Storm Forecast
Valid: Fri 20 Jun 2008 06:00 to Sat 21 Jun 2008 06:00 UTC
Issued: Thu 19 Jun 2008 18:04
Forecaster: TUSCHY

SYNOPSIS

Downstream of an amplified streamline pattern over the far eastern Atlantic Ocean, a more zonal flow pattern persists over parts of N - central Europe. Strong ridging will dominate during the next 24 hours. A flat upper - level trough over eastern Europe and weak pressure differences at the surface support enhanced convective activity over a wide area mainly along an eastward moving cold front.

DISCUSSION

... N - Italy, S - Austria and Slovenia ...

Latest synop data ( 17Z, 19th June ) reveal locally rich BL moisture with readings of 17 - 20 °C over N - central Italy. Sounding data have no real impressive look as instability release is quite marginal. For today not much change is in store for the area of interest as flat ridge builds in from the SW. Temperature profiles will not change a lot but models now increase instability values significantly to locally more than 1000 J/kg MLCAPE. Mid - level lapse rates steepen somewhat due to weak WAA, however modified soundings do not support that impressive instability values. We think that the environment gets characterized by low - end CAPE values and weak shear so the severe risk will stay low. We can't exclude locally higher instability values due to better BL moisture ( e.g. S and SE of Milan ), and an isolated large hail risk can't be excluded but otherwise the main risk will be strong wind gusts and sub - severe hail. The same for S - Austria where somewhat stronger 0-6km bulk shear values exist but again, instability will be the limiting factor.

An upgrade due to a large hail risk may be issued if later model data / sounding reports hint on a better thermodynamic environment than currently anticipated.

... NE Spain ...

Strong cap will be in place as LL levels stay warm. 500 hPa temperature cools down somewhat during the day, resulting in steeper mid - level lapse rates. Strong diabatic heating could lift parcels above the LFC but confidence is not high that activity will be as active as GFS forecasts. For now we expect only a few storms along the Pyrenees with a strong wind gust / marginal hail risk. This activity will be diurnal driven and it should decrease after sunset.

... Parts of S - Finland, Estonia, Latvia, Lithuania, Poland and Belarus ...

An eastward moving cold front will spark scattered thunderstorms and modest shear and instability could support multicells / an isolated supercell as some veering at mid - levels will be present. Isolated large hail will be possible despite overall weak mid - level lapse rates but the main risk will be sub - severe wind gusts and hail. DLS of 20m/s and a well defined and rapidly NE - ward moving vorticity maximum over Estonia during the evening hours could support a line of thunderstorms with an isolated severe wind gust risk but the overall environment does not support a level area.

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