Storm Forecast
Valid: Sat 26 Jun 2010 06:00 to Sun 27 Jun 2010 06:00 UTC
Issued: Sat 26 Jun 2010 04:48
Forecaster: VAN DER VELDE
A level 1 was issued for NW Russia for severe convective wind gusts, tornadoes and large hail.
A level 1 was issued for W Russia, Belarus, NW Ukraine mainly for excessive convective precipitation.
A level 1 was issued for NE Italy, Slovenia and Croatia mainly for a chance of tornadoes and large hail.
A level 1 was issued for N Algeria for severe convective wind gusts (dust storms) and large hail.
SYNOPSIS
A plume of warm humid air stretches all the way from the upper low over Romania to a low pressure area over northern Scandinavia. Between those areas, the largest instability is present along a stationary N-S frontal boundary just east of the Baltic states and Finland.
Other major instability areas are situated over the northern half of the Iberian peninsula, Algeria, and Italy-western Balkan.
DISCUSSION
...NW Russia...
An occlusion moving along the stationary boundary is the focal point of potentially severe convection. Main questions are whether convection will initiate there in the low LCL - high shear (0-3 km) area, which is favorable for tornadoes and severe gusts, or in the warmer, drier air to the east, favorable for large hail, where LFC-LCL distance is smaller but the shear as well.
The general setup contains 15 m/s 0-6 km shear, more than 200 mē/sē SREH 0-3 km,supportive of supercells, and 10 m/s/km shear maximum in the lowest layers, supportive of bow echoes and tornadoes. The shear direction is along the boundary, though, so it does not point at a long-lived squall line. Eastwards, LCLs rise from below 1000m to 2500m. MLCAPE values are a bit low, 500 J/kg in GFS, and capping or elevatedness may be an issue in some places.
...W Russia, Belarus, NW Ukraine...
Sufficient, persisting instability, deep convergence and slow storm motion vectors in a relatively moist airmass indicate potential for locally excessive convective rain sums. 0-3 km CAPE is large, while buoyancy is more limited above, which may increase precipitation efficiency.
...NE Italy, Slovenia and Croatia...
A shortwave trough moves over Slovenia and Croatia, providing ample lifting. CAPE is a bit limiting, but there is 15 m/s DLS, about 150 mē/sē SREH, and even 10 m/s LLS. It seems the overlap between low level shear and CAPE is dubious, but for deep layer shear more certain. Given the good forcing have chosen to highlight also the questionable overlap region by level 1 for some chance of large hail and/or a tornado.
...N Algeria...
A low pressure area over Algeria with a gradient parallel to the coast creates converging winds between the coast and the mountains. Storms will be high-based over the dry boundary layer, and gusts will be the primary threat, but good DLS (20 m/s) and SREH up to 200 mē/sē could pose some threat of large hail as well.
