Storm Forecast
Valid: Sat 27 Jun 2009 06:00 to Sun 28 Jun 2009 06:00 UTC
Issued: Fri 26 Jun 2009 22:13
Forecaster: DAHL

A level 1 was issued across the Alpine regions ... S Germany ... W Hungary ... and the Balkans mainly for heavy convective rainfall.

A level 1 was issued across the W Ukraine and Belarus mainly for tornadoes and large hail.

SYNOPSIS

A rather weakly defined but extensive quasi-stationary deep-layer cyclone is present over the Balkans/SE Europe, maintaining influx of warm/moist air across E and central Europe with the easterly low-level flow. High pressure persists over the northern parts of Europe, but in general, quiescent synoptic conditions prevail at the surface on Saturday. An Atlantic system will reach the extreme western portions of Europe early Sunday morning.

DISCUSSION

... E France ... E Benelux ... Germany ... Poland ... Czech Republic ... Slovakia ... Hungary ... Romania ... Moldova ... Balkans ... Austria ... Switzerland ... Italy ...

It seems that over much of central and eastern Europe, rather similar thermodynamic conditions will exist. These are characterized by rather weak CAPE, weak capping, rather low LCL heights and rather high low-level buoyancy values. Large-scale kinematic fields are rather unconspiocuous with generally less than 10 m/s DLS and negligible LLS.

Given weak capping, widespread thunderstorms are anticipated to develop with diurnal heating. Owing to rather slow storm motion and fairly decent low-level moisture, a threat for excessive convective precipitation will exist throughout the area. Also, some threat for non-supercell tornadoes exists given favorable LL thermodynamic fields. In addition, local flow modifications owing to orographic fieatures or outflow boundaries, as well as interactions of cells with one another may prove supportive of isolated marginally severe hail. The predictability of all these events in this regime is rather low and it is very challenging to highlight areas that are more favored than others. Will introduce a LVL1 where the highest threat for heavy rainfall seems to exist, based on slowest storm motions and strongest forcing for upward motion.

... Belarus ... W Ukraine ...

Low-level kinematic fields seem to improve from Baltic States across Belarus and the Ukraine in the afternoon and evening hours. Deep shear is expected to remain rather weak, though a small area of 20 m/s is expected over the Baltics in association with a small upper low. It seems that steep mid-level lapse rates will be advected into this region from the central Ukraine (cf 33791 ascent from Friday 12Z), so that rather substantial instability could build. However, lack of upward forcing may inhibit any convective development, which is the scenario supported by the models.

If storms develop, strong LLS suggests that storm-scale rotation may ensue, with a threat for brief tornadoes. Also, large hail and excessive rainfall may accompany the cells.