Storm Forecast
Valid: Mon 05 Jul 2010 06:00 to Tue 06 Jul 2010 06:00 UTC
Issued: Sun 04 Jul 2010 18:01
Forecaster: TUSCHY
A level 2 was issued for N-Italy mainly for excessive rainfall.
A level 1 was issued for N-Italy, Austria, SE-/E-Germay, W-Czech Republic and W-Poland mainly for excessive rainfall and to a lesser extent for large hail (despite Austria).
A level 1 was issued for parts of Romania and W-Ukraine mainly for excessive rainfall.
A level 1 was issued for Ukraine, Belarus and Lithuania mainly for excessive rainfall and isolated large hail.
SYNOPSIS
Weak pressure / height gradients persist over Europe. A progressive trough over UK moves eastwards and affects parts of central Europe. A quasi-stationary upper low over SE-Europe results in another day with numerous showers/thunderstorms. WAA over SW-Europe keeps the Iberian Peninsula stable and warm.
DISCUSSION
... N-Italy, Austria, SE-Germany and SW Czech Republic ...
The stage is set for an active thunderstorm day over that area with widespread showers and thunderstorms forecast.
First of all the activity north of and over the Alps. A weak prefrontal convergence zone over central Germany pushes to the east although this boundary becomes more diffuse betimes (high-level PVA atop this surface boundary also wanes during the afternoon hours). Prefrontal BL air mass features an high moisture content with dewpoints in the upper tens/lower twenties and high averaged 0-1 km mixing ratios. Thunderstorm initiation will be early in time and we can't exclude the possibility of ongoing convection during the morning hours with re-intensification thereafter. Shear over SE-Germany and W-Czech Republic remains weak, so slow moving showers/thunderstorms are forecast with locally excessive rainfall amounts. The same for Austria although there is a slight concern regarding strength of shear magnitude. High-resolution models indicate enhanced LL wind shear, as pressure gradients increase somewhat, next to 15 m/s DLS, so well organized multicells and even an isolated supercell may form. Despite excessive rainfall amounts, large hail and strong wind gusts accompany better organized storm structures. Storms along the decaying surface front over W-Czech Republic and E-Austria may last well into the night due to the persistent influx of warm/moist air next to ongoing convergence along the boundary.
Over N-Italy thunderstorms increase in coverage and intensity during the noon/afternoon hours. BL air mass features very high moisture content with dewpoints in the lower to mid twenties and high 0-1km averaged mixing ratios. No surprise that excessive rainfall will be the dominant hazard with slow moving storms. Nevertheless, thick mid-level CAPE profiels during the afternoon hours (as EML becomes more pronounced) may assist in an isolated large hail event, too. We decided to go with a level 2 due to the slow storm motion and the very moist air mass in the inflow layer. Local mesoscale model data inidcates a chance for 70 - 90 l/6h beneath slow moving clusters, so we think a level 2 may cover that risk the best.
... Central, E-Germany and west Poland ...
Focus for thunderstorms is the approaching upper trough during the daytime hours from France and Benelux. This trough picks up a cold front over SW/central/N-Germany during the afternoon hours and re-activates that boundary in respect of increasing shower/thunderstorm chances. Despite increasing shear, we do not yet expect any severe risk with that activity, as instability will be on the lower end side. However we have to monitor the BL air mass quality behind aforementioned convergence zone (see paragraph above). To complicate all that, we also have to deal with the lingering convergence zone over E-Germany, which also feels the affect of the approaching upper trough (e.g. stronger shear). This may result in organized storms over E-Germany during the later afternoon / evening hours onwards and a night time MCS event with excessive rainfall, strong wind gusts and marginal hail. (Some elevated CAPE persist well into the night hours.) We expanded the level 1 far northwards to cover a local rainfall risk over W-Poland during the night hours.
.... Romania to SE-Poland and central Ukraine to Lithuania ...
Two swaths with an augmented heavy convective rainfall risk occur over those regions and a level 1 was included. A few large hail events may occur. Thunderstorms over the Ukraine will last well into the night with ongoing heavy rainfall. Otherwise, thunderstorms weaken.
