Storm Forecast
Valid: Tue 22 May 2007 06:00 to Wed 23 May 2007 06:00 UTC
Issued: Tue 22 May 2007 03:51
Forecaster: VAN DER VELDE

SYNOPSIS

Three low pressure systems are present on the European map today. One low over Scandinavia with a trough and cold front affecting northern parts of Western/Central Europe, one low over the Iberian Peninsula and one low over the southern Balkan/western Turkey region. Between these lows, a large unstable saddle area with weak flow through a deep layer and only local forcing is present, allowing for mostly isolated thunderstorms.

These could become more organised along the northern parts of the central European thunder area as the cold front (with steep moisture gradient) comes in from the WNW. Compared to yesterday, a larger area is forecast by GFS to be uncapped and this seems well confirmed by the 00Z Tuesday soundings compared to 12Z Monday with colder mid levels and moister boundary layers.
Shear is insignificant though, evidenced by 00Z German soundings, so despite rather unstable profiles with steep lapse rates over the 900-600 hPa layer, hailstorms should be rare due to poor updraft/downdraft organisation in most cells. An isolated severe gust and flash flood seems possible.

Note that GFS 0-1 km average mixing ratio predictions seem in general 1-2 g/kg too low the past days.... leading to too conservative model MLCAPE estimates... and CIN should be less as well.

DISCUSSION

...Spain and Portugal...

Both instability and deep layer shear are forecast to increase compared to previous days, shear from moderate to high values (15-25 m/s 0-6 km and 1-8 km) and also low level shear from weak to moderate (8 m/s) to strong in the evening over the western parts (GFS18Z forecast >10 or 12 m/s). SREH3 is progged to reach over 250 m2/s2 over southeastern Spain during the afternoon. Abundant deep convergence should be present, but mid level QG support will switch from positive to slightly negative during the late afternoon... this may prevent to some extent development of a large MCS... but not too sure about that.
Main convective mode seems long-lived multicell and especially supercell storms with a chance of large hail, and some severe gusts. Chances for a tornado are more enhanced in/towards Portugal where low level shear would be better, though not fenomenal.
One or a few MCSes are possible during the evening, posing a main threat of severe gusts.

...Hungary-Romania-Serbia area...

This is an area where considerable MLCAPE will be present (>1000 J/kg possible) and okay shear will be present (>10 m/s DLS, >100 m2/s2 SREH3), allowing more organized clusters with threats of large hail and severe downburst winds in the high LCL/dry mid level environment.

...northern Turkey...

Moderate deep shear and some SREH conditions are favourable to produce isolated severe weather events... QG forcing is present but MLCAPE signals are weak.

...northern Algeria...

>300 m2/s2 SREH3 is calculated by GFS18Z. Despite absence of precipitation signals, if any storm manages to form, it is capable of especially severe gusts and dust storms... 00Z DAAG sounding shows an inverted-V (and strong shear) favourable for dry microbursts if CAPE is released from the shallow moist layer near the surface. LP supercells may be possible producing large hail.