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Winter 2013-2014 Discussion- Part 2


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Posted
  • Location: Outside Limavady.
  • Location: Outside Limavady.

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers??? 

     

    (someone with no bias)

     

    I am puzzled to be honest because I would've thought -8c uppers would sustain snow to all levels.

    Funny they are also forecasting rain for western scotland too. 

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    Posted
  • Location: Chorley, Lancashire
  • Location: Chorley, Lancashire

    Sounds great but the problem I have with their monthly forecasts are, they are always wrong!

    a few days ago the the forecast said westerlies will dominate December, so they have changed their minds already lol

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    Posted
  • Location: Chorley, Lancashire
  • Location: Chorley, Lancashire

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers??? 

     

    (someone with no bias)

     

    I am puzzled to be honest because I would've thought -8c uppers would sustain snow to all levels.

    Funny they are also forecasting rain for western scotland too. 

    I could be because the northerly winds would blow some milder air from the sea (sea surface temps will be warmer than inland temps) towards the northern extent and under cut the cold air inland.

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    Posted
  • Location: Chorley, Lancashire
  • Location: Chorley, Lancashire

    One quick word on the model debate, I think we can all see that the models are having a very difficult time of it. One model suggest one thing and another model the other. What i can deduce from this is there is much uncertainty and wouldn't look past 7 days in that regard. However when a zonal pattern is apparent, the models tend to have no problem in 'coming together ' and agreeing with each other so the fact they are all over the place is very interesting to see and very difficult to predict weather after a 7 day period with confidence. Maybe we are going to get a cold period and the models are struggling with the pre blocking pattern and certainly don't have any fluidity on a zonal period or blocking. Were in weather limbo people!!!!!

    Edited by iamstuart
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    Posted
  • Location: st albans
  • Location: st albans

    I could be because the northerly winds would blow some milder air from the sea (sea surface temps will be warmer than inland temps) towards the northern extent and under cut the cold air inland.

    warm air doesnt 'undercut' cold air. however, your first sentence is probably right as the flow comes onshore and  probably brings the dewpoints above freezing. there;s a lot more to snowfall than just uppers as JH always reminds us.

    Edited by bluearmy
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    Posted
  • Location: Ireland
  • Location: Ireland

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers??? 

     

    (someone with no bias)

     

    I am puzzled to be honest because I would've thought -8c uppers would sustain snow to all levels.

    Funny they are also forecasting rain for western scotland too. 

     

    Well the GFS shows that when the precipitation arrives Tuesday night the uppers aren't -8, they are only -2. And more importantly the dew points will be +4, no chance of snow. There could be some snow showers before that though, earlier on Tuesday.

     

    Posted Image

    Posted Image

    Edited by radiohead
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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers??? 

     

    (someone with no bias)

     

    I am puzzled to be honest because I would've thought -8c uppers would sustain snow to all levels.

    Funny they are also forecasting rain for western scotland too. 

     

    hi sm

    have a go yourself using the Guide I did on will it snow, in the Guides area, it is easy to use but the data will really only be available for all the parameters I think for GFS/Extra outputs. Remember to factor in your height amsl, in an unstable air mass that is 3C per 1000ft or whatever is the metric equivalent, and half that if it is not unstable. More complications in moderate to heavy precipitation in that the effects of Latent Heat will lower the air temperature, effectively lowering the zero C isotherm.  Let us all know what it gives you please?

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    Posted
  • Location: Chorley, Lancashire
  • Location: Chorley, Lancashire

     

    I could be because the northerly winds would blow some milder air from the sea (sea surface temps will be warmer than inland temps) towards the northern extent and under cut the cold air inland.

    warm air doesnt 'undercut' cold air. however, your first sentence is probably right as the flow comes onshore and  probably brings the dewpoints above freezing. there;s a lot more to snowfall than just uppers as JH always reminds us.

     

    Yes ' undercut ' wrong term lol but you knew what i meant lol Posted Image

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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers

    Remember, 850hpa temps aren't a sole decider on forecasting snowfall.Don't take these charts too literally as they are from the 06z GFS Op, but it does give a broad idea of a "milder upper sector" mixing out the colder air aloft through to the surface. This could easily be caused by the above average SST anomalies around the UK currently.A look at the 850hpa temps on Tuesday show -8c values as you say;post-12721-0-85077300-1384602808_thumb.jHowever, a look at the freezing level for the same time shows the threat of the colder air aloft mixing out at surface level, with it forecast by the GFS Op to be around 100m;post-12721-0-24582900-1384602885_thumb.jpost-12721-0-21985200-1384602908_thumb.jTherefore, suggestive of an elevated requirement for snowfall. A wintry mix once you get towards sea level. The Dewpoints only just on the right side of marginal too;post-12721-0-15490200-1384602984_thumb.jA look at Tuesday evening suggest a "pacier" mix out of the colder 850hpa temps. -5/6c still often considered good for snowfall;post-12721-0-89405700-1384603057_thumb.jBut look how the WBFL increases;post-12721-0-32668900-1384603089_thumb.jpost-12721-0-89799000-1384603097_thumb.jThis definetly suggestive of a less cold sector mixing out the colder air aloft. Some notable elevation required for snowfall in NI on Tuesday night. Dewpoints also representive of this;post-12721-0-82421000-1384603191_thumb.jNot saying the Meto are 100% right, as NI is definetly at risk of frequent and heavy sleet/snow showers Monday night into Tuesday morning. The risk does lessen as Tuesday progresses though as surface temps begin to impact the cold air, mixing it out at the surface and therefore giving the need for elevation as Tuesday progresses! Edited by AWD
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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    Could someone with ample knowledge please tell me why the met office are forecasting rain for low levels in Northern Ireland on Tuesday with -8c uppers??? 

     

    (someone with no bias)

     

    I am puzzled to be honest because I would've thought -8c uppers would sustain snow to all levels.

    Funny they are also forecasting rain for western scotland too. 

     

    Gibby was talking about this the other day sea temperatures around the UK are quite warm still after a mild Autumn so that will have an affect on any snow at the moment for those close to the sea.

     

    This cold spell is probably a 1 or so too early for snow

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    Posted
  • Location: Outside Limavady.
  • Location: Outside Limavady.

    Well the GFS shows that when the precipitation arrives Tuesday night the uppers aren't -8, they are only -2. And more importantly the dew points will be +4, no chance of snow. There could be some snow showers before that though, earlier on Tuesday.

     

    Posted Image

    Posted Image

    I am talking about the daytime on Tuesday it has 5c and heavy rain. 

    Remember, 850hpa temps aren't a sole decider on forecasting snowfall.

    Don't take these charts too literally as they are from the 06z GFS Op, but it does give a broad idea of a "milder upper sector" mixing out the colder air aloft through to the surface. This could easily be caused by the above average SST anomalies around the UK currently.

    A look at the 850hpa temps on Tuesday show -8c values as you say;

    Posted Imageimage.jpg

    However, a look at the freezing level for the same time shows the threat of the colder air aloft mixing out at surface level, with it forecast by the GFS Op to be around 100m;

    Posted Imageimage.jpgPosted Imageimage.jpg

    Therefore, suggestive of an elevated requirement for snowfall. A wintry mix once you get towards sea level. The Dewpoints only just on the right side of marginal too;

    Posted Imageimage.jpg

    A look at Tuesday evening suggest a "pacier" mix out of the colder 850hpa temps. -5/6c still often considered good for snowfall;

    Posted Imageimage.jpg

    But look how the WBFL increases;

    Posted Imageimage.jpgPosted Imageimage.jpg

    This definetly suggestive of a less cold sector mixing out the colder air aloft. Some notable elevation required for snowfall in NI on Tuesday night. Dewpoints also representive of this;

    Posted Imageimage.jpg

    Not saying the Meto are 100% right, as NI is definetly at risk of frequent and heavy sleet/snow showers Monday night into Tuesday morning. The risk does lessen as Tuesday progresses though as surface temps begin to impact the cold air, mixing it out at the surface and therefore giving the need for elevation as Tuesday progresses!

    I'm still puzzled why they are forecasting rain even on Monday night because the GFS would suggest snow.

    post-15021-0-66648700-1384603520_thumb.p

    post-15021-0-77418700-1384603726_thumb.p

    Edited by smithyweather
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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol

    I'm still puzzled why they are forecasting rain even on Monday night because the GFS would suggest snow.

    You know that GFS chart is for midday Tuesday yeah?It's for the reasons I've just described above!You'll probably find you could get something more wintry than the Meto forecast you posted above suggests!However, maybe not as wintry as what your expecting/hoping for? Edited by AWD
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    Posted
  • Location: Outside Limavady.
  • Location: Outside Limavady.

    No its not. At midday they have heavy rain and 5c, with -8c uppers it should be easily snow.

     

    I can see why its not snowing at midnight tuesday but midday tuesday no.

    Edited by smithyweather
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    Posted
  • Location: The Purbeck Microclimate, Dorset.
  • Weather Preferences: Gales, T-storms, Heavy Rain, Heat, Cold - Love it all.
  • Location: The Purbeck Microclimate, Dorset.

    Great post there AWD!

     

    A lot of folks do hang on to the dewpoints and 850hPa temps when it comes to looking for snowfall but as you alluded to, the wet bulb freezing level is a great chart to look at when the other elements are in place but snowfall looks unlikely. John H also touched upon the isothermic drag, heavier precip can drag that isotherm level down from aloft, so the snow can remain snow for longer as it falls.  

    I'm really not a fan of looking for snow (in a particular area) anymore than 24hrs out, a few miles make a massive difference, i like to look at all the hi-res models as close as possible to the event, then most of the time (if it looks like it will snow in my area) i can say to friends/colleagues, i can pretty much guarantee it will snow.  It is so easy for it to go wrong though, that's why i keep my head down in the MOD thread, some folks look for snow more than a week out, i have to ask the question, why? Posted Image

    Edited by Mapantz
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    Posted
  • Location: Outside Limavady.
  • Location: Outside Limavady.

    You know that GFS chart is for midday Tuesday yeah?It's for the reasons I've just described above!You'll probably find you could get something more wintry than the Meto forecast you posted above suggests!However, maybe not as wintry as what your expecting/hoping for?

    Well number 1 I thought it would be far colder than 5c, maybe 2c? Then I thought that we would see a window of heavy dry snow from 9pm Monday to 6pm Tuesday based on the current gfs run. 

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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol

    No its not. At midday they have heavy rain and 5c, with -8c uppers it should be easily snow.

    Let's just wait and see mate. 850hpa temps can't be taken solely when forecasting snowfall. It doesn't matter if the 850hpa temp is -8c if other factors are less favourable for snowfall. Other factors have to fit in too. You are definetly at risk of snowfall but equally you could get a wintry mix, a la your Meto forecast.Best lamp post watch come Tuesday. That's the most exciting and reliable way of observing snowfall anyway. Good Luck! :)
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    Posted
  • Location: Outside Limavady.
  • Location: Outside Limavady.

    Maybe they are just covering their backs. Or maybe Gavin is right and the sea temps will erode the cold, because it is still 11.8c at Castlerock.

     

    I am just basing my opinion on what normally happens and usually with -8c uppers we readily see snow right down to the beach so thats why I was surprised at them forecasting rain (not even sleet) seven miles inland (and at 50m)

    It is a really bad idea of them to forecast rain anyhow because it probably will snow and then people are going to be shocked when its not raining which is not on. I think they've done this before and I remember people ranting about how it was snowing when they forecast rain.

    Edited by smithyweather
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    Posted
  • Location: Near Keele, North Staffs
  • Location: Near Keele, North Staffs

    Maybe they are just covering their backs. Or maybe Gavin is right and the sea temps will erode the cold, because it is still 11.8c at Castlerock.

     

    I am just basing my opinion on what normally happens and usually with -8c uppers we readily see snow right down to the beach so thats why I was surprised at them forecasting rain (not even sleet) seven miles inland (and at 50m)

    It is a really bad idea of them to forecast rain anyhow because it probably will snow and then people are going to be shocked when its not raining which is not on. I think they've done this before and I remember people ranting about how it was snowing when they forecast rain.

     

    The sea is a considerably modifier at this time of year, and I would think that you would need to be on high ground Tuesday/wednesday to see settling snow, with some wet snow possible at lower levels in the North.

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    Posted
  • Location: Essex, Southend-On-Sea
  • Weather Preferences: Warm, bright summers and Cold, snowy winters
  • Location: Essex, Southend-On-Sea

    I wouldn't worry about DPs and this time yet.

     

    Your regional thread is the best sauce of information for this.

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    Posted
  • Location: falkirk, scotland, 16.505m, 54.151ft above sea level
  • Weather Preferences: dry sunny average summers and really cold snowy winters
  • Location: falkirk, scotland, 16.505m, 54.151ft above sea level

    last 9 ECM ensembles if anyone wants to compare

     

    post-18233-0-94510400-1384611166_thumb.gpost-18233-0-30419000-1384611167_thumb.gpost-18233-0-07361900-1384611168_thumb.gpost-18233-0-82300100-1384611168_thumb.gpost-18233-0-54255900-1384611169_thumb.gpost-18233-0-26659400-1384611170_thumb.gpost-18233-0-01254700-1384611171_thumb.gpost-18233-0-80457700-1384611171_thumb.gpost-18233-0-55075300-1384611172_thumb.g

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    Posted
  • Location: falkirk, scotland, 16.505m, 54.151ft above sea level
  • Weather Preferences: dry sunny average summers and really cold snowy winters
  • Location: falkirk, scotland, 16.505m, 54.151ft above sea level

    Notice how often low res gefs op is an outlier to the ecm ens mean.That's why it deserves little discretion and analysis.

     

    yip I only look at the GFS for fun now in its longer range unless its in agreement or to look for trends

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    Posted
  • Location: Ludgershall, Wiltshire
  • Location: Ludgershall, Wiltshire

    I have noticed that many of the seasonal models are flipping to a zonal mild winter from a more blocked pattern. I wonder what they are picking up on. The JMA, CFS and the Korean LR are now trending there and the latest EC three month, from Matt Hugo:"Nov update of the EC seasonal model has shifted from recent months. Now indicates a +NAO pattern and a mild/zonal winter. #WeShallSee"Not gonna write winter off but not a good trend.

    Trouble is, I believe most LR models flipped from a cold/blocked Winter to a mild/zonal one in December last year, although the SSW in January may have been responsible for derailing them.  Also, I read a thread on here from November 2009 and if I remember correctly the CFS flipped from a cold blocked to a mild/zonal outlook back then.  People were saying it had picked up on the strong El Nino but we all know what followed!  Obviously that's not to same the same is going to happen this year, but it shows that although the current trend is not nice to see, we shouldn't write Winter off.

    Edited by Don
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