Storm Forecast

Storm Forecast
Valid: Tue 11 Feb 2014 06:00 to Wed 12 Feb 2014 06:00 UTC
Issued: Mon 10 Feb 2014 22:51
Forecaster: TUSCHY

A level 2 was issued for W-Croatia and extreme SW-Slovenia mainly for excessive rain and an isolated strong tornado event.

A level 1 surrounds the level 2 mainly for large hail, severe wind gusts and a few tornado events. Excessive rain is possible, too.

A level 1 was issued for Sicily to S/C Italy mainly for excessive rain, large hail, strong to isolated severe wind gusts and an isolated tornado event.

A level 1 was issued for the E-Ionian Sea mainly for an isolated tornado and large hail event next to excessive rain.

SYNOPSIS

A slowly eastward shifting upper trough affects most of C Europe with downstream ridging present over SE Europe. More progressive synoptic features approach NW Europe during the night.

DISCUSSION

... Adriatic, Tyrrhenian and Ionian Sea ...

Leisurely eastward moving upper trough reveals neutral, later slightly negative tilt. This configuration fosters development of a strengthening LL depression, which moves from the Tyrrhenian Sea to the NE.

Prolonged period of intense moisture advection occurs over the Adriatic Sea with 20-25 m/s SE-erly winds at 850 hPa. Upper divergence and forcing of low-tropospheric fronts next to persistent upslope flow with aforementioned wind field assist in back-building/training MCS activity over SW-Slovenia and W-Croatia. Excessive rain with 100-200 mm/24h is likely with highest amounts in the mountains. Ingredients for supercells or well organized multicells converge over offshore and coastal areas with DLS in excess of 30 m/s and intense "frictional" LL shear/SRH-1. Especially tail-end storms will pose a large hail, severe wind gust and tornado threat. An isolated strong tornado event is well possible.

MUCAPE plume advects far inland with augmented chance for elevated storms all the way to Slovakia. This activity remains sub-severe but adds mm to the already noteworthy heavy rainfall risk.

We issued a level 1 also for isolated CI along the SE coast of the Adriatic Sea and the E coast of the Ionian Sea mainly for the overnight hours. Stronger forcing and weakly capped plume of 400-800 J/kg SBCAPE increase confidence in CI. Shear remains adequate for organized multicells with an isolated large hail, strong wind gust and heavy rainfall risk. Overlap of unstable marine layer with enhanced coastal LL shear also indicate an isolated tornado risk.

Lower CAPE but intense DLS exist from Sicily to S/C Italy. Mid/upper flow features winds in excess of 35 m/s with significantly less thereunder. Obviously, meager CAPE of 400 J/kg or less seems to be a limiting point and concerns exist that updrafts remain too shallow to take profit of the intense flow aloft. However, spotty ELs down to -30C indicate the possibility for isolated deeper udprafts, which could acquire multicell or even supercell characteristics. Large hail and an isolated severe wind gust/ tornado event will be the main risk. Due to the slow eastbound motion of the synoptic front however, repeatedly developing storms could affect the same spots, producing heavy rainfall amounts.

... UK, Ireland and Scotland ...

Scattered short-lived thunderstorms occur in a well mixed marine air mass beneath steep mid-layer lapse rates. Brisk westerly flow should result in a few stronger storms with an isolated severe wind gust risk. An isolated funnel/short-lived tornado event is possible although thermodynamics don't impress. Deep WAA ahead of another depression should suppress thunderstorm activity during the late night (00-06Z).

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