Extended Forecast
Valid: Wed 08 Jul 2020 06:00 to Thu 09 Jul 2020 06:00 UTC
Issued: Mon 06 Jul 2020 20:32
Forecaster: PUCIK

A level 1 was issued across Iberia mainly for severe wind gusts and to the lesser degree for large hail.

A level 2 was issued across northwestern Russia mainly for damaging wind gusts, tornadoes, large to very large hail and excessive rainfall.

A level 1 was issued across southwestern Russia, Caucasus and northeastern Turkey mainly for large hail, heavy rainfall and severe wind gusts.

SYNOPSIS

Synoptic-scale situation will be dominated by a deep cyclonic vortex centered over the Baltic Sea. Ahead of the vortex, strong low to mid-tropospheric flow is forecast along and ahead of the wavy frontal boundary. Ahead of the boundary, an elevated mixed layer will have advected from Turkey and Caucasus towards northern Russia, overlapping with abundant lower tropospheric moisture with mixing ratios at or above 12 g/kg. Widespread storms are forecast in a belt from Caucasus through southeastern Ukraine into western and northwestern Russia. Further storms are expected underneath the cyclonic vortex with modest lower tropospheric moisture and lapse rates exceeding 6.5 K/km. Isolated to scattered storms are also forecast over northern half of Iberia, underneath a cut-off low.

DISCUSSION

... Western and northwestern Russia ...

A severe weather outbreak is forecast over northwestern Russia with threats of damaging wind gusts, very large hail and also tornadoes, some of which could be strong.

Exact details such as prevailing convective mode and the corridor of the highest severe weather still remain uncertain at this time. However, NWP models agree on the overlap of substantial CAPE, locally exceeding 2000 J/kg and very strong lower-tropospheric wind shear. Along the frontal bundary, 0-3 km wind shear is forecast to exceed 20 m/s, with 850 and 700 hPa flow reaching up to 25 m/s. Models initiate scattered to widespread storms along the boundary. It is clear that potential will exist for very severe, long-lived storms that may be capable of all severe weather hazards. A long-lived convective windstorm, resulting from one or more fast moving bow-echoes, seems to be the most likely outcome of the situation as of now.

Models disagree on the location of the short-wave troughs along the periphery of the cyclonic vortex, which will be crucial in the movement of the frontal boundary and the evolution of the low-level wind field. ECMWF seems to be most aggresive with the south to north moving short-wave, quickly deepening surface low and associated ageostrophic flow resulting in strongly curved hodographs with SRH exceeding 400 m2/s2 in the 0-3 km layer near the warm front. In such case, strong tornado threat would be present in any supercell that forms in this environment. GFS and ICON simulate more southern track of the short-wave with more unidirectional shear profiles along the boundary, suggesting more pronounced severe wind gust than tornado threat. The highest corridor of severe weather would also be confined more to the southeast compared to the ECMWF.

Level 2 currently highlights the area with the highest anticipated severe weather risk, but its positioning will likely change in the subsequent forecast. If the model spread decreases in the following model runs, a Level 3 may become necessary.

... Iberia ...

NWP models unanimously agree on the presence of deep boundary layer with almost dry-adiabatic lapse rates extending up to 600 hPa. While there is some uncertainty regarding the coverage of storm initiation and the degree of CAPE, synoptic-scale lift ahead of the low may aid with the initiation and widely scattered, high based storms are forecast. Primary threat will be severe wind gusts, but large hail may occur as well closer to the coastlines, where more abundant moisture will result in higher CAPE values.