Storm Forecast
Valid: Mon 08 Jul 2019 06:00 to Tue 09 Jul 2019 06:00 UTC
Issued: Sun 07 Jul 2019 22:58
Forecaster: PUCIK

A level 2 was issued across E Spain mainly for large to very large hail, severe wind gusts and excessive rainfall.

A level 1 was issued across NW Spain and extreme N Portugal mainly for excessive rainfall and large hail.

A level 2 was issued across N, NE Italy, Slovenia, Croatia and extreme N Bosnia mainly for large to very large hail and severe wind gusts.

A level 1 was issued across NW Italy, Bosnia and Serbia mainly for large to very large hail and severe wind gusts.

A level 1 was issued for parts of Romania, Bulgaria into Ukraine and W Russia mainly for excessive rainfall, large hail and to the lesser degree for severe wind gusts.

A level 1 was issued across Caucasus and NE Turkey mainly for excessive precipitation and large hail.

SYNOPSIS

Two dominant synoptic scale features over Europe are a cyclonic vortex that will translate slowly across Iberia E-ward and an even larger vortex centered over the Baltic States and W Russia. Several short-wave troughs travel around the vortex in strong W to NW-ly flow. Closer to the surface, a frontal boundary will stretch from S France through the Alpine range into Bosnia, Serbia, S Romania, subsequently curving NE-ward across the Black Sea towards Russia. With moist airmass to the south and east of the cold front, abundant DMC activity is forecast across many places, including the forward flank of the vortex over Iberia.

... Iberia ...

As of Tuesday 22 UTC, scattered elevated thunderstorms are ongoing over E Spain in a large cloud shield. Surface observations clearly show advection of moist airmass inland in E to SE-ly flow. Towards the morning hours, elevated storms will likely be still ongoing over this part of the area, with threat of isolated severe hail. Subsequently, as daytime heating destabilises boundary layer, surface based storms are forecast to form. Storms will be initiated either by the local topography and/or by the pronounced convergence zone between moist airmass advected from the sea and very dry airmass further inland. In the environment of MLCAPE around 1000 J/kg and unseasonably strong DLS, reaching up to 30 m/s, well organised and severe convection is likely. With straight hodographs, splitting supercells and linear segments will dominate the convective spectrum.

Large to very large hail and severe wind gusts are expected, even though the lack of steep lapse rates through hail growth zone may mitigate the risk of hail to some extent. As the storms spread northward, they may cluster around the S-N oriented convergence zone with attendant heavy rainfall threat.

Heavy rainfall threat will be more pronounced towards NW of the threat area, over NW Spain, where slower storm motions and moister profiles will enhance the precipiation sums from the individual cells. Weaker shear will reduce the chances for large hail and severe wind gusts here.

... N Italy through Slovenia into Bosnia ...

Another round of severe weather is likely over parts of this area also on Tuesday. While over Slovenia and Croatia, the amount of low-level moisture has decreased compared to the previous days, very moist airmass persists over Italy with dewpoint readings around and above 20 deg C. The most likely area of storm initiation will be again southern Alps and high resolution NWP simulates supercells crossing Friuli-Venezia region and from Slovenia through Croatia to N Bosnia during Wednesday afternoon. In 20 to 25 m/s of DLS and MLCAPE around 1000 J/kg, large to very large hail and severe wind gusts may accompany these storms, though hail risk be lower over Slovenia than over Italy due to CAPE decreasing from W to E.

Initiation is more questionable over the Appenines and over Piemonte region. While over the Appenines, global models show some precipitation signals in the zone of MLCAPE exceeding 2000 J/kg with 20+ m/s of DLS, no precipitation is forecast for Piemonte. Nevertheless, decided to keep a Lvl 1 for this as any storm that forms would be capable of very large hail and severe wind gusts.

... Balkans through the Black Sea into Ukraine and Russia ...

A large lvl 1 was introduced along the S- and E-ward advancing cold front. Numerous storms will likely be ongoing already at the start of the forecast period, particularly over Romania and Ukraine. While the passage of the front is forecast to reduce the low-level moisture, NWP simulates that a tongue of moister airmass will remain S of the Carpathian mountain range, allowing for build up of around 1000 J/kg of MLCAPE and further storms may be expected here also in the afternoon hours.

Hodographs suggest DLS around 15 m/s, allowing for well organised multicells and some transient supercells. Isolated large hail and severe wind gusts will occur with stronger storms. Excessive precipitation is also likely, particularly over Ukraine, where mean flow will be parallel to the cold front, which could result in cell training and high precipitation sums.