CONVECTIVE FORECAST
VALID Wed 29 Jun 06:00 - Thu 30 Jun 06:00 2005 (UTC)
ISSUED: 29 Jun 08:36 (UTC)
FORECASTER: VAN DER VELDE

There is a slight risk of severe thunderstorms forecast across Eastern France, Southern Germany, Northern Italy, Switzerland and Austria, Slovenia

SYNOPSIS

An upper trough and cold front move into France and the British Isles today. Like the previous days, a very unstable airmass will be in place and generate numerous thunderstorms again. Instability will be elevated over the UK and Ireland, as well as most of the the Mediterranean (capped BL parcels). A large barotropic upper low / shallow sfc low pressure area near the Baltic States will again produce many showers and some thunderstorms.

DISCUSSION

...Eastern France, Southern Germany, Northern Italy, Switzerland and Austria, Slovenia...
As an upper trough and cold front move into eastern France, expect numerous thunderstorms to form in the unstable airmass (MLCAPE 1000-2000 J/kg). Due to the organised linear nature of forcing, expect a squall line or a few MCS systems to form in the afternoon/evening. These may produce widespread severe gusts and locally large hail. The moderate wind shear conditions (DL shear 30-40 kts, LL shear <15 kts, generally) seem just a tad on the low side to issue a moderate risk, therefore opted for SLGT. However, isolated storms may form rotating updrafts. This is especially probable in southeastern France and northern Italy, where GFS and NMM models expect 0-3 km SREH (100-200 m2/s2) to be largest. NMM clearly favors DL shear to be largest there too, and shows lower values in northern parts of the SLGT than GFS 18Z. Over Nrn Italy, more than 2000 J/kg MLCAPE may develop locally, but synoptic forcing is less apparent, although the cap is not strong. Supercells may form with a chance of large hail and perhaps even a tornado given enhanced SREH and LL shear. For the rest of the SLGT area, forcing is more local and conditions look good for large hail and severe downdraft winds, by cells that may be long-lived and/or develop rotating updrafts.

...Finland, Baltic States and eastward...
Setup seems ideal for land/waterspout type tornadoes and funnel clouds... Tallinn 00Z sounding showing very moist low levels, weak lower tropospheric winds and some low-level CAPE. Expect these profiles over large area, and especially where linear clustering of cells develops (convergence lines) spin-up of vertical vorticity should occur.

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