Storm Forecast
Valid: Sun 14 Jul 2013 06:00 to Mon 15 Jul 2013 06:00 UTC
Issued: Sun 14 Jul 2013 13:38
Forecaster: VAN DER VELDE

A level 1 was issued for northeastern Spain mainly for large hail.
A level 1 was issued for eastern Ukraine mainly for large hail.

SYNOPSIS

Three synoptic scale weather systems are actively supporting thunderstorms. An upper cut-off low is in a steady position over Belarus and Ukraine. It should easily trigger convection over a large area with modest CAPE. Higher CAPE is found in the warmer air east of the frontal zone, over southern and eastern Ukraine into Russia. This area will see upper vorticity advection approaching from the west which should trigger storms during the evening and night.
Instability remains in place over the northern half of the Iberian Peninsula as well as over Italy (where shear and instability seem weaker than previous days). Spanish storms are supported by a weak low pressure area, causing convergence of winds at the edges of the Spanish Plateau and the Pyrenees. The cooler low-level air advected by the sea breeze will keep a strip of some 50 km inland relatively stable.
A cold front over Finland also exhibits some CAPE, mainly at low levels.

DISCUSSION

...Spain...

Conditions look similar to previous days, but good vertical shear is now more limited to the eastern one-third. The GFS model also stabilized the upper levels over northwestern Spain as a result of convective activity in the past days. In the east, CAPE over 1000 J/kg is expected, collocated with at 10 m/s 0-6 kn shear vectors which support multicell clusters. If helped by orographic features, an isolated rotating updraft may develop. LCL heights are moderate to high (1500-2000 m). The resulting threats are large hail and possibly an isolated severe wind gust.

...Ukraine...

High LCLs over 2000 m support decent cold pools once convection forms, and with the incoming lift storms likely will cluster into mesoscale convective systems during evening and night. Although the strongest lifting by the upper trough will be situated over the cooler airmass with lower CAPE. There is moderate 0-6 km shear over eastern Ukraine, 10-15 m/s, an isolated supercell is not ruled out among the multicells, and either of those can produce large hail and perhaps severe wind gusts. If stronger lift would be better collocated with the more unstable airmass a level 2 would have been required for these phenomena.