Severe storm expected across Italy, Algeria and Southern Russia
BarboraSamkova last edited by BarboraSamkova
Valid: Wed 18 Sep 2019 06:00 to Thu 19 Sep 2019 06:00 UTC
Issued: Tue 17 Sep 2019 22:55
- A level 1 was issued for central Italy mainly for excessive rainfall.
- A level 1 was issued for Algeria mainly for severe wind gusts and large hail.
- A level 1 was issued for southern Russia mainly for severe wind gusts.
In between of an extensive ridge over the Atlantic and a deep low over Russia, an arctic outbreak is underway across much of central and eastern Europe. During the forecast period, a cold front is forecast to progress southwards across parts of Italy, Balkans and southeastwards across southern Russia. Here, the cold front will be accompanied by the strongest wind field and will pass in conjunction with a sharp short-wave trough moving rapidly eastwards. Much of the DMC activity is forecast to the south of the arctic airmass over parts of Spain, Italy and perhaps southern Russia.
Thunderstorm activity is forecast to pick up in the late evening and overnight hours as weakening cold front approaches the area. With abundant lower tropospheric moisture, CAPE values between 500 and 1500 J/kg are forecast, increasing from land towards the sea. Forecast soundings reveal low LCLs and rather skinny CAPE, favouring efficient heavy rainfall processes. Vertical wind profile will allow for at least modest storm organisation, with DLS around 10 m/s, but at the same time, storms will be slow moving, exacerbating the heavy rainfall threat.
While degree of convective initiation remains uncertain, at least isolated storms will likely form around the peak heating time in the early afternoon. With high LCLs, steep lapse rates and DLS around 15 m/s, multicells to brief supercells may be capable of severe wind gusts and/or large hail.
A powerful cold front will sweep across the area, accompanied by strong wind field. For example, 850 hPa windspeeds are forecast to reach between 20 and 25 m/s. While strongly sheared environment, with 0-1 km shear around 15 m/s and 0-3 km shear up to 30 m/s is likely, degree of CAPE build-up and convection initiation is uncertain. ICON is most aggresive with CAPE around 500 J/kg and substantial convective precipitation, hinting on strongly forced squall line capable of severe wind gusts. GFS and ECMWF produce less CAPE and also less convective precipitation. Nevertheless, will keep a Lvl 1 for severe gusts for this area.
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