Storm Forecast
Valid: Sat 09 Jan 2010 06:00 to Sun 10 Jan 2010 06:00 UTC
Issued: Sat 09 Jan 2010 03:16
Forecaster: VAN DER VELDE
A level 1 was issued for Montenegro, Bosnia-Herzegovina, southern Croatia, and Albania mainly for excessive convective precipitation.
A level 1 was issued for southern Italy mainly for excessive convective precipitation.
SYNOPSIS
Europe is caught in a classic dipolar pressure distribution with a high of more than 1040 hPa over southern Norway and a low of less than 1000 hPa over northern Italy. In between, a steep pressure gradient induces strong northeasterly winds over the continent, advecting the cold airmass as far west as British Isles, France and northeastern Spain. A warmer Mediterranean airmass flows to the north over the Balkan, forming a surface front which remains more or less stable from southeastern Germany to southern Belarus. Aloft, however, the same zero-Theta-E isotherm stretches as far as Latvia-Denmark-Netherlands-western France, and indicates significant upward-sliding of warm air over the freezing air near the ground, with as result widespread wintry precipitation potentially for long periods of time.
Active convective weather occurs over the central Mediterranean region, with a cold front moving from southeastern Italy at 06Z into the Albania-Bosnia area, and stick there for a while. In the following cold airmass, isolated to clustered storms should occur.
DISCUSSION
...Montenegro, Bosnia-Herzegovina, S Croatia, and Albania...
Models simulate storms developing in the early morning (03Z) over southern Italy at the cold front (presently nothing) which then moves as an MCS into this region. The storms could then keep regenerating for a while, with support of backbuilding Corfidi vectors. Models as AFWA-WRF and LaMMA-WRF 18Z produce a region of intense rain of 15 mm/hr for several hours. At convective scale this could mean locally much larger rates. Orographic lift can additionally regenerate convection as well as produce prolonged stratiform rainfall.
Besides rain, friction-induced shear and helicity values deeper inland are in support of tornadoes, but usually CAPE is lacking there. Over sea, there is only good deep layer shear without any veering. In general, the CAPE today is not predicted to attain values over 500 J/kg, but is concentrated in the lowest 3 km which on the other hand could help tornado/waterspout spin-up (isolated). Convective gusts are could reach 25 m/s.
...S Italy, W Sicily...
Long duration of onshore advection of convective cells could cause locally excessive precipitation with flash floods. There are signals of strong deep convergence and QG forcing in GFS in the evening and MCS mode from Corfidi vectors favors cell growth on the rear side of a system, which may be oriented WSW-ENE along the direction of forcing, so storms may become oganized in the form of lines of training cells, which can unload lots of rain once onshore. Waterspouts are possible as well, with large 0-3 km CAPE.
