Forecast Update
Valid: Wed 22 Feb 2012 09:00 to Thu 23 Feb 2012 06:00 UTC
Issued: Wed 22 Feb 2012 09:48
Forecaster: ESTOFEX

A level 1 was issued for Northern Tunisia and Southeastern Italy mainly for excessive precipitation.

SYNOPSIS

From macrosynoptical point of view, the most important feature remains a large ridge at mid and upper levels stretching from Atlantic to Western Europe and southern parts of Central Europe. Strong zonal flow is induced at its northern flank in the frontal zone and a short wave trough with attendant surface cyclogenesis is forecast to develop in the flow, affecting most of Western and Northern Europe during the forecast period. Towards south, a cut-off low will be centered to the south of Sicily with little motion during the day. Surface low at the forward flank of the mid level cut off is expected to slowly fill, especially in the late evening and night hours.

DISCUSSION

... Northern Tunisia, Southeastern Italy ...

Around the periphery of the low, strong low level flow is simulated by NWP, reaching up to 25 m/s at 850 hPa. This notion is supported by 00 UTC Trapani sounding which displays up to 20 m/s windspeed at the lower levels of troposphere. This strong flow is mostly connected to the warm front/occlusion of the surface low. Marginal instability is simulated in the area of the low, with MLCAPE values likely not exceeding more than 500 J/kg. Deep layer wind shear should remain rather weak in the area of interest, with low level shear being maximised inland with values over 15 m/s. Very humid conditions are expected around the fronts, with high RH in the low to mid levels of troposphere. With flow perpendicular to the coastlines, continuous initiation of cells might be expected with training pattern developing over certain spots. Weak point of this situation, precluding higher Level for threat of excessive precipitation, are rather meager values of mixing ratios - only around 7 g/kg. Still, the setup might be conducive to localised heavy rainfalls and Level 1 seems to be warranted for these areas.