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24-03-2021, 21:04   #1
Nqp15hhu
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Risk of Low Level snow showers in Ulster and W/NW Connaught on Friday Morning/Night

A short period of colder Polar Maritime air will be in place throughout Friday until Saturday morning. The airmass will be relatively cold.

There are two windows for low level snow: Friday morning 7am-10am and Friday 6pm-9am Saturday. The coldest air will be around Friday evening. The gap in time is due to a warm sector coming across the island on Friday afternoon (early).

This is based on the snow-rain charts on Meteociel and the height of the wet bulb zero line amongst other factors.

_________________________________________________________________

Charts

850hpa:





Warm sector


Colder air flowing back in




Freezing Level:

Needs to be <500 metres for low level snow.





Warm sector: snow limited to extreme mountain tops during this part of the day.







Wet Bulb 0c Level:

Needs to be <300 metres. It is marginal during Friday daylight hours.



Dew Point:





Rain/Snow line:






So, in summarising; there is a risk of low level (close to sea level) snow in any showers in the NW, N and W of the island on Friday morning and the overnight hours. The greatest likelihood is on Friday evening.

Elsewhere, inland areas of the Midlands of ROI may see some snow showers, but the S and SE will most likely be rain below 300 metres based on the charts. Areas on the far NW and W coasts may just see sleet or hailstones.

Last edited by Nqp15hhu; 24-03-2021 at 21:08.
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24-03-2021, 21:19   #2
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Level 2? Orange?
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24-03-2021, 21:21   #3
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Level 2? Orange?
Level 3,Red
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24-03-2021, 21:21   #4
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Just a heads up, a moderator may change that tag if it isn't an official warning, our policy here is to use operational weather warning tags (even in a few cases where perhaps people didn't generally agree with them). Not to say this won't eventually merit a warning, but that's how we roll. When I say "operational" I mean met.ie rather than UKMO although reference is often made to UKMO alert levels for Northern Ireland. At the moment the met.ie website has no operational warnings in place. That could change at any time. I think it could use a level one alert already but that's not up as of 2120h.
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24-03-2021, 22:46   #5
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UKMO aviation forecast for Scotland and Northern Ireland for 6 am. Only gives snow on mountains above 1500 ft (450 m).

Quote:
Valid for 0200-1100 UTC

Met Situation Valid at 0600 UTC
MOD TO STRONG SW UNSTABLE FLOW ACROSS THE REGION.
A FIRST OCCLUSION LIES FROM N6000 E00230 TO N6200 W00130, MOV ENE AT 25KT. A SECOND OCCLUSION LIES FROM GALWAY TO OMAGH, MOV E AT 15KT. A TROUGH LIES FROM N5530 W00830 TO BARRA TO BENBECULA TO N5930 W01000,
AND A WARM FRONT LIES FROM N5630 W01100 TO N5800 W01200, BOTH MOV ENE AT 30KT.

Strong wind warning
ISOL, OCNL SEA COT, MEAN 15-20KT GUST 25-30KT. ISOL, SEA COT IN HVY SHRA OR TSRAGS, MEAN 25KT GUST 35KT.

Freezing Level
GEN 3000FT, BUT 4000FT FAR S.

Weather Conditions

Zone 1


W OF A LINE N5430 W01030 TO ISLAY TO FORT WILLIAM TO N5830 W00530 TO N5930 W00430 TO N6030 W00630, MOV ENE AT 30KT:

GEN 40KM, WITH 3-6/8CUSC 3000FT/6000-8000.
OCNL, FRQ FRONT AND TROUGH, 7KM IN SHRA OR RA, WITH 1-3/8ST 1200FT/1500, 3-6/8CUSC 1500-2000FT/6000-8000 AND 3-6/8AC 8000FT/14000.
ISOL, 3500M IN HVY SHRA OR HVY TSRA, WITH 2-5/8ST 1000FT/1500 AND 7/8CB 1500-2500FT/24000.
ISOL, FRONT AND TROUGH, 3000M IN HVY SHRA OR HVY TSRAGS, WITH 4-7/8ST 700FT/1500, 5-8/8CUSC 1500-2000FT/6000-8000, 5-8/8AC 8000FT/14000, AND EMBD CB 1500FT/24000.
WRNG: HILL FG. MOD ICE AND MOD TURB IN CLD. SEV ICE AND SEV TURB IN CB. TS. OCNL MOD TURB BLW 6000FT. SN MON ABV 1500FT.

Zone 2
E OF ZONE 1, AND NW OF A LINE KILKENNY TO DUNDALK TO DUMFRIES TO PERTH TO INVERNESS TO KIRKWALL TO N5930 E00100, MOV E AT 15KT IN S, AND MOV ENE AT 30KT IN N:

GEN 40KM, WITH 3-6/8CUSC 3000FT/6000.
ISOL, OCNL FRONTS, 7KM IN SHRA, WITH 1-3/8ST 1200FT/1500, 3-5/8CUSC 1500-2500FT/6000-8000 AND 3-5/8AC 8000FT/14000.
ISOL FRONTS, 4000M IN HVY SHRA, WITH 3-5/8ST 1000FT/1500, 3-6/8CUSC 1500-2000FT/6000-8000 AND 3-6/8AC 8000FT/14000.
WRNG: HILL FG. MOD ICE AND MOD TURB IN CLD. ISOL MOD TURB BLW 6000FT. SN MON ABV 1500FT N.

Zone 3
REST OF REGION:
GEN 40KM, WITH 0-4/8CUSC 1500-3500FT/4000-6000.
ISOL, LAN TL 10 Z, 3000M IN BR, WITH 0-5/8ST 300-1000FT/1500.
ISOL, LAN TL 09 Z, 200M IN FG, WITH 6-8/8ST SFC/1000FT.
WRNG: HILL FG. MOD ICE AND MOD TURB IN CLD.

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24-03-2021, 22:48   #6
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I did say that the greatest risk was later in the day...
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24-03-2021, 22:52   #7
Gaoth Laidir
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I did say that the greatest risk was later in the day...
Their forecast only stretches to 6 am at the moment. We'll see later updates.
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24-03-2021, 23:24   #8
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There may be sleet or hail but any snowflakes will be mixed into the showers.

Most people now want a warmer spell coz we know any cold now just is a right mess.
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25-03-2021, 01:28   #9
M.T. Cranium
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Thread is quite valid and thanks for posting it, but it should be posted without any premature warning levels added in, that was the only point being made and more of an explanation of what I knew was going to happen when moderators spotted the thread with the orange level alert added. It may well come to pass and I would be quite willing to bet they will have a yellow alert at some point, if not the orange.

We have this procedure for a reason, for one thing, it is not legal to post warnings that are not official warnings and I try to avoid doing this in my own forecasting. The government weather agencies have a prime responsibility for alerting the public, if you ever think they are not living up to that, other channels can be used such as a discussion thread here, or contacting them directly (and good luck with that). You could in theory face legal trouble and your own reputation here will suffer if you over-warn on a regular basis as some "out there" have been doing with elaborate warnings going well beyond guidance (the tabloid press being a prime example).

Another reason for the procedure is that some readers may assume the warning is in place if we add the tag, but at that point it only represents the opinion of one (and perhaps more) weather forum participant, which can lead to problems. On rare occasions we do add a statement saying that a higher level of warning may be justified, sort of jumping the gun a bit on warnings we think may be coming along soon.

Easter weekend also looking quite cold with wintry precip potential there too.

Last edited by M.T. Cranium; 25-03-2021 at 01:36.
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25-03-2021, 08:57   #10
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Quote:
Originally Posted by M.T. Cranium View Post
Thread is quite valid and thanks for posting it, but it should be posted without any premature warning levels added in, that was the only point being made and more of an explanation of what I knew was going to happen when moderators spotted the thread with the orange level alert added. It may well come to pass and I would be quite willing to bet they will have a yellow alert at some point, if not the orange.

We have this procedure for a reason, for one thing, it is not legal to post warnings that are not official warnings and I try to avoid doing this in my own forecasting. The government weather agencies have a prime responsibility for alerting the public, if you ever think they are not living up to that, other channels can be used such as a discussion thread here, or contacting them directly (and good luck with that). You could in theory face legal trouble and your own reputation here will suffer if you over-warn on a regular basis as some "out there" have been doing with elaborate warnings going well beyond guidance (the tabloid press being a prime example).

Another reason for the procedure is that some readers may assume the warning is in place if we add the tag, but at that point it only represents the opinion of one (and perhaps more) weather forum participant, which can lead to problems. On rare occasions we do add a statement saying that a higher level of warning may be justified, sort of jumping the gun a bit on warnings we think may be coming along soon.

Easter weekend also looking quite cold with wintry precip potential there too.
That’s fair enough. I assigned the warning level from the point of view that members wouldn’t be expecting it with the mild weather we have had of late.

I also wanted people to know that the mild sector was going to be in place through the middle part of the day and not to become complacent in thinking that the cold was done.
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25-03-2021, 10:13   #11
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Quote:
Originally Posted by Nqp15hhu View Post
That’s fair enough. I assigned the warning level from the point of view that members wouldn’t be expecting it with the mild weather we have had of late.

I also wanted people to know that the mild sector was going to be in place through the middle part of the day and not to become complacent in thinking that the cold was done.
Believe me they would be expecting it, I doubt there is anyone on here who does not wait for the smallest hint of cold weather warm weather or a storm.
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25-03-2021, 10:16   #12
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So we are getting the cold for Easter, as expected. Great.
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25-03-2021, 11:08   #13
pauldry
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It will be an interesting day tomorrow anyways so we might as well have a dedicated thread for it. They mentioned a potential yellow level wind event for Saturday too so March going out with a bang after the quiet weather of late.

Yes Easter cold and potentially first half of April
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25-03-2021, 11:14   #14
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CONNACHT!!!!!!
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25-03-2021, 12:02   #15
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nothing for cork city? so i don't get my hopes up for nothing
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