Storm Forecast
Valid: Mon 18 Jul 2011 06:00 to Tue 19 Jul 2011 06:00 UTC
Issued: Sun 17 Jul 2011 17:43
Forecaster: TUSCHY
A level 1 was issued for N-Italy, S/E-Austria,Slovenia, parts of Croatia, Hungary, Slovakia, E-Poland, parts of Belarus, W-Ukraine and parts of Latvia and Lithuania mainly for a few large hail and strong to severe wind gust events.
A level 1 was issued for extreme W-Mediterranean mainly for strong to severe wind gusts and marginal hail.
SYNOPSIS
A large upper trough is still parked over far N/NW-Europe. Numerous short-wave troughs travel around this major trough with the most pronounced one crossing the Bay of Biscay during the night hours from the NW, re-intensifying the W-European trough. Scattered showers and thunderstorms also occur over E-Europe beneath lower geopotential heights with stable conditions over the far E-Mediterranean.
DISCUSSION
... N-Italy ...
A bit tricky the forecast with borderline thermodynamic parameters forecast supportive for organized convection. Overall set-up favors a weak cyclonic surface wave/depression over far NW Italy which supports weak onshore flow. Not much moisture advection needed with favorable BL dewpoints over the far N-Adriatic Sea (mid to upper tens). Local model and global model outputs all agree in pockets of enhanced MLCAPE, locally up to 1000 J/kg. We're not as optimistic with weak lapse rates moving in from the west. However, a few deeper and longer-lived updrafts are still possible beneath strong 30 m/s 500 hPa jet. Hence, updraft organization is possible with a few large hail and strong to severe wind gust events. Despite overall limited confidence in widespread initiation, we went ahead and issued a marginal level 1.
... Slovenia, S/E-Austria, parts of Croatia, W-Hungary and parts of Slovakia ...
Latest indications are that far NE Italy, Slovenia and far S-Austria may be the area with overall highest severe probabilities with favorable onshore flow from the N-Adriatic Sea. Thunderstorm initiation will be around noon onwards and storms rapidly move to the NE/E, also affecting W-Hungary, E-Austria, E-Croatia and parts of Slovakia during the afternoon and evening hours. Despite favorable DLS , overall severe risk diminishes to the NE with ongoing BL mixing and decreasing CAPE. A few large hail and strong to severe wind gust events are forecast with that activity. Again, model discrepancies regarding thunderstorm coverage remain significant, but a level 1 should be justified for that set-up.
...E-Poland, Lithuania, Latvia and Estonia...
A quasi-stationary N-S aligned baroclinic zone is present over E-Poland and serves as focus for a few thunderstorms during the forecast period. Modest CAPE/shear overlap may allow a few large hail and strong wind gust events. Thunderstorms move to the N and also affect Lithuania, Latvia and Estonia with similar risks.
Further east, shear diminishes rapidly to below 10 m/s DLS, but instability increases to 500 - 1500 J/kg MLCAPE. A few large hail events are possible with a few more intense updrafts. We therefore expanded the level 1 a bit to the east to cover that risk.
... Bay of Biscay, SW-France, NE-Spain and far W-Mediterranean ...
A sharp and very dynamic short wave moves in from the NW during the evening and results in a re-intensification of the W-Europe trough. Accompanied by this short wave, a pronounced vorticity couplet crosses aforementioned areas. Marginal moisture recovery occurs ahead of this feature with a weak moisture tongue seen in lower tropospheric theta-e fields. An isolated thunderstorm is possible over extreme SW-France due to impressive forcing and low-end CAPE. Main risk will be strong wind gusts, as 850 hPa LLJ moves in and we can't ruled out a very isolated tornado risk along the coast with onshore moving storms and enhanced helicity values. However the overall risk seems to be too marginal for a level area.
Thunderstorm probabilities rapidly increase over the far W-Mediterranean as dynamic short wave interacts with rich moisture from the Mediterranean and a thunderstorm cluster may form along the NE-coast of Spain, spreading rapidly east/northeastwards. Initiation probably occurs just after midnight. Shear supports strong to severe wind gusts and marginal hail with that activity. Thunderstorms keep going beyond the forecast period.
... NW/parts of W-CNTRL Europe ...
Beneath the large upper trough, cold mid-levels and a well mixed maritime air mass assist in numerous areas with somewhat enhanced thunderstorm probabilities. Not much severe is expected as shear will be weak, but a few marginal hail events are expected. Thunderstorm coverage decreases after sunset.
