De Atmosfeer Staat Op Ontploffen #149

quote:

Storm Forecast
Valid: Wed 24 May 2006 06:00 to Thu 25 May 2006 06:00 UTC
Issued: Tue 23 May 2006 20:20
Forecaster: GATZEN

SYNOPSIS

Amplified long-wave trough present over western Europe ... with an axis stretching from Finland over Germany to eastern Iberian Peninsula. To the east ... subtropical high over Africa/central Mediterranean ridges into Black Sea region. In the range of this ridge ... warm and well-mixed airmass originating from Sahara desert advects northeastward into Balkans. To the west ... cool maritime airmass covering northern, western, and central Europe spreads southeastward into western and northern Mediterranean east of surface high pressure over Iberian Peninsula, France, and Alpine region. Frontal boundary over northwestern Balkans is expected to remain quasistationary.


DISCUSSION

Balkans

Rather dry boundary-layer airmass is present over Balkans ATTM. On Wednesday ... warm and well-mixed mid-troposphere airmass is expected to overspread the region ... and low-level moisture may recover during the day in the range of surface convergence along the frontal boundary over western Balkans. Latest model output suggests mixing ratios around 10 g/kg near the convergence line ... and CAPE will likely reach 800 J/kg. Expect that low-level airmass will be capped ... and QG forcing should be weak in the range of the upper ridge ... initiation is not expected along sea breeze convergence lines near Black Sea. To the northwest ... short-wave trough propagating NE-ward over Italy/Alpine region will likely produce lift near the frontal boundary ... and intense stratiform precip should affect the region north of the boundary. In the late afternoon/evening hours ... DCVA of propagating trough should likely overspread the frontal boundary over western Romania ... where increasing low-level convergene and low-level moisture should weaken capping inversion. It is expected that thunderstorms will form along the surface boundary that move northeastward. Near the frontal boundary ... DLS will be enhanced and may reach more than 20 m/s ... and storms should organize into multicells and supercells given high 0-3 km SRH values. Severe wind gusts should be the main severe threat given dry and well-mixed layers ... while large hail is not ruled out with the stronger storms. Persisting QG forcing as well as increasing WAA due to low-level stabilization in the evening hours should support one or two MCS moving NE-ward into Ukraine later on. Severe wind gusts and intense precip should be the main severe threat ... while embedded supercells should be capable of producing large hail. A tornado or two is not ruled out as low-level helicity is quite strong near the frontal boundary.


Italy

Cold front moving over Italy will be focus for a few thunderstorms that should form around noon due to diurnal heating and QG forcing provided by propagating short-wave trough. Given strong DLS ... a few well-organized multicells and mesocyclones are expected ... capable of producing large hail and severe wind gusts. Thunderstorms should quickly weaken as cold front moves southeastward.


Southern British Isles, Benelux, northwestern Germany

In the range of the trough axis of propagating short-wave trough/jet streak ... cool airmass is expected to destabilize in response to diurnal heating. Amount of instability and low-level forcing is quite unclear ATTM ... but given enhanced low-level wind shear and quite strong DLS ... current thinking is that a few shallow mesocyclones can not be ruled out.... capable of producing severe wind gusts and a tornado or two.