Storm Forecast
Valid: Mon 26 Jul 2010 06:00 to Tue 27 Jul 2010 06:00 UTC
Issued: Sun 25 Jul 2010 23:21
Forecaster: DAHL

A level 1 was issued across E Bulgaria and E Romania mainly for severe wind gusts, large hail, and heavy convective rainfall.

A level 1 was issued across NE Poland mainly for heavy convective rainfall.

A level 1 was issued across parts of the central Mediterranean regions, mainly for large hail and severe wind gusts.

A level 1 was issued across the N Baltic States and S Finland, mainly for severe wind gusts and tornadoes.


SYNOPSIS

A deep, quasi-stationary upper trough is extending from the North Sea into the central Mediterranean Regions. Warm/moist air is present at low levels to the east and south of this feature, while a modified polar air mass is advected into the central portions of Europe. SFC analyses/forecasts reveal synoptically quiescent conditions prevailing over most of Europe.

DISCUSSION

... Bulgaria ... Romania ... eastern Poland ...

MLCAPEs on the order of 1000 to 1500 J/kg are anticipated to develop over eastern Romania and Bulgaria as well as over the western Black Sea on Monday. Deep shear is simulated to be in the 15 - 20 m/s range, most of the shear existing above 1 km altitude. This suggests that multicellular storms with the chance of some mesocyclones may form, capable of severe outflow winds and large hail. In addition, excessive rainfall may occur, especially if one or more MCSs form. WRF12km advertises an MCS that will move from central Bulgaria and to central Romania on Monday night along the low-level baroclinic zone. This activity should move away from the favorably sheared area, so the main threat should shift to heavy rain and possibly a few marginally severe wind gusts. The models do not indicate any CAPE in this region by the time of the MCS occurrence, but this may be tied to the consumption of CAPE by the parameterized convection.

Farther north along the low-level baroclinic zone, GFS and WRF indicate another nocturnal MCS over central Poland. This activity will likely suffer from the lack of shear and the main threat should again be heavy convective rain and maybe a few marginally severe wind gusts.

... NW Italy ... Corsica ... Sardinia ... Tyrrhenian Sea ... extreme S Italy ...

Scattered thunderstorms should develop at the SW periphery of the upper long-wave trough in response to diurnal heating and QG forcing for upward motion as short waves pivot around the main trough. MLCAPE may struggle to exceed 1000 J/kg, but DLS of 20 m/s should aid in the development of line segments and possibly a few supercells. The main threats with this activity should be severe wind gusts as well as large hail.

... N Baltic States ... S Finland ...

It seems that a less conspicuous severe thunderstorm episode may unfold over the Baltic Region. This activity will be tied to a band of 15 to 20 m/s 700 hPa winds. WRF advertises MLCAPE on the order of 1500 J/kg over the Baltic States, surging into S Finland during the night. GFS simulates rather patchy maxima of 1-3 km shear (15-20 m/s) and 0-1 km shear (10 - 12.5 m/s), which temporarily become juxtaposed with the area of positive CAPE. The 0-6 km shear is simulated to be less than 10 m/s, however. Still, this kinematic setup suggests that at least briefly-organized line segments and/or mesocyclones may develop, capable of severe wind gusts and, given the strong LLS, a few tornadoes.

... Coastal areas of NW Germany and the Benelux countries ...

Diurnally driven showers and thunderstorms are anticipated beneath the upper thermal trough mainly over the western portions of Germany and the
Benelux countries. Low LCL heights, rather strong LL buoyancy and a lack of vertical shear suggest that a few misocyclonic funnels and maybe some water-/landspouts may occur, mainly near the coastal areas. Overall severe probabilities are too low for a LVL1, however.