Forecast Update
Valid: Mon 15 Oct 2012 16:00 to Tue 16 Oct 2012 06:00 UTC
Issued: Mon 15 Oct 2012 16:03
Forecaster: TUSCHY
A level 3 was issued for Sicily, Malta and far S-Italy mainly for excessive rainfall amounts, very large hail, damaging wind gusts and tornadoes (a signifcant event is possible).
A level 2 was issued for NE Tunisia, the Tyrrhenian Sea, parts of S/C Italy, parts of the Ionian and Adriatic Sea mainly for excessive rainfall amounts, large hail, strong to severe wind gusts and tornadoes.
A level 1 surrounds the level 2 mainly for similar hazards with less coverage and intensity.
SYNOPSIS
Please refer to the main outlook issued at Sun 14 Oct 2012 23:33 Z.
DISCUSSION
... Level 3 and the Tyrrhenian Sea ...
Final storm mode was dictated by mesoscale features until now as seen with back-building and long-lived thunderstorm activity over the C-Tyrrhenian Sea, where a pronounced quasi-stationary outflow boundary caused persistent CI. Further south in the level 3 area, explosive storm cluster developement occurred between Tunisia and Sicily, but this activity remained more progressive and weakened on its way towards Sicily, as it crossed the consolidating warm front/moisture boundary. However, those clusters can't weaken the ongoing moisture return to the north, which is seen in surface data behind the clusters, showing dewpoints in the lower twenties and southerly to southeasterly winds of 10-15 kt (probably channeled between Tunisia and Sicily). Also, southbound moving outflow boundaries south of Sicily weaken quite rapidly which is also a reason of the strengthening southerly background flow. 12Z Trapani samples the environment quite well (although still displaced from the most unstable air mass) with MLCAPE approaching 2000 J/kg, SRH-1 and -3 of 164 and 230 m^2/s^2 respectively and 0-3/0-6 km bulk shear of 18 and 22 m/s respectively.
As of 15Z, the prefrontal wind shift (ahead of the actual cold front) is still over NE Algeria and Sardinia and is characterized by a rapid increase in DMC from N Tunisia to Sardinia. Further improvement of shear and CAPE is forecast over the level 3 area and there is no striking reason to downgrade this area. In fact, we added Malta into the level 3 as decaying outflow boundaries from the daytime storm clusters might serve as additional foci for CI as the major trough approaches. All kind of severe remains possible with that activity.
No major changes were performed to the rest of the level 2 area. The level 1 was expanded to the NW over N-Italy to reflect the heavy rainfall potential until the cold front approaches.
... N-Adriatic Sea ...
We upgraded all of the N-Adriatic Sea to a level 1 and expanded the 50-% lightning area and the level 2 area far to the north. Latest data indicates a more northerly path of the consolidating LL depression and hence a better influx of moist/unstable air that far to the north. Shear remains supportive for organized DMC, which re-develops repeatedly especially along the coast of the NE Adriatic Sea and NE Italy. Heavy to excessive rain will be the main hazard, but more discrete storms along the coast can produce isolated large hail, strong wind gusts and an isolated tornado/waterspout event.
Confidence in an heavy upslope rainfall event along the S-Alps also increases with a pronounced deformation zone in progress. Run-off may be hampered by a gradually lowering transition zone from rain to snow, but still excessive rain may produce some flash flood concerns.
... NW Spain ...
We downgraded NW Spain due to timing issues of the wave. Latest data indicates a somewhat later arrival with less MUCAPE until 06Z and therefore no level area is needed. Nevertheless, heavy rain starts to affect NW Spain after 03Z.
