Storm Forecast

Storm Forecast
Valid: Tue 18 Apr 2017 06:00 to Wed 19 Apr 2017 06:00 UTC
Issued: Mon 17 Apr 2017 22:19
Forecaster: DAFIS

A level 1 was issued for Portugal and Spain mainly for large hail and severe wnd gusts.

A level 1 was issued for Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania mainly for excessive precipitation, large amounts of small hail and severe wind gusts.

SYNOPSIS

A trough pushes cold mid-level air masses over Central Europe and heavy snow showers will continue to affect several countries during Tuesday, and maybe some thundersnow events may occur. This potential area is highlighted by a 15% of lightning activity, where large amounts of graupel is also forecast. At the leading edge of this trough, under the jet stream, we can find several ingredients to produce and sustain lightning phenomena, especially during the night of Tuesday.
A meso-low is found off-shore Portugal, destabilizing the area, while a short-wave trough over Spain will also provide some lift to moist air masses. Finally, another short-wave trough travels from Black Sea towards Russia, where several thunderstorms are expected, but just out of our domain.


DISCUSSION

DISCUSSION
Spain and Portugal

A level 1 is placed over Portugal, in the area influenced by a meso-low, with steep lapse rates and some hundreds of CAPE are expected to build up. Apart from diurnal heating, the advection of positive vorticity will lead in widespread lift of moist air masses, and large hail is expected. MLCAPE is calculated by GFS to reach 2000 J/kg on shore of Portugal and West Spain, while large CIN will suppress any convective activity near the shore. Moreover, CI is quite questionable in East Spain, where we will have WAA up to 850 hPa, but in the mid-levels geopotentials will decrease after 12z, resulting in steep lapse rates. Every storm that will form in this environment will be able to produce large hail and severe wind gusts.

.... Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania ....

Modest CAPE values over Italy decrease the potential of severe weather, but strong DLS overlapping with moist LL air masses, under the advection of positive vorticity may result in some thunder storms, able to produce severe wind gusts. During the late afternoon and night of Tuesday, as the long wave trough will progressively move south, a LL convergence line is expected in the Adriatic Sea, steering a plume of moist air masses. Albania seems to get the highest amounts of precipitation during the night, but also small hail and wind gusts may verify a level 1. Models produce up to 800 J/kg MLCAPE but it is difficult to estimate exactly the evolution of a MCS in a highly sheared environment. 850 hPa will reach 15-18 m/s and can easily reach the surface.

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