Storm Forecast
Valid: Fri 03 Jun 2011 06:00 to Sat 04 Jun 2011 06:00 UTC
Issued: Thu 02 Jun 2011 12:49
Forecaster: TUSCHY

A level 1 was issued for most of the Balkan States and surrounding regions mainly for isolated large hail and locally excessive rainfall amounts.

SYNOPSIS

Blocking high over low pattern persists over Europe. The cut-off low over the Iberian Peninsula advects a warm and moist air mass from the central Mediterranean towards the north. At the same time, a strong and quasi-stationary high pressure area, centered over the North Sea, advects somewhat drier air to the south. Both air masses converge over parts of south-central Europe, where widespread thunderstorm activity is forecast.

DISCUSSION

...Level 1 area ...

Despite weak shear, a moist air mass is present, weakly capped and placed beneath somewhat steeper mid-level lapse rates. Numerous UVV maxima can be detected but it is hard to distinguish between real lift and model bias as intense "model convection" occurs. Nevertheless, outflow boundaries from nighttime thunderstorms, topography and daytime heating allow widespread initiation. Isolated large hail and strong downbursts may occur during the initiation stage, however rapid clustering is forecast with short storm motion vectors. Keeping rich tropospheric moisture in mind, an augmented threat of flash flooding exists. Thunderstorms keep going well into the night.

A somewhat augmented waterspout risk exists along the E-coast of Spain all the way to the Balearic Islands, as cold upper low remains in place. However, only modest 0-3 km CAPE signals are forecast with weak convergent flow, so no real threat is seen for a concentrated outbreak of waterspouts, calling for a level area. Nevertheless, a few spout reports are well possible. During the night, conditions become better for scattered thunderstorms over the Balearic Islands as 20 m/s DLS overlap with 800 J/kg MLCAPE, so a few severe thunderstorms are possible with large hail the main risk.

Finally, S-Germany/E-France will be monitored for higher thunderstorm probabilities, as LL shear is quite strong, both speed and directional shear, favorable for LL mesocyclones (strong wind gusts/isolated tornadoes). However, very limited initiation is forecast, so no higher risk level is issued right now.

For the rest of the thunderstorm areas, conditions don't warrant a level 1 as either instability or lower tropospheric moisture preclude an appreciable risk of severe. Kinematics also remain too weak.