Storm Forecast
Valid: Tue 25 Apr 2017 06:00 to Wed 26 Apr 2017 06:00 UTC
Issued: Mon 24 Apr 2017 21:51
Forecaster: DAFIS

A level 1 was issued for Spain mainly for severe wind gust, excessive rainfall and large hail.

A level 1 was issued for S Germany, N Austria, Czech Republic and Poland for severe wind gusts and large hail.

SYNOPSIS

The longwave trough that caused the last week's cold blast has a negative tilted axis over East Europe, heading towards Russia. Another trough is expected to affect West Europe the following days, where the jet stream curves around its southern flank, and strong vertical shear, apart from upper-level cooling, will take place. At the surface, an elongated cold front will cross West Europe during Tuesday and WAA is expected ahead of a warm front in the eastern parts of the continent. Isolated to scattered thunderstorms are possible in several areas as shown on the map, producing graupel/small hail and gusty winds.

DISCUSSION

.... Spain ....

Strong DLS will be present near the CAPE max over N Spain and this can enhance updrafts enough to increase hail size up to 2-3cm (if CAPE values of near 1000 J/kg verify). Wind flow below 500 hPa is expected to be rather weak until 12-15z and PW values reach 25mm, so excessive precipitation from slow moving storms cannot be ruled out. Later, when the powerful jet enters N Spain and steep lapse rates form, we expect the peak of thunderstorms' intensity. Activity should gradually stop during the night.

.... Central Europe ....

As the cold front moves south during Tuesday, WAA along the highlighted level 1 area will provide also moist BL air masses, and this boundary will be found under the strong jet stream. GFS produces marginal CAPE up to 1000 J/kg in response to diurnal heating over SW Poland and high 0-3km SREH can provide rotation of some thunderstorms. These storms will probably form clusters with primary threats of severe wind gusts. Winds near 850 hPa may exceed 25 m/s at the leading edge of the trough.