martinastro
Martin Mc Kenna
Global Moderator
Hero Member
Posts: 5182
Maghera, N. Ireland
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« Reply #30 on: March 30, 2010, 02:01:06 pm » |
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Synoptic Discussion - 30/31st March - Winter Returns
Deep low crosses the UK bringing Rain, Snow and Strong Winds
A sharpening upper trough is crossing NE across the UK deepening the surface depression under marked vorticity advection and upper level diffluence. The Jet stream has moved south again with the main jet core now pushing through the Bay of Biscay into Europe. Cold air is being dragged into the depression from the north.
Over the next 24 hrs the effect of the upper trough deepens the low as it moves east across the UK. The low currently over SW Wales and moving ENE (though actual movement will be a little north then south then east - but overall movement is NE) The low deepens to around 977-978mbs as it moves over the southern parts of N England overnight and through tomorrow. The main problems are relating to the cold air which will become increasingly dominant around the northern and western parts of the low as it moves East.
WBFL's are currently reasonably high over most parts with sub 200m only over the highlands of Scotland, and sub 500m over Western N Ireland and the rest of Scotland (north of the central belt) Over the next 12hrs stronger cold advection, a deepening low and nocturnal cooling all act to produce cold advection below 850mbs across Scotland and Ireland and later parts of Wales and N W England. Rain is currently falling over large parts of N Ireland and Scotland and largely is rain below 250m or so... However its already Mod Snow above 250m across Scotland and the highlands are seeing sig falls. The mountains of N Ireland are already seeing snow and this snow level will drop as the day goes on with WBFLs below 200m across almost all of N Ireland and most of Scotland (except far SE) by 21Z tonight. This means rain turning to snow even at low levels and accompanied by a very Strong NE Wind - as the low deepens gusts to 45-55mph are possible giving blizzard conditions and the weight of the snow causing potential problems to power distribution (very heavy wet snow) Conditions could become VERY NASTY indeed across Scotland and N ireland this evening and overnight. CAUTION Should be noted and travel will likely be disrupted. By this evening snow in the Central belt and population centres of N Ireland likely to see 5-10cm of snow and lots more on high levels. 20-30cm easily possible, with both the NAE and GFS having spot 50cm+ totals over the Highlands and Sperrin mountains by 06Z tomorrow. Given BLizzards then spot blown accumulations could easily exceed 60-70cm snow. The strong winds lasting into the night and tomorrow morning with further snow lasting through the night and tomorrow across Scotland - though WBFLs rising a little through N Ireland tomorrow.
Further South occlusion is coming east - reports of Snow on Dartmoor as its ushering in much colder air (okehampton just 1.7C at 10Z) the cold air dragging WBFLs down to below 200m across Wales and N W England with risk of developing wrap around (which will form overnight) lingering across Wales and N W England later tonight and early tomorrow with snow descending to 100m or so over Wales and NW England and to 200-300m over Southern England and the SOuth Midlands. (10cm Lake district and NW Wales easily possible)
Strong winds developing to the South of the wraparound - with 40-50kn gusts likely over Southern England esp headlands where isolated 60mph+ gusts are possible overnight and at first tomorrow.
Heavy bursts of rain also possible at times in the south as the mild air is ushered out of the way. ....
PJB 11.35
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