Snow and forecasts.

ninebeanrows

Think it's about time to open up a thread to deal specifically with the upcoming cold spell which is now supported universally by the NCEP models.

St. Patricks Day itself looks like being a mixed day, it will dawn fine and probably sunny countrywide with temperatures reaching a very mild 14c in the south towards midday but cloud will increase in the north with rain towards nightfall, this will be the first signal for a change to much much colder weather.

From early Sunday Arctic air will dig south and temperatures will notably decrease with figures countrywide no more than 4 or 5c by evening.

Heavy showers will move south on a stiff northwesterly wind and it will feel bitter, showers will begin to turn to snow by afternoon and appreciation of snow is likely by nightfall almost anywhere but expecially in the north.

There is a chance of more organised features moving south overnight Sunday and into Monday as the deeply unstable Northerly winds push down extremely cold air. This is when there is a decent chance of a polar low feature perhaps forming west of Scotland and tracking down the Irish sea.

Nightime temperatures will be low as low as -6c in places, with daytime temperatures rising to 4 or 5c in the sunny spots but dipping to 1 or 0c in the heavy snow showers.

The liklthood is for shower activity to die down during Wednesday but for this to remain cold with harsh ground frosts continuing

All models are onboard this evening and the cold spell looks almost set in stone.

GFS @ 96hrs http://www.wetterzentrale.de/pics/Rtavn961.png
UKM @ 96hrs http://www.wetterzentrale.de/pics/Rukm961.gif
ECM @ 96hrs http://www.meteociel.fr/modeles/ecmwf/run/ECM1-96.GIF?15-0

So wrap yourself up warm for a journey into mid-winter from Sunday

Supercell

Devil is gong to be in the detail.
No doubt northern and northwestern areas will see a lot of showers and lying snow at elevation.
I suspect you and Snowbie might do well out of this WC too, unless we get a proper polar low then all bets are off.

Personally I'm hoping for an possible October 2003 scenario here, could do rather well out of such an event.

Snowbie

Id be surprise if we didnt get a PL forming in this type of setup,im more confident of it than seeing snow showers tbh.I think we need to be very close to the time to forecast troughs etc.No doubt there will be a few but affecting only Northern areas unless something happens to swing in from the Irish sea.Bideing my time again for this one.

Incidently 2 of the heaviest snowfalls that I remember here happened in march.
I can remember 6 inches plus here on one paddies day when I was a kid.
(Longfield -you can only imagine how much there was in annamoe that time! given what fell down here)
That was on a north north easterly I think and probably an Irish sea travelling polar low.

Thats just to remind ye that lying snow near the coast is possible in mid to late march.
That snow stayed for almost a week by the way and was long before WC was born.

lucernarian

It's not brilliant for my patch though:p

I need an NNE or further eastwards to get a long distance sea path. Northwesterlies never ever gave significant snow here in my lifetime. Recent winters have taught me that northwesterlies mean troughs of light snow/hail, cold, bright days and if there is any proper snow, it lasts 10 minutes.

Met.ie have the synopsis generally correct in my humble opinion, but they don't leave the possibility of organised snow for the most northern parts of Ireland. I think that after Sunday, humidity will be a bit too low and the country as a whole will have been cooled down, blunting the edge of the convection.

With the cold upper temps, I'll speculate that this combines to give light snow/graupel showers for many areas. It looks like Munster will be left out of this party.

IF the wind can get a shift northeastwards, then the east coast will have a high risk of heavy snow showers, over a warm sea like that with low thicknesses and geopotential heights.:D But that won't happen. Mabye a polar low on Sunday night will bring an acceptable amount of snow;)

Supercell

Tristrame wrote:

Incidently 2 of the heaviest snowfalls that I remember here happened in march.
I can remember 6 inches plus here on one paddies day when I was a kid.
(Longfield -you can only imagine how much there was in annamoe that time! given what fell down here)
That was on a north north easterly I think and probably an Irish sea travelling polar low.

This kind of post is not helping my blood pressure levels Tristrame!!
I'm rather excited about this, reckon it could be an all or nothing type thing here (huge snowfall from a polar low) or bugger all snow while WC and Snowbie go nuts about blizzards where they live robbing my snow :eek:

Supercell

To_be_confirmed wrote:

It's not brilliant for my patch though:p

Not brilliant like if you lived in Antrim, Armagh or Donegal or somewhere in northern areas of the Island but think you will see more stuff than us here in Dublin and Wicklow, unless there's a polar low (which to be honest is a low probability).

I reckon you will see snow showers, and if they happen over night, some early morning snow cover.

lucernarian

I'm glad you posted about the polar low possibility, I just came across this chart which might brighten your spirits:

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?time=2007031512&field=Sea+Level+Pressure&hour=084hr

Enjoy:)

Snowbie

Now thats a chart if it where to be real,there is a less than a 24hr forecast for these PL.Conditions have to be right over open water and unfortunately we are still outside of a defo for snow atm(realistically)Excellent chart though,spells disaster to the east for transport.

Supercell

Snowbie wrote:

Excellent chart though,spells disaster to the east for transport.

Now don't be putting a curse on it Snowbie, disastrous snowfall = us snow fans get a snow day and get to run amok making snowmen and acting like we forgot our age (at least that's the case with me !).

ninebeanrows

Nah i think a polar low = warmer upper air temps = rain or sleet

I think a really cold northerly with some troughs would be nicer, although these little lps coming down on the flow could be brilliant it brings the added risk that we see rain! rather than a few showers of heavy snow!

Supercell

Lol WC, nice

Have you planted those rulers in the garden yet?

ninebeanrows

18z GFS suggesting widespread snow across Ireland overnight Sunday with a distrubance and possible polar low moving south as 500hpa air of -40c and lots of precip rolls down the country:D

http://www.wetterzentrale.de/pics/Rtavn841.png
http://www.wetterzentrale.de/pics/Rtavn8417.png
http://www.wetterzentrale.de/pics/Rtavn844.png

ninebeanrows

Snow Snow Snow

http://www.wetterzentrale.de/pics/Rtavn964.png

Snowbie

Longfield wrote:

Now don't be putting a curse on it Snowbie, disastrous snowfall = us snow fans get a snow day and get to run amok making snowmen and acting like we forgot our age (at least that's the case with me !).

Refering to transport chaos due to lots of snow.Im overdue a snowday,hell i want two.

Weathecheck wrote:

I think a really cold northerly with some troughs would be nicer, although these little lps coming down on the flow could be brilliant it brings the added risk that we see rain! rather than a few showers of heavy snow!

Id prefer the continuous stuff myself.Showers are alright by night but by day that big bright light in the sky would be a nuicance melting our snow.
If a PL ran down the Irish sea it would offshore the winds which are perfect for us and Mothman and Tristrame for snow.Chances of snow settling would increase.

ninebeanrows

Becoming windy on Saturday night with heavy showers of rain and hail developing in the west and north. Very cold and very windy on Sunday with strong, gusty northwest winds. Widespread heavy showers of rain, hail and sleet. Highest temperatures of just 4 to 7 degrees. Continuing very cold and windy on Monday more wintry showers of rain, hail and sleet. Snow is possible on high ground in parts of Ulster and Connacht. Still very cold on Tuesday, but not as windy or as showery

You have to laugh!!!

I always thought sub-zero dewpoints, temps of less than 3c, 850's down to -8c and thicknesses of 520dam would = snow but i must be wrong... or am i?

Terrible forecast from Met Eirean, how they think there is going to rain in the showers on Monday and late Sunday is actually beyond me!!

ninebeanrows

Some sexy Fax Charts

arctictree

Its all still lookin good for late Sunday/Monday.

Normally when met say 'highest temps of 4 - 7c' it means the average daytime temp would be around 3 and would drop a couple of degrees in the showers. Coupled with night time temps, we could see some good snowfalls, if the precip is around....

A

Snowbie

But if avg temp is around 3 maximum temp will be higher in sunshine around 5 or 6c for low level areas not good for snow.

Weathercheck wrote:

Terrible forecast from Met Eirean, how they think there is going to rain in the showers on Monday and late Sunday is actually beyond me!!

Its a wintry forecast WC but cautious,and they are not that far wrong either for now.As temperatures go you cant call them this side of the weekend for the back end of the weekend and is why they have put a wintry mix instead of snow.
If we get any showers(thats if the troughs from north make it this far south) they will start off as a sleety type and in the heavier ones will gradually turn to snow but in sunshine temps will get up to at least 5c maybe 6c and on sunday and monday sunshine will be in abundance.Its your third fax chart(mon 12utc) that has caught my attention with a front moving down from the north on a course with us for the evening.This is the one to watch and the wicklow mtn lads should take note of this if this comes off.

Snowbie

Snowbie wrote:

But if avg temp is around 3 maximum temp will be higher in sunshine around 5 or 6c for low level areas not good for snow.

With dewpoints several degree's below freezing and heavy precipitation in an airflow with thicknesses as low as 516 dam,you most likely will get snow at sunshine temps of 5 or 6c as that will not be the ground air temp that is under the shower and it's going to be several degree's colder in the layers of athmosphere down through which the precip will be travelling very fast.
Too fast in heavy showers for most of it to turn to rain.

I'd imagine you could have showers that start as sleety rain but quickly in the middle of the shower fall as snow.
They will be all snow I think on the high ground.

Its a wintry forecast WC but cautious,and they are not that far wrong either for now.As temperatures go you cant call them this side of the weekend for the back end of the weekend and is why they have put a wintry mix instead of snow.
If we get any showers(thats if the troughs from north make it this far south) they will start off as a sleety type and in the heavier ones will gradually turn to snow but in sunshine temps will get up to at least 5c maybe 6c and on sunday and monday sunshine will be in abundance.Its your third fax chart(mon 12utc) that has caught my attention with a front moving down from the north on a course with us for the evening.This is the one to watch and the wicklow mtn lads should take note of this if this comes off.

In fairness to Glasnevin, they are damned if they do and damned if they don't.
Remember the february snap and their warnings...Right egg on their faces that time as the weather that had all the conditions for snow didn't play ball.

This time with a forecast like they have given, they are likely to be erring on the other extreme unfortunately and be wrong again.
Their colleagues in Bracknell for instance have given a 60% risk of disruption in NI.
In this airstream for Glasnevin to be thinking snow will be confined to high ground in the north and west is dodgy.

But then yer man was on duty on the radio this morning Gerry Murphy saying the same thing-rain and sleet and last year I told ye what I thought of his forecast of "snow on high ground at night"...It turned out it snowed on the coast in Dublin in the day time.
That was a bad forecast as was this mornings I think.

I think they should have at least indicated a level of risk for snow in all areas and I reckon they will later to be honest when they've seen more output (unless it changes which is unlikely).

*edit*

Just for sauce

http://expert.weatheronline.co.uk/cgi-bin/geturl/daten/profi/en/2007/03/16/basis06/enen/rart_07031812_1606.gif?e41678d46fdffa5b55ae7daef08a4656

Snowbie

Two issues here also i said in the other thread:convection and cold air mass.
Cant see normal convection in this building up north and traveling south for a start only pep'd up by a trough line if it all makes it by Louth across to Mayo.

Also the cold air mass involved here.The moisture content be low in the atmosphere over the Dublin,Wicklow,Wexford being cold,very cold with dp below freezing is good news for snow in practice and theory but geographically too far south for showers to reach here albeit light in this sort of airstream unless we get a near gale-gale wind we would see some traveling south then.

This has become gospel to me as so many times this happens,its just the odd clump we get buidling over Antrim and making it down south is what i have experienced before but that is a rare occurance.1/10 chance in a northerly stream(Maybe this time who knows).

In fairness to Glasnevin, they are damned if they do and damned if they don't.

I quite agree.Its hard to forecast even this close to the event if its going to snow in the bottom 2/3 of the country.The North,NW and west are the obvious exceptions but if you where to ask me if i was a meteorologist in the head of the European HQ in Bracknell wheather it snow in Dublin come monday in this setup the answer be 50/50.
But as you and i know we have had these situations before and are what we experience.Its both practice and theory.
Whole different story if that front moves south.Well then thats frontal snow and is compleatly a new ball game then.

Snowbie

Snowbie wrote:

Also the cold air mass involved here.The moisture content be low in the atmosphere over the Dublin,Wicklow,Wexford being cold,very cold with dp below freezing is good news for snow in practice and theory but geographically too far south for showers to reach here albeit light in this sort of airstream unless we get a near gale-gale wind we would see some traveling south then.

From memory , this looks similar to the october 2003 northerly if not better.
Dam wise it's better obviously.
Thats why I'm prepared to think that this could be interesting potentially even for Dublin and Wicklow.
It's bound to be interesting for the North and west.

Weathercheck

Weathercheck wrote:

North leinster in the highest risk zone:eek:

Everything changes



Mind you I never put much sted in those maps.

ninebeanrows

Yea not to bothered with that map either as nothing has changed since yesterday..

Met Eireann have now issues a warning Kind of confusing

Weather Warning
It will become windy and very cold for Sunday and Monday.
Wintry showers of hail, sleet and snow will occur.
Showers will be most frequent in Ulster, Connaught and north Leinster.

Issued at 1100 hours 16/03/07

Actually it was issued at 1148 am after they read my post

Snowbie

Tristrame wrote:

From memory , this looks similar to the october 2003 northerly if not better.
Dam wise it's better obviously.
Thats why I'm prepared to think that this could be interesting potentially even for Dublin and Wicklow.
It's bound to be interesting for the North and west.

Warmer sst's in autumn then creating far more instability over the sea for us in 2003 but this is Ireland science and theory never see to come together in this country anything is possible at the end of the day i suppose.Bide my time till the first flake on this one.

darkman2

Looks like the best effort for lying snow will be Sunday night. Indeed looks like we are in a better posistion then most of the UK. Word of warning though - warm sectors have a nasty habit of appearing near troughs;)

http://91.121.0.76/modeles/gens/run/gens-2-2-78.png?6

Sunday itself during the day will be cold enough for snow and there should be accumulations in Northern areas certainly by Dusk.

http://www.meteociel.fr/ukmo/run/UW60-7.GIF

ninebeanrows

UKM again showing a feature moving down the Irish Sea, this is npticeable as 850hpa temps rise to -5 around the centre while are sub -7/-8c elsewhere..

Going to be very interesting watching the Sat Pics late Sunday.:D

darkman2

Yet another very good run and ive no doubt now that we are going to get smashed on Sunday and Monday with Sunday night bringing accumulations to all but the far South East. Lapse rates are excellent and 500mb temps are very low. Warm SST's and low thickness. Its just a superb recipe for instability. Windy too which means those showers will be moving quite smartly. We also have to keep an eye on the trough coming south Sunday night.

Supercell

Counting on WC and Snowbie to give advance warning of the snow as it moves south on the way to me!! (hopefully).
Blessington could be plastered imho.

darkman2

http://www.wetterzentrale.de/pics/brack1a.gif