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FI Charts ( T120+ onwards) Winter 2021/2022 **READ MOD NOTE IN FIRST POST**
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Good progress for snow fans on this morning's ICON
Low pressure not making the same sort of inroads north as previous runs and that's exactly what we want in terms of trend. The further south the better. It probably won't work out here but it's the trend that matters.
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Uppers generally -8 to -10 and negative dewpoints if we want guaranteed snow and to avoid melting rapidly. Anything milder and it's likely to be marginal particularly near coastal counties. Today's runs can only be better than yesterdays. We need that low to sink properly south. If it slides across Ireland then cold rain for most and proper cold air may not get in.
GFS 00z is very mild for Christmas Day and Stephens Day but turns much colder from the 27th and stays very cold to the end of it's run. It may not get there for Christmas but at least there is some decent cold after.
This GFS ensemble member is a complete outlier and going for nearly 50cm of snow for Meath/Dublin. Extremely unlikely to happen.
GEM is similar but is alot milder with a chance of it turning much colder, it also has some nasty looking low pressures around this time period.
ECM alot better than yesterday but we really need these lows to sink further south, we are on a knife edge between very mild weather along the south coast vs much colder air north of that.
As for snow there is no real point looking at that yet. We're still a week away from the potential cold and so many of the colder runs have mild air very close to out south so we need to get the cold and blocking properly in place before looking at any snow potential.
For Christmas Day itself it does appear we have lost the trend to keep things high and dry as it turns progressively more unsettled from about the 23rd of December. The final week of December is likely to feature plenty of precipitation which may be mostly of rain over Christmas but turning more wintry in nature after Stephens Day. Snow is looking more and more likely at some point between the 27th and New Years Eve, but before we start getting excited we need another 3 to 4 days to see where does the cold go and will we get very cold air along with decent levels of precipitation.
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GFS 6z rolling out. Similar to the 0z it's going for a mild and wet Christmas Day particularly along the south coast and it begins to turn colder from the north. Rain or showers will begin to turn wintry from Stephens Day.
By Stephens Day temperatures in the 2 to 4C range and sub zero by night. After this temperatures may struggle to get above 0C across parts of Ulster and Leinster but closer to 3C generally. New Years Day could be an ice day with a long fetch northeasterly sourced from svalbard down across Ireland with a baltic north-east wind chill. By this stage anything that falls out of the sky would be of snow and temperatures in some eastern areas may struggle to get above -2C or even -3C.
If this was to verify night time temperatures close to -10C would be possible or even colder if there was lying snow. This would probably be our coldest spell of weather since December 2010.
Polar lows are also a possibility with this set up where showers would merge forming localized snow storms.
If this GFS run was to verify this would be a fairly substantial and bitterly cold setup that could take a week or more to shift. This could well be a cold outlier as this is a very cold run indeed.
On this particular run snow is covering much of the country by this point and parts of Leinster particularly around Wicklow would be buried in snow.
It's important not to get too excited over this particular run as this is so far away and very unlikely to verify as is but great to see the GFS playing around once again with some proper mid winter cold.
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The GFS 6z is not a cold outlier until the very end of it's run, it is in the coldest portion of the ensembles but there are several others that are going colder than the operational run including the control run, however the operational run does become a cold outlier after New Year's Day.
Getting back to Christmas Day itself that is starting to look like wide support for a fairly mild day but it could also be a day of transitioning from mild to cold. The day itself is also looking quite wet with maybe some wintryness on northern hills. Low ground may have to wait till the 27th of December for snow.
Hopefully the GFS 12z and ECM 12z will continue to upgrade this cold and not flip back to mild.
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GFS 6z now going for a fairly signifcant warming around New Years stretching from Ireland to Siberia. This isn't an SSW but it's getting closer to one. The PV starting to come under quite a bit of pressure.
So much model watching to come over the next 2 weeks.
Much of Europe into the freezer by this point.
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GEM 12z similar to the UKMO and brings the cold in on Christmas Day as the low pressure dives to the south.
Temperatures in Ulster and Leinster would struggle to get much above freezing if this verified. Still mild in the south-west but the mild temperatures would be pushed away fairly quickly.
In this setup we could see snow across parts of Northern Ireland but mostly rain elsewhere as the dew points are generally a few degrees above freezing. But i'd imagine the dew points would lower quickly and rain could turn to snow as the day progresses.
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Just to illustrate the importance of this low and what happens if it fails to sink south. The Icon 12z parks the low off the west coast of Ireland so no cold air gets in. Infact all of Ireland and the UK are mild on Christmas day for this reason.
This is certainly not what we want so fingers crossed that the high sinks well to our south. We will probably spend the next 3 to 4 days figuring out where this low will end up.
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RE: Christmas snow risk.
The latest ECM run is out and small changes from this morning's output, ultimately pointing to the arrival of colder weather on Xmas Day. It is an upgrade in terms of snowfall risk for Ireland although in this run, snowfall may be more likely in southern rather than northern areas as outlined below.
Cold encroaches into Ireland from northeast about 12 hours earlier on Christmas Eve
Christmas Day sees some pretty cold uppers tracking southwest across the island
By Christmas Day, the slider low is tracking a little further south (good news for those looking for snow come Xmas Day into Stephen's Day). The risk of snowfall as the pressure system meets cold air over Ireland extends further south and may indeed be confined to the southern half of the island. Ultimately the low pressure system tracks to our south and towards the Bay of Biscay in this run. Cannot imagine the low can track much further south than this so it will ne interesting to see if it holds its course as we are close to a best case scenario right now in terms of cold rather than mild airmass taking hold on Xmas Day and St Stephens Day.
By Stephen's Day there is a slack north-northeasterly over Ireland.
Trend is your friend etc. but a long way to go on this, bearing in mind that the GEM and GFS are indicating that the snow risk is largely limited to Ulster and perhaps high ground a little further south. A long way off yet but great to see all the same if you like snow (at Christmas!).
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Certainly cold enough for snow. The ECM 12z get's the cold right down to Northern Spain. However it's more of a northerly so may be a lot dryer as pressure is slightly higher.
But really we nowhere near close enough to worry about snow as these charts will change several times over the next few days. ECM finishes with winds going back into the east off a very bitter continent and that's as far as we can see for now.
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Lots of eyes on the charts tonight.
Like others having watch them closely now for a number of days thinking that the chance is certainly increasing for cold sticking around for a number of days post Christmas. ECM is currently lacking of much precipitation but long way to go with that , have seen many variations over the last few days and snowfall largely gone today but the finer details will become clearer after the weekend. The charts wouldn't pick up streamers or troughs at this stage ( or a sneaky polar low ! ). Currently looking like widespread sharp frosts at least and very cold days. Atm Christmas day looks like struggling to get up past 4C or 5C away from the coasts.
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back to tonights ECM and the precipitation charts are in. This is a much dryer run than this mornings ECM. It's better for cold but it's a northerly so this leaves us high and dry for the most part with snow trains down the Irish sea into Wales.
Christmas Day some sleety rain near the south coast. Dry elsewhere.
Stephens Day is again largely dry, some snow showers near Irish sea coasts and these would not penetrate much inland due to the more northerly based winds. These showers quickly back off into the sea and head towards Wales.
Most places would stay completely dry under this set up.
Hopefully this will become more of a north-easterly or easterly over the next few days.
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