Storm Forecast
Valid: Wed 24 Sep 2008 06:00 to Thu 25 Sep 2008 06:00 UTC
Issued: Wed 24 Sep 2008 00:09
Forecaster: PUCIK
SYNOPSIS
A split flow pattern will prevail at midlevels across Europe, as a large ridge stretches from Atlantic into S Scandinavia.The first branch is directed across the northern fringes of Europe, with several troughs and cyclones quickly traveling eastwards. The second branch will develop to the south of of cold-core mid and upper tropospheric low, having windspeeds around 25 m/s at 500hPa. Several vorticity maxima will rotate around the low during forecast period. At the surface, large high pressure system will affect most of Europe, guaranteeing stable conditions. Models such as ECMWF suggest that shallow cyclone will develop over Ionian sea and move towards Greece.
DISCUSSION
...The Meditteranean...
Each model run suggests different location of
TSTM initation, especially over western part, where only slight destabliziation is expected, with MLCAPEs in hundreds of J/kg. Initiation seems to be tied to the passage of vorticity maxima. As models tend to change their location and degree of destabilization considerably, it is very difficult to draw a precise map, so we have decided to stick with a broad TSTM area.
...Tunisia, NW Algeria...
Despite meager destabilization across the region, with MLCAPE values only around 500 J/kg, models are suggesting that deep convection will develop. DLS should be in range between 20 and 30 m/s, so if storms manage to sustain themselves in strong mid-level flow, they might attain good organisation. With enhanced SREH values, locally reaching over 200 J/kg, chance for rotating updrafts will increase. Therefore, we are expecting, that few supercells might develop and produce at least marginally large hail, warranting LVL 1 over the region. Also, lack of upper level support will prevent from more widespread development, leaving few isolated cells over the area.
...Ionian Sea, Greece, Aegean Sea ...
Conditionally unstable airmass should be available across the region, with MLCAPEs around 1000 J/kg, especially over the southern part. Both strong moisture convergence and vertical motion signals point to the fact, that widespread convective initation will occur. Storms should develop into an environment characterized by a moderate deep level shear, ranging from 15 to 20 m/s and enhanced SREH, especially across the western coast of Greece with values above 150 J/kg. So, storms that develop should be well organized, probably including few rotating updrafts. Chances for isolated, strong supercells are however, quite low, as cells should organise themselves into a large cluster/MCS and move eastwards across Greece. Still, few stronger/rotating cells in southern part of complex or embedded in it might produce isolated large hail. GFS shows very steep low-level lapse rates combined with high MLCAPEs for 0-3 km layer over the highlighted area. Also, SREH within 0-1 km layer should locally exceed 120 J/kg. These conditions might lead to the few waterspout/tornado reports, especially over the western coast of Greece.
Models hint on significant convergence occuring with the passage of low, yielding widespread thunderstorm development. Moreover, humid airmass with mixing ratios above 12g/kg is advected from the south towards the low, guaranteeing a good moisture supply for storms. So, high threat of flash flooding will exist with the various storm complexes over both Italy and Greece.
