Storm Forecast
Valid: Wed 22 Aug 2012 06:00 to Thu 23 Aug 2012 06:00 UTC
Issued: Wed 22 Aug 2012 06:45
Forecaster: PUCIK
A level 2 was issued for Poland, Lithuania and Western Belarus mainly for severe wind gusts, large hail and tornadoes.
A level 1 was issued for Latvia mainly for severe wind gusts and tornadoes.
A level 1 was issued for Northwestern Ukraine and Eastern Belarus mainly for severe wind gusts and excessive precipitation.
A level 1 was issued for Czech Republic and Western Poland mainly for severe wind gusts and to the lesser degree for large hail.
A level 1 was issued for Southeastern France, Switzerland, Southern Germany, Austria and Slovakia mainly for large hail and severe wind gusts.
SYNOPSIS
As a de-amplifying ridge moves towards Russia, a band of strong southwesterlies/westerlies with several embedded PV maxima is forecast to overspread most of Western and Central Europe, especially the northern half. Closer to the surface, a frontal zone translates towards southeast across Germany, Czech Republic and Poland, within the mild surface trough that is connected to the larger scale low pressure system over the Northern/Norwegian Sea and Scandinavia.
00 UTC soundings show some modest latent instability over most of Central Europe, with the highest degree over southern Germany. Also, strengthening wind fields are discernible close to the frontal zone. Currently, between 5 and 6 UTC, a quasi-linear MCS formed over borders of Germany/Poland and Northern Bohemia, progressing eastwards.
DISCUSSION
... Poland, Western Belarus, Lithuania ...
SE-ly surface flow combined with 20-25 m/s of SW-ly flow around 500 hPa level should contribute to moderate to strong DLS bulk values in the area (15-25 m/s) which should favorably overlap with tongue of MLCAPE that is well simulated by all of NWP. Dewpoints in the upper teens already present over Poland are also quite supportive of at least moderate CAPE builtup, albeit quickly progressing linear system might cross some of the region of Lvl 2 before significant amount of day-time heating sets in. Also, anvil of the MCS spreading in strong SW-ly upper level flow might be an another issue hindering the amount of heating. Moderate values of SREH are simulated, especially over nothern part of Lvl 2, in the zone of the frontal trough, and many models also show that LLS will be enhanced here, with bulk values reaching 10-15 m/s. Forcing will likely come from either the frontal zone itself or outflow boundaries already set-up by existing convection. A vorticity maxima arriving over the region might help with CIN removal, especially later in the day.
Despite some issues mentioned above, a favorable setup for severe DMC looks to be in store for this region. A lvl 2 is introduced as well organised convection, including supercells and bowing segments within MCS, is quite probable in such vertical wind profiles. Supercells will likely be capable of large hail, severe wind gusts and especially over northern part of level, also of tornadoes. In case of strong quasi-linear MCS, severe wind gusts will be likely, possibly even with an isolated report of extremely severe wind gusts if bow-echo develops with such system. An excessive precipitation event is not ruled out either towards the later stages of MCS and with supercells.
... Czech Republic, Western Poland ...
A linearly oriented MCS progresses in moderate to strong wind shear over the region, but likely only involving modest CAPE release. Isolated severe wind gusts are possible, as mid-level flow continues to be perpendicular to the orientation of the system. Threat might quickly decrease for this region in the matter of next several hours. An isolated large hail event is not ruled out either, especially in case isolated DMC forms ahead of the squall line.
... France, Switzerland, Southern Germany, Austria ...
Some moderate wind shear is forecast for the region, overlapping with weak to moderate latent instability. Mountain-induced circulations, as well as the frontal zone itself will likely initiate scattered DMC. Some well organised multicells are possible, with even supercells not ruled out either (especially concerning S Germany in the late afternoon and evening hours). Such convection might be capable of large hail and/or severe wind gusts. A level 1 looks sufficient attm as only isolated severe is expected.
... Latvia, Eastern Belarus and Northwestern Ukraine ...
Lesser degree of overlap between instability and wind shear is simulated here and convection might arrive quite late here (Belarus and Ukraine). Therefore, threat will likely be less than within the Level 2, but still, isolated severe wind gusts - thanks to the strengthening flow close to 700 hPa and possibility of linear MCS or tornadoes (Latvia - strong LLS in place) are possible.
