Storm Forecast
Valid: Sat 12 Sep 2009 06:00 to Sun 13 Sep 2009 06:00 UTC
Issued: Fri 11 Sep 2009 20:19
Forecaster: KOROSEC
A level 1 was issued for Aegean sea and western Turkey mainly for excessive rainfall.
SYNOPSIS
A weak upper-level cut off low affects Turkey where the most severe weather and especially heavy rainfalls will take place. Another upper level low ejects into extreme southern Mediterranean by Sunday morning. An intense trough accompanied by a surface cyclone cuts off over Scandinavia towards the end of forecast period. At surface, a quasi-stationary SW-NE oriented weak cold front makes only small progress towards SE across east-central Europe. A strong ridge with large high pressure area persists over western Europe.
DISCUSSION
... Aegean Sea and western Turkey ...
Parts of Turkey will again see severe storms with heavy rainfalls as the main threat. A weak upper-level cut off low with a weak surface cyclone will slowly move eastwards across the western Turkey during the forecast period. Models are confidently agreeing in quite high instability in place, especially over parts of Aegean sea and along the SW-ern Turkish coast. Resulting from very warm sea waters beneath the cool mid-levels. In weakly capped environment, numerous showers and thunderstorms will form. Strong upslope flow from the sea onshore, slow moving storms and very high water content throughout the troposphere, should result in excessive rainfalls across the western and northwestern Turkey. Complex topography of western Turkey should also serve as an additional lift and orographic precipitation will even increase the severity of thunderstorms. Serious flash flooding could become an issue, especially over the areas where severe flash flooding happened earlier this week.
... Italy, northern Balkans towards Poland ...
A weak surface cold front extending from southern Poland SW-wards into northern Balkan peninsula serves a focus for convective activity. Rather steep mid-level lapse rates and diurnal heating will result in a few hundreds of CAPE, while only weakly capped. Numerous showers and thunderstorms should form. Given the only weak deep-layer shear below 10m/s in place, severe storms are not expected. Rather slow moving storms and moderately moistened airmass suggest that a few storms with threat for heavy rainfall could form, as well as a large hail event or two. Especially there, where instability seems more concentrated, e.g. NW Balkan states.
... Spain and Portugal ...
These areas will be affected by cooler mid-levels, while quite rich moisture is present in the boundary layer. Several convergence lines are visible on the models, mostly along the mountainous terrain. Quite steep lapse rates should result in about 500-800 J/kg of MLCAPE by diurnal heating Showers and thunderstorms will form and a few hail events could occur. Storms will mostly be diurnal driven and should diminish quickly after the sunset. However, models simulate that activity over NE Spain towards Balearic Islands could persist into the nighttime hours.
... NE Algeria, N Tunisia and extreme southern Mediterranean sea ...
Another weak upper-level low will move from Algeria ENE-wards during the late afternoon hours and overnight. Moderate instability will be available, but not well overlaping with deep-layer shear. Still, a few organized storms can be expected. High PWAT values suggest that the main threat with these storms will be excessive rainfalls, while locally large hail will be possible as well. As the low moves over the extreme southern Mediterranean sea later on, storms will continue to form over warm waters. Ascent ahead of the upper low suggests that an MCS will likely form along the front overnight.
.. Baltic sea ...
A forming upper-level cut off low over Scandinavia will be rapidly moving southwards towards the Baltic sea. Only weak instability signals are present on the models, so widespread convective activity is not expected. But very strong deep layer shear will be in place. Given the still warm water temperatures of Baltic sea, a few storms could form and gain some organization in strongly sheared environment.
