Storm Forecast
Valid: Wed 20 Aug 2014 06:00 to Thu 21 Aug 2014 06:00 UTC
Issued: Wed 20 Aug 2014 07:26
Forecaster: PUCIK
A level 1 was issued NE Spain mainly for large hail and severe wind gusts.
A level 1 was issued for N Italy towards Croatia and SW Hungary mainly for large hail and severe wind gusts.
A level 2 was issued for N Adriatics mainly for large hail, severe wind gusts, excessive precipitation and tornadoes.
A level 1 was issued for NE Belarus and parts of W Russia mainly for severe wind gusts and tornadoes.
SYNOPSIS
A deep, long-wave trough resides over N Europe, filled with cold airmass at mid-troposphere, its base stretching towards the N Mediterranean. Strong 500 hPa flow is surrounding the trough and at its eastern flank, an embedded short-wave is observed. This feature is expected to cross the Baltic States and Belarus towards W Russia. Another short-wave will move from British Isles towards Germany and the Czech Republic. Two main foci for DMC development are forecast:
1/ Ahead and along the wavy frontal boundary spanning from N Italy towards W Russia.
2/ Under the cold airmass especially over parts of Scandinavia, the Northern and the Baltic Sea.
DISCUSSION
... NE Spain ...
00 UTC Barcelona sounding reveals strong westerly mid-tropospheric flow along with moist, surface southeasterly flow. Lack of steep lapse rates will likely preclude strong instability build-up. Nevertheless, models do show CAPE values on the order of several hundreds J/kg. This, combined with the strong DLS, with values over 20 m/s, may support supercellular DMC, capable of large hail and/or severe wind gusts. Due to the already ongoing storms over far NE Spain, likely over the Pyrenees, it seems that Lvl 1 is warranted for the region.
... N Italy towards N Croatia and SW Hungary ...
00 UTC soundings from the area reveal moderate mid-tropospheric flow, with speeds around 15 m/s and lack of steep lapse rates. Surface observations reveal Td values of 16 to 19 deg. Easterly surface flow is observed over NE Italy due to the development of shallow surface low over NW part of the country. With ample day-time heating and slight cooling at 500 hPa, it seems reasonable that marginal to moderate instability will build-up over the region. Furthermore, mid-level flow is expected to strengthen, reaching speeds over 20 m/s, especially concerning the western part of the area. Models are quite optimistic regarding CI, so that scattered storms will likely form by the afternoon. Due to the strong DLS (values 20 to 25 m/s), some of the storms will likely attain supercellular characteristics with threat of large hail and severe wind gusts. A tornado event is not ruled out near the Adriatic coastline, where enhanced LLS is simulated towards the evening. As short-wave trough approaches towards the evening and night hours, storm coverage may quickly increase, resulting in an MCS with threat of excessive precipitation, propagating along the Adriatics coastline. A small Lvl 2 is introduced for the region, where all threats will be present during the forecast period.
...NE Belarus to W Russia ...
Ahead of the cold-front, slightly unstable airmass is forecast, with MLCAPE values on the order of hundreds J/kg. Embedded in the strong southerly to southwesterly flow at mid-levels, a sharp short-wave will translate over the region to NE. In the zone of strong, unidirectional wind shear, a linear MCS could likely form along the front, quickly traveling with the zone of maximum forcing from the trough. Thanks to rather strong LLS, such system may be capable of severe wind gusts and an isolated tornado event is not ruled out completely.
