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22-02-2018, 22:07   #1
Donegal Storm
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Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

MOD NOTE

This thread is for Technical Discussion Only - for everything else use the event chat thread Off topic posts will be moved there.

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Not looked at the models since last night but nothing much has changed from what I can see, still expecting a big downgrade every time I have a look but so far so good. The main issue I can still see is the high could sink over us leaving us with a nondescript cold inversion but hopefully hopefully it won't come to that

Latest GFS pretty much as we were, cold from Monday with snow potential from Tuesday evening. Still pointless looking at smaller details


Last edited by Lumi; 23-02-2018 at 08:03.
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22-02-2018, 22:12   #2
sdanseo
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I wouldn't usually cross post in both threads, but 18Z GFS is just beautiful.
Everything that falls out of the sky from 24hrs through 240hrs is snow or ice.


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22-02-2018, 23:06   #3
Kermit.de.frog
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it now looks like the cold is definitely locked in at this stage but the snow sure isn't. Sunday/Monday will be a much better idea of how the snow will shape up next week.
Light snow showers should start moving on to the east coast on current model wide guidance sometime Monday afternoon or evening and continue overnight, getting progressively heavier and more frequent through Tuesday.
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22-02-2018, 23:29   #4
gabeeg
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The GFS is a showing pretty much a steady stream of snow in from the east.

Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?
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22-02-2018, 23:33   #5
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Just checking the GFS mean and all systems are a go for whiteout conditions for a lot of the country. That if it verified. Starting out mainly on Tuesday that little kink should drive lake effect snow showers from the north east for a time before wind changes back more East.

The Atlantic slider low looks a very promising solution as it has been flagged before and dropped and back again and I feel it is here to stay meandering around our little isle for a few day.

Buy the bread and freeze it folks cause this could be our epic snowfall event that has eluded us since the 60s 70s and 80s.

Of course thus is not a forecast but the size and force of this easterly push due to the burrowing of the easterly winds through the atmosphere from the SSW is a remarkable event anyway and we are in the firing line for once to perhaps achieve the perfect winter/ Spring storm.
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22-02-2018, 23:36   #6
highdef
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Quote:
Originally Posted by gabeeg View Post
The GFS is a showing pretty much a steady stream of snow in from the east.

Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?
Afternoon sun had very little to do with those Irish Sea streamers back in 2010 and the same will be the case next week. One of the main reasons for those showers to develop is due to a large difference in temperature between the sea and the atmosphere. The sun has little or no bearing on their development so the showers can continue on night and day, pretty much 24/7. There are several other factors required for their development but I don't want to go too off topic on this thread.

Last edited by highdef; 22-02-2018 at 23:45.
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22-02-2018, 23:36   #7
JCX BXC
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Would anyone care to give their thoughts on the possible convective showers over land building up? While not my area of expertise, I have read online regarding possible over land showers building up as surface temperatures rise quicker in the stronger late February/early March sun.

It would certainly help get me a dusting here in West Clare if the forecast low pressure systems don't arise.

On another note, the GFS has a beautiful parting snow front near the end of the 18Z run (+336, around the 8th) dumping possibly feet of snow countrywide. Long way off but as I've said several times before, it's nice to dream

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22-02-2018, 23:37   #8
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Quote:
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The GFS is a showing pretty much a steady stream of snow in from the east.

Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?
A northeasterly wind would favour the northeast, east and southeast.

As the cold dry airmass flows southwestwards off the northwest coast of England, its' lowest layers get modified enough for cumulus to form. As they continue their track over the sea, these cumulus quickly grow in size, and start producing precipitation by around Angelsea. By the time they reach the east coast they are fully fledged cumulonimbus, complete with hail, snow and graupel, and potentially, thunder and lightning. The distance required for clouds to first start to form is a delicate balance of airmass temperature and dewpoint, windspeed and sea surface temperature. The faster the wind, the further the airmass can travel before clouds can form, and vice versa. Right now, all data suggests this is the likely situation, particularly from midweek.
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22-02-2018, 23:38   #9
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Quote:
Originally Posted by gabeeg View Post
The GFS is a showing pretty much a steady stream of snow in from the east.

Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?
The sun had little effect fueling the streamers in 2010, it was mere coincidence that the other parameters lined up in the afternoon.
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22-02-2018, 23:38   #10
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The 18z actually brings in -45C temps at 500 hPa for a few hours, insane.
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22-02-2018, 23:45   #11
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Charts kind of look like a more potent version of the first cold spell at the end of 2010. There was actually a decent continental component at the end of Nov that year with isobars briefly stretching from western siberia to Ireland accompanied by 850s slighly below -10 for a day or two. Whats being modeled now however looks much stronger with a superior air source also.
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22-02-2018, 23:45   #12
Rougies
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Originally Posted by JCX BXC View Post
Would anyone care to give their thoughts on the possible convective showers over land building up? While not my area of expertise, I have read online regarding possible over land showers building up as surface temperatures rise quicker in the stronger late February/early March sun.

It would certainly help get me a dusting here in West Clare if the forecast low pressure systems don't arise.

On another note, the GFS has a beautiful parting snow front near the end of the 18Z run (+336, around the 8th) dumping possibly feet of snow countrywide. Long way off but as I've said several times before, it's nice to dream
The effect would be almost non existent due to still relatively low sun strength, dry cold ground and little growth in vegetation. Plants/trees/grasses pump out loads of water vapour when they're growing/in leaf.
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22-02-2018, 23:48   #13
typhoony
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the non-computerised Fax chart for next Tuesday...

http://www.meteociel.fr/ukmo/fax/fax120s.gif?2

probably just light snow away from the east coast
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22-02-2018, 23:49   #14
Kermit.de.frog
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GFS ensemble mean does offer quite a bit of support for the more outlandish portion of the 18z run and ECM evolutions. Interesting times ahead.

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22-02-2018, 23:50   #15
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the non-computerised Fax chart for next Tuesday...

http://www.meteociel.fr/ukmo/fax/fax120s.gif?2

probably just light snow away from the east coast
That nice kink over the Irish Sea should aid convective activity - locally heavy falls by Tuesday evening I would think.
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