Storm Forecast
Valid: Wed 08 Jul 2020 06:00 to Thu 09 Jul 2020 06:00 UTC
Issued: Tue 07 Jul 2020 21:35
Forecaster: PUCIK
A level 3 was issued across northwestern Russia mainly for severe to extremely severe wind gusts, tornadoes, some possibly significant, and large to very large hail.
A level 2 was issued across western and 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.
A level 1 was issued for northern Turkey mainly for heavy rainfall.
A level 1 was issued across Iberia mainly for severe wind gusts and to the lesser degree for large hail.
SYNOPSIS
Synoptic-scale situation will be dominated by a deep cyclonic vortex centered over the Baltic Sea. A short-wave trough will stretch from Belarus towards Ukraine at 06 UTC Wednesday and is forecast to move towards northeast during the day. Ahead of the vortex, strong low to mid-tropospheric flow is forecast along and ahead of the wavy frontal boundary. In the warm sector, an elevated mixed layer will have advected from Turkey and Caucasus towards northern Russia, overlapping with abundant lower tropospheric moisture with mixing ratios around 12 g/kg. Scattered to 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
... Northwestern Russia ...
*** An outbreak of severe convective storms is forecast over this area, including potential for hurricane-force wind gusts, significant tornadoes and very large hail! ***
There is a general agreement in global models (ECMWF / GFS / ICON) regarding:
1. Advection of abundant lower tropospheric moisture towards northern Russia, which will overlap with steep mid-tropospheric lapse rates.
2. Presence of very strong southerly flow between 850 and 700 hPa reaching 20 - 30 m/s.
3. Initiation of several clusters of storms along the wavy frontal boundary with cold front moving eastwards and warm front rapidly progressing northward.
4. Short-wave trough lagging the low-level frontal boundary with mid to upper tropospheric synoptic-scale lift simulated over the cool airmass west of the boundary.
Differences in the individual models stem from the differences in the evolution of areas with strong-lift along the wavy frontal boundary. GFS and ICON simulate the strongest lift along the frontal wave early in the forecast period while ECMWF simulates the strongest lift in the 12 - 15 UTC time frame. This will likely affect the timing of the strongest storms.
All of the models simulate significant overlap of MLCAPE values exceeding 1000 J/kg and over 20 m/s of 0-3 km bulk shear, but the exact positioning of this overlap, as well as the location of simulated storms, differs. ECMWF simulates most severe storms along the western fringe of the Level 3, while GFS simulates the best conditions along the eastern fringe of the highlighted area.
Despite the differences in the models, confidence is high that one or more long-lived convective systems will develop during the forecast period with a high threat of damaging wind gusts. Given the degree of low-level shear and the abundance of moisture and CAPE, some of the wind gusts will likely reach hurricane-force. Very large hail may occur with more isolated storms in the warm sector, or in the early formative stages of the MCS developing along the frontal boundary.
Threat of significant tornadoes will be conditional on the convective mode and also the degree of SRH along the frontal wave. While GFS shows mostly straight hodographs, ICON and especially ECMWF maintain significant overlap of high CAPE values and SRH exceeding 300 m2/s2 in the 0-1 km layer with strongly curved hodographs. Combined with low LCLs and surface-based inflow parcels, any isolated supercell may be capable of a strong tornado in such an environment.
A Level 3 is introduced for an area, which should see the highest risk of extremely severe storms during the forecast period. That said, the exact evolution of the situation will strongly depend on the short-term evolution of the frontal boundary and the abundance of convective storms in the morning hours over the western part of the highlighted area. Thus, the situation should be revisited in the morning hours to narrow down the corridor of the highest severe weather threat.
... 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.
