Forecast Update
Valid: Wed 22 Jul 2009 13:00 to Thu 23 Jul 2009 06:00 UTC
Issued: Wed 22 Jul 2009 13:24
Forecaster: PUCIK

SYNOPSIS

Refer to the Storm Forecast

DISCUSSION

... France, W Germany and the Benelux....

The level 2 has been expanded to the northwest as models are now simulating a wave in the frontal boundary, which could travel across the Benelux. Additionally, more of southwestern France has been included.

The frontal zone is warm and humid and numerical models exhibit an area of surface based instability, supported by sounding observations. This instability should persist into the night hours. Kinematic parameters such as wind shear and SREH indicate that a high potential for rotating storms is present with shear in the lowest 3 km exceeding 25 m/s and SREH over 300 J/kg. In such an environment, supercells with a tornadic potential will easily develop out of isolated cells (very low LCLs, high SREH in the lowest km and shear 0-1 km close to 15 m/s point to the slight chance of significant tornadoes). The supercells will also have a threat of large hail again.

The wave low is expected to move northeastward across France during the afternoon. After storm initiation across southwestern and central France, rapid clustering is likely and an MCS will probably form, accompanied by damaging wind gusts and possibly tornadoes. The highest threat should exist between 18Z and 00Z, when the forcing will be the strongest (an effect of the short wave trough plus an approaching jet-streak).

N Germany, S Denmark, extreme S Sweden...

Furthermore, the level 1 has been expanded to the north across northern Germany, southern Denmark and southern Sweden, where storms might form in moderately unstable environment and moderate wind shear (0-6 km around 15 m/s) so that an isolated large hail event is not ruled out. Due to the complexity of the situation, Level 1 is issued for the regions, where models point to at least a slight chance of isolated severe storm events.

Poland...

A larger part of Poland is now included in the level 1, as convective storms are expected to develop there, within an environment of rather strong deep-layer shear. It is likely that some well-organized multicells and a few supercells develop, which could bring large hail and a few severe gusts.