Storm Forecast
Valid: Wed 17 Dec 2008 06:00 to Thu 18 Dec 2008 06:00 UTC
Issued: Tue 16 Dec 2008 23:45
Forecaster: PUCIK

SYNOPSIS

At midlevels, a trough over the western Mediterranean is expected to slightly shift NE wards. A belt of strong southerly winds are observed on its forward flank, reaching 40 m/s at 500 hPa. Several impulses are expected to rotate around the trough. To the east , a large ridge will stretch from Turkey to E Russia, guaranteeing stable conditions over this region. A very strong impulse with short wave trough will quickly move eastwards and is expected to affect Scandinavia by the end of forecast period. Surface pressure fields reveal a large semi-permanent high over Russia and a ridge will cover parts of SW Europe. A string of low pressure systems will affect Scandinavian states and a large, but shallow low will move eastwards over the Mediterranean. By 12Z, its center should be over Italy. Most of Europe will be under the influence of cool and stable airmass, though few areas should experience deep moist convection and these will be discussed more thoroughly below.

DISCUSSION

...Ionian Sea, Adriatic Sea, N Greece...

As mentioned above a belt of strong mid-level flow will occur ahead of the propagating trough and a large values of DLS are expected in its axis. At the same time, in the WAA regime, slight destabilization is expected, aided by the strong lift induced by mid-level impulses. MLCAPE values should reach 500 J/kg Also in the lower levels, flow should be strong, with windspeeds at 850 level between 20 and 25 m/s. The region of the enhanced flow will be mostly confined to the eastern parts of the Ionian and Adriatic seas. DLS values will reach above 30 m/s, shear in the lowest 3kms above 15 m/s. Moreover, considerable veering of the winds will increase SREH values, which may locally climb well above 300 J/kg. Environment will be therefore conducive to the organised convection. Lift provided by the mid level trough will easily initiate convection, which should mostly be of linear character, possibly with embedded rotating circulations.

A level 1 is issued for the areas where the best instability / shear / helicity overlap will exist. A marginally severe hail can be expected with the stronger isolated cells. Severe gusts can occur as well, as suggested by the existence of strong low level wind field. Few tornado / waterspout reports are anticipated, especially in the coastal areas where a marginal overlap of instability and low level shear will exist. Also, high SREH values will aid in the development of rotating circulations. Threat should be highest between 06 and 12Z over the Adriatic sea and by the Thursday morning over the Ionian Sea and N Greece.

... Balkan states to S Hungary...

A belt of elevated instability is simulated by the few consequent GFS runs, stretching from the Adriatic Sea to Hungary under the mid-level impulse. Strong flow, both at mid and lower levels will dominate the region, yielding high wind shear values. No threat level is issued at the moment, as thunderstoms should stay elevated and embedded in the stratiform rain.
Still, we are issuing a TSTM area for the region, as low ELs, strong surface convergence and ICAPE values up to 500 kJ/m2 are displayed by the model.