Storm Forecast
Valid: Wed 08 Jun 2016 06:00 to Thu 09 Jun 2016 06:00 UTC
Issued: Tue 07 Jun 2016 20:23
Forecaster: PUCIK

A level 1 was issued for Central, Southwestern Germany, Eastern France, Switzerland and Northern Italy mainly for the excessive precipitation and to the lesser extent for large hail.

A level 1 was issued for Northwestern Russia mainly for severe wind gusts.

SYNOPSIS

At mid-troposphere, a highly amplified ridge will stretch from Iberia towards Ireland and Iceland. On its forward flank, in northwesterly flow, a short-wave trough will move from N France towards Sardegna and Corsica. Towards northeast, a deep low will make its way across Scandinavia towards SE. At the same time, much of E and SE Europe will be under relatively cool mid-tropospheric temperature.

As in the previous days, most of the DMC activity will be confined to Central-W Europe, where abundant low-level moisture contributes to low to moderate CAPE values in the very weak flow pattern. This will continue also in the current forecast period, although the moisture will be slowly eroded in the northern part of area due to the advection of drier airmass. Towards northeast, isolated to scattered DMC will form ahead of the advancing cold front that will cross Baltic States and N Poland by Wednesday night.

DISCUSSION

... Central Germany, SW Germany, E France, Switzlerland, N Italy ...

Tuesday 12 UTC soundings from Essen, Idar, Trappes, Payerne and Milano well document the thermodynamic setup that features low to moderate CAPE values (up to around 1500 J/kg) and steep low-level lapse rates. All soundings also show very weak flow favouring slow moving to quasistationary storms. Model output simulates slight decrease in lapse rates towards this forecast period. Loci of the storm activity will shift southwards as dry air is advected from the Northern Sea. Widespread initiation is expected once again with low LCLs / LFCs and also with the aid of two short-waves that cross the region. The first one, aforementioned in the synopsis, will likely aid in sustaining some DMC activity already in the morning hours especially over E France and W Germany. The second one will follow in the evening / night hours, crossing W Germany / E France on Wednesday night.

DLS is forecast to increase on the western flank of the short-waves, but this will influence the DMC only on the western fringe of the highlighted area. Otherwise, in weak shear, chaotic, short-lived multicell clusters are forecast, likely lined up along the local convergence zones. Models simulate numerous convergence zones, one of them ahead of the advancing dry air over Germany and France, others e.g. over S France or N Italy. Excessive precipitation will be the primary threat due to the slow moving nature of storms and sufficient low-level moisture. Large hail may occur with stronger multicell storms, especially over N Italy. Wet downbursts and landspout tornadoes will be possible as well, but should be of much smaller coverage than the excessive rainfall.

... Northwestern Russia ...

A strong cold front will push across the area with 850 to 700 hPa flow of around 15 m/s, resulting in DLS above 10 m/s. A strongly forced low-topped squall line is quite possible in this scenario with a threat of isolated severe wind gusts. Higher end risk is precluded by a lack of higher CAPE values and also by a lack of stronger flow at both low and mid to upper troposphere.