Storm Forecast
Valid: Sun 18 Jun 2023 06:00 to Mon 19 Jun 2023 06:00 UTC
Issued: Sat 17 Jun 2023 21:09
Forecaster: PUCIK
A level 2 was issued across parts of N Spain and S France mainly for large to very large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across SE Spain mainly for severe wind gusts.
A level 1 was issued across NW Spain and France mainly for large hail and excessive rainfall.
A level 1 was issued for parts of the British Isles mainly for excessive rainfall.
A level 1 was issued for parts of Latvia, Lithuania, Poland, Slovakia, Romania, Bulgaria, Greece and Turkey mainly for excessive rainfall.
A level 2 was issued for parts of Georgia, Azerbaijan and Armenia for large to very large hail and excessive rainfall.
SYNOPSIS
A ridge builds over the Mediterranean, its axis stretching from Algeria through Sardegna into Germany. A highly amplified flow pattern sets up around the ridge with deep troughs on either side. Stronger flow is forecast at the eastern flank of the trough over the Atlantic and at the base of the trough over Turkey. Thunderstorm activity will be confined to these two troughs and their attendant frontal systems.
... Spain to France and the British Isles ...
At the time of forecast writing (21 UTC Saturday), widespread storms have been ongoing across N Spain and S France. Scattered storms have been observed across the English Channel. Models suggest that the activity will likely continue overnight, potentially complicating forecast scenario with remaining cloudiness and outflow boundaries.
Going from the south to north, primary convective hazards will change from severe wind gusts to large hail and subsequently excessive rainfall.
Across SE Spain, initiation is questionable. A combination of long hodographs and deep boundary layer suggests the possibility of high-based supercells capable of intense downbursts within their RFD.
Further north, low-level moisture will increase, especially N of the Pyrenees. While the lapse-rates will not be particularly steep, there will be an abundance of CAPE above -10 deg C isotherm. Combined with relatively high LCLs and 0-6 km bulk shear between 15 and 20 m/s, supercells capable of large to very large hail are forecast. Storms will initiate across well defined convergence zones and will likely grow upscale with time. This may result in isolated severe wind gust threat. With the approach of the trough and availability of MUCAPE throughout the night, elevated clusters of storms may pose a threat of marginally large hail or very heavy rainfall well after the sunset.
Across N France, S UK and Ireland, forecast profiles suggest a prevalence of heavy rain risk with very moist profiles, low LCLs and locally also the dominance of CAPE within the warm part of the cloud. A sharp short-wave trough will cross the UK along with a frontal system that should yield widespread storms that spread N and E during the afternoon and evening hours.
... Bulgaria to Latvia ...
Several Lvl 1s have been issued for a risk of heavy rainfall given moist profiles and abundance of CAPE in the warm part of the troposphere. The threat levels were introduced where models agreed on the positioning of convergence zones and/or substantial convective precipitation. It is possible that isolated heavy rainfall occurs also outside the Lvl 1 within general thunder areas.
... Turkey ...
Substantial flash flood risk is forecast to evolve with the trough crossing W Turkey during the day. Widespread storms are forecast across the whole W part of the country and also along the Black Sea coastlines. Ahead of the upper-level trough, storms will continue well into night hours. Large hail will be possible in the southern parts of Turkey, where higher LCLs and stronger shear are forecast.
... Georgia, Armenia, Azerbaijan ...
Fat CAPE profiles will combine with 0-6 km shear > 15 m/s, yielding a significant threat of large or even very large hail threat. Storms will spread east during the day and will first form over the mountains.
