Forecast Update
Valid: Tue 30 Mar 2010 13:00 to Wed 31 Mar 2010 06:00 UTC
Issued: Tue 30 Mar 2010 13:31
Forecaster: TUSCHY
A level 1 was issued for Germany and parts of Netherlands mainly for isolated large hail/severe wind gusts.
A level 1 was issued for parts of Italy towards Adriatic Sea mainly for large hail, severe winds, excessive rainfall and lesser extend for tornadoes.
A level 1 was issued for Northeastern Italy and western Slovenia mainly for excessive rainfall.
SYNOPSIS
Please refer to the outlook, issued at Mon 29 Mar 2010 23:57 UTC.
DISCUSSION
... Germany and the Netherlands ...
Latest satellite data prints the strongly negative tilted trough now over north-central/southeast France with high-level PVA spreading gradually eastwards (increasing cirrus band over W-Switzerland and E-France at 13Z). Over Germany, we had good insolation with T/Tds now running at roughly 15-20°C from north to south / 5-9°C , increasing from S/W-Germany to central/north Germany. Modified soundings reveal a convective temperature, which will be hit during the upcoming 1-2h or so (also fostered by first shower development). This activity is daytime driven and especially where BL air mass is well mixed, no real support for deep/persistent updrafts is present (12Z soundings also indicate, that not much CIN is left). Nevertheless, showers and thunderstorms increase in coverage and strength during the afternoon hours (dependent on the extent of the cirrus shield and attendant diabatic heating, with regional differences in final TSTM coverage expected).
As forcing and double-front move in from the west during the late afternoon/evening hours, thunderstorm coverage will increase rapidly from west to east with a more organized appearance along the leading convergence zone/cold front. Also, some high-level divergence is in place, so thunderstorm coverage will become scattered.
No significant jet feature ejects out of France with strongest wind field mainly displaced to the cold sector/second cold front, where thermodynamics become worse. Shear is therefore marginal with multicells likely, posing an isolated large hail and strong wind gusts risk. A line-up along the cold front is probable with an MCS feature propagating from west/central Germany to the east/northeast or even due north over N-Germany, where mid-level winds back to southerly directions. One positive point could be the time of year, where a combination of still early loss of daylight, cold postfrontal air mass and a deep mixed layer (S-Germany) could increase the strength of downdrafts, which may locally increase the wind gusts risk to our severe criterion. The combined risk of isolated large hail/severe wind gusts but also the increased coverage of storms were the reason for upgrading parts of Germany to a level 1. In respect of ingredient-based forecasting, there is no real hint on an elevated tornado risk.
Thunderstorms keep going well into the night due to the forced nature, although they become more elevated in nature with a deacrease of the severe risk and coverage.
... NE-France ...
A line of showers/thunderstorms currently accompanies the second front and strong wind gusts/marginal hail are likely during the frontal passage. This activity is either peaking in intensity or is just about to do so during the upcoming 1-2h, as CAPE diminishes betimes. We went with a thunderstorm area, but no level 1 was issued for that. However, this cold front could stay more active in respect of showers/ a sporadic thunderstorm all the way up to Belgium and extreme W-Germany with strong wind gusts and marginal hail.
... Italy ...
The level 1 was adjusted a bit to the SW but otherwise no further modifications were carried out.
