Storm Forecast
Valid: Fri 17 Apr 2020 06:00 to Sat 18 Apr 2020 06:00 UTC
Issued: Fri 17 Apr 2020 07:15
Forecaster: GATZEN

A level 1 was issued across the Pyrenees and south-western to northern central France mainly for large hail.

SYNOPSIS

A polar vortex is still placed over north-eastern Europe, and low-level northerly flow advect dry air into most of eastern Europe. Improving lapse rates and recovering low-level moisture is ongoing unter the influence of the European ridge and ahead of a weakening, quasi-stationary mid-level vortex west of Iberia and the Bay of Biscay. Embedded in the southerly flow, a short-wave trough will move across the Bay of Biscay today, promoting some QG lift over France. At low levels, a cold front will enter western France today.

DISCUSSION

France

Latest satellite imaginary indicates a cloud band across France that extends into the British Isles where some embedded storms are present. Model soundings show steep lapse rates over this area that partly overlap with ridge low-level moisture indicated by latest observations with dewpoints up to 12 C in north-western France. Today, diurnal heating will take place as clouds will disappear across parts of the area, and MLCAPE of some 100s J/kg is expected. In the afternoon, frontal lift will take place and new storms are forecast to develop. We expect multicells to form given about 10 m/s 0-3 km shear. Stronger deep-layer shear is not forecast to affect the storms due to a rather low EL height. Main threat is large hail with the stronger storms due to the low wet-bulb freezing level. Additionally, severe wind gusts are not ruled out in the eastern parts of the risk area where deeper boundary-layer mixing can lead to strong downdrafts. Storms are expected to translate to more elevated mode while spreading northward and affecting the Channel region later in the period.

Northern Spain

Some skinny CAPE and about 10 m/s 0-3 km vertical wind shear are forecast in the wake of the north-ward moving short-wave trough. Thunderstorms are forecast given weak CIN and some frontal and orographic lift. Some multicells can produce severe wind gusts and large hail, however, severe threat is limited due to weak CAPE.

South-west Mediterranean

Some elevated storms will go on over this area ahead of a short-wave trough ejecting from the base of the trough west of Iberia. Low-level air mass is stable and quite dry, therefore, severe weather is not very likely, although some large hail is not ruled out due to increased mid-level shear and the possiblility of multicells.

Central Europe

Some first storms are forecast over the mountains of Central Europe. GFS seems to be quite aggressive and possibly overestimates boundary-layer moisture in the afternoon. Storms will form in weak vertical wind shear and little CIN. Some larger hail due to the low wet-bulb freezing level is not ruled out, but overall potential is to weak for any risk or lightning area.