Storm Forecast
Valid: Wed 03 Jun 2009 06:00 to Thu 04 Jun 2009 06:00 UTC
Issued: Tue 02 Jun 2009 22:59
Forecaster: PUCIK

A level 2 was issued for Ukraine and Western Russia mainly for severe wind gusts, large hail and tornadoes.

SYNOPSIS

At midlevels, a deep trough with center over Scandinavia will stretch into the Eastern part of Mediterranean, remaining quasi-stationary and deepening slightly. Strong flow is observed around the trough with isolated spots of 30 m/s wind speed. To the west a narrow ridge has established over the Eastern Atlantic. Also at upper levels, the trough is very well developed and a jet surrounds its periphery. At the surface a low pressure system with center over Baltic states / W Russia is forecast to deepen, reaching less than 992 hPa by the end of forecast period. Large trough will extend to south, with its axis copying approximately the location of the cold front, which will slowly translate eastwards. A well defined warm front will stretch from the center of the low to the east with and shift northwards during the day. Prominent WAA regime will dominate the warm sector of this cyclone. To the west a cold airmass will invade Central Europe in the wake of the low and a narrow ridge of high pressure will stagnate over Eastern Atlantic.

DISCUSSION

...Central Ukraine through Smolensk-Moscow Upland...

Ahead of the progressing cold front, a belt of moderate instability will develop as the warm and humid airmass with steep lapse rates at mid-levels is advected towards the north. Especially in the southern part of Level 2, MLCAPE values will likely exceed 1000 J/kg. With strong mid-level flow aloft, DLS values should reach more than 20 m/s by 15Z, locally even over 25 m/s. Shear in the lowest 3 km will be quite strong as well, with large swath of values over 15 m/s and by 18Z, due to the strenghtening low level flow, even over 20 m/s. Moreover, backing of the winds ahead of the trough will lead to the increased SREH values, which might exceed 250 J/kg in 0-3 km layer.


Environment seems to be very supportive of well organized convection, with expected storm modes being both multi and supercells. Due to the fact, that flow will be almost parallel to the front and wind shear confined to the lower levels (i.e. weak mid-level storm relative winds), we expect that storms will quickly cluster and isolated storms (possibly supercells) will form one or more MCS, tracking northwards.

Initiation of convection will be easily achieved, as the outflow boundaries from previous convection will probably play a role in the storm formation. At the same time, frontal uplift will combine with the passage of two troughs across the region. With the first isolated storm development, supercells being possible, large hail will be the main threat. Towards the evening, as the low level flow strenghtens, we expect the storms to cluster and in form of MCS track to the north. Bowing segments might develop and considerable chance of damaging wind gusts will be present in such case (supported by the strong shear in the lower levels and enhanced Delta Theta-E values). Strong low -level shear (locally over 15 m/s) and its overlap with moderate instability, enhanced values of SREH 0-1 km, low LCL values point to the threat of tornadoes and even a strong tornado can not be ruled out. Due to the combination of these threats, Level 2 is warranted for this region.


...Moscow area, east-northeastward to the Northern Hills...

To the north, close to the warm front, the release of instability should not be that prominent, but still, MLCAPE values of 500 J/kg should be present. ECMWF is more optimistic than GFS in this case. Strong wind shear will be present, especially at the lower levels with the lowest 3 km shear having more than 20 m/s. At the same time, sharp turning of winds with height (models simulate easterly surface winds, which will turn to southerly direction at 850 hPa level) are expected and therefore, also high SREH values, locally more than 400 J/kg.

Storms that will form in this region will have a high potential to become well organized, including supercells, but probably the storms will quickly cluster towards the evening hours with MCS forming around the frontal region. Large hail might occur with supercells, although this threat will be of less importance than severe wind gusts, which can become widespread in case that bowing segments manage to develop. Furthermore, a belt of very strong LLS and high SREH values will lie close to the warm front. Therefore, a tornado threat will exist, as storms will probably track from the south (where the unstable airmass will be placed) to this region, including the slight chance of a strong tornado.

Weather developments will be closely monitored for a possible update during the day.