mardi 11 février 2014

European Storm Forecast Experiment

Storm Forecast
Storm Forecast
Valid: Wed 12 Feb 2014 06:00 to Thu 13 Feb 2014 06:00 UTC
Issued: Tue 11 Feb 2014 21:33
Forecaster: PUCIK
A level 1 was issued for southern Ireland, Wales and England mainly for severe wind gusts and to the lesser degree for tornadoes.


Satellite loops already show rapidly deepening low pressure system headed for the British Isles, its center situated in the left exit region of 50 m/s/70 m/s jet-stream at 500/300 hPa level. Towards the east, an extensive trough will slowly fill over the Mediterranean with mid and upper tropospheric flow weakening at its forward flank as the surface low translates from the North Adriatics towards Romania, weakening. In contrast to Tuesday, overlap of steep mid-level lapse rates and moist low-levels will be much less pronounced over the parts of Mediterranean. Still, marginal CAPE values are simulated over the Ionian and Aegean Sea. In conjunction with the decreasing degree of vertical wind shear, it does not seem necessary to issue a Level. 15% prob of thunder seems viable though.


... southern Ireland, Wales, England ...

Yet another deep low pressure system is expected to affect the area. In the dry intrusion, behind the main stratiform rain shield, intense pressure gradient is simulated with 40 m/s windspeeds at 850 hPa level just south of the low center. Both ECMWF and GFS hint on some marginal instability build up in this zone. Intense forcing could support a strongly forced convective line, where convection (downdrafts) would contribute to the strength of the wind gusts, which should be already very strong (coastal areas over 130 km/h) due to the background situation. Level 1 seems to be warranted for this questionable setup for severe wind gusts. Tornadoes are not ruled out either, given the intense low level shear, though they might depend strongly on the convective mode (isolated cell vs convective line). Greatest threat should exist between 12 - 15 UTC.

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