Atlantic Storm Watch 2014: February/March

National Weather Warnings

STATUS YELLOW
Wind Warning for Atlantic coastal counties

Strong to gale force south to southeast winds veering south to southwest, will gust 90 to 100km/hr at times later this evening and early tonight in Atlantic coastal counties.
Issued:
Monday 10 February 2014 12:00
Valid:
Monday 10 February 2014 21:00 to Tuesday 11 February 2014 03:00

STATUS ORANGE

Snow-ice Warning for Donegal

Cold wintry weather expected.
Some falls of snow possibly early tonight before turning to rain, but likely to persist as snow on ground above 500ft. Rain clearing during the night, with wintry showers of sleet and snow moving into the area overnight. Cold and raw tomorrow with occasional heavy showers of hail, sleet and snow. Accumulations of 3 to 6 cm.
Issued:
Monday 10 February 2014 13:00
Valid:
Monday 10 February 2014 21:00 to Tuesday 11 February 2014 18:00

STATUS YELLOW

Snow-ice Warning for Connacht, Longford, Westmeath, Cavan and Monaghan

Cold, wintry weather expected later tonight and tomorrow with occasional heavy hail, sleet and snow showers likely, especially in parts of Connacht, Ulster and some midland areas. Accumulations of up to 3cm in places, especially on higher ground
Issued:
Monday 10 February 2014 13:00
Valid:
Tuesday 11 February 2014 04:00 to Tuesday 11 February 2014 18:00

maquiladora wrote: »

12Z HIRLAM is showing quite a strong storm for us.

SpaceTime wrote: »

We're going to have to start naming these storms, or at least numbering them. There have been so many it's starting to get confusing!

vicwatson wrote: »

Where is it all coming from since Dec 18th ??? we need to look at the issue of the driveforce.

M.T. Cranium wrote: »

The parade of storms since mid-December is basically the result of weather patterns over the Pacific Ocean, believe it or not, and this was foreseen in general terms in some of our long-range discussions. The chain of events is something like this: large ridge over the central to eastern Pacific drives very mild air far north into Alaska and northwest Canada, this creates a potent source region for 7very cold arctic air in the central Canadian arctic linked to Greenland, that cold air forces Hudson Bay to freeze a month early reinforcing a very cold pattern over central North America ... meanwhile the subtropical Atlantic has built up a warm anomaly from not being greatly disturbed by a weak tropical season, and thus without much retrogression to provide any counter-punch from the east, the Atlantic has all the ingredients needed to create storms off the east coast of North America, some of which have already had a history moving through North America, others being new creations such as this most recent storm. Then with no significant northern blocking or cold air source in Europe, the jet stream is locked into long waves this winter, more or less a freeway for storms. Many of them have taken the usual track between Ireland and the Faeroes, but this most recent one interacted with a nasty little kink in the jet stream that was an offshoot of the "polar vortex" phenomenon that has been quasi-permanent in the region south of Greenland. It was that kink showing up in the forecast models which caused me to go into storm alert mode on Monday-Tuesday (the GEM is good on these things although I don't rely much on the derived products, just use the basic structure and fit the outcome to that).

The pattern may slowly change to something more benign if we can see a disruption to the long waves, some at least weak northern blocking towards early March, or just a higher amplitude to this pattern allowing Ireland to hide behind the stronger heights of an amplified ridge and let Iceland take a turn at receiving all these storms.

From my research I would say there is a second-order reason for multiple intense storms and that happens to be that certain factors which can often be offset in timing are slowly moving through a reinforcement this winter, that will gradually fade out later in 2014 so that by winter 2014-15 there will be a more normal scattered distribution of energy peaks that I associate with storms. This past storm occurred at one of these reinforced peaks which is why I commented on Tuesday that this storm, already looking ominous on models, could be something of an overperformer.

While we're into a discussion of the storm, I would mention that the model output held quite a few clues that helped us to make some fairly decent forecasts, most notably the indication of rapid pressure rises across the inland south. We often think of pressure falls being correlated with strong winds but rapid 3-hr rises are even better indicators, and these could be calculated from the model output. This is probably why the very strong winds made such dramatic inland progress.

Watching the storm unfold early on Wednesday you could see a southern energy centre keeping pace with the main centre of low pressure and this came ashore in Kerry about 1100h, got disrupted by the terrain there and I think watching the radar this then allowed the atmospheric dam holding back this surge of strong winds to break, and the gales came pouring into Clare and Limerick at that time while the modelled offshore hurricane force winds swept along the south coast.

Anyway, a very interesting storm to watch, it was still slowly deepening over land during the afternoon.