a good snowpack.

A better 18z operational than the 12z I see with it slightly more in line with the Euro models.

I think you're wrong- I saw a snow cover back in December 2009 in Cleadon fail to thaw noticeably despite maximum temperatures of 1 or 2C- to be pedantic it probably did thaw a little bit, but it thawed by less than one centimetre per day. And on the 23rd, when the temperature reached 3.8C, it only shaved one centimetre off the snow cover.

The depth of a snowpack is affected heavily by how much accumulated in the first place, and on the 3rd and 4th March 2001, an 8cm snow cover in Cleadon merely halved in depth despite two days of almost unbroken sunshine and highs of 3.0 and 3.6C respectively. In March 1970 snow stuck around for over a week in many parts of southern England, in sunshine and highs between 2 and 5C. Note that this is March we're talking here, and not February! I generally think of 3-4C as the threshold above which an established deep snowpack will thaw considerably if the dewpoints are below zero, but if the dewpoint is above zero then it may thaw with the temperature near freezing.

[Bobby]

The depth of a snowpack is affected heavily by how much accumulated in the first place, and on the 3rd and 4th March 2001, an 8cm snow cover in Cleadon merely halved in depth despite two days of almost unbroken sunshine and highs of 3.0 and 3.6C respectively. In March 1970 snow stuck around for over a week in many parts of southern England, in sunshine and highs between 2 and 5C. Note that this is March we're talking here, and not February! I generally think of 3-4C as the threshold above which an established deep snowpack will thaw considerably.

Doesn't the humidity affect the thaw rate too? We had a dusting last week that didn't melt in the shade at all for 2 days despite maxes of 3-4c (from a crisp sunny Northerly). While in setups under dull moist atlantic air I've seen quite quick thaws with temps of 1-2c.

[james26]

I've lurked in the background on this site and after about 4 years of a daily ritual of looking through the models and reading what's going to happen by all the super knowledgeable members on here I thought I'd finally send a post! On Hayling Island we experienced a very rare event in January and had 4" of level snow right to the seafront - and much of me is hoping for the same again next weekend (I hope). Anyway, I know not to get off topic so just want to say THANK YOU to all and a big good luck whatever happens. 18z looking good for SE but just want that high to retrogress a little quicker to get a better stab of the cold pool to the S and E of our shores and the unstable airstream.

Cheers

James

[Lewis]

Thanks SFL

Ironically I'm now experiencing a pretty heavy fine hail/sleet shower, which I suppose bodes well for tomorrow/Tuesday as colder air moves in. I'm particularly looking at snow potential for the early part of the week as I fly off to Barbados for ten days on Thursday morning and would be gutted if I didn't get to see anything from this promising cold spell, although sadly it seems as though its almost certain I'll miss out on the most potent cold which looks likely to move in late Thursday/Friday/Saturday.

Will appreciate that update in regards to the NMM, am I right in thinking many regard it very highly when looking at foreasting snocw in the close time frame?

KK.

O.o barbados, not bad ay! Enjoy some cold weather and leave home with a couple of inches on the ground, then before you know it, you get off the plane and the humid air hits you and your in paradise.

You are located in the best place out of the entire united kingdom for this cold spell. Regarding the NMM, it's the most accurate model avaliable, as the resolution is very high, during the time i have used it for calcuating dew point temps, 850's etc it's been 99% correct. Of course no model is 100%, not even the UKMO'S/Metoffice's.

Paul or the netweather team will put me straight on this, but i'm sure the models don't include/take into consideration local conditions for example moderation off the North Sea, the best way of calcuating the NMM's accuracy is in real time, look at your temp/dew point and then look at the NMM model and compare, you'll find it's on the mark most times. It's also fantastic for precipitation.

If you keep an eye on your dew point if you have a weather station (if it's 0c or below you'll be fine) if you don't have a weather station you can use http://www.xcweather.co.uk which gives local conditions.

Lewis

[bluearmy]

not sure why many are surprised that once, GFS op has picked up on the euro's tendency for suppression of the high, it overdoes it and therefore likely gets it wrong. GFS op does this a lot which is why so many are so critical of it. 'over compenastion' would be a reasonable description although its a little unfair of the euros to trend a little further nw now that gfs has worked out that the high would be further se than it was showing.

as for the latest FAXES - they ask more questions than give answers. looking at the euro trough, not sure we want that to make too much headway west - that warm front would give a big snowfall but it might not last too long!! a glancing blow would seem ideal.

[Thundery wintry showers]

Doesn't the humidity affect the thaw rate too? We had a dusting last week that didn't melt in the shade at all for 2 days despite maxes of 3-4c (from a crisp sunny Northerly). While in setups under dull moist atlantic air I've seen quite quick thaws with temps of 1-2c.

Apologies- I must have done a final edit to the post after you replied. The humidity is indeed a major factor- 3-4C is the threshold I tend to think of when dewpoints are below zero, but I've known snow cover thaw rapidly at 1C with a dewpoint of 1C- indeed it happened in Norwich on the 10th January this year.

[Kentish Kiwi]

O.o barbados, not bad ay! Enjoy some cold weather and leave home with a couple of inches on the ground, then before you know it, you get off the plane and the humid air hits you and your in paradise.

You are located in the best place out of the entire united kingdom for this cold spell. Regarding the NMM, it's the most accurate model avaliable, as the resolution is very high, during the time i have used it for calcuating dew point temps, 850's etc it's been 99% correct. Of course no model is 100%, not even the UKMO'S/Metoffice's.

Paul or the netweather team will put me straight on this, but i'm sure the models don't include/take into consideration local conditions for example moderation off the North Sea, the best way of calcuating the NMM's accuracy is in real time, look at your temp/dew point and then look at the NMM model and compare, you'll find it's on the mark most times. It's also fantastic for precipitation.

If you keep an eye on your dew point if you have a weather station (if it's 0c or below you'll be fine) if you don't have a weather station you can use http://www.xcweather.co.uk which gives local conditions.

Lewis

Many thanks for the information, help and advice Lewis; have really appreciated your consistent input over the last few days. Will definitely have a look at the NMM when I get a chance. Have to say that little IMBY ramp from you certainly got me a little more excited, a couple of inches snow cover before I leave would be absolutely perfect.

Night, KK.

[Lewis]

Many thanks for the information, help and advice Lewis; have really appreciated your consistent input over the last few days. Will definitely have a look at the NMM when I get a chance. Have to say that little IMBY ramp from you certainly got me a little more excited, a couple of inches snow cover before I leave would be absolutely perfect.

Night, KK.

Not a problem Kiwi, it's a pleasure to be of help, best of luck with the cold snap and enjoy your holiday!

[notananorak]

Yes, it is probably stating the obvious but with temperatures above 0c during the day there

will be thawing of any lying snow whether it be January or in this case February. To combat a

slightly stronger sun compared to January the temperatures need to be at freezing to +1c at

best to ensure a good snowpack.

Actually no - the wet-bulb temp is most significant. In the shade so long as there is a -ve wet-bulb then snow will not melt - the drier the air the more enhanced the effect. The reason that WBFL's are more important than just FL's in forecasting downward snow penetration. The evaporative cooling preservation holding back melting even in sun ( low angle ) other than against warmed surfaces. How often have you noticed frost/ice/snow unmelted in the shade when air temps are +3C? Down to very low dewpoint air.

[Lewis]

Sub 528 thickness (DAM) hits the east coast around 6-7am tomorrow according to the NMM model;

850 temps colder in the east and are at -8 even right on the coast, so this is supportive of snowfall given the lower sst's.

Showers at that time pushing will inland across EA and the SE as the day goes on heavy snow showers affecting Yorkshire/Lincs/NE England;

Dew points;

Shows it as very marginal, but tbh, 0.5c is still fine if the 0C isotherm is low enough, although it's when you tend to get the larger wetter flakes.

0C Isotherm;

generally 300-400m, as low as 100m further North.

As we go through tomorrow the isotherm drops too 100-150m quite widely. Dew points drop off slightly 0 - -1c in places.

Conclusion: Impossible for me to call it, based on the model output purely i would say marginal for some, perfect for others. It's basically down to nowcasting. Best of luck everyone!

[kent]

A wet bulb temperature is the same as the outside air effect you feel when your skin is wet. So go outside in your bathers hose your self down with the garden tap and if you think thats cold enough to thaw any lying snow then think again lol

[ScottSnow]

Apologies- I must have done a final edit to the post after you replied. The humidity is indeed a major factor- 3-4C is the threshold I tend to think of when dewpoints are below zero, but I've known snow cover thaw rapidly at 1C with a dewpoint of 1C- indeed it happened in Norwich on the 10th January this year.

The snowfalls from the 30th Jan northerly lasted pretty well in clear sunny weather with minimal reduction in depth even though max temps were 3 to 4C through the day. You also tend to find that snowcover lasts longer if it goes through a freeze thaw process which consolidates the sowpack and gives it more resistance to rain or sun.

On the models - Now that the cold weather is here snow possibilities will begin to crop up, sometimes out of the blue with nowcasting and radar watching the name of the game. There is the possiblity of an easterly/northerly combo which could give us at least a 10 day cold spell. The GFS 18z certainly shows some big snow potential later in the run.

[john mac]

I havent had a chance to look at the FAX charts this evening, How are they looking?

[reef]

Paul or the netweather team will put me straight on this, but i'm sure the models don't include/take into consideration local conditions for example moderation off the North Sea, the best way of calcuating the NMM's accuracy is in real time, look at your temp/dew point and then look at the NMM model and compare, you'll find it's on the mark most times. It's also fantastic for precipitation.

The models do take into effect the moderation of the North sea, but they generally dont have the resolution to map it accurately. The NMM is a much higher resolution meaning it can map the temperature difference to within a few miles. (2 miles I believe).

Also bear in mind when looking at the ground temperatures on the GFS it will place a figure which is the average temperature over the grid square. This means that its not necessarily accurate for higher ground, coastal areas and indeed frost hollows on cold nights. This is why we tend to get the values a degree or two off. Another factor is that the GFS shows the max or min temperature for the 6 hours before the time period, so it could be correct at midnight and appear completely wrong by 4am.

Its difficult to call for the early part of next week. A 'wintry mix' would probably be the most accurate guess. Lying snow wont be too common early on though, as temperatures will be a bit too high. What does lay wont last long, especially in any sunshine. Later on looks more favourable.

[Lewis]

I havent had a chance to look at the FAX charts this evening, How are they looking?

Fantastic fax charts;

http://www.wzkarten3.de/pics/brack0a.gif - T+ 36

http://www.wzkarten3.de/pics/brack1.gif - T+ 48

http://www.wzkarten3.de/pics/brack2.gif - T+ 72

http://www.wzkarten3.de/pics/brack2a.gif - T+ 84

http://www.wzkarten3.de/pics/brack3.gif - T+ 96

http://www.wzkarten3.de/pics/brack4.gif - T+ 120

Edited February 8, 2010 by Storm Force Lewis

[john mac]

Fantastic fax charts;

http://www.wzkarten3.de/pics/brack0a.gif - T+ 36

http://www.wzkarten3.de/pics/brack1.gif - T+ 48

http://www.wzkarten3.de/pics/brack2.gif - T+ 72

http://www.wzkarten3.de/pics/brack2a.gif - T+ 84

http://www.wzkarten3.de/pics/brack3.gif - T+ 96

http://www.wzkarten3.de/pics/brack4.gif - T+ 120

You wernt wrong mate, they are pretty special charts, snow should get more potent as the week goes on. <_<

[snowray]

I've lurked in the background on this site and after about 4 years of a daily ritual of looking through the models and reading what's going to happen by all the super knowledgeable members on here I thought I'd finally send a post! On Hayling Island we experienced a very rare event in January and had 4" of level snow right to the seafront - and much of me is hoping for the same again next weekend (I hope). Anyway, I know not to get off topic so just want to say THANK YOU to all and a big good luck whatever happens. 18z looking good for SE but just want that high to retrogress a little quicker to get a better stab of the cold pool to the S and E of our shores and the unstable airstream.

Cheers

James

Welcome James.

You have certainly joined at an interesting time to say the least!

We still have some interesting charts and this week is by no means nailed yet, I think Weds onwards will certainly be the most interesting period, probably not as much snowfall that we might have hoped for a couple of days ago early on, but could make up for it later on. So, lots still to play for I would think.

Regards

Snowray

Quick Edit: My hot tip is for the Eastern half of Kent to get the best snowfall this week, Canterbury, Dover way. (Not around this way on the London border though unfortunately)

Edited February 8, 2010 by snowray

[TEITS]

Some of the ensembles beyond the E,ly are mouthwatering. All show quiet different possibilities but the general trend is cold.

I still maintain that between 15th - 23rd Feb a big snow event is possible. Look at the chart below from the GEFS Parallel control run. That is some serious cold.

Ideally when the Scandi trough backs S we would ideally like this further E. If this happens then the chances of a bitterly cold NE,ly are possible. Alternatively what some of the GEFS ensemble suggest is cold N,ls spread S but at the same time a LP tracks along the channel. This also brings the risk of a big snow event.

After reading Chionomaniac posts in the Stratosphere thread I feel the models may struggle with the pattern beyond the E,ly. Im confident of the Greenland HP but its what happens after that is uncertain. However many of the outcomes are mouthwatering.

[john mac]

Some of the ensembles beyond the E,ly are mouthwatering. All show quiet different possibilities but the general trend is cold.

I still maintain that between 15th - 23rd Feb a big snow event is possible. Look at the chart below from the GEFS Parallel control run. That is some serious cold.

Ideally when the Scandi trough backs S we would ideally like this further E. If this happens then the chances of a bitterly cold NE,ly are possible. Alternatively what some of the GEFS ensemble suggest is cold N,ls spread S but at the same time a LP tracks along the channel. This also brings the risk of a big snow event.

After reading Chionomaniac posts in the Stratosphere thread I feel the models may struggle with the pattern beyond the E,ly. Im confident of the Greenland HP but its what happens after that is uncertain. However many of the outcomes are mouthwatering.

A great post as ever Dave

There would be armagedeon on here if that chart verified, What are your thoughts on the Fax charts this evening?