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

DOCARCH

Mod Note: Moved some posts into the general chat thread.

Need to keep this thread focused on technical discussion only and clear for emergency services.

tbayers

M.T. Cranium wrote: »

Main points of interest:

Today's sleety mix idea would only be for first hour or two near shoreline, would expect all change over to snow and starts as snow more than a km or two inland ... could get heavier this afternoon and evening as even colder air arrives aloft.

Extreme streamer potential on Wednesday with -14 C 850s, strong east-northeast surface gradient and lowest thicknesses (sub 504 north of Dublin for a time).

Blizzard like storm Thursday into Friday ... the uppers relax as the low zips past to the south (or loops and heads east still an option), but not enough to make much of a phase change, the more likely scenario is for the heavy snow to move north due to rotation of the occlusion with the flow over southern counties still coming from southeast and mixing cold air with slightly warmer maritime flow, rain would only be likely near the coast south of about Gorey around all of the south coast to about Tralee. Inland at any appreciable elevation, snow tapers to flurries and sleet in south (even on GFS and ECM scenarios).

Very strong east-southeast winds for south Cork and much of Kerry with downsloping acceleration for places like Tralee and Dingle.

Various models introduce concepts of second or third attempt lows pushing at the block, no reason to think they will be any more successful than first one unless they track well north and even then they seem to get surrounded by cold air and cut off from the warmth of Biscay waters fairly quickly.

Still no real clarity but many signs of a severe snowfall event that is not immediately washed away by melting and rainfall, and which could continue across parts of the north and even central counties into Friday and even Saturday.

I think the most immediate concern is how extreme Wednesday is looking, could have snow and blowing snow with -5 C temps and -10 or lower windchills. That parcel of air is still back over Poland whereas later today you could look at northeast England for guidance, heavy snow reported around Newcastle and border regions.

The show is about to begin, this has just been the orchestra tuning up.

So is it a case now we are definitely going to see snow Thursday evening on the South and South East coasts. Or are we still debating whether we will see a significant snow event or not on Thursday night?

ninebeanrows

Hirlam has 10-15 widely across Greater Dublin by lunchtime tomorrow, few sweet spots with 15-20

M.T. Cranium

tbayers wrote: »

So is it a case now we are definitely going to see snow Thursday evening on the South and South East coasts. Or are we still debating whether we will see a significant snow event or not on Thursday night?

Nothing is ever definite in weather but this seems hard to avoid unless the low just falls apart and doesn't come anywhere near Ireland, in which case you would still have local snowfall potential from streamers. I would rate it 80% likely.

JanuarySnowstor

M.T. Cranium wrote: »

Nothing is ever definite in weather but this seems hard to avoid unless the low just falls apart and doesn't come anywhere near Ireland, in which case you would still have local snowfall potential from streamers. I would rate it 80% likely.

Cork being right on the coast I'm not convinced.
I think it could quickly turn to sleet rain Thursday night as the wind goes onshore.
I very much hope I'm wrong

lucernarian

igCorcaigh wrote: »

ICON proving its worth recently.

We'll see on Friday when the weather is actually happening...

JCX BXC

JanuarySnowstor wrote: »

Cork being right on the coast I'm not convinced.
I think it could quickly turn to sleet rain Thursday night as the wind goes onshore.
I very much hope I'm wrong

That's not what the models are suggesting, if this occurs it won't occur until you've a nice fall anyway!

ninebeanrows

EC plumes still showing good spread from Saturday this morning!!

More consensus for Friday to be full snow event though.

Apologies but this is looking at the plumes for Dublin so IMBY centric, but i can't check them all.

jdcv94

lucernarian wrote: »

We'll see on Friday when the weather is actually happening...

I remember reading on here a few days ago that ICON was one of the unreliable models right? ECM/UKMO are the main ones to look at.

igCorcaigh

jdcv94 wrote: »

I remember reading on here a few days ago that ICON was one of the unreliable models right? ECM/UKMO are the main ones to look at.

It was the first to pick up on the Easterly

Elmer Blooker

Its looking like the country will end up covered in an area of slack low pressure with a rise in temperature as the easterly gets cut off. Reminding me more of 1987 than 1982 at the moment even if '87 wasn't a frontal event.
For all the talk lately of the "sun being too strong" for snow to lie it will a bog standard cloudy low that will bring the thaw.
I doubt if we will see even clear skies at night. Tragic that the Scandy high collapsed like a ton of bricks!



Still, not a bad forecast from M.E.

THIS WEEKEND: A little less cold, with wintry showers becoming more scattered. The emphasis will all the while be on the southern and eastern counties, with onshore winds in these parts.

SeaBreezes

igCorcaigh wrote: »

It was the first to pick up on the Easterly

And the first to pick up on the low, and it's eventual progression. The other models have been following it this week.

bpmurray

Quick question for the experts & enthusiasts in this area. I use Windy (windy.com) for my wind predictions for fishing, and find it's generally reasonably accurate. Given the imminent destruction of all life on this planet by Emma & the Beast, I was looking at a part of it I usually don't pay much attention to, the "new snowfall" function. This allows for selection of models based on ICON, ECMWF and GFS which suggest a total fall of 29.8cm, 55.5cm and 27.3cm respectively. Which of these is most likely to be correct, or would that be an Ecumenical Matter?

Danno

bpmurray wrote: »

Quick question for the experts & enthusiasts in this area. I use Windy (windy.com) for my wind predictions for fishing, and find it's generally reasonably accurate. Given the imminent destruction of all life on this planet by Emma & the Beast, I was looking at a part of it I usually don't pay much attention to, the "new snowfall" function. This allows for selection of models based on ICON, ECMWF and GFS which suggest a total fall of 29.8cm, 55.5cm and 27.3cm respectively. Which of these is most likely to be correct, or would that be an Ecumenical Matter?

It's hard to know which one will be correct - some models perform better than others, however 30-55cm of snow is crippling, eitherway. It will be interesting re-evaluating the performances of each model after this event, it will serve as a reliability litmus test for future events.

KingdomRushed

The intensity of precipitation for Thursday into Friday has dropped off on 6z GFS, with a more broken and moderate profile now and looking less blizzard of the century. Waterford and Wexford to get it worst. It is looking like all to fall as snow however.

davidsr20

KingdomRushed wrote: »

The intensity of precipitation for Thursday into Friday has dropped off on 6z GFS, with a more broken and moderate profile now and looking less blizzard of the century. Waterford and Wexford to get it worst. It is looking like all to fall as snow however.

Here we go again. How can some people hype it up and then others pull the Matt out again.

Mickeroo

davidsr20 wrote: »

Here we go again. How can some people hype it up and then others pull the Matt out again.

He's talking about a specific model.

KingdomRushed

davidsr20 wrote: »

Here we go again. How can some people hype it up and then others pull the Matt out again.

Don't worry it's still loads and loads of snow, sorry if you misinterpreted it. It's just the precipitation intensity is somewhat more moderate than what was progged 24 hours ago, no yellow shading on the precipitation maps this morning.

jdcv94

KingdomRushed wrote: »

Don't worry it's still loads and loads of snow, sorry if you misinterpreted it. It's just the precipitation intensity is somewhat more moderate than what was progged 24 hours ago, no yellow shading on the precipitation maps this morning.

Follow MT's forecasts, following each model run by run will show you all kinds of stuff. The models are struggling with this unique flow and I wouldn't trust anything forecast after Thursday at the moment.

Jpmarn

My reading on the situation on Thursday night into Friday is persistent snow is set in from the south. It is looks like that there be near blizzard conditions over the southern half of the country as Storm Emma interacts with the bitterly cold airmass. This snow will work up northwards by Friday morning. The snow in the south will tend to change back to rain in the southern half country before it clears off during Friday afternoon. It looks like snowfall will persist for much of Friday in the northern half of the country. Any gale force winds on Thursday night into Friday morning should abate by Friday afternoon.

Rebelbrowser

KingdomRushed wrote: »

The intensity of precipitation for Thursday into Friday has dropped off on 6z GFS, with a more broken and moderate profile now and looking less blizzard of the century. Waterford and Wexford to get it worst. It is looking like all to fall as snow however.

Depends what site you look at unfortunately. On meteociel the GFS representation of snow is always lower resolution (it seems to me) than on other sites. For example the 6z GFS on weatheronline shows it turning to rain from the early hours of Friday onwards in Munster. See below. Like januarysnowstorm I see us in Cork getting a snow to rain event sadly. What we want down here is what the rest of ye don't, namely for this low to stay well south and for only its northern most parts to affect (south) Ireland.

ninebeanrows

6z Harmonie shows between 12 and 24mm of liquid across Greater Dublin through from 00z to 15z

Do the math! Kildare and west Dublin the sweet spots as showers slow down.

cherryghost

GFS is showing pretty much a full 24hrs of non stop heavy snow Thurs eve to Fri eve along the East. For the rest of the country, heavy snowfall from midnight until early morning before moderating. Later in the day sleet/rain to follow from the south but slow to progress, might not see rain elsewhere until Saturday.

- GEM wants to keep the band heavy over Thurs night but a quicker move north and clearance by Lunch Friday
- UKMO wants the front to stall. It's definitely the most optimistic in terms of accumulation and keeping the cold through the weekend.
- ECM is middling between UKMO and ECM.
- NAVGEM is similar to UKMO, a stall and dumping countrywide before attempted clearance on Saturday
- ICON is similar to GFS intensity this morning but wants dumping across Munster and East Leinster but wants a stall as it hits the cold front.
- ARPEGE wants heavy snow to go further inland and further north but a quick depression into sleety rain by Friday lunchtime countrywide
- FIM is a cold lovers delight. Stalling system. Heavy snow Thurs night into Saturday morning.

Such deviation now. Either way we seem to be guaranteed heavy snow for a period.

Oneiric 3

Latest infrared satellite image.



The beast is drawing ever closer.

munsterlegend

cherryghost wrote: »

GFS is showing pretty much a full 24hrs of non stop heavy snow Thurs eve to Fri eve along the East. For the rest of the country, heavy snowfall from midnight until early morning before moderating. Later in the day sleet/rain to follow from the south but slow to progress, might not see rain elsewhere until Saturday.

- GEM wants to keep the band heavy over Thurs night but a quicker move north and clearance by Lunch Friday
- UKMO wants the front to stall. It's definitely the most optimistic in terms of accumulation and keeping the cold through the weekend.
- ECM is middling between UKMO and ECM.
- NAVGEM is similar to UKMO, a stall and dumping countrywide before attempted clearance on Saturday
- ICON is similar to GFS intensity this morning but wants dumping across Munster and East Leinster but wants a stall as it hits the cold front.
- ARPEGE wants heavy snow to go further inland and further north but a quick depression into sleety rain by Friday lunchtime countrywide
- FIM is a cold lovers delight. Stalling system. Heavy snow Thurs night into Saturday morning.

Such deviation now. Either way we seem to be guaranteed heavy snow for a period.

I think you need to amend ECM one!

pistolpetes11

Ok Folks let try and keep it on Topic in here please

Gaoth Laidir

Latest snow-depth reports at 10 am. The 34 cm at Bingley is erroneous, ignore it. F means patchy cover .

Oneiric 3

Latest Td (Dew Point) temps.



-6.7c in Valentia and -6.6c at Mace Hd. Amazing how even a small bit of land track can dry out the air and bring those values down along the west coast.

sideswipe

I'm thinking Sally Gap will impassable for a week or two:eek:

Gaoth Laidir

Current wet-bulb temperatures, showing the warm sector through the north and also western Scotland. The real cold comes in behind it later.