Storm Forecast
Valid: Wed 31 Oct 2012 06:00 to Thu 01 Nov 2012 06:00 UTC
Issued: Wed 31 Oct 2012 07:33
Forecaster: PUCIK

A level 1 was issued for Northwestern Mediterranean, Western and Southern coastline of Italy, Adriatics, the Ionian Sea mainly for excessive precipitation and to the lesser degree for tornadoes and large hail.

SYNOPSIS

A complex synoptic scenario will unfold over Europe with several disturbances observed. Over western half of the continent a significant trough amplifying from the deep cyclonix vortex at 500 hPa towards southeast will affect British Isles and Western France till Thursday morning. Next, a short-wave trough moved off the Iberia and is beggining to affect Western Mediterranean. In the strong 500 hPa flow exeeding 20 m/s, the axis of the trough should be situated over the Adriatics by the end of the forecast period. Significant surface cyclogenesis is forecast at the forward flank of the trough. A ridge is forecast to start building over Eastern Europe, behind the retreating trough that will move towards northeast. This ridge is associated with a development of very large high pressure system centered over southern Russia. Between this feature and a large-scale low system over Western Europe a strong southerly low level flow will establish from the Central Mediterranean to Central Europe.


DISCUSSION

... Northwestern Mediterranean, Italy western and southeastern coastlines, Adriatics and the Ionian Sea ...

A developing depression centered to NE of the Balearic Islands is nicely visible at the satellite loops around 6 UTC Wednesday. Mallorca 00 UTC sounding sampled only rather weak latent instability present over the region, but satellite loop does show some convective elements in the cloud system of the low. As the low deepends, strengthening low level flow should reach 20-30 m/s at 850 hPa (especially over the Ionian and Adriatic Sea), transporting moisture from the southern Mediterranean towards north. Poor lapse rates will preclude any higher CAPE apart from the Ionian Sea and S Italy, where higher lapse rates might get advected from N Africa by W-ly flow with MLCAPE values possibly around 1000 J/kg. Strong DLS and LLS is forecast, especially as the low level jet establishes by the afternoon hours.

Obviously, the highest threat will be an excessive precipitation. This will be most prominent where the low level flow will perpendicularly impinge on the coastline, creating strong uplift of at least marginally unstable parcels. Especially towards the evening and night hours over the Ionian Sea, a strong parallel or leading stratiform MCS is possible with the cell backbuilding along the LLJ axis. Currently it looks like that the best potential for excessive precip will exist over the SE Italy and the Ionian Sea (N Greece / Albania), where the highest values of low level moisture and instabiliy will be present. Strong LLS might be favorable for some isolated tornadoes, but this threat will be limited by the lack of a dicrete supercellular convection. Furthermore, large hail is possible, albeit the best conditions will exist over the Ionian Sea (overlap of moderate instability and strong DLS in the night hours) and decline towards the coastline of Greece.