Storm Forecast
Valid: Tue 03 Dec 2013 06:00 to Wed 04 Dec 2013 06:00 UTC
Issued: Mon 02 Dec 2013 17:27
Forecaster: TUSCHY

A level 1 was issued for S-Italy and parts of the Ionian Sea mainly for excessive rain.

SYNOPSIS and DISCUSSION

An extensive high pressure area covers most of W/C and E Europe and continues the tranquil forecast period for those regions. Flanked by lower geopotential heights to its north and south, unsettled conditions will be confined to Scandinavia and the Mediterranean.

Embedded in strong westerlies, numerous mid/upper layer waves affect N-Europe. Scarce BL moisture keeps marginal thunderstorm probabilities confined to the offshore and coastal areas of Norway. Despite impressive looking overflow signals in models due to the persistent and strong cross-barrier flow regime, no serious vorticity maximum is expected with faint thermal ridging spreading east ahead of another impulse. Therefore, active marine convection is expected, but no line of organized convection is forecast. With a brisk background flow (850 hPa roughly 20 m/s), not much downward impulse is needed for strong to severe wind gusts. Limited electrified activity and disorganized behavior preclude a level area. Far N-Norway will be exposed to very strong winds as 850 hPa winds increase to 30 m/s and more. Shallow convection probably mixes those winds down to the surface but remains too weak for lightning activity. Hence no level area was added.

For the Mediterranean, a southbound dripping frontal boundary and a leisurely eastward moving upper low over the Ionian Sea dictate shower and thunderstorm development. CAPE aob 500 J/kg and weak shear preclude organized convection. However, enhanced easterly winds (850 hPa up to 15 m/s) just south of the front or in the NE quadrant of a diffuse surface low support an ongoing heavy to excessive rainfall risk for S-Italy with repeatedly onshore moving showers and thunderstorms. This risk gradually vanishes after sunset. The same for Malta and most of the Ionian Sea, where slow moving clusters produce excessive rain.