Storm Forecast
Valid: Tue 26 May 2020 06:00 to Wed 27 May 2020 06:00 UTC
Issued: Mon 25 May 2020 21:21
Forecaster: DAFIS

A level 1 was issued for the largest part of Central Europe, the Balkans, and Asia minor mainly for excessive precipitation (rainfall and small hail) and to a lesser extent for large hail and severe wind gusts.

A level 1 was issued for Spain mainly for severe convective wind gusts.

SYNOPSIS

The main synoptic feature of this outlook is the long-wave trough in Central-Eastern Europe that is expanding unseasonably south, creating negative geopotential anomalies in the Balkans. The largest part of this area will experience DMC and local severe weather events are expected. Another cut-off low is found over Iberia, creating a favorable environment for DMC. West-NW Europe is under the influence of a high-pressure system resulting in subsidence and weak surface winds, whereas two surface cyclones have developed in W Russia.

DISCUSSION

.... Central-Eastern Europe and Asia Minor ....

A pronounced PVA will be located over the Balkans the following days and together with strong diurnal solar heating will be the main mechanisms for CI. Steep mid-level lapse rates and the humid low-troposphere create a few hundreds of CAPE, locally exceeding 1000 J/kg MLCAPE in the forecast maps. In addition, saturated vertical profiles create more than 15-20 mm of effective PWAT under the core of the trough where storm motions are weak. The main threat inside the level-1 area will be excessive rainfall from slow-moving storms and locally high amounts of small hail are also expected. Freezing levels below 2500 m suggest that small hailstones will survive to the surface, posing a threat in large quantities during stationary storms.

On the leading edge of the trough, a jet stream increases DLS up to 30-35 m/s in NE Italy-NW Balkans, Greece, and Turkey. Despite that, the storms that will manage to form under this jet should be low-topped in NE Italy and NW Balkans, with cloud-tops below 7 km with CAPE confined below 4-5 km. A few storms may locally produce severe convective wind gusts at the surface. In Turkey, DMC is expected in the afternoon and apart from large amounts of small hail, also large hail cannot be ruled out given the overlap of strong DLS and CAPE.

.... Spain ....

A combination of synoptic lift and diurnal heating will steer DMC in Iberia. The cut-off low destabilizes warm and moist air masses where low/mid-level lapse rates exceed 7 K/km. DLS and storm motions will be weak but storms will be able to produce severe wind gusts given the high-cloud bases and heigh delta-thetae values. Forecast soundings also show high NCAPE values which increase the threat for large hail where CAPE is reaching 1000 J/kg.