Storm Forecast
Valid: Wed 23 Nov 2016 06:00 to Thu 24 Nov 2016 06:00 UTC
Issued: Tue 22 Nov 2016 21:22
Forecaster: PUCIK

A level 2 was issued for parts of NE Spain and S France mainly for excessive precipitation and tornadoes.

A level 1 was issued for NW Mediterranean mainly for excessive precipitation and tornadoes.

SYNOPSIS

At the mid-troposphere, a deep trough stretching from the NE Atlantic towards Iberia will split into two separate features in the beggining of the forecast period. The first one will be a trough crossing Scandinavia on its movement E-wards. Advection of colder airmass with steep lapse rates will result in scattered showers over the Norwegian Sea, but risk of lightning or severe weather is too low to warrant a Lvl. More robust DMC activity is forecast over the W Mediterranean, on the forward flank of the second feature, a low entering cut-off stage, centered over Iberia and only slowly moving E-wards. Convection will be associated with a WAA regime on the forward flank of the low, in strongly sheared environment.

DISCUSSION

... NE Spain towards NW Italy ...

DMC formation will be confined to the exit region of a cyclonically curved jet-streak at mid to upper troposphere and to broad LLJ, advecting warmer and moister airmass inland. Channeling of the flow due to local orography, especially in the Ebro valley and between Pyrenees and Massif Central, may ramp up the 850 hPa windspeeds up to 25 m/s. Several hundreds J/kg of MLCAPE are forecast given modest lapse rates and mixing ratios of around 9-10 g/kg. The primary threat will be heavy precipitation with rapid advection of moist air inland and possibility of repetitive cell formation as LLJ is forced to ascend due to local orography. Secondary threat will be tornadoes, given the strong LLS (well above 10 m/s) and low LCLs, especially if embedded supercell forms along the parallel-stratiform convective line. Threat will shift E-wards during the day towards NW Italy by Thursday morning hours. Lvl 2 is introduced for regions with most pronounced threat of heavy rainfall or tornadoes.