Storm Forecast
Valid: Mon 01 Dec 2008 06:00 to Tue 02 Dec 2008 06:00 UTC
Issued: Sun 30 Nov 2008 17:21
Forecaster: TUSCHY

... SYNOPSIS ...

There is no change as major upper trough remains over western/central Europe with a strong ridge downstream. Along the periphery of this trough, numerous disturbances affect most parts of west/central Europe with the strongest one crossing the Alpine region from the SW during the day.


... DISCUSSION ...

... Highlighted areas of Italy, Slovenia, Hungary and Croatia ...

A strong disturbance circled the large-scale upper trough yesterday and was evident in WV loops at roughly 39°N/3°E, around 16Z. Backed by good upper-level divergence in the left exit region of a 60m/s streak at 300hPa, this depression should keep its strength steady during the forecast, while moving to the NE. This feature is the main focus for organized thunderstorms beside numerous other disturbances, which also affect those regions as they remain much weaker/disorganized. A cold front traverses the highlighted area during the daytime hours from the SW. Main issue this time is the limited moisture content, as the airmass in the wake of the past cold front passage had not much time for modification over the warm Mediterranean. The 16Z dewpoint measurements show single-digit values all over the central Mediterranean. Steep mid-level lapse rates help to offset this missing ingredient at least partially, so some low-end destabilization just ahead/along the cold front seems likely. Abundant mid-level forcing pushes the surface front rapidly to the ENE and a forced line of enhanced convection is a possible outcome of this high shear/weak instability set-up, maybe set off into numerous lines. To which degree this convection will be electrified is hard to determine. Dependant on locally better BL moisture content, diurnal driven diabatic heating and regional enhancements along the topography could all play a major role in concentrated thunderstorm activities.

Shear is fairly strong with 0-6km bulk shear in the order of 20-30m/s, 20m/s at lowest 3km and about 15m/s LL shear, so strong to severe wind gusts are the main issue. Directional shear along the front is also augmented, so an isolated tornado/hail event can't be ruled out. SRH1 would increase over the eastern Czech Republic during the afternoon hours as cold front passes by, but very limited destabilization prevents the issuance of any level area.

Some modest SBCAPE along the east coast of the Adriatic/Ionian Sea and a rapid increase of LL shear just onshore favor a concentrated swath, where strong wind gusts and an isolated tornado can occur.

Very steep mid-level lapse rates over western Austria and SE Germany between 06Z-12Z and the passage of the aforementioned vorticity lobe can produce an isolated, elevated thunderstorm. Very scarce instability is available, so no severe weather risk expected. Thunderstorm coverage remains too low for any thunderstorm area.

... Highlighted areas over W/SW-Europe (all day long) ...

Various disturbances rotate around the major upper trough and a few thunderstorms can evolve out of those. Gusty winds and marginal hail are possible with strongest storms, but nothing severe should occur.