Arctic Outbreak Is A 'Done Deal' - Peter O'Donnell

Monday morning update from iWeather Online forecaster Peter O’Donnell on the upcoming wintry outbreak: “The thing that I find truly staggering is the scale of this arctic outbreak, it basically reverses the normal southwesterly flow over the North Atlantic and changes it to northeast everywhere north of about 47 deg by next Friday." 

"We have to keep in mind that we're looking at weather maps that very few people have seen in real time, maybe if you were working in a met office in late 1962 or early 1963, or in Feb 1947. That's how dramatic this pattern is”.

“Now as to the details, those will come into focus better when we know for sure how robust the cold surface layers will be once the inevitable push back comes. The theme keeps developing towards the theoretical energy peak on the 20th (full moon is 21 Dec 08z). This is really exciting to me as a researcher and forecaster, to see how this is evolving towards a winter storm scenario, but before that happens there will be on-shore streamers forming in various coastal areas moving some distance inland.  So I think the way this is evolving at present, we should be fairly confident of a widespread snow cover developing in Ireland during the four days Thursday to Sunday before a two to three day storm window of opportunity. That snow cover of course would play into the development potential by further cooling the surface air masses.”

“As for conditions over in Britain, that looks positively frigid with the slack gradient that follows the initial onslaught of very cold air, they are bound to get enough of a snow cover to guarantee extreme cold under those sorts of upper conditions. Could see local -16 to -24 C overnight lows in parts of Scotland and northern, even central England, inland Wales on those maps, and that should equate to potential for lows similar to the last cold spell in Ireland.”

“This signal is so robust and long-heralded on the models I feel like the general idea is a done deal now, it's down to the details. The key event will be the pushback of low pressure around the south in the time frame of Mon 20th to Wed 22nd. This could very well turn out to be a snowstorm. This may sound like backwards logic but a very cold winter should have snowstorms, and snowstorms should occur when the cold has stopped.”

Irish Weather Online's Daily Long Range Weather Forecast is provided by Peter O'Donnell. Peter is a Canada-based climatologist who specialises in providing long range weather forecasts for Ireland and the United Kingdom. See Monday's forecast HERE

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