Storm Forecast
Valid: Tue 11 Jul 2017 06:00 to Wed 12 Jul 2017 06:00 UTC
Issued: Mon 10 Jul 2017 23:20
Forecaster: DAFIS
A level 2 was issued for Belraus and W Ukraine mainly for large hail, excessive precipitation, severe wind gusts and tornadoes.
A level 2 was issued for N Italy, Slovenia and NW Croatia mainly for large hail, excessive precipitation and severe wind gusts.
A level 1 was issued for parts of East and Central Europe mainly for large hail, excessive precipitation, severe wind gusts and tornadoes.
A level 1 was issued for N Italy, Austria, SW Hungary, Croatia, Slovenia and N Montenegro mainly for large hail, severe wind gusts and excessive precipitation.
A level 1 was issued for English Channel, Benelux and extreme NE France mainly for severe wind gusts.
SYNOPSIS
A low-pressure system in the Baltic Sea creates a tight pressure gradient in Poland and more to the east during Tuesday. Under this gradient, a weak surface cold front will trigger DMC. Once more, we expect widespread lightning activity over the largest part of Europe, as the long-wave trough moves gradually to the east. Several convergence zones and vorticity maxima will provide lift to moist and warm, thus unstable air masses, mostly in Central and East Europe. Mediterranean Sea and surroundings will remain under a strong cap due to WAA. Moreover, in the early morning of Wednesday, a vigorous short-wave trough will enter continental Europe, above the English Channel, where we expect a new round of short-lived but vigorous convection.
DISCUSSION
.... E Poland, Belarus, W Ukraine and NE Slovakia ....
Elevated convection from the previous day will continue to affect this area. As the cold front of the low-pressure system pushes some unstable air masses to NE-E, with some 13-14 g/kg mixing ratio and lapse rates above 6.5-7 K/km, MLCAPE can reach up to 2.500 J/kg over the area highlighted with a level 2 threat area. Meager DLS does not look very promising for many supercells, but enhanced 0-3km shear and helicity can lead to 1-2 supercells, able to produce all kinds of severe weather. Excessive precipitation threat is issued for all level 1 areas, surrounding level 2, but mostly for the north part of level 2 area and the Baltic States. More to the south, fat mid-level CAPE profiles (primarily due to more steep lapse rates) suggest an increased threat for large hail and over Ukraine, the rather dry PBL may assist some microburst, with damaging wind gusts. This scenario is also supported by the delta-thetae values in GFS (16-18K). Between 12-18z LLS of more than 10 m/s (0-1km) is calculated by GFS, so tornado threat is also elevated, mainly in Belarus and Ukraine. Elevated convection is expected until the end period of this outlook, propagating towards Russia.
.... N Italy, Slovenia, N Croatia ....
The pooling of warm and moist air masses south of the Alps, along with a vorticity lobe that will cross the area during the afternoon of Tuesday, will provide a favorable environment for vigorous DMC. DLS of more than 20 m/s suggest that any storm that will form in N Italy will become organized to MCSs and supercells, able to produce large to very large hail and severe wind gusts. Orographic features will also assist some excessive precipitation events in NE Italy, Slovenia and NW Croatia. For the eastern parts of Slovenia and Croatia, severe wind gust threat is significant. Rather straight-line forecast hodographs, show a hint that the convective mode will be discrete storm cells, organized in large systems, propagating to the east by the end time of this outlook. Marginal large hail or large amounts of small hail can be confirmed in S Germany and Austria, as well as excessive precipitation events, due to saturated vertical profiles in the models outputs. Flash floods are also expected in E Germany and W Poland in the morning of Tuesday.
.... English Channel Benelux NE France ....
There are some uncertainties between the global models about the amount of CAPE available under the vigorous short-wave trough during the early morning of Wednesday, bringing some impressive amounts of PV. Current opinion based mainly on CAMs (AROME solution) is that a cluster of fast-moving storms will develop in SE England, crossing the English Channel and entering continental Europe before 06z on Wednesday. Saturated vertical profiles and strong LL winds, suggest that storms will be able to produce short-living downpours, but very strong to damaging wind gusts, especially in the coasts of Belgium and the Netherlands. Finally, 1 or 2 tornadoes are not ruled out near the coasts, where LLS and helicity are noteworthy.
