Storm Forecast
Valid: Sat 27 Oct 2012 06:00 to Sun 28 Oct 2012 06:00 UTC
Issued: Fri 26 Oct 2012 22:11
Forecaster: TUSCHY

A level 2 was issued for parts of SW-Italy and the NE Adriatic Sea mainly for excessive rainfall amounts.

A level 2 was issued for the SE Adriatic Sea and far N-Ionian Sea mainly for excessive rainfall amounts, large to very large hail, severe wind gusts and an isolated tornado risk.

A level 2 was issued for parts of the Ionian Sea mainly for large to very large hail, severe wind gusts, heavy rain and an isolated tornado risk.

A level 1 surrounds all those level 2 areas for a similar risk but with less coverage.

A level 1 was issued for the NE Aegean Sea mainly for heavy rain and isolated large hail/severe wind gusts and a stray tornado risk.

SYNOPSIS

An extensive branch of the polar vortex affects all of Europe. A baroclinic zone separates cold and dry air to its north from a moist and unstable air to its south. Numerous vortices along that boundary move slowly to the NE.

DISCUSSION

... C-Mediterranean ...

An impressive vortex spins up along a barocline zone, which runs from France to the Alps to Belarus. That elongated vortex splits up into numerous vortices during the forecast, with the strongest one evolving over SE France/NW Italy during the night. An extensive warm sector covers all of the C-Mediterranean with numerous fronts moving in from the NW betimes. Strong large-scale forcing and diffluence aloft affect the area of interest and assist in CI all day long.

A plume of rich moisture south of Sicily advects to the north atop the Ionian Sea and points towards the coasts of W-Albania and Montenegro. Otherwise, LL mixing ratios reveal lower values to the west and north, which is still adequate for moderate CAPE build-up as a widespread cool-down of the mid-levels continues. 500-1000 J/kg MLCAPE are again forecast for the Tyrrhenian Sea and parts of the Adriatic Sea. Substantial higher values (in excess of 2000 J/kg) are forecast over the Ionian Sea into the S-Adriatic Sea. Again a pile-up of BL moisture is forecast along westward facing coasts, where regionally higher CAPE values evolve.

The gradient flow remains strong, but very complex built-on with various streaks affecting the area of interest with different timing and over different height levels. Robust 20-30 m/s DLS overspreads the plume of high CAPE over the Ionian Sea with decreasing magnitude towards the north. To summarize that, overall conditions remain supportive for organized DMC over all of the C-Mediterranean.

Of main concern will be the level 2 areas over parts of W-Italy and the SE Adriatic Sea/far N-Ionian Sea, where excessive rainfall amounts are forecast with QPF amounts in excess of 100 mm/24h. Over NW Albania and Montenegro, amounts in excess of 200 mm/24h are possible. Repeatedly onshore moving showers and thunderstorms are likely with a persistent 20m/s LLJ advecting rich moisture ashore. Any more discrete or tail-end storm will be likely severe with severe wind gusts, large hail and a tornado risk. Despite more limited CI over the Ionian Sea, the level 2 was expanded far offshore due to the favorable overlap of shear/CAPE and hence expected supercell risk.

Another level 2 area was added for the NE/E coast of the Adriatic Sea due to excessive rain with a prolonged period of onshore moving DMC. Again, rainfall amounts might exceed 100 mm/24h. The level 1 was adjusted to the NE (e.g. including S-Austria and all of Slovenia mainly for the rain risk).

All those level 2 areas are surrounded by a large level 1, where conditions still support organized DMC with heavy rain, large hail, strong wind gusts and an isolated tornado risk.

The low probability lightning area was extended far to the NE where at least some MUCAPE will be present. Any temporal diabatic heating may locally increase CI probabilities for surface based convection and an isolated large hail/strong wind gusts risk might occur. However models diverge too much for issuing any specific onshore level 1 areas.

A level 1 was also issued for the NE Aegean Sea mainly for organized multicells with heavy rain, large hail, severe wind gusts and an isolated tornado risk. Peak activity will be after sunset.