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Thundery wintry showers

Dry Zone E Anglia-Midlands-Cse In Recent Easterly

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I thought I'd give some fairly detailed analysis on why this happened, since it has influenced the opinions of quite a number of people who live within the dry zone, e.g. a recent post by The Enforcer in MOD relating to troughs.

Firstly, at 00Z on the Monday 29th November an easterly flow had become established over the north, and was in the process of establishing over the south:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101129.gif

This brought a mix of sunny spells and snow showers to most northern and eastern regions, although conditions were marginal near the east coast where showers turned sleety at times. The wriggling front over N England helped to pep up the shower activity at times and there were widespread reports of thundersnow, while a fair number of snow showers developed over East Anglia and the south-east, though they did not make it as far inland from the Midlands south as they did to the north.

By 00Z on the 30th November, however, we saw a weak occluded front form, draped across the Midlands and East Anglia and all the way out into the heart of continental Europe:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101130.gif

This initially brought some light snowfalls to East Anglia accompanied by slightly more marginal temperatures, such that in many areas the snow was wet and sleety and struggled to accumulate, instead serving to thaw any existing snow cover and turn what remained to ice following the subsequent refreeze. The front hung around for much of the day on the 30th, suppressing instability over the North Sea and giving a mostly dull dry day to the corridor extending from East Anglia to the Midlands, while heavy thundery snow showers occurred from Lincolnshire northwards and also developed over parts of south-east England.

By 00Z on the 1st December the front had fizzled, but troughs, parallel to the easterly flow, had aligned themselves over Lincolnshire and over SE England and increasingly brought in longer outbreaks of snow:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101201.gif

...while much of East Anglia and the south Midlands stayed in a dry slot of suppressed convective activity in between the two troughs.

By 00Z on the 2nd December, the troughs had fizzled out but a new trough developed over south-east England, again roughly parallel to the easterly flow, and replaced the previous one:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101202.gif

...and this maintained the dry slot over much of East Anglia and the south Midlands for another day, in a narrow belt of suppressed convection to the north of the trough.

The 3rd December had long been progged to give the snow lovers in Norfolk and north Suffolk some relief with sunshine and snow showers, but come 00Z on the 3rd, the north-easterly flow was only very sluggish and so snow showers were mostly confined to the north Norfolk coast:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101203.gif

So in a nutshell I don't think the event necessarily shows that troughs and fronts are a bad thing for snow lovers- on balance the zone from Lincolnshire to south-east England probably had deeper lying snow than if there had been a pure reliance on snow showers from the North Sea. However the snow lovers in that dry corridor were just very unlucky with how the troughs set up.

Northern England & Scotland did not have this issue around 26-28 November as the troughs/fronts that gave heavy snowfalls there were mostly aligned perpendicular to the flow:

http://www.wetterzentrale.de/archive/2010/brack/bracka20101127.gif

http://www.wetterzentrale.de/archive/2010/brack/bracka20101128.gif

...and this resulted in organised snow spreading west across a large swathe of those regions giving a fairer distribution of snow.

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Good analysis there! i was in the 'dry zone' and only got about 2cm of snow overall! very very dissapointing indeed

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Contrary to the snowbelts of regions around the world, it seems there was a drybelt.

It must of hurt being in the middle of the two monster streamers (Wash, Thames), during that day, radar watching would of been painful.

Brilliant analysis TWS good.gif

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While West Yorkshire did not suffer to the same extent, there was a dryish zone here in that in a normal easterly we would see on off snow showers, but all the 22cm this cold spell came from organised fronts/troughs, especially hard veiwing when the Wash streamer gave 45cm in Linconshire. There was also an annoying event last tuesday night (30th Nov), when the streamer/occlusion moved north until 9pm when it arrived here, and then after 30 minutes of the heaviest snow i have seen, moved back south (of course the morning after it moved back north to make snowy wednesday).

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It was particularly frustrating living in Norwich because on four successive days the GFS and NAE projected snow showers spreading south into Norfolk the next day, and on each occasion the models U-turned at 6-18 hours' notice (highlighting the fact that such troughs are very hard to pinpoint at even 24 hours out). I recall though that by Tuesday some of the runs were already suggesting that the inland parts within the zone could see little or no snowfall and some saying "this is getting ridiculous!".

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It was particularly frustrating living in Norwich because on four successive days the GFS and NAE projected snow showers spreading south into Norfolk the next day, and on each occasion the models U-turned at 6-18 hours' notice (highlighting the fact that such troughs are very hard to pinpoint at even 24 hours out). I recall though that by Tuesday some of the runs were already suggesting that the inland parts within the zone could see little or no snowfall and some saying "this is getting ridiculous!".

Indeed, a similar thing happened to me with the BBC precipitation forecasts on two or three occasions.

In regards to the models, i have to say that i found the GFS precipitation forecasts very dissapointing in that it severely underestimated the amount of precipitation (it forecast me snow on only 2 occasions) and even when it did, it was wrong. The best example was the 30th Nov, the GFS had the front not reaching me at all and not reaching Doncaster until 00:00, by 18:00 Doncaster was seeing heavy snow, by 22:00 i was seeing heavy snow before the move back south, a complete fail.

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Thanks for that info TWS - I too live in Norwich and was very frustrated by (non-)events a fortnight or so ago, loving snow as I do :D

If memory serves me correctly, this sort of thing seems to happen a lot here - I have talked to my (offline) friends about there being an apparent snow-shield over central to north-east Norfolk! Over the last few years I've watched likely - sometimes heavy - snow appear to fizzle out on the radar as it approaches Norfolk, whether it be frontal snow or streamers setting up around us.

We know that large bodies of water help to modify the atmosphere, to generate or maintain some of this snow for us, due to the lake-effect - as I understand it a body of (relatively) warm water sending up energy and moisture into cold air, condensing out and freezing to then fall back down as snow - sometimes heavy. I believe this is what helps set up streamers.

Do you think that it is possible that whilst areas of the North Sea to the North and South East of Norfolk have relatively deep water, for some reason the shallower waters off the Norfolk coast (there are loads of sandbanks and shallow water that stretch well out to sea to the N, NE and E of Norfolk) may mean the waters there are shallower and cooler and therefore creating less convection = less lake effect? Less energy into the air may slightly tip the balance away from snowy towards... nothingness for us here!

Looking at the Sea Surface Temperatures in the North Sea, there does appear to be a cooler 'blob' (to use Daniel Corbetts terminology!) in the area I've mentioned. When I have seen apparent precipitation heading our way, it seems to be over this area that it fizzles out.

Could be a coincidence I guess, but do you think this is a possible cause of the apparent pattern I believe I have seen over the last few years?

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I think it's more likely to be a short-term statistical quirk- in fact long-term averages suggest that on average Norwich is one of the snowiest cities in the southern third of the UK and quite well placed within East Anglia to catch snow showers from north and east winds and not warmed as much by the North Sea as the coastal fringes.

The perception of Norwich having a snow shield probably stems from recent experiences of Norwich largely missing the showers in easterly outbreaks (2nd Feb 2009, 17/18 Dec 2009, plus the very extreme case a couple of weeks ago) and instances when the UK had very marginal snow events and a number of North Sea areas including Norwich missed out due largely to North Sea modification (winter 2006/07, and much of Feb 2009). Last winter didn't have the high snow depths that many other regions experienced, but snow lay on more days overall at Norwich for the 2009/10 winter quarter as a whole than at most other locations from the Midlands southwards (the Met Office "days of snow lying" maps highlight this).

But you get short-term statistical quirks like that all the time. For instance Durham is traditionally the snowiest city in England and gets 30-40% more days of lying snow than Sunderland, however during the period 1999-2008 inclusive, Durham kept missing out repeatedly, it was probably quite a long way down the list of snowiest English cities and if anything had slightly less than Sunderland.

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Those are probably the periods I am thinking of TWS

Thanks for that - interesting stuff for us Norvicencians!

Bring on a good dump this week then :-)

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Its a statistical quirk alright for this particular area. The heaviest snowfall, possibly ever, and certainly in the 67 years that I have data for, some 34cm fell from 1730 30/11-0830 01/12. The previous heaviest was, off the top of my head, 26cm in, again, I think either 1981 or 1987?

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