Technically, we did have bitter cold N American air over the UK, but after the passage through warm Atlantic, the cold air was confined to midde and upper layers of troposphere. Only the lowest layers has been warmed up extensively, especially during last 2 days (it became rPm airmass), becoming very moist and even having little Tm airmass properties. The surface air being very unstable, rose vigorously like helium balloons, producing widespread heavy showers and even thunderstorms, which even persisted and developed far inland (had thunder over E Anglia yesterday morning).
The only true very cold, snowy weather over the UK comes from 3 sources:-
1. From the E and NE, from Scandinavia and NW Russia. This occurs when a high pressure settles over Scandinavia, or when there is a pan Arctic high pressure, the latter that occurred in late March 2013. This produces the coldest weather in UK in Winter, and can be very persistant.
2. From the N, from the Arctic. This often occurs briefly as Atlantic depressions moves away to the E and passes over N Sea, but sometimes last much longer if a high pressure settles over Greenland. This condition usually produces the earliest and latest snowfalls in a year in UK (i.e, say April, May or even June, or October)
3. In Situ, when a high pressure settles for a while over the UK, although it helps to have a initial polar airmass to encourage clear skies at night. The persistant night time cooling cancelling out any feeble daytime warming produces very cold, dry conditions. Snow usually occurs when fronts encroach from the Atlantic, when the rain turns to snow over the cold ground. It often occurs only briefly; the snow turning to sleet then rain as mild conditions move in from the Atlantic. However, the bitter cold weather can persist if the Atlantic low moves to the SE and dives into Europe (the easterlies then, of course, develop).
The only closest we have to this myth, is when a bitter cold, wintry spell occurs in N America, and then the weather system changes over here, say, bringing E'sterly type conditions; something which appears to be on the forecast according to latest GFS charts (although, whether this will actually materialise, only time will tell). But the true cold, snowy weather does not arrive here from N America (the only true cold, wintry conditions, of course, occurs on top of Scottish Mountains).
Edited by user
08 January 2014 12:41:06
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