Storm Forecast
Valid: Wed 13 Jul 2016 06:00 to Thu 14 Jul 2016 06:00 UTC
Issued: Tue 12 Jul 2016 21:52
Forecaster: PUCIK

A level 2 was issued for N Italy, SE Austria, Slovenia, N Croatia and SE Hungary mainly for large to very large hail, severe wind gusts, excessive precipitation and tornadoes.

A level 2 was issued over N Belarus and parts of W Russia mainly for (strong) tornadoes, large hail and severe wind gusts.

A level 1 was issued for E Austria, Hungary, Slovakia and E Poland mainly for severe wind gusts, excessive precipitation and large hail.

A level 1 was issued for Central to NE Germany and NW Poland mainly for marginally large hail.

SYNOPSIS

Dominant macro-synoptic feature will remain to be a large cyclonic vortex over much of NW Europe. At its base, a short-wave trough will quickly move from S France towards NE Italy and SE Austria. Strong mid to upper tropospheric flow surrounds the vortex, with 500 hPa windspeeds reaching up to 35 m/s at the southern flank of the short-wave. As strong flow overlaps the moist airmass ahead of the advancing frontal system, a potential for well organised and severe DMC will exist in a belt from N Italy towards Belarus and W Russia. Further thunderstorms will develop in the core of the vortex, where cold mid-tropospheric temperatures promote steeper lapse rates and at least marginal CAPE.

DISCUSSION

... N Italy, SE Austria, Slovenia, N Croatia, SE Hungary ...

Despite the lack of steep mid-tropospheric lapse rates, dew points around 20 deg C should result in MLCAPE values between 1000 and 2000 J/kg, locally perhaps even more. A belt of moderate latent instability will overlap with impressive DLS, ranging from 20 to 35 m/s, increasing as the short-wave trough approaches from the west. Scattered to widespread initiation is anticipated along the convergence zone over N Italy. It is also quite possible that some storms will already be ongoing quite early in the forecast period. They will spread eastward during the day and their coverage will increase rapidly towards the evenining and night especially near the N Adriatic region as short-wave trough passes the region. With strong DLS, well organised convection is anticipated, including a few long-lived supercells. These will be capable of large to perhaps even very large hail (lack of steep lapse rates being the limiting factor) and severe wind gusts. Towards the evening, LLS will ramp up, elevating the tornado risk with any still ongoing supercells. An MCS will likely form near the N Adriatic in the evening, moving NE-wards with predominant threats of excessive precipitation and severe wind gusts.

... E Austria, Hungary, Slovakia, E Poland ...

Models simulate initiation over the Carpathian mountain range over N Slovakia / extreme S Poland in the afternoon hours in marginal to moderate CAPE and DLS above 20 m/s environment. Across other regions, initiation earlier in the forecast period is more uncertain and the location of remnant outflow boundaries / convective debris from previous day will play an important role in this setup. Any storms that form will have a chance to become supercells / well organised multicells capable of large hail and severe wind gusts. With the approach of pronounced trough in the evening and night hours, a rapid increase in storm coverage is forecast with one or more large MCS developing over the region, moving NE-wards. Primary threats will be severe wind gusts and excessive precipitation.

... Belarus to W Russia ...

Basically all NWP models agree on the track of the surface low from E Poland towards W Russia during the day. Ahead of it, strong WAA regime along the warm front will contribute to impressive long and curved hodographs with high SRH values locally well above 300 m2/s2. Degree of low-level shear is simulated to increase towards 18 UTC, as 850 hPa flow ramps up to 20 m/s just south of the warm front. Along and south of this front, moderate MLCAPE values around 1000 J/kg are forecast. Combination of these factors will yield an environment supportive of strong supercells capable of large hail, severe wind gusts and strong tornadoes. Convective mode remains a bit uncertain atm with most storms forming and clustering north of warm fron with primary threats of severe wind gusts. Lower certainty regarding development south and/or along the of warm front and a rather narrow band of higher CAPE values preclude Lvl 3 issuance atm.

... Central Germany to NW Poland ...

A low-end Lvl 1 is introduced for region with marginal CAPE on the order of few hundreds J/kg in the core of the vortex with cold mid-tropospheric temperatures. DLS around 20 m/s is forecast and as scattered storms form, some of them may become supercells capable of marginally large hail. Limiting factor will be meager LLS and marginal values of CAPE.