Storm Forecast
Valid: Wed 24 Nov 2010 06:00 to Thu 25 Nov 2010 06:00 UTC
Issued: Tue 23 Nov 2010 14:24
Forecaster: PUCIK

SYNOPSIS

A large cyclonic vortex will be present over the most of Europe during the forecast period at midlevels. Strong flow, reaching more than 20 m/s at 500 hPa will surround this vortex, along with several short-wave troughs rotating around it. One of these troughs is expected to cross Great Britain during the day, another one will be observed over the Czech Republic by Wednesday morning and the last one will be placed over Ukraine and the Black Sea. This latter one will quickly move northeastwards during the day. Very similar structure of the vortex will be observed at 300 hPa.

Closer to the surface, a deep low pressure system is expected to stall over the Baltic states while in its trough, thanks to the PVA ahead of the short-wave trough, cyclogenesis is forecast. This will result in a separate low, moving northeastwards over Northern Ukraine, Belarus and Western Russia. The main frontal zone will lie over the Mediterranean with northward extention associated with the frontal system over Eastern Europe (linked with the above mentioned forming surface cyclone). Most of Europe will otherwise be under a cold airmass with stable conditions.


DISCUSSION

... The Northern Sea ...

In an arctic airmass advection, high lapse-rates are simulated along with synoptic scale forcing and low-end instability over the Northern Sea. Despite the fact that the EL temperatures are expected to be below -15°C, with mixing ratios mostly below 4 g/kg and weak convergence, only very sporadic lightning is expected, not warranting 15% thunder line.

... Eastern coasts of the Ionian/Adriatic Seas ...

In a prevailing westerly flow, surface convergence on the eastern coasts should help in the initiation of the storms. Approaching trough at mid-levels and its PVA might contribute to the upward motion and subsequent destabilisation, but simulated CAPE values suggest rather low-end instability, mostly below 500 J/kg. Even though wind shear should be enhanced, in the 0-6 km layer reaching more than 20 m/s for the southern part of the thunderstorm area, fact that the storms will stay low-topped along with a weak instability and no strong, concetrated forcing precludes the issuance of Level 1. Some sub-severe hail or a waterspout are not completely ruled out.

... The Black Sea ...

Strong flow is simulated along and ahead of the advancing cold front, with more than 20 m/s at 850 hPa level and over 30 m/s at 500 hPa level. However, instability built-up is expected after the cold front passage, associated with the advection of cooler airmass with higher lapse rates over the warm waters of the sea. With only slight overlap between the low-end instability (only around 500 J/kg of CAPE) and strong wind shear, along with no concentrated forcing behind the cold front, chance of severe thunderstorm will be very low, not warranting a Level 1. Some strong wind gusts might occur though, especially around Wednesday 06 UTC, when the overlap between strong low level wind shear and instability should be the greatest.