Storm Forecast
Valid: Fri 23 May 2014 06:00 to Sat 24 May 2014 06:00 UTC
Issued: Thu 22 May 2014 21:20
Forecaster: TUSCHY
A level 1 was issued for E/SE Germany, W-Poland the Czech Republic and parts of Austria mainly for large hail (an isolated very large hail event can't be excluded), strong to isolated severe wind gusts, excessive rain and an isolated tornado event.
A level 1 was issued for SE-Norway and SW Sweden mainly for an isolated large hail event.
A level 1 was issued for CNTRL UK mainly for an isolated tornado event.
A level 1 was issued for parts of France, Belgium, far W-Germany and Luxembourg mainly for an isolated large hail and strong wind gusts event. A tornado or two are possible.
A level 1 was issued for parts of Italy, Slovenia and Croatia mainly for large hail (an isolated very large hail event is possible) and strong to severe wind gusts. Excessive rain accompanies storm clusters over N-Italy.
A level 1 was issued for parts of N-Tunisia mainly for an isolated large hail event.
A level 1 was issued for parts of SW-Turkey mainly for an isolated large hail event.
SYNOPSIS
The rotation center of a big cyclonic vortex remains just offshore of SW UK . Numerous impulses within its periphery affect NW Europe with the strongest one crossing France during the day from SW to NE. Another upper low is situated over SE Europe with weak ridging in between.
At lower levels, a pronounced front bisects Europe with cool and modified marine air to its west and warm/moist air to its east. This front moves leisurely to the east and becomes quasi-stationary during the overnight hours roughly from Sweden to E-Austria to Sicily. Another Atlantic front affects W/NW France with enhanced thunderstorm chances.
DISCUSSION
...E/SE-Germany, W-Poland, the Czech Republic and N-Austria...
Ongoing uncertainties exist with overnight's convection ... not necessarily how far east convection spreads (rather tight model clustering with this concern) but how far outflow boundaries or even the synoptic cold front itself push east with augmented post frontal pressure rises noted over CNTRL Germany during the night. Latest idea is to place the front from Rostock to Berlin to the W-Czech Republic and SE Bavaria at 06 Z. Some west/east oscillation of this boundary is forecast as weak LL vortices travel along that front to the north.
Most likely daytime initiation (around noon) is forecast over the N-Alps to SE-Bavaria. During the afternoon hours, storms also fire along the convergence zone along the German/Polish border to the Czech Republic but extent of thunderstorm coverage remains a bit unclear with weak synoptic forcing forecast. Also we can't ignore cluster of storms over Saxony in past few WRF runs due to a stronger LL depression/wave, which slackens eastbound motion of the front. Therefore we issued a broader level 1 over E-Germany and W-Poland. During the evening and overnight hours, northbound traveling and intensifying 300 hPa speed maximum and attendant right entrance overspread ongoing storms and it supports upscale growth into numerous large clusters, which affect the highlighted area from S to N.
CAPE/shear overlap ( 500-1000 J/kg MLCAPE and 15-25 m/s DLS) favors well organized multicells/supercells with large hail. An isolated very large hail event is possible. Strong to isolated severe wind gusts accompany strongest storms, especially from SE Bavaria to the Czech Republic, where 0-3 km shear exceeds 15 m/s. Betimes, clustering storms pose an enhanced risk of excessive rainfall (PWs in excess of 30 mm) and cold pool driven swaths of strong to severe wind gusts. An isolated tornado event is forecast with ramp up of LL shear mainly in the proximity of the front itself and in the proximity to LL vortices along that front.
...CNTRL/NE France, Belgium, far W-Germany and Luxembourg...
Models differ with magnitude of BL moisture although most of them show a peak of LL mixing ratios over NE France.
With a weakly capped air mass in place and gradually strengthening synoptic forcing due to an approaching mid-level impulse and attendant synoptic front from the SW induce CI already before noon. Thereafter, scattered thunderstorms spread north/east and affect Belgium and far W-Germany during the evening with overnight storms spreading north towards SE UK. Forecast soundings show adequate shear/CAPE for organized storms, capable of producing large hail and strong to isolated severe wind gusts. Due to low LCLs an isolated tornado event can't be ruled out with backing winds along/ahead of the front.
... CNTRL-UK ...
Vertically stacked low with a distinct low-tropospheric circulation wraps the occlusion with moist/warm air around its center beneath cold mid-levels. A tongue of 200-500 J/kg weakly capped MLCAPE wraps around the vortex. LLCAPE in excess of 100 J/kg, LCLs below 800 m and backed/convergent flow indicate a chance for a few funnel/short-lived tornado events. This risk diminishes after sunset as storms weaken.
...Norway, Sweden ...
Northward fanning plume of unstable air moves beneath the tip of a synoptic ridge with warm mid-levels and weak mid-level lapse rates. Hence CAPE will be the main issue with less than 400 J/kg forecast. Both DLS and LL shear would support organized storms and highest confidence in isolated severe currently exists for S-Norway and SW-Sweden. Organized storms may produce isolated large hail, strong gusts and an isolated tornado event.
...N/CNTRL Italy to the NW Balkan States...
Beside ongoing storms from the previous night, slowly eastbound moving front sparks scattered to widespread storms quite early during the forecast period. Over Italy, overlap of 20-25 m/s DLS with 400-800 J/kg MLCAPE cause organized convection with large hail and strong wind gusts. An isolated very large hail event can't be ruled out. Clustering storms tend to produce excessive rain with slow motions and effective PW in excess of 25 mm.
Further east over Croatia, parts of Slovenia and W-Hungary, EZ and GFS both show MLCAPE in excess of 1000 J/kg. Despite DLS below 10 m/s, strong to severe pulsating storms with large hail are forecast and once again an isolated very large hail event can't be ruled out. High-based storms produce a few strong to severe downburst events. Weak forcing, strong cap and high CI temperatures keep convection very isolated during the day with an upswing during the night as the front pushes east.
...N-Tunisia...
Weak mid/upper waves cross the area of interest during the forecast. Strong cap is in place, but interaction of synoptic forcing and the orography cause isolated CI during the afternoon and evening. Up to 800 J/kg MLCAPE, steep mid-layer lapse rates and 30 m/s DLS cause organized storms with large hail. Storms move east and offshore during the night while weakening due to a strengthening cap.
...Romania, Bulgaria and W-Turkey...
Roughly 500 J/kg MLCAPE and weak shear support daytime driven convection. Pulsating storms pose a temporal hail threat during the mature phase. Storms rapidly decay after sunset. Turkey was upgraded due to more consistent CAPE signals in models.
