Storm Forecast
Valid: Sat 07 Jun 2014 06:00 to Sun 08 Jun 2014 06:00 UTC
Issued: Fri 06 Jun 2014 22:11
Forecaster: PUCIK
+ + + Corrected + + +
A level 1 was issued for England mainly for excessive precipitation, large hail and to the lesser degree for tornadoes and severe wind gusts.
A level 1 was issued for France and BENELUX mainly for large hail and severe wind gusts.
A level 1 was issued for Western Russia, Eastern Belarus Western Ukraine, and Northeastern Romania mainly for large hail and severe wind gusts.
SYNOPSIS
A cyclonic vortex will remain located over the eastern Atlantic, with strong southerly flow simulated on its forward flank. An "EML" is advected towards the north (France, BENELUX, W Germany) from N Africa. A cut-off low will slowly translate from S Sweden towards the Baltic states during the forecast period. In between of these two aforementioned features, a ridge will stretch from the Mediterranean towards central Europe. There will be two foci for thunderstorm initiation - the first being in a belt from S France towards S England and the second being much larger, spanning much of Scandinavia towards the Balkans and Turkey. In between, more quiescent conditions should prevail.
DISCUSSION
... England ...
A short-wave trough is forecast to cross the region by 15 UTC Friday, so that any severe activity will likely happen by this time. GFS and ECMWF are in strong disagreement regarding the timing and degree of evolving instability - while ECMWF simulates the highest instability during the morning hours, GFS counts with the afternoon destabilisation. The main culprit behind this disagreement may be the amount of morning convective debris and subsequent stratiform precipitation. Nevertheless, as strong mid-level flow overspreads the region, DLS values above 20 m/s may overlap with at least marginal CAPE values. This would suggest some potential for well organised DMC, including supercells, which may pose the hazards of large hail or marginally severe wind gusts. Especially in the morning hours, stronger low-level flow will contribute to LLS above 10 m/s, so if some supercells manage to develop at that time (and provided they are not elevated), isolated tornado event is not ruled out. As storms cluster thanks to the forcing by the approaching short-wave, excessive precipitation threat will be enhanced.
... France towards BENELUX ...
Bordeaux 12 UTC Thursday sounding captured the spread of EML towards the north. By 12 UTC Friday, EML will likely have overspread much of the region. There is a disagreement in models regarding the degree of low-level moisture - with GFS being the more aggresive one. Perhaps the best low-level moisture, based on the actual observations, will be available over S France. A significant difference in the values of CAPE between models, lack of apparent synoptic-scale forcing (apart from ill-defined frontal boundary) and influence of overnight convection make for a tough forecast for this region. Models agree on moderate to strong vertical wind shear, with DLS ranging from 15 (Netherlands) to 30 m/s (S France). However, shear vector should be parallel to the boundary, favouring storm clustering along the front. Regarding initiation, in the afternoon hours NW France and BENELUX will have higher odds of seeing a storm while towards the evening, some storms should initiate also over S and Central France. Again, much of this may also depend on the morning convection and leftover outflow boundaries. In scenario with much uncertainities, a broad Level 1 is introduced for the risk of well-organised DMC - multi or supercells capable of large hail and severe wind gusts.
... Western Russia towards Romania ...
Several soundings from the area (e.g. Smolensk) show steep mid-level lapse rates atop moist boundary layer, favouring moderate to high CAPE values. Not much of a change will occur to the situation in this forecast period. GFS and ECMWF both count on moderate to strong instability, ECMWF even going for more than 3000 J/kg of CAPE over SE Belarus and adjacent parts of Ukraine. This should happen in the relatively weak vertical wind profile, perhaps apart from the northern part of the region, where approaching cut-off should provide for DLS slightly above 15 m/s. Conditions look prime for some strong multicells capable of large hail and/or severe wind gusts. If the ECMWF version of high CAPE materializes, with locally slightly enhanced shear along the boundaries, even a brief supercell capable of isolated very large hail may occur.
