Storm Forecast
Valid: Sat 11 Jul 2009 06:00 to Sun 12 Jul 2009 06:00 UTC
Issued: Fri 10 Jul 2009 18:49
Forecaster: TUSCHY
A level 2 was issued for S/SE Bulgaria and extreme NW-Turkey mainly for large hail.
A level-1 was issued for N-Greece and Macedonia mainly for large hail.
A level-1 was issued for Bulgaria, Romania and parts of Moldova mainly for excessive rain.
A level-1 was issued ofr Estonia, Latvia and Lithuania mainly for large hail.
A level-1 was issued for S-Finland mainly for large hail.
A-level-1 was issued for parts of Denmark and the Kattegat mainly for waterspouts.
SYNOPSIS
A gradually eastward moving upper trough, centered over N-Europe, still affects most parts of central-/N- and E-Europe. During the end of the forecast period, another upper low evolves somewhere over Romania/Bulgaria. A strong depression enters the forecast area from the west and affects Ireland, UK and Scotland during the forecast with strong winds and heavy rain.
At the surface, the main feature of interest is a gradually eastward moving cold front over Romania and Bulgaria, wich becomes stationary over the extreme W-Black Sea during the night hours.
DISCUSSION
Uncertainties on the mesoscale still don't permit to focus on a smaller area. Nevertheless, conditions are supportive for a potential serious flash flood risk over E/NE-Bulgaria and parts of central/SE/E/NE-Romania during the following 24h.
... Parts of Greece, Macedonia, Bulgaria and NW-Turkey ...
Widespread thunderstorm initiation is forecast as an upper trough approaches from the NW with an attendant surface cold front slowly entering the area of interest from the west. Boundary layer moisture is adequate for moderate to strong instability release with MLCAPE values of 1000-2000 J/kg, increasing from west to east. Surface dewpoints remain in the mid tens over N-Greece and W-Bulgaria with values up to 20°C over SE-Bulgaria and extreme NW-Turkey. 0-6km bulk shear increases towards S-Bulgaria, Greece and the Aegean Sea with values of 15-25m/s. Initiation ought to take place either in the weakly capped prefrontal airmass or along the eastward moving cold front already during the morning hours. Activity will be widespread and numerous large thunderstorm clusters evolve during the daytime hours, which move N/NE-wards in the mid-/upper level steering flow. During the initiation, large to very large hail, severe wind gusts and even isolated tornadoes are forecast, the latter risk due to 100-200 J/kg LL CAPE release. As thunderstorms start to merge betimes, the main hazard shifts to torrential rainfall amounts with a flash flood risk as wind field at mid-levels becomes weaker beneath another developing upper low.
The highest flash flood risk ought to be found over SE/E/NE Bulgaria. During the late night hours, thunderstorms finally move offshore, but models differ somewhat how far offshore the front will move. If it stalls next to the coast, repeated thunderstorm development could produce serious flash flooding over E/NE Bulgaria and SE-Romania due to the favorable inflow path of very moist air from the Black Sea.
It is not yet clear how widespread thunderstorm initiation will be over the Aegean Sea. Both the approaching trough axis in the evening hours and the surface cold front later in the night could serve as foci for initiation. In addition, surface dewpoints in the lower twenties along the coast and a weakening cap during the night hours all point to the augmented possibility for thunderstorms. Shear and instability would be strong enough for organized thunderstorms, even supercells will be possible. For now, we decided to ignore at least partly the pessimistic model runs and include parts of the Aegean Sea.
... Romania ...
Regarding initiation, the cold front and the approaching trough/developing upper low all serve as foci for widespread thunderstorm development during the daytime hours. Some uncertainties are present in respect to which degree upstream thunderstorm development modifies the mid/upper atmosphere (e.g. anvil debris and/or cold pool dominated and decaying thunderstorm clusters with more stratiform rain). However, this plays a role mainly for the prediction of large hail, given roughly 1000 J/kg ahead of the cold front and 10-15m/s DLS. The main hazard will be intense rain amounts beneath northward traveling thunderstorm clusters.
Dependent on the excat position of the developing mid/upper low, another round of convection could evolve during the night hours, if the cold front indeed stalls next to the coast. With influx of very moist air from the Black Sea, the frontal forcing and upper divergence, everything would be in place for anouther round of thunderstorm clusters probably affecting E/NE Romania. Intense rainfall with flash flooding is the main risk. It has to be noted that even Moldova could be affected.
...Denmark, Sweden, Finland, Estonia, Latvia and Lithuania ...
Moderate instability release but limited shear support multicell thunderstorms with an isolated large hail threat, primarily over S-Finland, Estonia, Latvia and Lithuania. Denmark and S-Sweden are placed beneath cyclonic vortex. Background shear remains weak and LL lapse rate at least somewhat steepened, so a few waterspout/tornado reports are possible.
... E-Spain ...
Placed under the right entrance region of a mid-level jet, and increasing BL moisture /CAPE release along the coast increase probabilities for thunderstorm initiation. Any developing thunderstorm experiences modest shear/instability with an isolated large hail threat. Due to the very isolated nature of thunderstorms, no level area was issued.
