Storm Forecast
Valid: Mon 10 Jul 2017 06:00 to Tue 11 Jul 2017 06:00 UTC
Issued: Mon 10 Jul 2017 00:38
Forecaster: VAN DER VELDE

A level 2 was issued for mainly

SYNOPSIS

At 06Z, a broad upper trough is situated across western Europe, with the main upper low over the Norwegian Sea. Several shortwave troughs travel along in the southwesterly upper flow. One such shortwave should move from NE France across NW Germany during the morning, and is associated with the main surface low over the European mainland, likely associated with a mesoscale convective vortex from nocturnal storm activity, if GFS predicts it at the right location. This feature marked by strong low-mid level vorticity should move toward southern Sweden. It is followed by an area of subsidence and poor lapse rates in the afternoon over central Germany and Czech Republic, which would prevent much convection. Over France however, the main axis of the trough, marked by a PV / dynamic tropopause feature, shfts eastward, likely triggering widespread storm activity. The other main area of storm activity is at the warm front and trough over the Hungary-Slovakia-SE Poland-Belarus area.


DISCUSSION

In general, the strongest lapse rates and highest cloud bases are over NE Spain, S France, and the Hungary-Poland region, as well as the stronger deep layer shear. Still moderate shear of 10-15 m/s 0-6 km is present north of 47 deg North where higher moisture content and little capping is present. MLCAPE ranges between 700 and 1500 J/kg in the main areas. Excessive rain events can occur mainly over the moist warm sector region east of the N Germany low, where storm motion would be slowest and PW and RH highest, a well as in the system itself if it maintains an MCS.

...Hungary, Slovakia, S Poland...

An area with 0-1 km shear greater than 10 m/s and 0-3 km SREH of 200-300 m2/s2 is predicted by GFS centered over Slovakia. With no linear triggering features, this indicates that supercells are the likely convective mode, and tornadoes are possible especially in the low LCL region of Slovakia and S Poland. Over Hungary, supercells would be possible and high-based since LCL rises to 2000-2500m. This benefits updraft width and ice growth in the mixed phase region in storms, with large hail as result. Also local severe wind gusts can occur.

...France, NE Spain...

The overlap between strong shear and decent CAPE and quite weak capping should lead to storms with decent potential for large hail production, in particular the areas where LCL is not low: the larger regions around the Ebro Valley and Rhone Valley. Since forcing does not seem very linear at low levels, a squall line may not form at the passage of the upper trough, and instead many clusters and more isolated supercells may form, likely split-cells given unidirectional hodographs. SREH from more circular hodographs is found near the Pyrenees.