Storm Forecast
Valid: Sat 11 Jun 2016 06:00 to Sun 12 Jun 2016 06:00 UTC
Issued: Sat 11 Jun 2016 07:07
Forecaster: TASZAREK

A level 2 was issued for S Austria, NE Italy, Slovenia, W Hungary and N Croatia mainly for the large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for part of CNTRL and SE Europe mainly for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for CNTRL and S British Isles mainly for excessive precipitation

A level 1 was issued for W Russia and CNTRL Ukraine mainly for large hail, severe wind gusts, excessive precipitation and tornadoes.

A level 1 was issued for N Algeria and N Tunisia mainly for large hail and severe wind gusts.

A level 1 was issued for E Spain mainly for large hail and severe wind gusts.

SYNOPSIS

Weakly horizontal MSLP gradient continue to spread over most of the W, S and CNTRL Europe. A thermal boundary between polar air masses runs from SE France, trough Alps up to N Romania. On the southern side of this border a widespread thunderstorms will develop in the weakly sheared environment due to diurnal heating, rich boundary layer's moisture and mid-level divergent flow. On the northern side of the boundary, weakly sheared scattered thunderstorms will be possible over British Isles, France and S Germany with potential of producing excessive precipitation. NE Europe is under influence of a deep trough centred over Estonia and Latvia. Within a well pronounced warm sector on its eastern flank and approaching cold front, severe thunderstorms in the highly sheared environment will be possible. A cyclonically curved polar jet stream within this system will stretch from NE Poland up to W Russia. Subtropical jet stream extends from Atlantic Ocean trough strongly capped E Spain, W and CNTRL Medditereanean and dissolves before reaching Balkan Peninsula.

DISCUSSION

...parts of CNTRL and SE Europe...

A mixing ratio up to 10-11 g/kg with 6.5 - 7.0 K/km lapse rates and strong diurnal heating develops CAPE up to 1000-1500 J/kg. The wind flow is generally low and with rich moisture vertical profile (PW > 30mm) creates threat for excessive precipitation and local flash flooding, especially given a widespread CI in the belt from N Italy up to NW Romania. Locally enhanced DLS up to 15 m/s may help in the cell aggregating and form multicell clusters with severe wind and large hail threat. However, due to only moderate instability and moderate shear these should prevent form reaching an extremely severe intensity. Due to local terrain interactions and wind profile enhancement, some local supercells with hail and wind potential cannot be ruled out. Increased probability for supercell thunderstorm will fall on N Italy where DLS will exceed 20 m/s. A MCS or two in the line from N Italy up to NW Romania are plausible in the late afternoon hours.

...W Russia...

Within a deep trough centred over Latvia and Estonia and a well-pronounced unstable warm sector with CAPE up to 1000-1500 J/kg on its eastern flank, an organised severe thunderstorms are expected. Thanks to strong mid-level flow with DLS up to 20-25 m/s, thunderstorms in the wam sector may quickly organise into multicell and supercells capable of producing large hail, severe wind gusts and tornadoes given locally enhanced LLS. On the cold frontal boundary a main threat will be related to severe wind gusts and in lesser extent large hail. Threat for severe weather should decrease after 18-20 UTC when the instability will significantly drop.

...British Isles...

Slowly moving thunderstorms in the environment of weak CAPE and shear but moist vertical profile (PW > 30mm) are expected to develop due to diurnal heating. Thanks to PVA in the evening hours, their potential in producing heavy precipitation may be maintained until evening hours, thus creating a local threat for excessive precipitation, especially in N England.

...E Spain...

Thanks to SE advection of very moist airmass converging along the coastline and overlapping with > 7 K/km lapse rates a CAPE up to 1000-1500 will develop in the afternoon hours. Because this area is in the range of weakening sub-tropical jet streak, an enhanced DLS up to 20-25 m/s will cover instability areas. Although ingredients are favourable for the severe convective storms (especially large hail and severe wind gusts), a strong cap (CIN ~ -100 J/kg) rather inhibits any convective activity. However, a level 1 was issued, because some of the NWP models indicate a weak signals for CI, and if any thunderstorm will initiate in this environment, severe weather event cannot be ruled out.