Man With Beard
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Posts posted by Man With Beard
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Latest NAE a big upgrade for South Hants and IOW - 14mm (ie 10-15cm snow) for Isle of Wight by tomorrow morning
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Still snowing, not all light either, if this keeps on all day we'll easily get above 5cms on surfaces prone to settling. Still expecting a heavier period this afternoon.
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Continues to snow lightly, probably 1cm now but still not sticking to the roads
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Snow getting a little heavier and starting to win the battle with the road outside
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Like a massive attack of dandruff here in Portsmouth. A nice covering on cars, roofs and grass but it will need something heavier to settle on roads.
Checking all the models this morning, I'm still expecting a heavier batch this afternoon. Check out the NNM precip totals on Meteociel, there will be a massive event here this evening if they are right!
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I wonder if the IOW might be upgraded to an Amber warning soon? Even the NAE goes for 10mm of snow by Shanklin over the next 36 hours. And the whole lot is still perilously close to the south coast, NAE being consistent in keeping the main batch 10-20 miles off shore though. Still, it got the rain in Devon over 40 miles wrong today!
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Out of the six charts I've seen, this is what I see for Dorset/Hants coastline for tomorrow (sorry about Cornwall/Devon, just too much info to get my head round!). Just highlights how hard a forecast it is to make:
NAE: Occasional light snow
UKMO: Light to moderate snow
GFS: Light to moderate snow
HIRLAM: Heavy snow around middle of the day
WRF: Light snow by midday, becoming moderate by evening
ECM: Light to moderate snow, becoming heavy by evening
Take your pick! Or ditch them and watch the radar / look out of the window tomorrow
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The 12z NAE;
GFS;
And UKMO;
All broadly similiar now in keeping the main thrust of PPN in the channel and over northern France. The Channel Islands could do pretty well out of this, along with the Isle of Wight and the extreme south coast, say Southampton/Portsmouth area, but move inland from the south coast and your chances quickly decrease.
The 06z GFS was always on its own with its northward extent, and thus needed further support from the 12z models. We still have the NMM and ECM to go. Otherwise its just a case of hoping for a model boob up and developments differing on radar.
Still game on for the extreme south coast and Channel Islands however. Good luck to those down there.
I would say there's quite a difference in intensity though - I would have thought GFS and UKMO signify far higher snow totals on the coast.
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Been studying NAE's forecasts of today's rain/snow event in Devon. At 24, 18 and 12 hours out, they had the rain either over south or mid Devon. Looking at the radar right now, the heaviest precipitation is over North Devon - between 40 and 70 miles north. So the NAE can be that wrong even at incredibly short range.
(...Am I taking this a bit too far?
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Heavier snow back into the south on GFS 06Z
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Great post by Ian Ferguson on MOD just now urging caution with any conclusions snowy or non-snowy (sorry can't copy and paste on my phone). This scenario has very little history in model output within T24 - just think of the variables, the front has not even developed yet, extreme cold uppers, genuine low pressure. Unless the models push the whole thing 50 miles south, this will be a radar watching exercise for anywhere within 30 miles of the south coast.
Taking just the NAE, nothing will happen. But taking all model output, you could guess at 5mm precip near the coast (maybe 10mm on S. Devon, IOW or Sussex coast), up to 2mm slighty inland (maybe Salisbury, Winchester, Petersfield, etc), other than that, prayer is needed! But this is just model output - all subject to change for better or worse.
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ECM latest precip totals on south coast back up to 18mm+ for Monday/Tuesday
www.yr.no/sted/Storbritannia/England/Portsmouth/langtidsvarsel.html
No experience with how accurate they are but it's the ECM apparently so let's see.
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GFS T42...The heavy stuff still mighty, mighty close
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NAE is only out to +18 ATM
Precipitation charts come out first
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NAE 18Z still keeps precipitation mainly in the channel. Bit closer though. A little more for SW.
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Latest ECM still has 6-12mm precipitation for Pompey on Monday/Tuesday ... by the way, replace the word Portsmouth with your town for your area
www.yr.no/sted/Storbritannia/England/Portsmouth/langtidsvarsel.html
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Virtually the whole country under -12C uppers - a collector's item
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Latest NAE similiar to the UKMO, with the heavier PPN kept in the channel on Monday;
The far SW look favoured for something decent however.
If you study the charts for T36 and T42, though, the heavier snow is clearly heading north; you would expect snow over much of the south at T54
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Higher elevations of the southwest would surely get a blizzard out of this approaching storm, coastal regions more of a mix but wind and waves on south coast will be hazardous. Think it may cut off heavy snow east of IOW as it seems more likely to start moving southeast into Brittany. But parts of Devon, Somerset and Dorset could see 20-40 cm.
The main difference I see so far on the 00z is the cold air clamping down harder on the low and deflecting it faster to the south.
This may reduce snow potential in Kent, southeast and London but otherwise the North Sea very much in play and parts of east Midlands, Yorkshire and northeast could see locally heavy amounts. The southwest however may have isolated snow emergency situations developing given the combination of wind, snowfall and cold.
I'm going to stick up for Roger a little bit here. Of course we are used to last minute downgrades in the UK but if we look at what the models are actually saying right now (and this is T48, of course, not T144), 20mm precipitation plus somewhere close to the south coast does not seem out of the question (and Roger quite rightly said "could" in his post). Yes, these precipitation charts are often wrong but I recall a situation in January where 10mm was forecast for me by NAE at T12 but we ended up with far more than that and local flooding - so totals can go up as well as down. Regarding warm ground temperatures, I remember early April 1989 I think it was, there were first 3 days of 18C+ in bright sunshine, four days later and there was 3 inches of snow on the ground where I was in a far more marginal situation than this.
The only thing that's risky to do atm is to provide a localised forecast. There must be high confidence that someone will see 20mm of precipitation falling as snow on Monday, but whether that's Exeter, Jersey or Oxford, too early to say.
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Great summary AMD up there, thanks! Still looking particularly good for Cornwall and South Devon. For the immediate south coast, still ok but a close call. For everyone else, gonna need a bit of luck (unless you don't like snow!). Extreme cold nailed on now though.
Edit: just checked ECM precip charts for my area, seems like an upgrade for Monday, between 20mm and 30mm (!) and all snow! http://www.yr.no/sted/Storbritannia/England/Portsmouth/langtidsvarsel.html
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All main models keep the shortwave more north-west at T144 this morning, resulting in varying degrees of warmer weather by T144.
In the nearer timeframe, Monday's front doesn't move as far inland and moves away quicker on Monday night. The SW and perhaps southern coastal towns still see decent snow though.
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I've seen a lot on 'last minute shifts south'. In my experience, this either happens when a shortwave goes under a block, or when a low pressure system is forecast too deep. This is not a shortwave, and overcooked low pressures normally get sorted out by the models by T48. So I think we're fairly close to ruling out the automatic 'south shift' parameter. I also recall many frontal systems moving in from the south-west ending up much further north. All to play for.
Here's my guess for the south coast: no snow - 20%, a little snow 0 to 5 cm - 30%, a decent snowfall 5cm+ - 40%, and even rain - 10%.
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Cherbourg isn't all that far from us?
:p And admittedly it could be there. But at least we're in the game!
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GFS 06Z prep charts have 60mm rain falling near the channel isles from Sunday evening till Tuesday lunchtime. Ok, it may not all be snow and that figure may change drastically but it does underline: at under T72, the charts have serious snow potential. Someone somewhere not far from us is going to get hammered.
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:p
South West & Central Southern England Regional Discussion 10/03/13 17z---->
in Regional
Posted
Snow getting heavier all the time and sky looking darker. Must be getting on for an inch on surfaces (apart from roads which are still clear, but if this keeps up I would expect them to go white before too long). Can't believe there's no amber warning, looking at the radar this could go on a while.