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

Mullaghteelin

GFS data for Dublin Airport in a handy chart
EIDW

Shannon Airport:
EINN

The GFS usually over estimates the dew points by a degree or two in Dublin, so keep that in mind.

M.T. Cranium

The ECM went in a different direction than GFS or GEM which had downplayed the low coming up from Biscay, instead ECM brings the centre right into the southeast of Ireland and loops it back around to the southwest, but slowly pushing the cold air back north.

If that verified, heavy snow would change to rain across much of the country over the weekend of 3rd-4th. A compromise between the models would bring the loop back to last night's scenario. I wouldn't consider this outcome locked in at 144-168 hours and other guidance that much different.

Snowfall potential overall for the cold spell is still spread over a large range. For Dublin and much of central Leinster, I think the 25% intervals are 5 cm (lowest prob), 12 cm (25%), 25 cm (50%), 40 cm (75%) and 60 cm (max). For Cork I would go with slightly lower numbers, maybe 4, 10, 20, 30 and 45.

Franz Von Peppercorn

M.T. Cranium wrote: »

The ECM went in a different direction than GFS or GEM which had downplayed the low coming up from Biscay, instead ECM brings the centre right into the southeast of Ireland and loops it back around to the southwest, but slowly pushing the cold air back north.

If that verified, heavy snow would change to rain across much of the country over the weekend of 3rd-4th. A compromise between the models would bring the loop back to last night's scenario. I wouldn't consider this outcome locked in at 144-168 hours and other guidance that much different.

Snowfall potential overall for the cold spell is still spread over a large range. For Dublin and much of central Leinster, I think the 25% intervals are 5 cm (lowest prob), 12 cm (25%), 25 cm (50%), 40 cm (75%) and 60 cm (max). For Cork I would go with slightly lower numbers, maybe 4, 10, 20, 30 and 45.

That doesn’t include the Friday night potential snow (and potential rain) event, right?

M.T. Cranium

All included in the estimates ... being conservative, I could imagine even higher totals over five days but this is what I am going to forecast.

Kermit.de.frog

ECM 12z snow depth by Friday in inches. Don't take too seriously

https://weather.us/model-charts/euro/ireland/snow-depth-in/20180302-1200z.html

snowstorm445

Kermit.de.frog wrote: »

ECM 12z snow depth by Friday in inches. Don't take too seriously

https://weather.us/model-charts/euro/ireland/snow-depth-in/20180302-1200z.html

And they said the ECM was a bad run. :eek: I'd happily take that even it were to thaw soon afterwards.

Artane2002

I know it's impossible to predict at the moment but do you think that low ploughing into the southeast bringing milder air is the likely outcome? I've heard that historically, models tend to underestimate how hard it is to shift cold so does that mean it is more likely than not that the low tracks further south than predicted?

Villain

The metrogram for ECMWF for Kilkenny is the best I’ve ever seen, max below 0c with light precip showing from Tuesday afternoon up to as far it goes Thursday Afternoon.

After that is FI but interesting to see how it looks Monday

George Sunsnow

Artane2002 wrote: »

I know it's impossible to predict at the moment but do you think that low ploughing into the southeast bringing milder air is the likely outcome? I've heard that historically, models tend to underestimate how hard it is to shift cold so does that mean it is more likely than not that the low tracks further south than predicted?

Best guess and (that’s if it makes it) is it will stall somewhere

ZX7R

With the jet stream smashed and part of it down towards Spain direction, how is it possible for the low to move north against the flow of the jet in that area.
Thoughts anyone

snowstorm445

Latest ECM run a good bit milder than its ensemble mean apparently (although upper temperature still rises overall).

BLIZZARD7

Cold air is more dense and harder to shift, I fully expect the models to be far to progressive with the Atlantic today. Watch that change in the next 48 hours.

Artane2002

I'm a novice (though I've been model watching for 2 years!) so take this with a pinch of salt but what I think will happen is that the low won't quite make it up here. Remember, it will be bitterly cold here so that cold should weaken the system and it won't be able to get very far north. I think something similar happened in March 2013? In fact, that front that gave some snow in the east a few Mondays was almost killed by the cold. The cold predicted for this week is far more intense so should we not see something similar this time?

Just a reminder that I'm a novice and I'm not sure if what I'm saying is 100% accurate so correct me if I'm wrong please. Thanks in advance 🙂.

lucernarian

BLIZZARD7 wrote: »

Cold air is more dense and harder to shift, I fully expect the models to be far to progressive with the Atlantic today. Watch that change in the next 48 hours.

In what way is there too much progression? By extension if that aspect were true, we'd also miss any low hitting us from the southeast by the end of the week.

BLIZZARD7

lucernarian wrote: »

In what way is there too much progression? By extension if that aspect were true, we'd also miss any low hitting us from the southeast by the end of the week.

I'm thinking it's more likely to completely miss us than blow mild air up across the country, a subsequent low might do that but I doubt the first one will. What we want is the inbetween solution where we are left under the colder air and the low nudges up close enough and stalls dumping copious amounts of snow on us and it not immediately melting as the low pulls back south east - that is in a perfect world though so we will have to see how it plays out.

mirrorwall14

Can I just check Model Run "actual" times?

00z is 330
06z is 930
12z is 1530
18z is 2130

Where do the other models output times slot into the day?

sdanseo

mirrorwall14 wrote: »

Can I just check Model Run "actual" times?

00z is 330
06z is 930
12z is 1530
18z is 2130

Where do the other models output times slot into the day?

That's correct for GFS and a few others

ECM only runs twice a day and takes longer to filter through, coming at 1830 and 0630 ish

snowstorm445

mirrorwall14 wrote: »

Can I just check Model Run "actual" times?

00z is 330
06z is 930
12z is 1530
18z is 2130

Where do the other models output times slot into the day?

That's for the GFS. The ECM comes out at 6am and 6pm, UKMO around the same times as the GFS (at 3:30am and pm), the ICON slightly beforehand (about half an hour I think).

snowstorm445

Snow piling into the south coast Thursday night on the latest ICON.

Artane2002

I think the UKMO 12Z comes out around 3:50pm. If that's the case then one can assume the 0z comes out at 3:50am.

sdanseo

ICON is having a very funny run. It's showing rain under -12 uppers on Wednesday.

Reckless Abandonment

sdanseo wrote: »

ICON is having a very funny run. It's showing rain under -12 uppers on Wednesday.

Does ICON not only show precipitation, not type of precipitation.

gabeeg

Reckless Abandonment wrote: »

Does ICON not only show precipitation, not type of precipitation.

No, sure it's showing precipitation type in those very charts

adam240610

Reckless Abandonment wrote: »

Does ICON not only show precipitation, not type of precipitation.

There's snow shown in that chart on the upper right corner.
Does not look right at all

sdanseo

Reckless Abandonment wrote: »

Does ICON not only show precipitation, not type of precipitation.

No, I thought it had 2 types of chart, the "Précipiations" (not showing type) and the "Type Précip." (red and blue)

But the first chart with blue/green colour schemes also has the white hatch markings and corresponds with the red/blue "type precip" chart.

It's a bit odd. There is zero chance that anything falling out of the sky when it's -2 on the ground can be rain, surely?

For clarity, this is the ICON-EU as opposed to the ICON/DWD

gabeeg

I think it has shat itself

Not to worry

Nettle Soup

The RTE forecast sounded good but I noticed it had heavy rain down for the west on Thursday in the final snapshot of the week ahead.
That must be freezing rain surely?

sdanseo

There's something just doesn't look right about the low coming from the south as shown on GFS.

It's intense enough, but moving very slowly and just too perfect of a circle. Just looks completely wrong.

Soccarboy11

GFS looks as if its going a similar way to the 12Z ecm?

Daniel2590

The low seems to be coming up from the south, sitting over us for a while and then heading back out to the Atlantic?