Storm Forecast
Valid: Sun 01 Aug 2021 06:00 to Mon 02 Aug 2021 06:00 UTC
Issued: Sat 31 Jul 2021 15:10
Forecaster: BEYER
A LVL 3 was issued for far W Austria, parts of Slovakia, Hungary as well as small parts of SE Poland and W Ukraine mainly for (extreme) severe and damaging wind gusts, (very) large hail, and excessive precipitation.
A LVL 2 surrounds this LVL 3 mainly for the same threats but with less probability for extreme events.
A LVL1 was issued across Austria, E Czechia into Central Poland and Lithuania mainly for excessive rainfall.
A LVL 2 was issued for NE Italy into Slovenia mainly for large hail, severe wind gusts, and to a lesser extent for excessive precipitation.
A LVL 1 was issued for parts of W Russia, parts of Finland, and Estonia mainly for severe wind gusts and to a lesser extent large hail. A tornado cannot be excluded.
A level 1 was issued across the high terrain of the Caucasus and Turkey mainly for excessive rainfall.
SYNOPSIS and DISCUSSION
For the overall description of the general weather situation and the convective development please refer to the extented outlook of Pucik.
Herein differences will be explained.
... W Austria, parts of Slovakia, Hungary as well as small parts of SE Poland and W Ukraine...
The main difference to yesterday's extended outlook is an upgrade to an LVL3. Moderate to high CAPE values can overlap with strong shear values. Most of the shear is concentrated in the 0-3 km layer with values locally up to 25 m/s! As a result, long hodographs are present with veering low levels. Models thus forecast plenty of storm relative helicity that supports rotating updrafts.
High-resolution models suggest the development of supercells and linear elements that with the support of the strong mid-level flow and 0-3 km shear have a high probability to develop into several bowing segments. As a result extreme severe and damaging wind gusts are possible.
In the southern part of the LVL 3 area, LCLs are rather high with inverted-V shapes in the forecast soundings. This enhances the chance for extreme severe wind gusts with any organized storm that can form there.
In the northern part of the LVL3 area into the LVL2 area, LCLs are much lower mainly due to a higher LL moisture. Given the fact that also LL shear has partly values of more than 10 m/s, there is a chance that a tornado may develop.
Still further north into the LVL1 area (from Austria and E Czechia into Central Poland and Lithuania) the main focus lays on excessive precipitation given plenty of moisture as can be seen by PWAT values of locally more than 40 mm.
The whole system is moving northeastward during the forecast period while the risk of severe weather will decrease step by step during the night with a risk mainly for excessive precipitation approaching the end of the forecast period.
...NE Italy into Slovenia...
Nothing special has changed so far. Still, a good overlap of about 1000 J/kg with DLS of around 20 m/s can be found. Thus organized convection and supercells are forecasted with the main threat pointing to (very) large hail and severe wind gusts.
... Parts of W Russia, parts of Finland and Estonia...
The reasoning named in the extended outlook is still valid. Long straight hodographs are present in parts of the forecast region, especially to the south. Having also moderate CAPE values around 1000 J/kg organized convection and supercells can develop that then can bring severe wind gusts and locally large hail.
Still, some model uncertainty is present which thus makes it difficult to find the region of best CAPE-shear overlap. The southern part of the LVL1 area is closest to a possible LVL2.
... Caucasus and Turkey...
Nothing has changed here with excessive precipitation being the main threat due to weak storm motion and high BL moisture.
