Storm Forecast
Valid: Sun 13 Sep 2009 06:00 to Mon 14 Sep 2009 06:00 UTC
Issued: Sat 12 Sep 2009 22:34
Forecaster: SCHLENCZEK
A level 1 was issued for E / NE Spain mainly for large hail and spouts.
A level 1 was issued for parts of the Adriatic Sea mainly for waterspouts.
A level 1 was issued for SW / W Greece mainly for large hail, severe winds, excessive rainfall and tornadoes.
SYNOPSIS
High pressure over the British Isles will continue through the period while a small upper low over the Baltic Sea moves southward into SE Germany. Near the core of the upper low, diurnal heating as well as mid level cooling will result in some low-end instability over the eastern and central parts of Germany. Isolated showers and weakly electrified thunderstorms are expected.
The upper low mentioned above is only one small feature within a large area of low geopotential heights over most portions of eastern and southern Europe. Showers and thunderstorms are expected along a cold front from N Ukraine / W Russia via N Italy towards N Iberia where some hundred J/kg of CAPE may form. Over the E Mediterranean, another cold front stretches from S Turkey via the Bosporus region towards the SW Black Sea and SW Russia. In the late evening / night hours, an upper vort-max will overspread the Ionian Sea and SW Greece.
DISCUSSION
...Iberian Peninsula, N Morocco...
In the vicinity of an upper trough, diurnal heating will lead to some hundred J/kg of CAPE, at the Mediterranean coast even up to 1.5 kJ/kg. The background flow at all levels is relatively weak and deep layer shear should not exceed 15 m/s in most places. An isolated large hail event in E / NE Spain is not ruled out and warm SSTs combined with cold mid levels may allow an isolated waterspout as well. Even though SFC dewpoints in the upper tens / lower twenties are forecast, LCL heights should be around 1.5 km AGL which will limit the waterspout threat. A level 1 for E / NE Spain should be marginally warranted. Some thunderstorms over the Mediterranean Sea may continue through the night while most storms over land will probably decay very soon after sunset.
...Central Mediterranean, Italy...
A tongue of moderately warm and moist air at lower levels overspreads most parts of the western and central Mediterranean. MUCAPEs in order of 1000 J/kg are forecast and isolated to scattered thunderstorms should develop during the day. As mid and upper level winds less than 15 m/s are forecast, most storms should be briefly organized and short-lived. Nevertheless, steepening LL lapse rates will increase the chance of waterspouts but with cloud bases well above 1 km AGL the probability should be too low to issue a level 1.
...E Germany...
Ahead of the approaching upper low, insolation as well as mid level cooling will create a slightly unstable environment over the eastern half of Germany. Strong QG forcing is expected with this low which will lead to showers and thunderstorms. Although SRH values are slightly enhanced and deep layer shear around 15 - 20 m/s is forecast, the probability of short-lived supercells that might be tornadic should be too low for a categorical threat level. Locally, LL shear around 10 m/s is expected and a funnel / brief tornado is not ruled out. Both shear and CAPE will gradually decrease through the evening / night hours, limiting the threat of severe weather.
...SE Poland, Belarus, N Ukraine, W Russia...
In this region, the production of CAPE depends on insolation and values around 500 J/kg MUCAPE could be assumed. The absence of vertical shear and QG forcing should preclude severe convective weather. Locally, strong gusts and (mostly) small hail are possible. Thunderstorm activity should begin in the late morning hours and will likely end in the late afternoon.
...Adriatic / Ionian Sea, W Greece, Balkans...
Some moderately warm and moist air with about 1 kJ/kg CAPE over the Adriatic Sea / Ionian Sea is advected towards the Balkans and W Greece. Thunderstorm activity will likely begin in the early afternoon. Deep layer shear around 10 m/s could be sufficient for some briefly organized multicells with isolated large hail / severe gusts. Later in the evening, an upper vort-max approaches SW Greece and a MCS may form, posing a threat of severe winds and excessive rainfall. If some storms develop ahead of this MCS, they will profit from 15 m/s deep layer shear and about 200 J/kg SRH3 and should likely become supercellular. Those storms may produce large hail, severe gusts and also some tornadoes as LL shear is quite strong and LL lapse rates should be very steep along the coast. The greatest threat of severe weather is expected between 18 UTC on Sunday till 06 UTC on Monday. This region should be monitored as this setup may lead to widespread severe weather on Monday.
...NW Turkey, Bosporus, W Black Sea...
Some remnants of the convective systems from Saturday should move northward towards the Bosporus region and W Black Sea. Relatively weak shear and forcing should limit the severe threat. Most storms should dissipate after sunset.
