St Patrick's Weekend Snow Risk - Technical Discussion Only - READ MOD NOTE POST #1

I'm having problems with that link MT.

Edit: got it working on the desktop site seems to be problems from the old app

Harmonie showing some sweet spots getting 20-30cm, more generally Leinster 5-15. All streamer line dependent

kittyn wrote: »

@Weathercheck ....... So where roughly are these sweet spots?

About as easy to forecast as the winning lotto numbers at this point.

The real moneymaker in this setup is to be found at mid-levels, in the form of a concentrated pool of very cold sub-minus 20 air advecting low partial thicknesses westwards. It gets into the east by sunset Saturday, so this will mark the start of the heaviest showers. By midnight to 6 am we're in the core of it, so showers should be reaching their peak by sunrise Sunday, gradually losing intensity throughout the morning and afternoon. Note: the 850 hPa charts don't really show the same level of change, remaining within a degree or two of -10 °C throughout.

MS paint of Harmonie accumed precip by 18z Sun

The current temperatures in Scandinavia are awe-inspiring given the calendar date:

http://www.meteociel.fr/observations-meteo/temperatures.php?region=su

this is the high pressure area that will drift down to Scotland and then Ireland over the next three or four days.

Temperatures near the core of the arctic high are quite extreme, -35 C at one location in south central Norway. I see higher pressures than modelled too, but that's probably a false conversion from elevation situation (1047 mbs near that -35 C reading). Winds continue to howl out of the east from northern Poland to the central North Sea and now into Britain too, arctic front appears to be approaching Wales (it is oriented WNW-ESE but will start to form more of an arc this morning and slam into Leinster around 0900h. Somewhat delayed response likely in terms of streamer production, would expect sporadic ones later morning then more organized by mid-afternoon.

We've had some good entries to our snap contest, if you missed it, join in. I plan to get a moderator to lock this contest thread at 1201h today then we can open it up for commentary on the results by Sunday morning perhaps.

Not planning any significant changes to forecast after reviewing all guidance, looks to be on track.

The 06Z radiosonde ascent from Albemarle (just west of Newcastle, England, so upwind from us) shows the inversion at around 700 hPa about 2 degrees weaker than forecast. Actual temperature is -15 while the 00Z ECM had it at -12 to -13 for that area at 06Z.

This means either the high is weaker/further north than forecast or the cold pool is making slightly faster progress east. This could mean slightly heavier showers earlier for the east this evening.

Sub-zero wet-bulb temps making steady progress westwards.

I am expecting the first flickers from the Irish Sea around 5/6pm, all lit up from midnight through to 9am with frequent well stacked streamers, merging into continuous snowfall at times, this snow moving inland tomorrow afternoon and clearing from the east coast.

However, increasingly likely some streamers will return to parts of east coast on Sunday night and into Monday morning.

S. Dublin, Wicklow, Wexford and parts of Kildare will be the jackpot winners this time I feel.

Calibos wrote: »

Excellent. Was getting worried as MT's forecast read like he favoured Dublin North, Meath, Louth and Ulster for the heaviest falls. What are the models saying about windspeeds? Are coastal districts going to get a decent bite of each streamer cherry or will high winds take them inland too quickly before they slow down due to Orographic Braking? Also are the winds going to be high enough to lift Salty Sea Spray aloft which could dampen accumulations close to the east coast shorelines.

Looking at the charts, I have a suspicion that two things will happen:

1. Areas very close to the coast will have very little, if any lying snow.
2. The snow showers/bands will get more inland than the charts are currently showing, with the greatest snowfalls and depths occurrings a little bit inland (say 10 - 30/40km inland), much like the recent event a few weeks ago.

cherryghost wrote: »

Yes its almost identical situation now to a few weeks ago. Crazy really, we'd pray for something like this for years and it happens twice within 3 weeks of each other. Inland constant snowfest until Monday morning from tonight onwards

Took the words right out of my mouth

Weathercheck wrote: »

Hirlam is beauty-

Wind slightly weaker this time so coastal margins may do better than last event.

Hopefully still enough kick in it to carry them into Kildare

Weathercheck wrote: »

I am expecting the first flickers from the Irish Sea around 5/6pm, all lit up from midnight through to 9am with frequent well stacked streamers, merging into continuous snowfall at times, this snow moving inland tomorrow afternoon and clearing from the east coast.

However, increasingly likely some streamers will return to parts of east coast on Sunday night and into Monday morning.

S. Dublin, Wicklow, Wexford and parts of Kildare will be the jackpot winners this time I feel.

Don't forget Waterford.

The consensus of our snap forecast contest (twelve entries) was along these lines ...

Maximum snowfall 29 cm

Maximum snow at Dub A or Casement 14 cm

First report of thunder/lightning (83% predicting some) at 1824h

Max wind gust 51 knots most likely Dublin or south coast

Min overnight temp --8.3 most likely Mullingar or Ballyhaise (and while not asked for this, probably Monday or Tuesday)

My own forecasts are either similar or a bit more extreme although not much.

Would say looking at UK radar it will be game on around 1630-1700h.

Gonzo wrote: »

if Leinster can get streamers similar to whats over in the UK all through tonight, could be some very decent coverings by the morning. The streamers do look much more widespread and beefy compared to the Beast.

Looks like snow should have begun for you, assuming you're at home.

1-3 cm snowfall forecast for Dublin and Casement up to midday Sunday.

EIDW AD WRNG 04 VALID 180001/181200 SNOW FBL 1 TO 3CM FCST =
EIME AD WRNG 03 VALID 180001/181200 SNOW FBL 1 TO 3CM FCST =