Forecast Update
Valid: Mon 06 Jul 2009 11:00 to Tue 07 Jul 2009 06:00 UTC
Issued: Mon 06 Jul 2009 11:25
Forecaster: TUSCHY
A level 2 was issued for NE/E-Spain mainly for large hail and severe wind gusts.
A level 1 was issued for most parts of Italy, Slovenia, S-Austria and parts of Croatia mainly for large hail and excessive rainfall.
A level 1 was issued for N/E-France, SW/W/NW-Germany, Luxembourg, Belgium, the Netherlands and parts of Switzerland mainly for large hail and severe wind gusts.
A level 1 was issued for S-/E-UK mainly for large hail and tornadoes.
SYNOPSIS
Please refer to the main outlook.
DISCUSSION
... E/NE-Spain ...
We went ahead and upgraded parts of the level-1. 00Z Barcelona reveals very unstable conditions with 2000 J/kg MLCAPE and strong speed shear in the main updraft region. Dewpoints remain in the mid-tens, however very moist airmass is present to the south/east, so some increase is still possible. No major change is forecast in the mid-levels with moderate lapse rates and constantly increasing DLS, so supercells with large to very large hail and severe wind gusts are all possible. Initiation is imminent or already underway along the coast and thunderstorms develop further to the west later this afternoon as a weak vorticity lobe approaches from the west.
Latest WV loop has the strong short wave now over the Balearic Islands, which already caused a few storms over NE-Spain. 00Z sounding of Palma de Mallorca indicates a stout cap but a few storms are now present in high resolution visible images. Elevated nature is quite likely but the activity decreases during the next few hours as the short wave has passed. No real forcing mechanism is seen, which could foster further development. Nevertheless, surface dewpoints of 19-24°C and steep lapse rates keep 'loaded gun configuration' present throughout the day, so any storm, which manages to form will cause mainly large hail. Low probability thunderstorm lines (not yet made public) were expanded further east, now including all of the Balearic Islands.
... Italy ...
Not a lot of changes were performed over Italy. The level-1 was expanded further towards the south as surface dewpoints of 20-24°C now cover all of Italy with slightly lower values over the NW. 00Z and 06Z soundings either show very unstable conditions or an atmosphere, which becomes increasingly favorable for abundant CAPE release, probably in the order of 1000-2500 J/kg MLCAPE. Explosive development is forecast in a weakly sheared environment with hail and flooding rain the main risk. Please refer to the main outlook for further details.
Low thunderstorm probabilities (not yet made public) were expanded over extreme S-Italy and Sicily due to the approaching short wave (which now exits the Balearic Islands). A few elevated storms are possible with isolated large hail the primary risk.
... S/E-Austria ...
Thunderstorm probabilities were increased with good BL moisture and some insolation, so scattered thunderstorms are expected or already ongoing. Shear is weak but isolated large hail and excessive rainfall is possible due to roughly 1kJ/kg MLCAPE release and increasing anvil layer shear (supporting more persistent updrafts). Hence a marginal level-1 was introduced.
... France, parts of Germany, Belgium, the Netherlands and Luxembourg...
The level-1 was enlarged as dew points in the mid tens continue to surge northeastwards beneath increasingly colder mid-levels. Daytime driven convection is already in progress althoug updrafts still look quite small and disorganized on the radar. However, better instability release during the afternoon hours ought to increase the risk of isolated large hail and severe wind gusts, especially over Belgium and the Netherlands as LL shear strengthens.
... Parts of United Kingdom ...
An upgrade was performed due to the risk of tornadoes over S-UK, as shear at low and mid-levels is on a slight increase. In addition, 00Z soundings of Ireland already revealed some LL CAPE release, which will be seen, too in 12Z sounding data over parts of UK. Another reason for the level-1 was the marginal hail risk and locally intense convective precipitation.
