Storm Forecast
Valid: Tue 10 Jun 2008 06:00 to Wed 11 Jun 2008 06:00 UTC
Issued: Mon 09 Jun 2008 19:35
Forecaster: VAN DER VELDE

SYNOPSIS

A low pressure system moves over central Scandinavia. A stationary upper cold pool is present over Spain, another over eastern Turkey, while a high pressure area is situated over the Atlatic Ocean SW of Ireland. Western to Central Europe is dominated by quiescent conditions with isolated to clustered thunderstorms in the afternoon and evening.

Cloud base height will be lowest in NE-Spain, France, N-Italy (600-1000m), and highest over the Balkan (1500-2500 m). The air should remain unstable enough (in terms of CAPE and minimal CIN integrated over a vertical column) to allow continued thunderstorm activity into the early night hours over NE-Spain/Mediterranean, France, Switzerland/S-Germany, as well as N-Algeria.

Weak vertical shear (<10 m/s 0-6 km) and weak forcing over much of Europe suggest successions of single cell storms and some multicells where convergence zones are present. Dry boundary layer over the Balkan area may induce cold outflow (enhanced gusts), as well as better hail growth (possible result of smaller warm cloud depth), but likely not severe to an extent requiring level 1. Cannot exclude isolated marginally large hail over a large area.
Stronger shear vectors (>10 m/s) in combination with CAPE are present over SW-France, N-Spain, Sweden and Finland, and Algeria.


DISCUSSION

...S-Finland...

GFS model predicts some instability following the cold/occlusion front passing over Finland in the late afternoon and evening, at the north side of the jetstream. In the frontal zone itself this also seems to be the case and LCL heights are low there (around 500 m), while 0-1 km shear (>12 m/s) and deep layer shear are in support of isolated tornadogenesis.

Over Sweden, instability builds mostly after the cold front with higher cloud bases and not much shear.


...Morocco, Algeria...

Strong deep layer shear (>30 m/s 1-8 km, 20 m/s 0-6 km, >150 m2/s2 SREH3) in an area with deep QG lifting and 500-1000 J/kg MLCAPE from a deep layer show potential for rapid supercell and large multicell development with an attendant threat of large hail and damaging gusts. The storms will likely merge into a large MCS drifting off to the east-northeast, with GFS 12Z creating a mesolow.


...E-Spain, Balearic Islands...

During the morning, GFS predicts thundery convection near Valencia. This will probably be just a rainy event, after which this area will not participate much in the afternoon convection round.
At the edge of good deep layer shear, SE-Spain is likely to see a few storms develop in the afternoon, which may produce large hail. However, confidence for severe weather is not very high as CAPE and forcing are modest.
During the night, elevated storms may develop in high shear environment near and over the Balearic Islands, as best indicated by uncapped-parcel layer depth parameter and most-unstable parcel EL height. Elevated storms are not often reported to produce severe weather, but some may manage to organize rotating updrafts capable of large hail production, or severe gusts. This area should be monitored for possible update to level 1.

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