Storm Forecast
Valid: Tue 29 May 2007 06:00 to Wed 30 May 2007 06:00 UTC
Issued: Tue 29 May 2007 09:36
Forecaster: VAN DER VELDE

SYNOPSIS

Large upper low resides over central Europe. At its eastern flank, low surface pressure is centered over eastern Germany and also over the Adriatic Sea. The associated cold front has stalled over eastern Germany, with an occlusion over Denmark, while colder air advances the front from the south over Poland.
The large body of warm humid low level air is confined by the warm front from Denmark, eastern Sweden, southern Finland into northern Russia.

Within the warm airmass, MLCAPE will typically range from several hundreds to locally over 1500 J/kg (00Z sounding in Lithuania). This makes large hail possible with any storm that develops, as well as isolated severe gusts helped by the high LCL heights over a large area. However, only regions in central/eastern Europe where GFS indicates to have the best low level convergence or QG lift signals have been highlighted with a level 1.

DISCUSSION

...eastern Germany, Denmark...

Strong forcing is forecast to be present through the warm sector in this area. A few hundred J/kg MLCAPE and moderate shear conditions (10-15 m/s DLS) are likely to result in long-lived multicell to perhaps marginal HP-ish supercell storms with the main threat of large hail. Although SREH pattern does not overlap well with instability, expect locally near the warm front and (secondary) occlusion points, e.g. over far northeastern Germany, stronger backing of surface winds. GFS storm-relative low level winds are maximized in this region. Low level shear is at most marginal but may locally be good (>10 m/s 0-1 km). Will not exclude an isolated tornadic event, but main threats of large hail and flash flooding will be most significant.

...Finland, northern Russia...

Along the south side of the warm front and north of a surface convergence line over Estonia there is good SREH, >200 m2/s2, which may induce storm rotation, but deep layer shear is marginally favourable (around 15 m/s 0-6 km). Expect supercells or long-lived muclticell clusters with a chance of large hail and flash flooding, mostly.

...western Ukraine into Poland...

Ahead of the cold front, deep convergence is progged in unstable airmass with high LCLs... but marginal shear. Do expect clustering of storms with main threats of isolated severe gusts and large hail.

...eastern Belarus, western Russia...

There is more dynamics here, as a wave with a consistent patch of QG lift migrates northward, with moderate deep layer shear (>15 m/s), SREH and enhanced storm-relative flow... Given the speed of the feature, an MCS with severe gusts is possible as it moves into considerably dry unstable air.

...Adriatic, Thyrrenean, and Ionean Sea...

As cold unstable, moist airmass with steep low level lapse rates is present in weak flow environment, wind shift lines may spin up several waterspouts. Chances are best for the Adriatic Sea, but potential shifts southeastward during the second half of the period, with good low-level CAPE forecast but with lower convective cloud tops lowering thunder chances.