Storm Forecast
Valid: Sat 02 Jul 2011 06:00 to Sun 03 Jul 2011 06:00 UTC
Issued: Sat 02 Jul 2011 10:42
Forecaster: VAN DER VELDE
A level 1 was issued for SW Finland mainly for local excessive convective precipitation.
A level 1 was issued for Lithuania, NE Poland and Latvia mainly for (spout-type) tornadoes.
A level 1 was issued for parts of Moldova and Ukraine mainly for local excessive convective rain.
A level 1 was issued for a part of western Russia mainly for large hail.
A level 1 was issued for parts of Italy mainly for large hail.
A level 1 was issued for S Montenegro and N Albania for local excessive convective precipitation.
A level 1 was issued for parts of Spain mainly for severe wind gusts and large hail.
SYNOPSIS
A low pressure area is centered over Lithuania. Several fronts and convergence lines with associated warm unstable air spiral into it: from the Ukraine, from Russia, and from Scandinavia. A cold front will enter also the Italy/Balkan region.
Over the Iberian Peninsula, at the approach of an Atlantic upper trough, a thermal low forms while mid level lifting steepens the lapse rates. It introduces a new period of activating storms this weekend.
DISCUSSION
...Spain...
In advance of a large trough, the airmass over Spain destabilizes. Very steep 2-4 km lapse rates are in place, and LCL heights initially remain high at 2500-3500 m. Madrid 00Z sounding shows a typical "inverted-V" type of profile. GFS simulates ICAPE or MUCAPE with weakly capped parcels in a large area and deep layer, but CAPE itself will be weak, and EL temperatures only around -30°C. Moderate DLS can produce clusters of storms, perhaps with some rotating updrafts. The shear increases after 21Z with GFS plotting more than 20 m/s 0-6 km shear and locally over 250 m²/s² SREH and more than 10 m/s 0-1 km shear vectors in eastern Spain. Given still large LCLs, the scenario of a fast-moving MCS at night with possibly bow echoes with potential of severe convective wind gusts and perhaps some large hail, is the main reason for the level 1. The forcing is relatively lacking, coming in from the west late and will not reach eastern Spain. This lack of synergy prevents from issuing a level 2 at this point. During the afternoon local severe gusts may also occur more to the west, given dry profiles (dry microburst chance) and fast storm-bearing layer winds. Additionally, with such high LCLs and low precipitable water, an increased threat of local "dry lightning" causing wildfires exists.
...SW Finland...
Very slow storm motion and high effective PW in a convergent flow can result in storms causing flash floods.
...Lithuania and surroundings...
Near the surface low pressure center, convergence and vorticity in an environment of good low level CAPE, moist air and weak storm motion can result in isolated spouts. On the south side, deep shear is moderate and LCL lower which may enhance potential for tornadoes.
...parts of Moldova and Ukraine...
Strong QG lifting takes place over the region. Moderate MLCAPE will be modestly overlapped by >15 m/s deep layer shear, which could organize storms into multicells, perhaps an isolated supercell. However, large hail chances are reduced by relatively large warm cloud depth and decreasing buoyancy in the cold cloud region. Instead, the storms may rather produce copious rain given large effecitive PW and storm motion parallel to the triggering front.
...part of western Russia...
Moderate vertical shear (10-15 m/s 0-6 km, 15-20 m/s 1-8 km) and MLCAPE over 1000 J/kg and forcing coming from a band of PV. This can produce clustered storms with a chance of large hail. Local excessive precipitation is not ruled out due to training of storms, which may backbuild eastward along the front into higher CAPE.
...Italy...
Modest CAPE exists in an environment of weak mid level lapse rates and large warm cloud depth. While aforementioned factors lower the large hail chance, 20-25 m/s DLS is present and can organize storms into supercells, which may overcome these limitations.
... S Montenegro and N Albania...
Local excessive convective precipitation is possible as GFS simulates persistent upslope moisture lifting, strong convergence at sea and weak CAPE during the night as the cold front and PV max passes slowly, especially during the late night. A persistent thunderstorm may form and dump locally large amounts of precipitation.
