Storm Forecast
Valid: Sat 04 Feb 2017 06:00 to Sun 05 Feb 2017 06:00 UTC
Issued: Sat 04 Feb 2017 03:02
Forecaster: TASZAREK

A level 1 was issued for N Portugal, N Spain and SW France mainly for excessive precipitation and in lesser extent for severe wind gusts.

A level 1 was issued for parts of E Adriatic coast mainly for excessive precipitation and in lesser extent for large hail.

SYNOPSIS and DISCUSSION

A blocking ridge pattern over Scandinavia separates two long-waves over NW and far NE Europe. Strong horizontal pressure gradient with a jet streak and multiple shortwaves is stretching from Atlantic trough Iberian Peninsula, W Mediterranean and France. Within these shortwaves and enhanced lapse rates (> 7 K/km) combined with 6-8 g/kg mean mixing ratios, thunderstorms are likely to develop underneath the jet streak in SW Europe and CNTR Mediterranean. Although vertical wind shear covering these storms will be high (DLS ~ 20-35 m/s) and strong synoptic-scale lift will occur, an instability reaching only 200-400 J/kg will limit severe thunderstorm potential (mostly low-topped convection with weak updrafts). However, thanks to strong airflow in low levels (850 hPa > 25 m/s), storms may pose some risk in producing local severe wind gusts of convective origin, mainly in Spain and France.

Morning thunderstorms developing in the exit region of the jet over E Adriatic coast due to (1) local maxima of WMAXSHEAR, (2) steep lapse rates, (3) low elevation of 0C isotherm may be capable of producing 1-2 cm hail. However, due to CAPE being still low, > 2cm hail threat is rather limited. NWP models agree that the main risk associated with thunderstorms developing over Iberian Peninsula and E Adriatic Coast may be an excessive precipitation, mainly due to superimposing convective and stratiform precipitation. Local maxima with an enhanced orographic precipitation may exceed 60-80mm.

In the end of the forecast period, a strong cyclogenesis will take place in the Bay of Biscay, increasing the potential for an organized convective line and severe wind gusts.