Excessive convective rainfalls and flash floods possible today
Very hot, humid and partly unstable conditions continue during these days. An interesting situations unfolds today as a weak upper level disturbance crosses the Alps in the afternoon hours and will likely lead into destabilization across southern Alpine region. Given the high BL moisture, surface dewpoints from 17-20°C and 0-1km mixing ratios up to 13 g/kg, MLCAPE up to 2000 J/kg or higher will release. In rather weakly sheared environment, mostly pulse storms are likely in the beginning which will tend to cluster later when deep-layer shear slightly increases towards 10m/s. Not much of a shear, though, but enough for some organization and clustering. High PWAT (near 40 mm), extreme instability, weak shear and slow storm motion all point into serious excessive convective rainfall threat and local flash floods where storms will fire. Delta Theta-e values suggest that strong outflow gusts are possible as well.
As I was on shift today at ESTOFEX, find a more detailed discussion about conditions today across our region here below. A level 1 was issued to cover the flash floods threat:
Storm Forecast
Valid: Tue 13 Jul 2010 06:00 to Wed 14 Jul 2010 06:00 UTC
Issued: Tue 13 Jul 2010 05:51
Forecaster: KOROSECA level 1 was issued for south-central Alpine region including Slovenia and mountainous N Italy, parts of south-central Italy and SE France mainly for excessive convective rainfall, strong winds and marginally large hail.
SYNOPSIS
An intense trough which resulted in widespread severe storms on Monday continues tracking NE-wards across Scandinavia, while another deep trough/upper low enters western Europe and will result in another outbreak sequence on Wednesday afternoon. A weakening mid-level low over Ukraine moves slightly towards SE while slowly building omega-like ridge pushes into central Europe again.
At surface, a strong frontal system associated with the afforementioned robust trough serves as a focus for an outbreak of severe storms across Sweden. The cold front extend southwards into western Poland by the afternoon, while strong WAA ahead of the trough pushes warm front into the northern Scandinavia.
DISCUSSION
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… SE France, north and central Italy, southern Austria and Slovenia …
Placed in the hot and very moist boundary layer, high instability with MLCAPE exceeding 1500-2000 J/kg will result. These areas will again see daytime driven activity in slightly better sheared environment around 10 m/s than previous days. Even the threat for severe storms is rather limited, a low-end level 1 was issued to cover the most intense storms. Given the pulsating nature of the storms and high PWAT values over these areas, excessive rainfall and locally small hail will be the main threat. High delta theta-e culd also support locally strong wind gusts. A small level 1 area was also issued for parts of south-central Italy where similar conditions could support a couple of flash flood events as well. A bit better shear overlaps with instability over western part of level 1 area across SE France and western Alps. There, enhanced risk for intense convective rainfalls, strong winds and large hail exists. With an approaching trough towards the Wednesday morning, strong warm advection takes place from Spain NNE-wards into southern France. An elevated convection seems likely to form along the northwards advecting warm front over SW France during the second half of the night.
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After a severe weather outbreak yesterday over Benelux and Denmark, a robust trough today continues into Scandinavia, where level 2 was issued given the favorable conditions for numerous well organized severe storms capable of producing severe winds, intense rainfalls and a couple of tornadoes. Read more details about severe weather outlook across Europe in the source link here:
This summer pattern (a classic heat-wave for south-central Europe) will continue at least until the weekend. Very moist airmass with SFC dewpoints 21-25°C all over the southern Alpine region will create environment with extreme instability, but without any disturbances, neither any decent shear. And placed right beneath the ridge axis, days with high to extreme daytime temperatures (in excess of 35°C) are likely with only isolated pulse storms possible. However, models are pushing a short-wave trough across the central Europe towards Sat/Sun period, could be a potential for a cold front crossing and changing airmass later on. But given the still 5 days out, any details would be just a wild guess attm.
Stay tuned for future updates!
