Storm Forecast
Valid: Fri 18 May 2007 06:00 to Sat 19 May 2007 06:00 UTC
Issued: Fri 18 May 2007 09:24
Forecaster: VAN DER VELDE

SYNOPSIS

A large upper cut-off low resides over the Balkan and adjacent Mediterranean waters today. A pool of slightly unstable air is circled by the upper jet, with only in a band from southern Romania to northwestern Turkey moderate shear conditions west of a frontal cloud band visible on satellite.

An active low pressure area will affect Ireland and Great Britain, mostly with strong winds and generally non-thundery showers in the north.

Ahead of its cold front, slight instability may build up over central France, 00Z soundings with GFS 11 g/kg low level mixing ratios do allow deep convection, but only if local insolation would rise temperatures much more. There isn't much lift to be expected from the front there though.

Spain and Portugal may see instability developing during the afternoon, in strong insolation near a weak mid level low. Rather dry environment may create very strong gusts with any convection that develops.


DISCUSSION

...Adriatic, Thyrrenean, Ionean and western Aegean Sea...

The typical setup for a few waterspout events is in place... a large mid level cold pool with locally steep lapse rates, humid airmass, and low-level buoycancy along with weak winds near the surface (and in a deep column). Expect a few cases in the western part of the area, the focus shifting to the Aegean Sea later in the period.
More shear overlaps with more elevated instability over eastern Aegean, Crete and western Turkey, but with barely low level instability this is not likely to yield severe weather.... but large precipitation amounts are forecast by GFS in that area.


...northwestern Turkey into southern Romania...

Reasonably good deep layer shear (15 m/s 0-6 km or 1-8 km) and slightly enhanced SREH3 (100-200 m2/s2) are present, with decent low-level CAPE. This may be sufficient for an isolated rotating storm or strong multicell, with chance of marginally large hail, or severe gusts especially in the southeastern half with high LCLs and drier middle levels.

At the occlusion point in southwestern Romania, convection may profit from >300 m2/s2 SREH3 and low level shear >10 m/s (GFS00Z for this afternoon), as well as lower LCLs at the boundary... yielding some chance for a tornado.


...Russia...

Remaining instability in Russia seems mostly capped with only weak signals... but falls together with a band of good SREH and deep layer shear. If very isolated convection develops, large hail and severe gusts should be possible from a rotating storm.