Storm Forecast
Valid: Sun 05 Jan 2014 06:00 to Mon 06 Jan 2014 06:00 UTC
Issued: Sat 04 Jan 2014 17:40
Forecaster: TUSCHY

A level 1 was issued for Ireland, Scotland and parts of the UK mainly for severe wind gusts and isolated tornadoes.

Two level 1 areas were issued for parts of NW-Italy and the N-Adriatic Sea mainly for heavy rain and an isolated tornado event.

SYNOPSIS and DISCUSSION

A N-S aligned trough over N/C Europe feels the influence of another major vortex over the far N-Atlantic. Constricted from that trough, a pronounced mid-layer vortex evolves over the C-Mediterranean. This feature drifts from the Tyrrhenian Sea to the SE. Attendant surface low over the Gulf of Genoa weakens during the forecast and evolves into a diffuse and broad area of lower surface pressure with numerous more or less pronounced minima over the C-Mediterranean. Expect an active convective period over the C-Mediterranean with heavy rain along the downstream side of that vortex accounting to the main and most widespread risk. Upslope flow along the E-coast of the Adriatic Sea likely results in heavy to excessive rain with amounts in excess of 100 mm/24h. With only modest offshore SBCAPE in the range of 200-500 J/kg and no distinct LLJ expected (despite a 15 m/s LLJ west of Albania), no convectively induced excessive rainfall event is forecast with most of the activity remaining stratiform in nature. No level area was added for that risk.

Heavy to excessive rain probably also occurs over C-Italy with westward facing mountain slopes and similar rainfall amounts (up to 100 mm/24h). The same reasoning precludes the issuance of a level 1.

Two level 1 areas were issued for NW Italy and the N-Adriatic Sea, due to training thunderstorm activity (until the afternoon hours). Heavy rain and an isolated waterspout event are possible. The risk diminishes with the weakening and eastward sliding surface low.

For the complete C-Mediterranean, isolated waterspouts are possible. The environment is not really supportive for a more serious spout risk over the C/S Adriatic Sea with long-lasting WAA and also over the W-Tyrrhenian Sea to Sicily to the S-Ionian Sea with increasing BL winds. Best setup seems to evolve along the W-coast of Italy.

For Ireland, parts of the UK and Scotland yet another intense extratropical cyclone approaches from the west. Behind the eastward moving occlusion, a brisk westerly flow regime is forecast. 850 hPa winds increase to 20-30 m/s from W to E. No convection is forecast until noon (Ireland) and 18Z (UK).
This changes during the evening and overnight hours with the arrivial of a colder mid-layer air mass, enhanced BL moisture from a back-bent occlusion and numerous more or less pronounced mid-layer impulses. The strongest impulse likely crosses Ireland between 18-21Z and hits the North Sea between 00-06Z. Deeper updrafts with enhanced downward mixing are likely and as 850 hPa winds increase to aoa 30 m/s, severe to damaging wind gusts are once again forecast. This activity rapidly spreads east over the North Sea. There are some hints that once again convection could line up beneath those vorticity lobes (and attendant surface features), which could result in LEWP-ish structures. Concentrated swaths of severe wind gusts are possible with that kind of convection. Isolated tornadoes remain possible due to very strong BL shear and some LLCAPE (offshore and along westward facing coasts).

Between 00-06Z, isolated thunderstorms are also forecast over the SE North Sea, W-Denmark, the Netherlands and NW Germany. We kept the level 1 area offshore for now due to weakening forcing and warm EL temperatures. Strong to severe wind gusts will be the main hazard.