Storm Forecast
Valid: Wed 23 Aug 2023 06:00 to Thu 24 Aug 2023 06:00 UTC
Issued: Tue 22 Aug 2023 20:12
Forecaster: GROENEMEIJER

A level 2 was issued across West-Central France, mainly for large hail and heavy rainfall, and to a lesser extent severe wind gusts.

A level 1 was issued across a large region covering parts of France, Spain, the Alpine region, the Pannonian Plain and parts of the Northwest Balkans and of the Carpates, mainly for large hail and local heavy rainfall.

DISCUSSION

France...

A strong slightly anticyclonically curved jet is located southwest of a closed low northwest of Scotland. As the low moves eastward, slight frontogenesis on the northern flank of a deep mixed layer sets in across Northwest France, which will likely prove sufficient for convective initiation during the evening or overnight.

Storms are expected to develop late over western France as steep lapse rates advected from the Bay of Biscay and deep moisture become juxtaposed and weakly-capped elevated CAPE of 2000 J/kg should develop. Probably, initiation will not be before the evening and may be delayed to overnight. Given the 20-25 m/s of effective bulk shear and amount of instability, large hail will be likely and some very large hail, of 5 cm or larger, is not ruled out. In addition, a modest risk of wind and local heavy rainfall will exist.

More isolated, diurnally triggered storms will be possible elsewhere over France and northern Spain. These have a limited risk of producing large hail or downbursts.


Alps and further East...

Storms are likely to form across the Alps and Tatra mountains, and more isolatedly elsewhere across the level 1 area and its surroundings. Some of these storms may briefly produce severe weather including large hail or local heavy rainfall. The risk should quickly diminish around sunset.