Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

Reckless Abandonment

Looking at the Sat and radar for the UK. Am I right in thinking they are having more of a snow shower set up than a streamer set up ? . don't see long trains of constant snow, more heavy showers.

Gaoth Laidir

Reckless Abandonment wrote: »

Looking at the Sat and radar for the UK. Am I right in thinking they are having more of a snow shower set up than a streamer set up ? . don't see long trains of constant snow, more heavy showers.

Look at the current animation here. There is a streamer train coming out from between Norway and Denmakr but it evolves into open cell convection the further it goes. This is normal in a cold outbreak.

For the Irish Sea it sort of resets and goes back to the intial stage of streamers affected by land topography.

https://weather.us/satellite/great-britain/satellite-hd-5min.html#play

cherryghost

All I see in every chart is a likelyhood of 6 degrees on a Saturday, Friday I dont see any evidence of this.

patneve2

George Sunsnow wrote: »

Wind haelly got up here now near Arklow
Gusting above 40kmh from the NE
Air temp is up to 3.8c
DP is 0c

Def gusting over 30 kt here. I wouldnt want anything above 25kt gusts tnight. Looks like the wind strength imby is the only negative aspect in an otherwise synoptic nirvana

Calibos

patneve2 wrote: »

Def gusting over 30 kt here. I wouldnt want anything above 25kt gusts tnight. Looks like the wind strength imby is the only negative aspect in an otherwise synoptic nirvana

Is the current Gusting not just the passage of the Polar Low right now?

Casualsingby

Euro4 accumulations to 6am Thursday. Sweet spots for highest totals Westmeath, Offaly my interpretation winds so strong they blow showers away too fast from East and slow down over this area. Other sweet spot for highest total is around South Cork area. Large patches of no accumulations in South East.

Tazio

May not be too technical; but I find the direction of the jet stream kinda funny/peculiar (well to my amateur eyes anyway). Certainly an unusual weather setup/pattern on our doorstep. Very interesting.

Villain

Can't post it but Harmonie even at 18:00 on Thursday has snow well into Carlow!

munsterlegend

Villain wrote: »

Can't post it but Harmonie even at 18:00 on Thursday has snow well into Carlow!

Is it over much of Munster?! Sorry I have to ask!

Villain

munsterlegend wrote: »

Is it over much of Munster?! Sorry I have to ask!

Pretty much all covered.

cherryghost

Not so much change on this afternoons GFS. If anything precip shifted a bit west and signals snow could continue in Munster and East Leinster through Friday with lighter snow countrywide

snowstorm445

Substantial snow from Friday’s system doesn’t manage to reach Dublin on the latest ICON and GFS, good amounts of snow across the south and southeast however. ICON keeps (slightly less) cold entrenched over weekend.

cherryghost

snowstorm445 wrote: »

Substantial snow from Friday’s system doesn’t manage to reach Dublin on the latest ICON and GFS, good amounts of snow across the south and southeast however. ICON keeps (slightly less) cold entrenched over weekend.

Funnily enough it shows Dublin and East Leinster in general will get more snow Friday night!

snowstorm445

cherryghost wrote: »

Funnily enough it shows Dublin and East Leinster in general will get more snow Friday night!

Yes another system seems to split off later on, some more possible on Saturday night into Sunday according to the ICON. This could go on a fair bit longer than expected.

cherryghost

Hirlam wants showers to band together for about 10 hours of continuous snow at moderate/high intensity over Dub/Meath/Wicklow tonight. Definitely around 15cm on the table when people wake up in the AM.

GFS also backs this up.

MJohnston

Low looks a bit weaker on the 12z too as well as being further west? 972 centre vs 966 on the 6z

cherryghost

MJohnston wrote: »

Low looks a bit weaker on the 12z too as well as being further west? 972 centre vs 966 on the 6z

It does but conversely it means cold is starting to tighten its grip. Snow only passes the country by lunchtime Saturday on latest model. Intensity is lower in areas yes, but over accumulation is higher.

MJohnston

cherryghost wrote: »

It does but conversely it means cold is starting to tighten its grip. Snow only passes the country by lunchtime Saturday on latest model. Intensity is lower in areas yes, but over accumulation is higher.

Sure, I guess that was my point - the earlier threats of the low disrupting the cold block are long gone, as many had suspected would happen.

MJohnston

cherryghost wrote: »

Hirlam wants showers to band together for about 10 hours of continuous snow at moderate/high intensity over Dub/Meath/Wicklow tonight. Definitely around 15cm on the table when people wake up in the AM.

GFS also backs this up.

Personally I favour the ARPEGE for precip charts, and it's not too far off backing this up also, a little less intense perhaps. 3am tonight through 9am tomorrow looks like the peak for this particular night.

Of course, my favouring of the ARPEGE largely comes from its performance with all the north-westerlies this year, so I have no idea how well it'll handle the lake effect easterly action.

cherryghost

MJohnston wrote: »

Personally I favour the ARPEGE for precip charts, and it's not too far off backing this up also, a little less intense perhaps. 3am tonight through 9am tomorrow looks like the peak for this particular night.

Of course, my favouring of the ARPEGE largely comes from its performance with all the north-westerlies this year, so I have no idea how well it'll handle the lake effect easterly action.

That's fair enough logic, but I see HIRLAMs been spot on for Wicklow, Carlow and Wexford this afternoon where ARPEGE had very little precip. We'll see later how it rolls out anyway

kod87

Since the thursday night event is my only decent chance of snow here in tipp, I must say I'm disappointed that some models seem to be reducing the precipitation and extent of that low, this may very well end up being very "meh" for me in the south midlands. We shall wait and see before things get slightly milder and messier on saturday.

KingdomRushed

kod87 wrote: »

Since the thursday night event is my only decent chance of snow here in tipp, I must say I'm disappointed that some models seem to be reducing the precipitation and extent of that low, this may very well end up being very "meh" for me in the south midlands. We shall wait and see before things get slightly milder and messier on saturday.

Be careful about talking down the precipitation potential of this on here. I agree there is a clear trend toward it becoming less potent but also colder air holding on so it’s taking with one hand giving with another. Dublin is not going to see another 1982, that’s a hill I am willing to die on. In fact I can’t see 8 cm by Friday for city. Waterford might see a lot more

Artane2002

How good is the WRF-NMM? It didn't do awful during the northwesterlies/westerlies this year if I recall correctly?

kod87

Deedsie wrote: »

Nowhere in Tipp is in the Midlands. Midwest?

Surely the midwest is also the midlands, hence the MID part. Would that make kilkenny the mid east (nobody says that), so I think south midlands is a better description of my general location especially since I am in the eastern part, almost county kilkenny.

MJohnston

Artane2002 wrote: »

How good is the WRF-NMM? It didn't do awful during the northwesterlies/westerlies this year if I recall correctly?

From my tracking of performance it's at an E-grade level for both precip location and depth. Not great, but again these are different precipitation conditions, perhaps very different, from those other snow events, so I don't know how applicable those grades might be. ECM and ARPEGE are my best rated (B grade or so), HIRLAM is a mid-level performer (D grade), with ICON and GFS being worst (E for location, F for depth).

NAGDEFI

kod87 wrote: »

Surely the midwest is also the midlands, hence the MID part. Would that make killkenny the mid east (nobody says that)

Whether you're north or south Tipp and elevation above sea level could make all the difference late Friday early Saturday as regards snow or sleet/rain. Depending on how far north the milder uppers come north. All too far away to forecast at this stage. Maybe nowcast Early Saturday. Cold air could tuck in again as the front moves back south.

lucernarian

cherryghost wrote: »

That's fair enough logic, but I see HIRLAMs been spot on for Wicklow, Carlow and Wexford this afternoon where ARPEGE had very little precip. We'll see later how it rolls out anyway

I've been looking at radar precipitation over Louth (which Hirlam had flagged) but in fact there's been little or nothing falling there today when I asked earlier. We should track how precipitation actually falls vs these models today, could be worth knowing for the future.

MJohnston

As an aside - it would be great if when we're taking about "less" or "more" in terms of snowfall or temps or whatever, if we could avoid the relative comparisons and be more absolute?

For example, if people in the general thread hear someone talk about a downgrade in intensity, there's a tendency to think that means no snow at all, instead of just hypothetically a downgrade from a historic level of snow to just a once in ten years level of snow. We can avoid this confusion with more specificity!

lucernarian

MJohnston wrote: »

As an aside - it would be great if when we're taking about "less" or "more" in terms of snowfall or temps or whatever, if we could avoid the relative comparisons and be more absolute?

For example, if people in the general thread hear someone talk about a downgrade in intensity, there's a tendency to think that means no snow at all, instead of just hypothetically a downgrade from a historic level of snow to just a once in ten years level of snow. We can avoid this confusion with more specificity!

Don't feel strongly on this but I'm inclined to disagree. We shouldn't place numbers on things without reasonable evidence to do so, right? Or are you talking about current reports and the like?

That's then an issue for the general thread, not for here - it's their lookout if they can't use their own sense.

Maybe mentioning trigger words like "downgrade" or "upgrade" is the bigger problem if any. Temperatures are themselves relative (and unfortunately for us, the differences in marginal situations like Friday are such that "colder" can mean going from +0.5 to -0.5 when the band arrives, completely changing the meteorological outcome. It ends up being disingenuous when there are cliffhangers to deal with.

Met Éireann get around this by issuing practically no forecast for Friday...

Supercell

EIDW 17:00 taf encouraging for tonight :

TAF EIDW 271700Z 2718/2818 07015KT 9999 FEW012 SCT020 BKN035
PROB30
TEMPO 2718/2723 3000 -SHSN BKN010 SCT018CB
TEMPO 2800/2812 06016G28KT 2000 SHSN BKN010 BKN015CB
PROB30
TEMPO 2800/2808 1000 +SHSN BKN005
BECMG 2810/2812 08020G35KT
PROB30
TEMPO 2812/2818 3000 -SHSN BKN010 BKN018CB

In a nutshell, kicking off good and proper around midnight in Dublin area with a 30% chance of day after tomorrow conditions