Big Freeze Discussion [Happy New Year]

There's been some occasional hail or rain here this evening. I still have yet to bear witness to some nice snowflakes. Seems quite cold out, and I hope the hailstones don't melt too much on footpaths or roads before the night goes on. It's easier to walk on unfrozen hailstones than it is on slush... Believe me, my ass and back have felt it this evening.:o

I've underlined in the boards.ie forecast thread my concern that, however people may find today and Monday, the weather will become truly severe across much of the country on Tuesday and continue that way for the rest of the week, as the cold deepens and a stronger more organized northeast flow develops. In fact, I would advise people who need to stock up or prepare to get it done Monday if possible, because more isolated areas and higher rural areas could find it really difficult to get around once a bit more snow falls and temperatures fall several more degrees (especially daytime).

These things sometimes get downgraded, but in this flow pattern, a spell of more severe cold seems inevitable. Weather buffs will realize that the appearance of the 516 dm thickness contour rippling across the UK towards Ireland means severe cold in the UK and plenty of snow in eastern counties there, which can only add to the potential for cold (and indirectly snow) in Ireland as the flow chills further.

Its with great pleasure and glee that I can report some rogue snow flakes falling in Waterford !!!!:D The start of many more I hope !!!!!! The famine ends!!:)

baraca wrote: »

Could we finally be heading for the event that makes this cold spell one of the more memorable ones this tuesday ? Even if it doesn't snow it's gonna be bloody cold out there!

I think it has already reached that status of 'more memorable'.
To be fair theres not many of these long cold spells in my memory anyways

Good Morning Everyone

I certainly wouldn't be prepared to make a forecast for snowfall distribution & amounts for the whole week ahead. Now, it's not that it could well end up being correct, however there are so many variables in the mix. In addition, there may well be surprise snowfalls in such an unstable northeasterly flow.

For example, the 00Z UKMO output has a frontal trough, bringing snowfall, moving down across the country, from 01.00 Hours on Tuesday & during Tuesday itself:



It also develops rather heavy snow showers into Eastern & Southeastern areas from 01.00 Hours on Wednesday of next week.



This is but one run & therefore should not be taken in isolation. Therefore, the ECMWF 00Z run should be considered. Again, it clearly models the frontal trough moving south on Tuesday, which will almost certainly offer very decent snowfall potential for Northern areas & as demonstrated on the 00Z UKMO, could well remain relatively intact as it moves south, especially in areas nearer to Western & Eastern coasts.

T+72 - ECMWF 00Z - Snowfall Risk into the East & Southeast



Further Outlook

ECMWF 00Z

Overnight, the NWP guidance maintains very cold conditions until T+120 (Day 5) at least. There is strong support for a renewed Easterly flow towards the end of the week. However, there is uncertainty surrounding it's intensity. For example, it be somewhat slacker as shown on the ECMWF 00Z Guidance, but still with very cold upper air over the country - 850mb Temperatures of -8 and below. However, I wouldn't be too certain upon the ECMWF 00Z evolution as it was a clear Operational outlier for De Bilt, Holland - to our East. This is important because it is from that region that any further Easterly flow will be sourced:

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

UKMO 00Z

Meanwhile, UKMO 00Z has a keen Easterly flow continuing at T+120, with pressure remaining High to our variable North. It also has an even stronger Easterly flow developing between T+120 and T+144, backing slightly Northeasterly with time.

GFS 00Z

The evolution is rather more similar to that of UKMO 00Z than ECMWF 00Z. Very cold Northeasterly winds persist until late on Wednesday & early Thursday. It also has a renewed Easterly flow developing between T+120 & T+144 with a large blocking High over Scandinavia - that continues to build and back Westwards, very similar to that of the UKMO evolution.

Summary

In summary then, remaining bitterly cold for this coming week. There is a risk of snowfall from later on Monday through to late on Wednesday in particular, as described above. Amounts & distribution are still very uncertain & it's best to follow the Hi-Res Model guidance from T+24 when dealing with snowfall potential. Towards Thursday, conditions may become much slacker but still extremely cold as shown on ECMWF 00Z, with a light Easterly flow. However, it is quite possible, at least 60%, that a fairly potent Easterly flow will continue towards the end of the week with High Pressure over Scandinavia. The cold will be potent, the strength of the flow is uncertain.

In essence, at least 60% confidence of cold to at times bitterly cold conditions persisting to Day 6, with the risk of snowfall at times.

SA