Storm Forecast
Valid: Sun 23 May 2010 06:00 to Mon 24 May 2010 06:00 UTC
Issued: Sun 23 May 2010 05:42
Forecaster: SCHLENCZEK
A level 1 was issued for the Netherlands and NW Germany mainly for severe wind gusts and to a lesser extent for tornadoes.
SYNOPSIS
High pressure is centered over the British Channel and a weak upper trough is located over the Black Sea. A shortwave trough will approach from the North Atlantic, moving towards the southern North Sea. In the wake of this trough, cold polar air will replace a warm subtropical airmass over portions of central Europe. Another upper trough, initially located east of the Azores, moves towards W Iberia.
DISCUSSION
...Scotland, NE England...
Over N Scotland, a 30 m/s jet streak at 500 hPa is very close to a region with low-end instability. Right now, satellite images show much mid level cloudiness which will hinder insolation but a few storms may develop during the afternoon. Some storms should become well -organised multicells, capable of producing marginally severe hail and isolated severe wind gusts. The low expected storm coverage precludes a level 1 in this region.
...Netherlands, NW Germany from 18Z until 06Z...
Ahead of the shortwave trough, a weak cold front will form over the North Sea, moving to the SSE. In the vicinity of the frontal boundary, some low-end instability is forecast and QG forcing may be sufficient for initiation. If thunderstorms develop in this environment, they will profit from strong 20 - 30 m/s deep layer shear and 100 - 150 mē/sē SRH3. As the low / mid level wind field is relatively strong, the main threat should be severe wind gusts. Storms may either stay discrete or merge into a bowing line. A tornado is not ruled out as LL shear is strong and the cloud bases should be relatively low. A level 1 should be warranted.
...S Sweden...
In an environment with 15 - 20 m/s deep layer shear, diurnal heating may create a few hundred J/kg CAPE. Some multicells may develop and could produce marginally severe hail. After sunset, convective activity should come to an end as most of the CAPE is surface-based.
...Italy...
Diurnal heating will lead to moderate instability in a weakly sheared environment. Most of the storms that may develop should be briefly organised but a few pulsating storms may produce marginally severe hail. The hail threat should be maximised over N-central Italy. Storms will rapidly diminish after sunset as CAPE vanishes.
...SE / E Europe...
The situation in most parts of southeastern and eastern Europe is nearly the same as it is in Italy. Diurnal heating will lead to locally 1000 - 1500 J/kg CAPE in a weaky sheared environment. A few large hail events are not ruled out but given the sporadic nature of such an event compared to the large area, no threat level was issued. A short-lived tornado cannot be ruled out as well. Peak activity is expected in the late afternoon.
