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s4lancia

Are We More Prone To 'marginal' Winter Events Now?

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I often read that if the same synoptics that we had last winter occured 50 years ago, it would have been even more severe. I read that certain synoptics now which produce marginal events 'nowadays' would have been snow back in 1963 (for example). That whereby once it would have snowed under certain conditions we now get sleet/rain. Really? In my opinion, 2010 put that argument to bed.

There is no getting away from the fact that 1963 was an exceptional period with cold persisting in one guise for about a two month period but looking through the archive charts and marrying them up to the UK weather reports, was it really any different back then? What the reports don't show below is the persistent cold over the Jan-Feb period but even with the embedded cold, the far S, SW and NW was always most prone to sleet, drizzle etc. That was the same then as it is now.

1/1/63: Heavy rain affected parts of the far SW

2/1/63: Light to moderate snow persisted in many S districts

3/1/63: By day, snow or drizzle were small in amounts, but overnight the snow intensified in S areas

4/1/63:Rain fell in S counties and the snow further N gradually turned to sleet, rain and drizzle

5/1/63: Rain or sleet fell in many places during the day, turning more to snow in the S overnight

6/1/63: Precipitation was widespread but light, falling as snow or light rain..

7/1/63: Cloudy all period in the S with light rain or snow

8/1/63: Only a few coastal showers were reported

9/1/63: Snow showers were very light and scattered

10/1/63: A few snow showers fell in the far SW and along the E coast

11/1/63: There were a few snow showers in E coastal districts extending to the Midlands

12/1/63: Sunny in many areas with a few light snow showers,

13/1/63: Just a few snow showers, mainly in the E

14/1/63: Light snow showers fell in some S and E areas, turning more to rain in the NW

15/1/63: Less cold than of late with some sunshine and a few snow/sleet showers in the S and E but more of rain in the far N

16/1/63: Sunshine in some E areas with some rain moving S across W districts

17/1/63: Light snow fell in many places with sleet in the far SW

18/1/63: Mostly dry and clear in all areas, with a few snow showers, mostly in the E

19/1/63: Sunny in most places with a few light snow showers in the E and Midlands but of sleet at times in the NE

20/1/63: Snow showers fell in many S places with drifting

21/1/63: belt of moist and warmer air aloft moved WNW over the S half of the Br.Isles giving freezing rain or snow

22/1/63: An almost totally dry day with plenty of sun

23/1/63: An almost dry day and night everywhere with plenty of sunshine

24/1/63: Fog persisted in many places but elsewhere it was a sunny and dry day.

25/1/63: Cloud increased in the NW as the cold front approached, bring rain with it late in the period

26/1/63: Freezing fog persisted in many S districts but some places saw sun

27/1/63: Fog persisted in a few places but generally it was less cold than of late.

28/1/63: Light rain or drizzle fell in few places, particularly overnight in the E and SE

29/1/63: Mostly cloudy with light rain in the S and E and some fog in the Midlands

30/1/63: Rain moved steadily S through the period, turning to sleet and snow in the S and followed by wintry showers in the N

31/1/63: There was widespread but light snow in the S but sleet/snow showers followed into the N

1/2/63: Snow fell in many places during the whole period but was more in the form of showers in the N

2/2/63: ?

3/2/63: snow showers were widespread though light

4/2/63: Snow or sleet showers were widespread but accumulations were generally small

5/2/63: Overnight, persistent snow moved into SW areas turning to rain in the far SW

6/2/63: Cloudy almost everywhere and heavy snow pushed slowly NE across the SW of GB and through central Ireland followed by moderate to heavy rain in the extreme SW

7/2/63: Cloudy and windy most of the period with snow moving very slowly NE turning to rain in the SW

8/2/63: The mild air pushed slowly N and rain fell in the SW but remained as sleet and snow in Birmingham and further NE

9/2/63: fog formed in many places as the milder air moved over the cold and often still snow covered ground and light rain fell in the far N

10/2/63: It was very wet in the far SW with Culdrose 25 mm, Scilly 19 mm, Roches Point 22 mm, and Lerwick reported 11 mm of rain

11/2/63: Cloudy in all districts with light snow in the N, but moderate at times in the far S. Rain still affected the most extreme SW

12/2/63: Light rain and drizzle fell in S and E counties of England, sometimes freezing and with a little sleet or snow

13/2/63: Cloudy in the S and E with widespread, though light, sleet/snow or drizzle

14/2/63: ?

15/2/63: Rain fell in a NW-SE line, with snow in parts of the S and E

16/2/63: Cloudy in most parts all period, with rain in the far SW and sleet/snow elsewhere

17/2/63: Snow showers were widespread but light and a little rain fell in the far S and SW

18/2/63: Light snow showers fell in many places but further accumulations were small

19/2/63: Most stations were still reporting snow lying, except in the far SW

20/2/63: Snow was widespread S of Manchester, though amounts were small

21/2/63: There were light snow showers in many places with rain in the far NW

22/2/63: Light winds, variable amounts of cloud and a few light snow showers

23/2/63: few snow showers fell in the far SE and E of England and rain showers in the N and NW

24/2/63: Lights snow showers fell in the E and SE but most places remained dry

25/2/63: Most places were sunny and there was no recorded precipitation by day and just a little at night in the far NW

26/2/63: Sunny by day and clear and frosty at night in all except the far NW

27/2/63: Dry and very sunny in the E and S

28/2/63: Cloudfree except in the far W and N

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There will always be reports of rain/sleet/drizzle in any period of persistant cold. Only really when you get extreme spells like 1987/1991 are they almost entirely snow.

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I don't think 2010 put that argument to bed at all, but it highlighted that sometimes the argument is exaggerated.

Global temperatures in 2010 were about 0.5C higher than in the 1960s. Thus, on average, airmasses will be 0.5C warmer than the same airmasses were back then (though not all parts of the world have warmed at the same rate, so this is a crude generalisation).

But the impacts of a difference of 0.5C are often exaggerated. Only in the case of past snow events with temperatures around 0.5C would a rise of 0.5C be likely to make a major difference to the outcome, turning falling and lying snow into a sleety mix. Most past events with a temperature below 0C would remain largely unchanged while most of those with a temperature above 1C wouldn't have delivered significant accumulations in the first place anyway.

The issue of marginality was most prominent during February- I imagine that many of the marginal snow events over England and Wales during the second half of that month would have produced more accumulations had it been the 1960s. But, crucially, they would still have been short-lived, because maximum temperatures often reached 3-5C and, even more importantly, dewpoints often crept well above freezing.

During the December/January spell we often had ideal synoptics for non-marginal snow events and so being in a slightly warmer climate therefore made little difference. Even so, altitude made a difference to the amount of lying snow, e.g. at Cleadon the event of 19th December produced sleet initially followed by snow, and left 5cm of icy stuff on the ground, but on Cleadon Hills, just 40m higher up, there was 8cm of soft fluffy snow. Perhaps if it had been the 1960s, both locations would've had 8cm.

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I think there is a point to be made about whether there is a difference in a marginal winter event between one that occurs in a mild winter and one that occurs in a cold winter.

I think there probably is, I suspect that the early February snowfall we had in the Manchester area, the snow may have struggled to settle if it had been generally mild in the run up to it as the ground would have been "inheritantly mild". However, it was cold and the ground was "inheritantly cold" due to the frequnet frosts and therefore the snow stuck more readily. So I think you are more likely to see a snow cover for a marginal event during a cold winter than a mild one.

Thats my opinion.

Edited by Mr_Data

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