Storm Forecast
Valid: Sun 08 Aug 2010 06:00 to Mon 09 Aug 2010 06:00 UTC
Issued: Sun 08 Aug 2010 05:16
Forecaster: TUSCHY
A level 2 was issued for parts of Ukraine, Belarus, Latvia, Lithuania, Estonia, parts of Finland and extreme W-Russia for large/very large hail, severe to damaging wind gusts and tornadoes.
A level 2 was issued for large hail (a few significant events possible) over parts of Romania and Bulgaria.
A level 1 was issued for Benelux and parts of Germany mainly for tornadoes and for excessive rainfall amounts.
A level 1 was issued for Switzerland, parts of Austria and parts of Italy mainly for large hail and strong to isolated severe wind gusts.
SYNOPSIS
Cyclonic vortex over central Europe remains in place with ridging over E-Europe and SW-Europe, where hot and stable conditions persist (a few storms possible over parts of Spain). There will be various places where deep convection is forecast, mainly over E-Europe.
DISCUSSION
... Level 2 ...
In the US, this type of pattern is called "ring of fire", as thunderstorms mark the outer edge of a strong high pressure area. This will be the case, as extensive moisture convergence has established along the western/northern fringe of the hot Russian high. This boundary serves as focus for organized, deep moist convection throughout the forecast.
A combination of augmented BL moisture due to moisture pooling along that boundary and steep mid-level lapse rates cause CAPE values to climb to 1 - 2 kJ/kg in a narrow corridor. DLS of 15-20 m/s is more than adequate for rotating updrafts, enhanced by intense 0-3 km shear of 20 - 30 m/s and strong LL shear, both speed and directional magnitudes (augmented along the boundary itself but also, as surface wind fields backs as LL depression builds in from the SW). Supercells with large hail, severe downbursts and an augmented tornado threat are forecast in the level 2 area. Environment beneath 3km is supportive for strong cold pool development and severe storms tend to line up in numerous (probably small) MCSes with the damaging wind gusts risk becoming more widespread in nature.
The large hail and isolated severe downburst risk expands all the way to Romania/Bulgaria. A few significant hail reports are well possible.
... Benelux, Germany, Switzerland, N-Italy and parts of Austria ...
Cold-core upper low moves slowly to the east/southeast atop a northeastward surging warm/moist LL air mass, so conditions will be supportive for widespread thunderstorm initiation. With cooling 850 temperatures and a warm/moist boundary layer, abundant LL CAPE will be present in the level 1. Background shear remains weak with LCLs at or below 800 m, so numerous funnel/tornado reports seem possible with more persistent updrafts. In addition, slow storm motion and mean mixing ratio at or above 10 g/kg in the lowest 1000 m point to an augmented heavy rainfall risk with training or backbuilding storms, mainly over Benelux all the way to central Germany. Further south, shear magnitude increases with forward propagating storms forecast. An isolated large hail event next to strong wind gusts seems likely (heavy rainfall is possible along the westward facing slope of the Bavarian Forest during the evening hours onwards). This also includes Switzerland and N-Italy. Cold front passage over SE-Germany/N-Austria has a bad timing with decreasing CAPE values after sunset, but modest forcing and scattered showers/thunderstormy may result in a more or less organized MCS, moving eastwards during the night. Strong wind gusts will be the main risk with that activity.
