Cold Snap, T0-180Hours Only

YanSno · 30-01-2012 10:37AM

Things will get pretty interesting this afternoon as the serbian air makes it way over the continenthttp://www.uni-koeln.de/math-nat-fak...soTTPPWW00.gif
by this afternoon there will be a few wintry shower along the east and northeast as the front sweeps back to the atlantic gens-0-2-12.png?0

M.T. Cranium · 30-01-2012 10:44AM

For the first time on the 06z GFS run I'm seeing plausible charts for heavy snow streamer development (as opposed to potential) that could bury parts of Wicklow, Dublin, Meath and east Ulster in 20-40 cms of snow by Thursday (starting some time later Wednesday). The pressures and gradient may look a bit dodgy for this, but I think with the trends being established and just applying some basic climatology to the pressure pattern, there will be a bit of enhancement and meso-scale troughing, and then certainly enough push of severe cold across the Irish Sea to produce explosive potential with the direction of attack being from southeast. Places with orographic uplift in their favour could see locally very heavy falls. There will of course be local variations and shadowing effects of various hills. At least the Isle of Man won't be in the way (unless you're in east Ulster).

YanSno · 30-01-2012 10:52AM

i think there could be some explosive streamers from he irish sea on wed n thur.The gradient is good, you don't necessarily need much more than 25 knots of gradient to produce mega-streamer activity.

darkman2 · 30-01-2012 10:58AM

MT, how would you best characterise the difference between the Euro models and the North American models at 96hrs? Both sets of op runs seem to have an outcome that makes big differences to this part of the world. The Euros seem very progressive right now. GEM/GFS certainly the colder for the mid term holding the block up better.

patneve2 · 30-01-2012 11:01AM

If wind direction is due east then north dublin/louth tends to do the best but still to early to say that there will be streamers

ninebeanrows · 30-01-2012 11:01AM

M.T. Cranium wrote: »

For the first time on the 06z GFS run I'm seeing plausible charts for heavy snow streamer development (as opposed to potential) that could bury parts of Wicklow, Dublin, Meath and east Ulster in 20-40 cms of snow by Thursday (starting some time later Wednesday). The pressures and gradient may look a bit dodgy for this, but I think with the trends being established and just applying some basic climatology to the pressure pattern, there will be a bit of enhancement and meso-scale troughing, and then certainly enough push of severe cold across the Irish Sea to produce explosive potential with the direction of attack being from southeast. Places with orographic uplift in their favour could see locally very heavy falls. There will of course be local variations and shadowing effects of various hills. At least the Isle of Man won't be in the way (unless you're in east Ulster).

Yep if the trend continue a few more times, as in the whole things gets shunted another 100 miles further west we could be in business for some showers. Although i can't see 20-40cms! But i hope your right. Let us hope the 12z runs build on the 6z rather than indicating it is an outlier in the 144hr timeframe.

darkman2 · 30-01-2012 11:04AM

When the temperature graph for the 6z ensembles come out the average will be dramatically lower for the end of the week in Dublin compared to previous runs.

Average ensemble temperature

gens-21-0-84.png?6

So some pretty good support for the colder 6z run in the ensembles out to 96hrs.

YanSno · 30-01-2012 11:04AM

he could be right when is the last time you saw due points as low as this 81-101.GIF?30-6

ninebeanrows · 30-01-2012 11:05AM

A few GFS 6z Ensembles look decent.

Lots of uncertainty as early as T96hrs

The rollercoaster continues and admission is FREE:D

DOCARCH · 30-01-2012 11:10AM

Fup me!

With SST at around 9c in the Irish Sea, we could be in for a bit of fun alright!

mickger844posts · 30-01-2012 11:22AM

only one wrote: »

There's a lot of talk about the east getting snow but how about us guys in the south east ? Cork / Waterford ? We would like some snow lol

Snow potential chart for Thursday 15hrs.

pistolpetes11 · 30-01-2012 11:48AM

MOD NOTE :

Folks if your post has not got anything to do with Models/charts then dont post it here

Asking will it snow in my back garden,

Saying that looks nice,

Talking about the Irish /UK Met Offices,

One Liners,

Has nothing to do with this thread, its belongs in the Possible Siberian Blast thread.

Its going to be getting very busy in here the next few days , so to keep this thread neat and tidy for the folks who want to read/learn what the models are actually doing, breaches of these guidelines may have to be met with infractions

M.T. Cranium · 30-01-2012 11:59AM

DM2 and others, I see the model disparity as being caused by some kind of different processing of boundary layer issues as the arctic front moves west across Baltic regions. Since models don't think but just perform iterations, no living entity is actually thinking this, but to my eye the GFS is "thinking" that the extreme cold will create a thermal low and accelerate the westward motion of the cold air -- the Jan 1987 event had this look to it -- and perhaps the ECM and UKMO output has downplayed that aspect and therefore is more conservative in result (especially for Ireland, can't say that for southeast England there would be a huge difference).

This may sound quirky but I noticed in various other outbreaks that the GEM for some obscure reason does a very good job on thickness depiction across the region in cold spells, and it was signalling days ago that the 510 dam contour would make contact with southeast England. So I've been somewhat biased into following the GEM output as perhaps the most reliable of the set until I see definitive signs. GEM is similar to GFS at the moment.

Also I can't really see how -15C at 850 mbs gets almost to London and Siberian air stops at Bristol. That seems counter-intuitive. But nature will have the last word.

The NW snowfall potential maps may have a frontal stability error for Cork region, I would personally draw that map with about a 3:1 ratio of snowfall in Wicklow to Cork although similar in outline. Heading to where I should have been hours ago now ... back after the 12z circus comes through town.

ninebeanrows · 30-01-2012 12:04PM

Dew points falling now the
M1 bouy to 5c/1c
Belfast Harbour 5c/-1c

Dublin steady at 4c/3c

DOCARCH · 30-01-2012 12:12PM

M2 bouy is 4.9c DP 1.4c (at 1100).

5.3c DP 0.7c at 1200

pistolpetes11 · 30-01-2012 12:20PM

DOCARCH wrote: »

M2 bouy is 4.9c DP 1.4c (at 1100).

Going by the charts it would seem that some of cold air is about 6hrs ahead of schedule

We should only be seeing in the region of 4c at this time and in the region of 2c around 6pm fo dp's

Although actual temps seem good.

blackius · 30-01-2012 12:29PM

M.T. Cranium wrote: »

This may sound quirky but I noticed in various other outbreaks that the GEM for some obscure reason does a very good job on thickness depiction across the region in cold spells, and it was signalling days ago that the 510 dam contour would make contact with southeast England. So I've been somewhat biased into following the GEM output as perhaps the most reliable of the set until I see definitive signs. GEM is similar to GFS at the moment.

Agreed.
I can also add that with 30 odd years of experience with easterly attacks going back to the late 70's

The atlantic is always delayed coming back in.

The NW snowfall potential maps may have a frontal stability error for Cork region, I would personally draw that map with about a 3:1 ratio of snowfall in Wicklow to Cork although similar in outline. Heading to where I should have been hours ago now ... back after the 12z circus comes through town.

You might want to include wexford in your warnings,especially East,south coastal [ie wexford town area] and north wexford.
An angle of attack from a south easterly quarter in my opinion has the potential with those dewpoints to drive snow showers [should the 06z be right] over a long sea track/fetch right into wexford and from there north toLouth.

I don't have the time to dig out the historical charts right now but either in january or february 1985 [I'm not sure of the exact week of which month] There was a similar flow where it became slacker over the irish sea.
A shallow low developed off wexford which delivered large quanties of snow [it snowed all day iirc!] up the east coast.

A similar but much more localised event occured on dec 21 or was it dec 22 2010 which by the time it was finished dumped an extra foot of snow into coastal parts of south wicklow/North wexford.

blackius · 30-01-2012 12:34PM

Dewpoint at my location [arklow] is also falling steadily with a southeast flow currently off the irish sea indicating and confirming that cold is seeping in faster than programmed-currently 2.7c dp

premiercad · 30-01-2012 12:48PM

Is all starting to look good from later today,

M2 buoy DP 0.7 degC

Hirlam 06z for today 18GMT

darkman2 · 30-01-2012 12:49PM

blackius wrote: »

Dewpoint at my location [arklow] is also falling steadily with a southeast flow currently off the irish sea indicating and confirming that cold is seeping in faster than programmed-currently 2.7c dp

It seems broadly on track

1pm

6-101.GIF?30-6

7pm

Su Campu · 30-01-2012 01:01PM

I would totally disregard those Hirlam thickness charts for the reasons I pointed out a week or so ago. There is a big error with them, and also the theta-e values, which are running around 8-10 °C lower than reality.

blackius · 30-01-2012 01:07PM

darkman2 wrote: »

It seems broadly on track

1pm

7pm

Well thats the last time I rely on TWO [as posted by pistol above which has higher dew points]
I am relying on you guys today though as I won't see a pc before night and will be reading this on my phone.

darkman2 · 30-01-2012 01:15PM

blackius wrote: »

Well thats the last time I rely on TWO [as posted by pistol above which has higher dew points]
I am relying on you guys today though as I won't see a pc before night and will be reading this on my phone.

It's just a lower resolution on those charts. Keep us up to date with the dew point in your area though. Do you have a linky for your station?

Nabber · 30-01-2012 01:25PM

GFS midnight tonight. Cold is coming quiet fast.
Dew points in dublin are quiet steady at 3-4c. Wicklow mountians may do well out of this tonight.

blackius · 30-01-2012 01:27PM

I have an upload problem at the moment so no live website.
Hope to have it working this evening and will put a link in my sign then

arctictree · 30-01-2012 01:47PM

Nabber wrote: »

GFS midnight tonight. Cold is coming quiet fast.
Dew points in dublin are quiet steady at 3-4c. Wicklow mountians may do well out of this tonight.

2.8c at my location at the moment. Thats a variation of 0.3c in 14 hours!

Just dull and misty. Precip seems to have petered out on the radar but maybe more will arrive later. Need a drop of 1.5c for the snow.

Rebelbrowser · 30-01-2012 01:51PM

Su Campu wrote: »

I would totally disregard those Hirlam thickness charts for the reasons I pointed out a week or so ago. There is a big error with them, and also the theta-e values, which are running around 8-10 °C lower than reality.

Sorry Su if you've answered this already (haven't seen your post if you have), what's your read on the models now? I know you have been sceptical that the true cold would hit Ireland and you gave a very good explanation for this that, alas, went over my head. Is that still the case or have you an updated view given most recent model guidance?

darkman2 · 30-01-2012 02:30PM

Anything off the Irish Sea tomorrow will likely be of snow. A few light snow showers here and there i'd say. I suspect on current forecasts for tomorrow little accumulation of snow at low levels.

DOCARCH · 30-01-2012 02:36PM

darkman2 wrote: »

Anything off the Irish Sea tomorrow will likely be of snow. A few light snow showers here and there i'd say. I suspect on current forecasts for tomorrow little accumulation of snow at low levels.

ME going along with that:

Largely dry over Ulster and Leinster tomorrow, though there is the risk of a few snow flurries down along the east coast.

BTW, DP at M2 bouy now 0.3c

NIALL D · 30-01-2012 02:41PM

Nabber wrote: »

GFS midnight tonight. Cold is coming quiet fast.
Dew points in dublin are quiet steady at 3-4c. Wicklow mountians may do well out of this tonight.

so that pink shaded part is showing snow at 12 tonight ?

is that sea level ?

cheers ...

Cold Snap, T0-180Hours Only

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