Storm Forecast
Valid: Wed 22 Apr 2015 06:00 to Thu 23 Apr 2015 06:00 UTC
Issued: Tue 21 Apr 2015 21:18
Forecaster: PUCIK

A level 1 was issued for parts of Morocco and Algeria mainly for large hail and severe wind gusts.

SYNOPSIS

A ridge stretching from the Mediterranean into British Isles will weaken as a trough progresses from Iberia to S France. At the eastern flank of the ridge, a cut-off low will move S-wards over E Germany. E part of Europe will still be under a deep trough with prevailing N-ly to NW-ly flow as an arctic airmass has reached the Aegean Sea and S Turkey.

Much of Europe will be under dry and stable conditions, apart from several areas (such as NW Iberia and E Bulgaria), where modest CAPE will allow for scattered DMC.

DISCUSSION

... NW Iberia ...

Mid to upper tropospheric trough will lift N-ward across the region during the day along with cold mid-level temperatures. With advection of moister airmass inland, several hundreds J/kg of CAPE will be possible over this region. In low CIN environment and in the warm advection regime, scattered thunderstorms are forecast. Due to the rather weak vertical wind shear, with DLS values mostly below 10 m/s, DMC organisation will likely be limited to multicell clusters. Even though stronger cells may produce marginally large hail or excessive precipitation, low values of CAPE and DLS preclude higher coverage of threat.

... Morocco to Algeria ...

Perhaps due to the development of thermal low, models simulate moist onshore flow, setting up a sea breeze boundary well inland. With steep lapse rates above, CAPE values above 1000 J/kg will be possible along the boundary. As vertical wind shear reaches 15 to 25 m/s, well organised convection, including supercells is likely. Main limiting factor will be high CIN values with no other apparent forcing apart from the low-level boundary. Even though degree of inititation is questionable, storms that form will be capable of large hail and/or severe wind gusts.

... E Bulgaria, NE Greece, NW Turkey ...

Despite the presence of rather dry airmass, passage of trough at mid to upper troposphere filled with cold airmass will result in steep lapse rates. Towards the afternoon, thanks to daytime heating, some marginal CAPE will result. Strong DLS is simulated with values above 20 m/s. However, storms will likely be low-topped and in the lower levels, shear should be rather weak. Therefore, it is highly questionable, to what degree will storms be able to organise and this precludes Level 1. However, in the rather cold environment, any stronger cell may produce hail, even though mostly sub-severe.