Storm Forecast
Valid: Fri 23 Sep 2016 06:00 to Sat 24 Sep 2016 06:00 UTC
Issued: Thu 22 Sep 2016 17:46
Forecaster: TUSCHY

A level 1 was issued for parts of Spain, NE-Algeria and N-Tunisia mainly for large hail, a few severe wind gust events and excessive rain.

SYNOPSIS and DISCUSSION

Blocking pattern over Europe shows temporal weakening tendencies as a weak mid-/upper trough passes W-CNTRL Europe and enters the W-Mediterranean during the night. Parts of E/NE Spain are still covered by BL mixing ratios in excess of 9 g/kg, as colder mid-levels / 7.5 to 8 K/km mid-level lapse rates move atop. Resultant 800-1500 J/kg SBCAPE and 10-15 m/s DLS (decreasing towards Catalonia) will be adequate for organized multicells with large hail and strong to isolated severe wind gusts. Betimes, storms grow upscale into temporarily better organized clusters, which enter the far W-Mediterranean with a subsequent excessive rainfall, large hail and isolated severe wind gust threat. Would not be surprised to hear about an isolated tornado event along the coast, where LCLs drop below 1000 m and interaction with mesoscale boundaries along the coast may occur.
Weakening convection may reach the Balearic Islands during the night and thus the level 1 was expanded far east.
Rapid re-strengthening of the mid-level ridge further upstream is forecast from Portugal to the North Sea during the night with deacreasing thunderstorm activity from W to E.
The severe risk extends all the way to NE-Algeria/N-Tunisia.

Else, a strong cut-off low chokes off the westerlies and moves over S-Norway towards S-Sweden and the Baltic Sea. An intense 40 m/s mid-level jet, strong synoptic-scale lift and rapid cool down beneath its center will support scattered thunderstorms. Stronger storms may bring marginal hail and gusty winds, but most of the activity should stay sub-severe. An isolated funnel/short-lived tornado event is possible as LLCAPE values increase a bit during peak heating (e.g. over offshore regions).

A strong upper trough over NE/E Europe sends a dry and cool air mass far south and suppresses DMC activity over that area.