Model Output Discussion - 12th December Onward

[Heisenberg]

Also depends on how heavy the precip is which of course will bring the "evaporative cooling" effect into full swing given enough heavy precip. Still see signs of something pretty Wintry across the Midlands and Wales from the latest run of the 06z Gfs. :smilz38:

How far east is this likely to come? Some of the maps looks fairly close to the home counties? Or maybe im just pants at geography lol

[Zakos]

The fact that it's forecast to hit early morning is strongly in favour of snow. If it were midday I admit it probably would be sleet/rain.

[A.J]

You will be too far North Mark - and it won't be snow anyway !

On behalf of all of the midlands members I have this to say...."Speak to the hand because the ears aren't listening!"

I do agree an air of caution is required, conditions for snowfall on most of the model outputs this morning are marginal and there are plenty of twists and turns ahead, but there does seem to be increasing agreement on the track of fridays system and ppn spread, considering where the models were 24-48 hours ago

[shedhead]

06GFS sticks with the general trend out to 192hrs, becoming mild/very mild for all, but at least it should finally dry out as pressure rises from the south. Obviously this is not everyones cup of tea for Xmas, but given how wet it's been

down here it's bound to be more welcome than yet more wind and rain.

[Thundery wintry showers]

The precipitation event on the northern flank of the low looks like a classic "marginal" event with snow likely to low levels in heavy bursts due to evaporative cooling, but just rain or sleet in light to moderate bursts. Wet ground and high ground temperatures are unlikely to be a major issue, and the key will be the surface temperatures and the dew points. The most likely result for the majority at low levels is a wintry mix with little advance on slushy deposits on the ground, but some locations might get a significant dumping. In the meantime damaging winds are still possible in the south of England.

After that we still have about three days of north to north-westerly winds which will bring wintry showers to areas near north-facing coasts, but the majority of inland areas will stay dry. Shower activity is still hard to pin down at this stage. After that, an evolution towards a mild cloudy anticyclonic spell is definitely looking odds-on through to around the 21st December but after that it is unclear whether the spell will continue or whether high pressure will build further north introducing colder and possibly brighter weather.

[nick sussex]

In terms of chances for snow it's marginal, a weaker feature would have increased the chances and in terms of evaporative cooling this plays a greater role with less mixing when you have lighter winds.

Some of this could be mitigated with heavy precip but I certainly would urge some caution looking at those NAE charts, if we do see this track as being close to verifying then its really going to come down to nowcasting.

I doubt the UKMO will call snow as a definite but will be a bit more vague.

[ANYWEATHER]

How far east is this likely to come? Some of the maps looks fairly close to the home counties? Or maybe im just pants at geography lol

To Be Honest, very difficult one to call but Looking at the maps/charts ,anyone North of the M4 is the most likely to see the GREATEST, chance of snow .Still lots of twists and turns on this one. I do weather forecasts for a local Radio station and ive imformed them that there could be some travel disruption on Friday morning, but there gonna give me a call tomorrow morning to find if that scenario still stands, I would hate to imform the population of the Cotswolds, Gloucestershire, Worcestershire, and Warwickshire, of heavy snow and nothing happens!! :smilz38:

The precipitation event on the northern flank of the low looks like a classic "marginal" event with snow likely to low levels in heavy bursts due to evaporative cooling, but just rain or sleet in light to moderate bursts. Wet ground and high ground temperatures are unlikely to be a major issue, and the key will be the surface temperatures and the dew points. The most likely result for the majority at low levels is a wintry mix with little advance on slushy deposits on the ground, but some locations might get a significant dumping. In the meantime damaging winds are still possible in the south of England.

After that we still have about three days of north to north-westerly winds which will bring wintry showers to areas near north-facing coasts, but the majority of inland areas will stay dry. Shower activity is still hard to pin down at this stage. After that, an evolution towards a mild cloudy anticyclonic spell is definitely looking odds-on through to around the 21st December but after that it is unclear whether the spell will continue or whether high pressure will build further north introducing colder and possibly brighter weather.

Also one to note, from my experience "Marginal" snow can produce a lot of snow in some places whilst others have none just a few miles away. At least some interesting and seasonal weather to talk about!

[snow drift]

To Be Honest, very difficult one to call but Looking at the maps/charts ,anyone North of the M4 is the most likely to see the GREATEST, chance of snow .Still lots of twists and turns on this one. I do weather forecasts for a local Radio station and ive imformed them that there could be some travel disruption on Friday morning, but there gonna give me a call tomorrow morning to find if that scenario still stands, I would hate to imform the population of the Cotswolds, Gloucestershire, Worcestershire, and Warwickshire, of heavy snow and nothing happens!! :smilz38:

The North Cotswolds would be in the best place for snow on the northern side of the depression IF the low tracks on the route most models would indicate. The aptly named Snowshill would be where I would like to be for the next few days.

[Chris Jennings]

i live in norfolk where in 2011 not a single snow flake has fallen, in fact we could be heading for second winter drought in a row, must be living in a micro climate :smilz38:

[The Giant Daddy Jackpot]

Friday's event is certainly shaping up to be another classic "M4 corridor" marginal event. The Met are being very cautious about the warning of heavy snow for the south west in particular but who can blame them after some of their bad calls last winter.

[kold weather]

It is marginal but importantly the models keep the dew points around freezing by 06z Friday. Its the type of set-up that is heqavily dependant on timing. High ground will make a real difference to accumulations, but some areas would get plastered in the set-up the models are forecasting right now.

00z ECM is nearly identical to the NAE but drags the colder air down a little faster due to the low being weaker and a touch further south again.

[Thundery wintry showers]

Aye. My stance on this event is somewhat different to last year's potential "blizzard" that never came off, because last year most of us had a significant covering of powdery snow, which could have been thinned and turned to slush during a wet sleet/snowstorm, resulting in solid ice following a subsequent refreeze, but of course today very few of us have any snow cover, so I imagine that many will just be happy to see some of the white stuff even if it doesn't settle.

Showers from the subsequent Arctic regime will depend on wind direction. The latest GFS run again suggests that the winds will veer northerly for a time bringing snow showers into NE England and a wintry mix to East Anglia, but if the winds stay west of due north it will mainly be Wales and SW England that see showers.

[shedhead]

The precipitation event on the northern flank of the low looks like a classic "marginal" event with snow likely to low levels in heavy bursts due to evaporative cooling, but just rain or sleet in light to moderate bursts. Wet ground and high ground temperatures are unlikely to be a major issue, and the key will be the surface temperatures and the dew points. The most likely result for the majority at low levels is a wintry mix with little advance on slushy deposits on the ground, but some locations might get a significant dumping. In the meantime damaging winds are still possible in the south of England.

After that we still have about three days of north to north-westerly winds which will bring wintry showers to areas near north-facing coasts, but the majority of inland areas will stay dry. Shower activity is still hard to pin down at this stage. After that, an evolution towards a mild cloudy anticyclonic spell is definitely looking odds-on through to around the 21st December but after that it is unclear whether the spell will continue or whether high pressure will build further north introducing colder and possibly brighter weather.

I don't see this as being particularly unclear, so can I ask where else you see heights building to give us all a chance of colder and possibly brighter weather?

[kold weather]

The other thing that makes this set-up interesting is that a secondary low may well try and develop as the main low deepens and moves away. This will help to pep up the front as the cold digs down. Normally in this set-up the cold air would weaken any frontal system but the boost it gets helps to keep precip fairly strong allowing a slightly unusual set-up.

[Frosty.]

It will be on a knife edge whether low ground gets any snow although a higher risk at night obviously as temps drop a few degrees but wet bulbs look marginal. It's all a bit pathetic really as there was nothing marginal during the snow fest last december and now we are wondering who might get a few mm of slushy deposits before the mild weather returns next week and beyond although if the anticyclone builds in over the uk it will at least bring an increased incidence of fog and frost but nw britain probably milder and more changeable throughout next week and onwards...unless something dramatic happens in the mid range, it will become a very benign and to most on here, boring pattern although a few on here seem to take great relish in mild, dry and rather cloudy weather..I pity them.

Edited December 14, 2011 by Polar_ Low

[chionomaniac]

06GFS sticks with the general trend out to 192hrs, becoming mild/very mild for all, but at least it should finally dry out as pressure rises from the south. Obviously this is not everyones cup of tea for Xmas, but given how wet it's been

down here it's bound to be more welcome than yet more wind and rain.

I have to say that there is a junction around that time as to what happens next. Will we see a pressure rise over Scandinavia or will the zonal conditions come flooding back in as the 6z GFS shows? I am not convinced by this scenario painted by the GFS and even if this does occur I don't think that it will be long before another attempt occurs at pressure rises to our NE.

At some point this winter I suspect there will be a slow reversal of the zonal outlook to a more blocked outlook and the models are giving weak signals that this is about to start in the end third of December. It probably will be a slow transition taking a good few weeks unless a split SSW speeds things along.

Edited December 14, 2011 by chionomaniac

[Thundery wintry showers]

ECMWF at T+240:

http://www.wetterzentrale.de/pics/Recm2401.gif

GEFS ensembles showing a split between mild outcomes, average outcomes and fairly cold outcomes:

http://hw.nwstatic.co.uk/ensimages/ens.20111214/00/t850Tyne~and~Wear.png

You can argue that I am pointing at evidence that is too far out to be able to take seriously, but it's no less so than the insistence on a nailed-on mild Christmas period.

[Eskimo]

"IF"The met office issue a warning I said. I am aware of the changes run to run, but majority of the runs have showed heavy snow in the midlands. Snow is forecast to be heavy and prolonged. "IF"it does so, then it won't matter about the wet surfaces.

Sorry to bully, but trust me, I've seen snow fall all day and never stick, the temps look too high for anything exceptional other than occasional heavy wet snow for central areas and then higher eastern areas of england.

[No Balls Like Snow Balls]

Things will turn milder next week i am 99% sure of that, but for how long and how mild is far from agreed upon I think. It could quite easily last right into xmas or it might just be a 3-4 day warm up before turning cooler again in time for xmas. The mean 850's have stayed around average over the xmas period for more than a few runs so at this minute you would have to say temps will be average over the xmas period rather than very mild.

As for the snow potential on Friday, I fear a lot of people who are expecting snow will be dissapointed i have seen this dozens of time before that it turns out to be sleet / wet snow instead of the proper stuff that sticks, NAE forecasts snow for my area but really I do not believe I will see any snow my way.

Edited December 14, 2011 by No balls like Snow Balls

[Thundery wintry showers]

Yes, wet surfaces aren't the only obstacle to lying snow- the air temperature also has to be low enough (preferably less than a degree above freezing) as otherwise the snowflakes start to melt before they hit the ground.

[kold weather]

ECMWF at T+240:

http://www.wetterzen...cs/Recm2401.gif

GEFS ensembles showing a split between mild outcomes, average outcomes and fairly cold outcomes:

http://hw.nwstatic.c...ne~and~Wear.png

You can argue that I am pointing at evidence that is too far out to be able to take seriously, but it's no less so than the insistence on a nailed-on mild Christmas period.

I think the ECM is the solution we need to hope for, with the upper high getting far enough north. The GFS can sometimes be overzealous with westerly set-ups and doesn't always clock the northward extent of blocks. i've seen Bartletts turn into Scandi highs over the period of 5-7 days of model runs...so we'll see...

[nick sussex]

I'm quite impressed by the BBC forecasters in explaining the effects of the different tracks of that low.

It's a difficult one for some members in this thread, depending on where you live is what you'd prefer, the more the low deepens the further north its track is likely to be and with that more likely you'll have some extreme winds on the southern side of the low , of course that takes the snow risk further north, a weaker feature will likely end up with the low centred near the Channel and strongest winds in northern France with areas further south a better chance of seeing some snow.

[Heisenberg]

When you guys say mild over Xmas, it isnt that bad is it? I mean, I hear mild and my thoughts turn to November, with the really mild mush. But it looks like mild (in this instance) means average, which is what 5's/6's rather than 12's/13's? Still chilly, but fair enough its not cold....

[shedhead]

I have to say that there is a junction around that time as to what happens next. Will we see a pressure rise over Scandinavia or will the zonal conditions come flooding back in as the 6z GFS shows? I am not convinced by this scenario painted by the GFS and even if this does occur I don't think that it will be long before another attempt occurs at pressure rises to our NE.

At some point this winter I suspect there will be a slow reversal of the zonal outlook to a more blocked outlook and the models are giving weak signals that this is about to start in the end third of December. It probably will be a slow transition taking a good few weeks unless a split SSW speeds things along.

Agree chiono, but I still think we are talking late Dec for these signals to start appearing and mid Jan before they begin to manifest themselves nationally, though the NE might benefit at times before then. Prior to this a return to zonality is my most likely option, but with the Jet orientated more SW-NE and Tm far outweighing Pm air through the turn of the year.

TWS - England and Wales under HP possibly, rather more zonal for Scotland and N Ireland, but colder and brighter for Xmas looks a long shot to me.

[snowmadchrisuk]

To Be Honest, very difficult one to call but Looking at the maps/charts ,anyone North of the M4 is the most likely to see the GREATEST, chance of snow .Still lots of twists and turns on this one. I do weather forecasts for a local Radio station and ive imformed them that there could be some travel disruption on Friday morning, but there gonna give me a call tomorrow morning to find if that scenario still stands, I would hate to imform the population of the Cotswolds, Gloucestershire, Worcestershire, and Warwickshire, of heavy snow and nothing happens!! :smilz38:

Also one to note, from my experience "Marginal" snow can produce a lot of snow in some places whilst others have none just a few miles away. At least some interesting and seasonal weather to talk about!

Well to give you an example it is currently Snowing in Weston Super Mare right now , came as a surprise as we were suppose to have less chance than yesterday , and were A costal resort in the South West ... On Current charts Rain to Snow possible just about anywhere . Down here today the heavy ppn is making a huge difference . The track of the low will effect who get's Snow showers over the weekend also as it will depict the exact direction of the flow coming in IMO