Storm Forecast
Valid: Mon 27 Aug 2012 06:00 to Tue 28 Aug 2012 06:00 UTC
Issued: Mon 27 Aug 2012 05:03
Forecaster: SCHLENCZEK

A level 2 was issued for E Ukraine for excessive precipitation, large to very large hail and severe wind gusts.

A level 1 was issued for E Romania and central / E Ukraine for large hail, excessive precipitation and severe wind gusts.

A level 1 was issued for NE Iberia for large hail and severe wind gusts.

A level 1 was issued for W UK and parts of Ireland for severe wind gusts and tornadoes.

SYNOPSIS

While cool and stable conditions prevail over central Europe, a plume of hot and moist air is advected into SW Europe. A destabilization of this airmass may allow isolated severe convection over Spain and S France on Monday evening/ night.

Remnants of a very hot and unstable airmass over Ukraine will provide favorable conditions for severe thunderstorms with large hail and severe wind gusts over E Romania and central/ eastern Ukraine. Most of the activity will be tied to a cold front which separates hot and moist air in the east from a cool airmass further west.

Frontal convection can also be found along a cold front which belongs to a low pressure system W of Scotland. Although not much lightning is expected, a few severe weather events such as tornadoes and severe wind gusts are still possible.

Another region with a chance of thunderstorms is found over the Baltics and W Finland where low-end instability and rather low vertical shear are present. Besides the possibility of a funnel / weak tornado, no severe weather is expected.

DISCUSSION

...Iberia...

Although GFS shows only weak precipitation signals, the presence of moderate instability with some 50 - 100 J/kg CIN and 20 - 25 m/s of deep layer shear may be sufficient for a few isolated severe multicells or supercells which may produce large hail and severe wind gusts. Due to relatively low PWAT and a high cloud base, excessive precipitation and tornadoes are not expected. Although a very large hail event cannot be ruled out, the risk is covered by a LVL1 due to spatial uncertainties.

...Ireland and UK...

Some hundred J/kg of CAPE are forecast along the cold front of a strong low pressure system which slowly translates to the northeast. Strong winds at lower levels (20 m/s at 850 hPa) may support a few severe wind gusts if additional evaporative cooling accelerates the downdraughts. Due to strong LL winds and therefore some LL shear and locally enhanced SRH, an isolated tornado event is also possible.

...E Romania and E Ukraine...

Some 1500 - 2000 J/kg of CAPE overlap with 15 - 20 m/s of 0-6 km bulk shear in that area and QG forcing from an upper trough may initiate multicellular convection during the afternoon. Some remnants of MCSs from Sunday night may hinder insolation but it is almost certain that at least a few storms will form in an environment which is supportive for large hail and severe wind gusts. The main threat will likely be excessive precipitation as storms will tend to merge into large systems which may persist for several hours. Please note that the major part of the LVL2 area is too far east to be included in the map.