Storm Forecast
Valid: Fri 04 Sep 2015 10:00 to Sat 05 Sep 2015 06:00 UTC
Issued: Fri 04 Sep 2015 10:20
Forecaster: PUCIK

A level 3 was issued for parts of Central Italy mainly for excessive precipitation, large to very large hail, tornadoes and severe wind gusts.

A level 2 was issued in a belt from Balearic Islands towards Central Italy mainly for excessive precipitation, large hail, tornadoes and severe wind gusts.

A level 2 was issued for SE Spain mainly for large hail, severe wind gusts and excessive precipitation.

A level 2 was issued for W Adriatics mainly for excessive precipitation, large hail and to the lesser degree for severe wind gusts and tornadoes.

A level 1 surrounds Lvl 2s across W and Central Mediterranean mainly for large hail, excessive precipitation and severe wind gusts.

A level 1 was issued for E Spain mainly for large hail and severe wind gusts.

A level 2 was issued for W Ukraine mainly for severe wind gusts, large hail and to the lesser degree for tornadoes.

A level 1 was issued for W Ukraine and S Belarus mainly for severe wind gusts and large hail.

A level 1 was issued for Algeria and Tunisia mainly for large hail and severe wind gusts.

SYNOPSIS

Ahead of the advancing short-wave trough crossing Iberia, strong southwesterly flow is advecting a plume of steep lapse rates over the Western and Central Mediterranean. Combined with very moist lower troposphere, high values of CAPE are forecast. 00 UTC Pratica di Mare and Palma sounding already show 2000 J/kg of MLCAPE combined with more than 20 m/s of DLS. Surface observations show dewpoints well over 20 deg C at some stations near the coastlines. As lapse rates get even steeper, it is likely that CAPE will locally exceed 3000 J/kg.

DISCUSSION

... Belearic Islands towards Central Italy and the Adriatics coastline ...

An impressive setup is forecast with moderate to high CAPE values overlaping with 20 to 30 m/s of DLS. Such setup favours strong, very well organised DMC, including long-lived supercells or large MCS. Satellite loops are already showing pronounced thunderstorm in a belt from Balearic Islands towards Sardegna and Corsica. Storms will gradually progress eastward during the day towards Italy. The highest risk of severe weather will develop along the western coastline of Central Italy especially in the evening and night hours as low level shear exceeds 10 m/s and SREH reaches more than 250 m2/s2. The most prominent threat will be excessive precipitation, given the very high moisture content in the atmosphere, as well as training pattern of cells, which is already evident on the satellite. Due to the very strong DLS and steep lapse rates, storms will be capable of large to very large hail and severe wind gusts. Especially in the evening and night time, tornadoes will certainly be possible given the ramp up in the LLS and low LCLs of the storms evident from the soundings. It is likely that storms will be ongoing to the early morning hours without any signficant weakening of the activity.

A small Lvl 3 is issued for an area with the highest combined risk.

... Eastern / Southeastern Spain ...

Very strong DLS will likely aid in any storm initiating over the area to develop rotation and be capable of large hail and/or severe wind gusts. While Lvl 1 is issued for most of the area with limiting factor rather modest CAPE, Lvl 2 was issued for a small part of SE Spain, where higher CAPE values are forecast and coverage of severe may be higher.

... Western Ukraine, Southern Belarus ...

Ahead of the advancing cold front, NWP predict low to moderate degree of latent instability with surface dewpoints around 17 deg C over SW Ukraine. Plume of higher dewpoints will be advected towards NE during the day. At the same time, flow above 20 m/s at 500 and 700 hPa will result in strong DLS, favouring well-organised DMC. As a frontal wave develops over region and surface low deepens, scattered to widespread initiation is forecast. Along the cold front, storms will likely attain linear organisation with threat of severe wind gusts due to the strong low-level flow, reaching 15-20 m/s at 850 hPa. At the same time, any isolated storm may easily become a supercell capable of large hail. Towards the evening, tornado risk will increase with increase in the LLS, provided that isolated supercells exist at that time. After 18 UTC, risk will start to diminish as the instability becomes elevated.