Storm Forecast
Valid: Tue 30 Jun 2009 06:00 to Wed 01 Jul 2009 06:00 UTC
Issued: Tue 30 Jun 2009 05:07
Forecaster: VAN DER VELDE

A level 1 was issued for N/W Poland, Czech Republic, E Austria and surroundings mainly for excessive rainfall.

A level 1 was issued for the United Kingdom for excessive rainfall.


SYNOPSIS

Europe is largely free of synoptic scale low and significant high pressure systems, but the airmass is unstable over a large area. A weak upper ridge stretches from the Iberian Peninsula to Scandinavia, while 700 to 300 hPa heights are lower over the Balkan. A frontal system belonging to an Atlantic low will drag over Ireland and Great Britain.
Due to weak wind profiles, shear is less than 10 m/s virtually anywhere, and storms will tend to move very slowly, contributing to pulse type storms with local flash floods, to possibly more excessive convective rain events near persistent convergence zones. Isolated landspouts are also not ruled out.


DISCUSSION

...N/W Poland, Czech Republic, E Austria and surroundings...

In this area, 800-1500 J/kg CAPE is present in combination with LCL heights below 1200 m, weak winds and small Bunker's and Corfidi storm motion vectors. One or more convergence zones are present and stationary. 2-4 km lapse rates and DCAPE are weak, which is favorable for weak cold pools which would prevent boundaries from moving. Storms may persist in one location long enough to cause excessive precipitation, leading to flash flooding.
In the drier region to the east, isolated gusts or marginally hail are not ruled out.

...UK and Ireland...

A nearly saturated airmass with large precipitable water content is advected from the south and CAPE is predicted to develop, mostly over Wales and N England. Storm motion will be relatively slow and oriented along the source of lift. Regenerating convection may therefore keep training along a line for extended periods, leading to flash floods, while large scale models may underestimate precipitation. In Ireland the same moist airmass passes but with almost no instability (elevated), may need to be upgraded later on. The moisture load, weak lapse rates and deep warm cloud depth may reduce electrification.