Cold Spell - Feb 7th to 13th 2021 - Technical Discussion

There's a dewpoint spread of up to 11.1 degrees in the east today (Casement temp 3.9, dewpoint -7.2 C). Perfect February weather. Only in the far south is it more close to saturated. WBT at zero or below over much of the midlands, north and east.

Gaoth Laidir wrote: »

I haven't noticed such a pattern before and I've never seen it mentioned anywhere. Maybe it has something to do with statute miles, which is what is used for all visibilities in the USA METARs. 4000 and 1200 m would be 2.5 and 0.75 statute miles, respectively, which seem round numbers that would be reported in US METARs. Of course, aviation uses nautical miles for everything else, so here you have the confusing mix of units again.

Or else it's just coincidence. I see Aldergrove's TAF reports 5000 and 2000 metres (3.1 and 1.25 S.M.).

TAF EGAA 121104Z 1212/1312 12016KT 9999 FEW030
TEMPO 1212/1312 13020G32KT
BECMG 1308/1311 SCT007 BKN012
TEMPO 1308/1312 5000 -SN
PROB30 TEMPO 1309/1312 2000 SN BKN006=

I've seen Cb bases forecast at different heights than just 1800 ft, but given our climate, 1800 ft is probably the most common. That would be a 4.5-degree dewpoint depression (multiply dewpoint depression x 400 to estimate cumulus base height agl).

Maybe my imagination so. Thanks.

Nqp15hhu wrote: »

I’m just asking why the rapid rise in temps despite no change in synoptic situation from yesterday.

Just less cloud, I reckon. You got a bit more solar radiation in the hour up to midday than you did yesterday. Plus there's less snow coverage over NI today in general.

WRT to tonights likely Non Event for the East, I've made peace with it (at the risk of sounding melodramatic ). My Ninja 5cm in January that lasted 3 days (including the day it fell) meant Winter 2021 wasn't a total write off for me. I'll be happy enough if Spring bloomed and this was the last of the deep cold we got. Equally though, I'll be happy if we got another bite of the Cold/Snow Cherry late February or early March. Unlike others I've never been chasing long lasting deep cold and snow. A few days with a few inches on the ground is more than enough to make me very happy so the limitations to longevity of Late Feb or March Snow are of no concern to me really.

The fact that the models show nothing of interest out to day 10 doesn't have me throwing in the towel either. Day 10 takes us to the 22nd of February. The 2018 Snow didn't get going till the 26th or thereabouts. In other words, back in 2018 the Big Event wasn't showing up on the models on the 12th either. I'll only call it quits if theres nothing showing on the models first week of March for Paddy's Day. :D

Current airport warnings.

Dublin EIDW AD WRNG 01 VALID 130500/131000 SNOW FBL LESS THAN 1 CM FCST=
Casement EIME AD WRNG 02 VALID 130400/131000 SNOW FBL LESS THAN 1 CM FCST=
Knock EIKN AD WRNG 01 VALID 122300/130800 SNOW FBL 3 to 5 CM FCST=

The UKMO aviation chart for 00Z has that occlusion broken up and lying across western Connacht, moving NE at 10 kts, while the warm front is just into western Kerry, moving NE at 15 knots.

The weather described for west of a line Sligo-Waterford is widespread moderate, isolated heavy rain. For eastern Connacht it is light/moderate rain, but heavy snow on mountains and locally isolated heavy snow or freezing rain at lower levels.
Elsewhere (NE of a line Sligo-Waterford), isolated light rain/sleet/snow.

Gaoth Laidir wrote: »

What a Wicklow shadow!

This cold spell summed up in a nutshell

The Met Eireann warning reads
Snow accumulations of 5 cm possible (more on higher ground), accompanied by fresh to strong southeast winds.

There Criteria

STATUS YELLOW Snow/Ice
3cm or more in 24 hours

STATUS ORANGE Snow/Ice
3cm or greater in 6 hrs
5cm or greater in 12 hrs
10cm or greater in 24 hrs

Parts of the northwest and north based on there Criteria and model outputs including the Met.ie Harmonie model should be under a Orange warning.

AuntySnow wrote: »

I do
But are you a night owl ?

The timing could not be worse! This has been a very painful cold spell:o

Let's hope it ends in a flurry!