Storm Forecast

Storm Forecast
Valid: Wed 01 Sep 2021 06:00 to Thu 02 Sep 2021 06:00 UTC
Issued: Tue 31 Aug 2021 19:32
Forecaster: PUCIK

A level 1 was issued across Spain mainly for excessive rainfall and large hail.

A level 2 was issued across southeastern Spain and the Balearic Sea mainly for (very) large hail, severe wind gusts, and excessive rainfall.

A level 1 was issued across parts of Algeria and Tunisia for large hail and severe wind gusts.

A level 1 was issued for central Russia mainly for severe wind gusts and to the lesser extent for tornadoes.

A level 2 was issued across the eastern Black Sea and the western Caucasus mainly for excessive rainfall.

A level 1 was issued across the Black Sea mainly for excessive rainfall.


The synoptic-scale situation will be dominated by an extensive ridge covering the British Isles and much of western Europe, and a trough centered initially across Ukraine. In between these features, the northerly flow has been established from Scandinavia towards the Alpine Range and the Carpathians. Warmer and moister airmass is forecast across the Iberia and the western Mediterranean, as well as the Black Sea. Both of these regions will also be influenced by mid-tropospheric troughs, yielding unsettled conditions with scattered to widespread thunderstorms.


... Iberia ...

Synoptic-scale lift from the mid(upper)-tropospheric trough is forecast to spread across the area during the day. The strongest mid-tropospheric lift is anticipated across southern Iberia, while the strongest lower-tropospheric lift will take place in the warm advection regime over eastern Spain and the Balearic Sea. Here, low pressure that has developed to the north of Africa will induce easterly low-level flow advecting moist airmass inland. At the same time, an elevated mixed layer with steep mid-tropospheric lapse rates will spread over the Balearic Sea, yielding MLCAPE values > 3000 J/kg. It is likely that numerous storms will be ongoing across Iberia already in the morning.

Interior Spain will experience predominantly a threat of excessive rainfall from slower-moving multicells, forming in the environment of 10 to 15 m/s of 0-6 km bulk shear. Stronger cells may also be capable of large hail. Bulk shear will rapidly increase towards the southeast and will reach 20 to 30 m/s with 0-3 km bulk shear up to 20 m/s. Long hodographs will result in a mixed mode of well-organized systems and supercells capable of (very) large hail and damaging wind gusts. Easterly onshore flow may result in repetitive cell development in some areas, exacerbating the heavy rainfall threat. Further offshore towards the Balearic Sea the warm sector will be strongly capped, but strong low-level forcing may erode it and storms will spread over the sea especially in the evening / during the night.

... Northern Africa ...

While the NWP simulates little to no convection over the area, low-level forcing or local presence of uncapped profiles highlights a risk of isolated convective initiation. Storms will form in the environment of steep mid-tropospheric lapse rates and strong vertical wind shear, posing a risk of large hail and also damaging wind gusts.

... Central Russia ...

A frontal wave is forecast to cross the area with a small patch of 6.5+ K/km mid-tropospheric lapse rates, yielding MLCAPE values in between of 500 and 1000 J/kg. Moderate to strong unidirectional shear mostly confined to the lower troposphere points at an enhanced risk of severe wind gusts. Tornadoes are not ruled out either given that 0-1 km bulk shear will locally exceed 10 m/s. NWP disagrees concerning the coverage of storms in the warm sector and it is possible that only isolated storms will occur in the Lvl 1, most of them staying in elevated mode north of the boundary with little severe threat.

... Black Sea, Caucasus, and southern Russia ...

Severe weather will ramp up in the evening to late-night hours as the mid-tropospheric trough approaches the area. MLCAPE values between 500 and 1500 J/kg are forecast over the Black Sea and the adjacent coastlines. 0-6 km bulk shear will increase to 20+ m/s as the mid-tropospheric flow strengthens with the trough arrival. Thus, well-organized storms will be possible, including supercells. The highest risk is anticipated across the eastern Black Sea and the southwestern Caucasus, where the onshore and upslope flow will result in multiple rounds of storms, posing the threat of excessive rainfall. This threat will likely last well into Thursday. Besides heavy rainfall, large hail and severe wind gusts may occur with stronger multicells or supercells.

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