Storm Forecast
Valid: Wed 12 May 2010 06:00 to Thu 13 May 2010 06:00 UTC
Issued: Tue 11 May 2010 21:33
Forecaster: PUCIK
A level 1 was issued for Central Italy and Corsica mainly for large hail.
A level 1 was issued for Bulgaria and Southern Romania mainly for large hail and severe wind gusts.
SYNOPSIS
The main feature of the synoptic-scale will be a large, negatively tilted trough over the Eastern Atlantic. Most of Europe will be under weak, southerly to southwesterly flow at 500 and 300 hPa, with the exception of a belt from the Southern Mediterranean, Italy to Southeastern Europe with a 40-50 m/s winds at 300 hPa level. At the surface, a shallow surface low will cover most of Northern Africa, the Mediterranean and Central Europe.
In a rather inconsipicuous synoptic situation, ahead of the diffuse frontal system stretching from extreme western Russia to Central Europe and the Mediterranean, low end to moderate instability built-up is forecast with scattered showers and thunderstorms possible in a relatively large area over the Mediterranean, Central, Southeastern and Eastern Europe.
DISCUSSION
... Central Italy, Sardegna ...
A belt of strong mid and upper level flow will enhance the DLS values, which are expected to reach 20-25 m/s, enough to sustain well organised storms, including supercells. Models are quite consistent on simulating at least slight instability built-up with local NMM model being more optimistic than GFS regarding this factor. With lack of strong synoptic-scale factor, isolated to scattered storms will form with stronger cells profiting from favorable vertical wind profiles. In such configuration, marginally severe hail might occur with well organised thunderstorms and low-end Level 1 is warranted for this region.
... Bulgaria, Southern Romania ...
Moderate instability built-up is forecast thanks to the diurnal heating and slow upward motion in the left-exit region of strong mid and upper level flow. MLCAPE values might exceed 1000 J/kg, with some models being even more optimistic. Strong flow might sustain DLS values in the range of 15-25 m/s, with the highest values over Central Bulgaria. With slightly backed flow thanks to the approach of the trough in the lower troposphere, SREH values will reach, especially towards the evening, more than 100 J/kg in the 0-3 km layer. Such conditions are conducive of well organised mutlicells and supercells, capable of large hail and severe wind gusts. Limiting factor will be the forcing, however, with GFS breaking out only very little precipitation over Bulgaria. WRF model seems to be more optimistic with isolated spots of precipitations. The highest storm coverage is expected over Southern Romania towards the evening. Strong convergence, deep layer of unstable airmass and low LFCs are suggestive that Bulgaria will also see some convective initiation. With the questions remaining about the degree of storm coverage, only a high-end Level 1 is issued, but an upgrade might become necessary later on.
... Southwestern/Western Hungary, Northern Croatia, Eastern Slovenia ...
Scattered storms are expected to develop thanks to the diurnal heating in weak flow regime and DLS values around 10 m/s. GFS predicts a bullseye of instability over the region with MLCAPEs over 1000 J/kg. NMM agrees with GFS on the moderate instability, although with more northerly placement. In locally more favorable wind profiles, stronger cells might be capable of marginally large hail, but at the moment no Level is issued for this region.
... Extreme Western Russia ...
Ahead of the surface cold front, a moderate instability is simulated with MLCAPEs possibly reaching more than 1500 J/kg, although this might be partly caused by the overestimation of the dewpoints by GFS. With weak DLS, most of the area having its values under 10 m/s, pulse storms or multicell clusters are expected. Stronger cells might be capable of marginally severe hail, but its coverage should be too low to warrant a Level 1 at the moment.
