Storm Forecast
Valid: Sun 05 Dec 2010 06:00 to Mon 06 Dec 2010 06:00 UTC
Issued: Sat 04 Dec 2010 16:24
Forecaster: SCHLENCZEK
A level 1 was issued for W Iberia mainly for excessive rainfall and to a lesser extent for tornadoes, severe wind gusts and large hail.
A level 1 was issued for S Turkey and Cyprus for tornadoes.
SYNOPSIS
Most convection on Sunday will be tied to a developing low pressure system over the Azores which should reach Iberia during the period. Remnants of another low over the eastern Mediterranean may allow some isolated thunder as well. Another region with a few hundred J/kg CAPE is the North Sea and the Norwegian Sea but overall lightning probability is too low for a thunderstorm area.
The setup over western and central Europe is not very interesting from the convective perspective but the precipitation expected near the frontal system of a weak surface low from the North Sea may cause problems as it still remains unclear whether most precipitation will be snow or freezing rain.
DISCUSSION
...Portugal and extreme NW Spain...
Up to 500 J/kg CAPE forecast by ECMWF (compared to 400 - 800 J/kg by GFS and similar values by WRF-NMM) combined with approx. 20 m/s 0-6 km shear are expected for the coastal regions of W Iberia. Some QG forcing from the upper cut-off low which moves eastwards should be sufficient for initiation and numerous storms, mostly multicells, are expected to form. As there is plenty of LL moisture and not much CIN, storms will likely merge into a messy cluster / MCS with possibly isolated large hail and isolated severe wind gusts but the main threat will be excessive precipitation. At first, when convection will be more isolated, one or two tornadoes may occur along the coastline. Storms will likely continue through the night hours but the greatest threat of severe weather (except for heavy rain) should be expected in the afternoon and evening hours.
...SW Turkey...
Low-end CAPE and mostly rather weak vertical shear (10 - 15, locally 20 - 25 m/s DLS) may allow some thunderstorms along the Turkish coast and the eastern Mediterranean. GFS 00 and 06 suggest the greatest threat of severe weather (isolated large hail, isolated weak tornado) for S Turkey and Cyprus which is partly outside of the forecast map. The other regions will probably not get enough reports to justify a level 1.
Minor threat areas:
...North Sea...
Showers and isolated thunderstorms may develop in the vicinity of an upper trough over the North Sea. Even though rich BL moisture should lead to low LCL / LFC heights, strong winds at lower levels should preclude any waterspout.
...Norwegian Sea...
Quite similar conditions w.r.t. the North Sea region are expected over the Norwegian Sea. Lightning is probably too sparse for a low probability thunderstorm area.
...Gulf of Lion, N Mediterranean, Gulf of Genoa...
Rather low EL heights but locally enhanced LL CAPE and steep low level lapse rates are forecast for this region. This may allow one or two waterspouts during the day. A threat level is not issued as these events have a very conditional nature and global models are not consistent w.r.t. the area of most LL CAPE.
...Adriatic, Ionian Sea, Aegean Sea...
Outside the thunderstorm areas, there is a region with some uncapped LL CAPE, steep lapse rates but low EL heights. As described in the N Mediterranean region before, isolated waterspouts are not ruled out.
