Forecast Update
Valid: Wed 24 Jun 2009 10:00 to Thu 25 Jun 2009 06:00 UTC
Issued: Wed 24 Jun 2009 10:13
Forecaster: TUSCHY
A level 1 was issued for parts of Poland mainly for excessive rainfall.
A level 1 was issued for parts of Belarus and N/NW-Ukraine mainly for excessive rainfall and severe wind gusts.
A level 1 was issued for NW Turkey mainly for large hail and severe wind gusts.
A level 1 was issued for S-Balkans mainly for excessive rainfall and large hail.
SYNOPSIS
Weak geopotential height gradients cover most part of Europe, so widespread thunderstorm activity is expected for most parts of Europe in the range of surface convergence zones/topography or short waves.
DISCUSSION
... N-Ukraine, S-Belarus and S/SE/E-Poland ...
Extensive confluent surface streamline pattern is forecast and has already established over Poland and Belarus. Rich boundary layer moisture, typified by dewpoints in the mid to upper tens and adequate temperature decrease throughout the mid-levels assist in the release of 1-1.5 kJ/kg MLCAPE. Shear at all levels remains weak with 0-6km bulk shear around 10m/s. However, thunderstorms over S-Belarus and extreme N/NW-Ukraine could pose a severe wind guts threat due to the large delta-Theta-e spread and augmented DCAPE. Profiles in this region show high effective precipitable water amounts, which ought to increase precipitation loading, so wet microbursts are the main hazard with those storms. It can't be ruled out that a swath of severe wind gusts occurs due to favorable cold-pool formation, especially when MLCAPE values exceed aforementioned 1.5 kJ/kg (e.g. Smolenks yesterday with 2.5kJ/kg MLCAPE). Weak diffluent streamline pattern in almost all levels yield slow moving storms with a tendency for clustering and torrential rain amounts.
Further west, a weak shear and moderate instability environment persists and rapid/widespread thunderstorm development will occur during the next few hours. Storm motion is slim, so either slow propagation of thunderstorms or local training yield a risk for excessive rain amounts with flash flooding possible. WRF still develops a near stationary line of storms over S/CNTRL/NE Poland in the vicinity of somewhat enhanced LL convergence and persistent moisture advection from the east. If indeed a cold pool driven storm cluster evolves further east, strong wind gusts may also play a role over E-Poland, however for that, no model support exists.
... The Balkans ...
Weak shear, low to moderate instability release and a weakly capped airmass result in widespread thunderstorm development with numerous clusters possible. Lokal flash flooding beneath those clusters is the main hazard although strong wind gusts and marginal hail can't be ruled out, too.
... NW-Turkey ...
Rapidly approaching vorticity maximum from Greece serves as focus for isolated thunderstorm initiation, essentially confined to the NW-coast, where dewpoints in the upper tens will be adequate for roughly 800 J/kg MLCAPE release. DLS in the order of 25m/s with strong directional shear yield a large to isolated very large hail risk next to severe wind gusts, before storms move offshore. We will stick with a level-1 due to the limited thunderstorm coverage.
... E/NE Spain ...
EZMWF and GFS/WRF have a bimodal temporal solution regarding thunderstorm initiation over NE-Spain. Right now, the boundary layer is dry/well mixed and no significant impulse will affect the area until the night hours, so we lean more towards the GFS solution, which has an increase of thunderstorms along the Pyrenees during the night hours. Steep mid-level lapse rates, DLS of 15m/s and enhanced SHR-3km make large hail a potential thread.
Further to the south, over E-Spain, very steep lapse rates come offshore, but airmass will stay capped. Models keep this region dry although numerous short-waves draw through from the west mainly during the evening and late night hours. An update may be issued, if early evening conditions indicate a chance for at least isolated thunderstorm development. Shear would be more than adequate for very large hail.
... S-Balkans and W-Bulgaia ...
Placed under the left exit region of a constantly eastward shifting upper level jet, divergence persists in the upper levels at least throughout the daytime hours. A large thunderstorm cluster is already ongoing with roughly 20m/s DLS, so next to torrential rain amounts, large hail and severe wind gusts are possible. Conditions remain favorable for repeated thunderstorm development with an augmented hail threat over W-Bulgaria and NE-Greece and an excessive rain risk over the complete level area.
