Storm Forecast
Valid: Sun 24 Jun 2018 06:00 to Mon 25 Jun 2018 06:00 UTC
Issued: Sat 23 Jun 2018 07:27
Forecaster: TUSCHY
A level 1 was issued across parts of Sardegna, Sicily and Greece mainly for isolated large hail and locally excessive rain.
A level 1 was issued east of Ladoga mainly for isolated large hail and a low-end tornado threat.
SYNOPSIS
A deep cold-core vortex remains entrenched over the Baltic States. Numerous mid-level waves circle that vortex with one strong impulse sagging south along its western fringe towards the CNTRL Mediterranean (fueled by a strong upper jet over CNTRL Europe). This causes an elongating NE/SW aligned upper trough axis to impact most of S-/SE-Europe.
Upstream ridging extends from Algeria to the North Sea and remains steady state in strength. A marginal eastward shift is anticipated.
Another cyclonic vortex pauses W of Portugal but it expands its area of influence towards Portugal and NW-Spain in the shape of cooling mid-levels.
A cold front, driven by the Scandinavian vortex, pushed a dry air mass far south with better BL mixing ratios now confined to the Mediterranean and surroundings. Some moisture recovery is forecast over the Iberian Peninsula and also over NW-Europe as modified Atlantic air approaches from the NW. Despite the eastward departing cold front, no synoptic-scale fronts impact today's thunderstorm forecast.
DISCUSSION
... NW-Spain ...
The vortex to the W advects a marine air mass ashore, which affects Portugal and far W/NW Spain. This moisture partially overlaps with a NW-ward moving EML over Spain, where mid-level lapse rates exceed 8 K/km. Hence a confined CAPE plume evolves over far W/NW Spain which is mostly capped. Focus for spotty CI resides along the orography like the Galician Massif or the Cantabrian Mountains. A weak wave at mid-levels could insert some lift beyond noon on a temporal scale and one or two updrafts my be able to break the cap along the border area of the thermal ridge. In general however, synoptic-scale subsidence should persist. Elevated CAPE on the order of 1 kJ/kg and DLS of 15-20 m/s would cause any updraft to become organized with isolated large hail and sporadic severe downburst events the main hazard. No level 1 was added due to uncertainties with respect to CI. We expanded the lightning area offshore to account for some elevated overnight activity in ongoing WAA regime.
... CNTRL and E Mediterranean ...
Subtle waves cross the broad area of interest during the forecast and assist in temporarily enhanced CI. During the day, this occurs mostly over onshore areas whereas during the night, the focus gradually shifts more offshore. In addition, the approaching upper trough induces persistent and moderate synoptic-scale lift over the CNTRL Mediterranean during the night, which supports active overnight convection over the Tyrrhenian Sea and surrounding areas. Passing waves and the approaching trough push DLS in the 10-15 m/s range, which could support a few organized multicells with large hail and locally heavy rain. Small level 1 areas were added where ingredients favor a few severe events.
... E of Ladoga ...
A depression moves towards S-Finland and pushes a narrowing warm sector through the level 1 area. Of concern is decoupling of best forcing from moderate CAPE (up to 800 J/kg MCLAPE) but also only slowly eroding CIN. Models break out some precipitation and forecast soundings show adequate shear for a few multicells. Rapid splitting and clustering should keep any svere risk on an isolated scale and hence a borderline level 1 was added for isolated hail and a low-end tornado threat (the latter due to augmented LL shear and low LCLs).
... Far NE Germany to Belarus, Ukraine and Romania ...
Diurnal driven cold sector convection is anticipated with no severe risk due to weak CAPE and shear. Pulsating convection brings graupel and gusty winds with a diminishing thunderstorm activity beyond sunset.
