Storm Forecast
Valid: Thu 09 Jul 2020 06:00 to Fri 10 Jul 2020 06:00 UTC
Issued: Wed 08 Jul 2020 22:27
Forecaster: GATZEN
A level 2 was issued across western Russia mainly for large hail, severe wind gusts and to a lesser extent excessive rain and tornadoes.
A level 1 was issued across south-western Russia towards Georgia and Armenia mainly for excessive precipitation.
A level 1 was issued across northern, cdentral and eastern Spain and northern Portugal mainly for large hail and severe wind gusts.
A level 1 was issued across central Austria mainly for large hail.
SYNOPSIS
Downstream off the zonal flow that has established across most of Europe, a mid-level trough progresses across eastern Europe. A well-developed frontal boundary continues to move east, with a very moist and unstable air mass to the east of it. With ongoing advection of this air mass towards the north, another high-latitude severe convection day is expected on Thursday.
In the wake off the frontal boundary, rather calm conditions are forecast for most of Europe due to weak lapse rates and/or limited low-level moisture. An exception is the Iberian Peninsula, where steep lapse rates are present that overlap with sufficient low-level moisture.
DISCUSSION
Russia
On Thursday, the frontal boundary will continue to move east. Again, a highly unstable air mass is expected east of the cold front, with CAPE in the order of 1000 to 2000 J/kg, thanks to rich low-level moisture and steep mid-level lapse rates. Some frontal lift is expected to develop during the day. Especially GFS indicates that storms form along and ahead of the front during the day. Strong vertical wind shear within the level 2 area of 15 to 20 m/s both 0-6 and 0-3 km bulk shear will support storm organization inculding MCSs and supercells.
In the southern portions of the level 2 area, deeper boundary layer mixing is expected to increase outflow dominant storms with a potential of downbursts. Large to very large hail is also forecast with supercells. In the northern portions, moist profiles will be present, and supercells may be capable of producing tornadoes given around 10 m/s 0-1 km shear. The highest potential is expected along the northern edge of the level 2 where strongly curved low-level hodographs are expected in the warm air advection regime. Strong tornadoes are not ruled out.
At the western and northern fringe of the level 2 zone, elevated storms are forecast with a less pronounced severe weather threat, although vertical wind shear is expected to be strong. Storms that root to the boundary layer will be capable of producing all kinds of severe weather including tornadoes.
South-western Russia to Georgia and Armenia
The frontal convergence zone is expected to persist over this region, where rather rich low-level moisture still overlaps with steep lapse rates. Vertical wind shear is weak, however, well-mixed boundary-layer over southern Russia and Georgia support some local downbursts. Over the Caucasus mountains, slow-moving storms in an environment with skinny CAPE profiles are forecast to cause local flash floods.
Iberian Peninsula
A mid-level vortex enters the Iberian Peninsula. Steep lapse rates are present and overlap with some low-level moisture that also supported storms on Wednesday. Initiation is forecast over the mountains during the day. Deep boundary layer and associated downdraft CAPE will support downbursts. Across the eastern part of Spain, strong deep layer shear is forecast along the flanks of the trough. Storms that form in this environment can become supercells capable of large hail and severe wind gusts.
Austria
A weak frontal wave passes across the Alps on Thursday, with warm air advection spreading east across Austria. Weak easterly low-level winds and moderate north-westerly mid-level flow will cause moderate deep layer shear. Some storms are expected to develop over the mountains that can develop rotating updrafts. Some large hail is forecast. Limited CAPE will reduce severe weather potential and storms are forecast to be rather short-lived.
