Storm Forecast
Valid: Tue 04 Feb 2014 06:00 to Wed 05 Feb 2014 06:00 UTC
Issued: Mon 03 Feb 2014 21:36
Forecaster: TUSCHY

A level 1 was issued for S-Ireland, SW UK and the offshore areas mainly for severe wind gusts.

SYNOPSIS

Finally, stout blocking high over W-Russia starts a weakening trend with a shift to the SE (Black Sea). This enables the active N-Atlantic (in respect to vigorous extratropical cyclone development) to spread fronts further east.

False color RGB/WV loops ( 3rd Feb 2014 until 20 Z) show a rapidly developing depression between 46 to 51° N and 24 to 35 °W. Strengthening warm conveyor belt features widespread cloud top temperatures below -50 °C and a recent warming trend in the dry slot area up to -17°C was seen. Placed beneath a 70 m/s upper-level jet with very strong divergence at 300 hPa, rapid intensification to a sub-950 hPa depression is forecast. During the start of the forecast, the evolution of a warm seclusion is expected with full support of phase diagrams of all models. During the forecast period, the mature system starts a drift to the NE and away from the dynamics of the upper level jet. This scenario keeps the depression's surface pressure shy above 950 hPa for most of the forecast with a marginal increase during the end of the forecast ... as the center approaches Ireland from the SW.

DISCUSSION

... Ireland and UK ...

06Z until noon:

A pronounced mid-level thermal trough with readings well below -30°C at 500 hPa crosses UK from SW to NE. Rather steep mid-layer lapse rates atop modest BL moisture offer some SBCAPE of 500 J/kg offshore and up to 300 J/kg onshore. Latest IR image (20Z) has an area with active convection west of Ireland and UK including spotty lightning activity. This will affect mainly the coastal areas of W/SW UK, before waning onshore. Sleet and gusty winds will be the main hazard, although an isolated funnel event can't be ruled out with some LLCAPE forecast. Beyond noon, WAA of the intense marine cyclone should induce a shutdown of any ongoing convection.

00Z-06Z including NW France:

The occluded cyclone comes closer to Ireland and UK. With cooling mid-levels, offshore convection should increase in coverage and intensity over the Bay of Biscay, the W-English Channel and just south of Ireland. Sleet and severe wind gusts will be the main hazard with 850 hPa winds aoa 25 m/s. Intense gradient flow along the back-bent occlusion features 850 hPa winds of 40 m/s, but very slim DMC probabilities exist. Severe to damaging winds start to affect SW UK during the end of the forecast, but current indications show little to no input of convection to the final wind magnitude. A broad level 1 area was issued for the wind gust risk with marine and onshore moving thunderstorm activity. However right now, no organized severe risk (e.g. forced line of DMC) is anticipated with this event.

... SE France/NW Italy and the N-Adriatic Sea ...

Numerous eastbound moving convergence zones beneath an weakening upper trough should result in ongoing clusters of showers and isolated thunderstorms, which slide east along the coast of SE France and NW Italy. Some temporal back-building is possible with heavy rain the main risk.

A similar setup is forecast over the N-Adriatic Sea, where a band of temporarily training showers/thunderstorms shifts from NE Italy to NW Croatia betimes while weakening. Heavy rain is forecast.

No level 1 areas will be added due to slim CAPE signals and the progressive nature of those fronts. Still, flash flooding over NE Italy is possible given history of torrential rainfall amounts during the past days.

... NE/E/SE-Adriatic and E-Ionian Sea ...

Shallow to isolated deep convection with signals of various convergence zones and modest LLCAPE support the idea of numerous spout events along the east coasts of the Adriatic and Ionian Sea (all the way to W-Greece). Due to missing foci, no level area was issued.