Storm Forecast
Valid: Fri 19 Jan 2007 06:00 to Sat 20 Jan 2007 06:00 UTC
Issued: Fri 19 Jan 2007 01:46
Forecaster: VAN DER VELDE

SYNOPSIS

Major depression causing widespread (extremely) severe winds yesterday proceeds over Eastern Europe, with weakening pressure gradients and winds during the day, except close to the center of the low drifting off to the northeast, north of Moscow.

Deepest convection is likely to remain close to the jetstream and mid level vorticity maximum, taking a southeastern direction into the Ukraine, Romania and Turkey during the evening.

Additional convection is expected under the trough over the southern Baltic Sea, though with low moisture content of the air, only sporadic thunder is forecast. This goes also for Denmark into western Norway, and Scotland and Ireland early Saturday morning.

DISCUSSION


...Ireland, Scotland...

A small level 2 has been issued for northern Ireland and western Scotland, where in the latest hours convection may reach land with a small but agressive wind field at the southwest of a new developing depression (affecting Denmark Saturday). Convectively induced gusts may reach up to 25-35 m/s. Over land there are significant shear and helicity values due to friction, in a good updraft this may result in an isolated tornado, but given marginal instability (low mixing ratios 3 g/kg but steep lapse rates) and uncertainty about overlapping forcing, this threat is minimal compared to the threat of gusts.

...Ukraine, Romania, surroundings...

Vorticity maximum passing through Romania in the morning ( left jet exit) may enhance convective activity, in the evening another maximum over the Ukraine. Initially any storms in the strong pressure gradient wind field can potentially give convectively induced gusts of around 25 m/s. During the whole period, around 15 m/s LLS and low LCL heights persist over a large region and if a sporadically stronger storm profits from this, a tornado could result (the level 1 may as well be larger, have chosen the region where most instability and forcing signals were present in GFS).

...northwestern Turkey...

The left jet exit and mid level vorticity maximum earlier over Romania will affect this area in the evening, probably late (newer GFS-18Z and MM5-18Z postpone relative to GFS-06Z). Pressure gradients will be eased down here, so not much of a gusty situation, but the positioning at the left jet exit with strong deep layer shear, moderate SREH and still quite strong frictional low level shear (>10 m/s) and low LCL heights make for a good tornado chance if enhanced convective activity indeed is realized.