Storm Forecast
Valid: Tue 19 Jul 2011 06:00 to Wed 20 Jul 2011 06:00 UTC
Issued: Mon 18 Jul 2011 20:49
Forecaster: KOROSEC

A level 2 was issued for Tyrrenian sea mainly for large hail, severe wind gusts, excessive convective rainfall and tornadoes.

A level 2 was issued for CNTRL Adriatic sea and parts of western Balkans mainly for large hail, severe wind gusts, excessive convective rainfall and tornadoes.

A level 1 was issued for surrounding level 2 area over the rest of N-CNTRL Mediterranean and Alpine region mainly for excessive convective rainfall, strong winds and large hail.

A level 1 was issued for Baltic States through Poland, Slovakia, W Ukraine, W Romania and Hungary mainly for large hail, strong winds gusts and lesser extent for heavy rain.

SYNOPSIS

An unseasonably strong and negatively tilted large upper trough still dominates across W-CNTRL Europe while making a slow eastwards progress. The main feature today will be a powerful DCVA maximum traveling from S France into the northern Mediterranean. At surface, a large cyclone is placed over central Europe, moving slowly towards NE where another secondary low forms over N-CNTRL Italy. There are two cold fronts that will be the focus for severe storms today. One extending from Baltic states towards N Balkans and the second one associated with the upper disturbance crossing N-CNTRL Italy. Locally, intense severe storms (a few significant events possible) are expected.

DISCUSSION

... N-CNTRL Mediterranean and Italy, Adriatic sea, western Balkans ...

An active convective weather is expected over the central Mediterranean once the intense UL disturbance approaches from the NW. A strongly negative tilted trough supports persisting WAA from the SW Mediterranean over the area of interest, resulting in moderately unstable environment and strong QG forcing. With rather impressive ML flow and strong deep layer shear in excess of 25 m/s, environment appears conductive for organized severe convection. Convective activity will likely continue/spread from the previous night from western Mediterranean. Intense multicells and supercells should be the primary mode, capable of producing large hail and damaging winds. Quite high PWAT values suggest that persisting SW flow should enhance the excessive convective rainfall threat where upslope flow will establish. This will be most pronounced around the Alpine region, when strong UL forcing and divergence will be placed. While combined with severe convection it could cause high flash flood threat, especially over parts of western Balkans and central Italy. Training cells effect appears possible in these areas, resulting in high amount of rainfall in short period of time.

As there will be strong LL jet/wind field along the Tyrrenian sea and Adriatic sea, enhanced SREH seem reasonable there. These conditions, combined with moderate instability (around 1000-2000 J/kg MLCAPE) as seen on GFS and ECMWF models, become supportive of a few tornadic supercells as well. Therefore, a couple of tornadoes could occur.

Later in the forecast period, the activity will spread into the Balkans with mostly excessive rainfall threat overnight. A cluster(s) of storms is possible moving from Adriatic inland where still favorable wind shear in place and some instability, seem likely to embedded intense cells including a supercells, bringing strong wind threat. A convective line is also possible if intense complex/MCS forms, especially from N Adriatic sea inland onto the NW Balkans. Activity will last well into the night hours as instability improves once the ML lapse rates steepen beneath the cold upper low moving across the N Adriatic sea by Wednesday early morning.

... Baltic States through Poland, Slovakia, W Ukraine, W Romania and Hungary ...

Activity over these areas today will be mostly aligned to the cold front over this large level 1 area. Healthy BL moisture should result in moderately strong instability after 12z, around 1500 J/kg MLCAPE seem reasonable to be available. Coupled with near 10-15 m/s of deep layer shear, scattered multicells and supercells will form. The main threat should be large hail, strong winds and locally intense rain. Activity should diminish quickly after sunset when instability vanishes.

A level 1 was also extended for possible isolated storms along the NE Alpine region where favorable shear/SREH seem supportive for some organized storms. Combined with several hundreds of MLCAPE and easterly LL wind field, a few storms with larger hail threat cannot be ruled out there. Scattered convective activity will result behind the upper cold core from NW Alps towards Benelux, mostly during the daytime/heating hours.