Storm Forecast
Valid: Wed 12 Oct 2016 09:00 to Thu 13 Oct 2016 06:00 UTC
Issued: Wed 12 Oct 2016 08:20
Forecaster: PUCIK

A level 1 was issued for NW Morocco mainly for excessive rainfall and to the lesser degree for tornadoes.

A level 1 was issued for Gulf of Lion mainly for excessive rainfall.

A level 1 was issued for Moldova and parts of Ukraine mainly for excessive rainfall.

SYNOPSIS

Dominant feature at the macro-synoptic scale is an extensive high pressure system centered over Scandinavia with prevailing easterly flow over much of Eastern and Central Europe. At the mid-troposphere, south of the high, two lows can be found. The first one centered just NW of the Iberia at Wednesday morning, is slowly shifting SE-wards inland. Towards E, another low situated over Central and E Europe will split into two separate centers, one heading for BENELUX and another one crossing the Black Sea inland. A strong mid to upper tropospheric westerly flow connects both lows at their southern flank.

While continental Europe should experience mostly dry and/or stable weather, more abundant low-level moisture over parts of Southern Europe and the Mediterranean will result in the latent instability and some DMC activity during the forecast period. In case of Iberian low, increasing S-ly flow will begin advecting steeper lapse rates from N Africa over the Southern Mediterranean. At the same time, more abundant moisture will be advected N-ward during the period. The ingredients will overlap favourably on Thursday and Friday and especially the Northern Mediterranean coastlines should prepare for an active severe weather period!

DISCUSSION

... NW Morocco ...

A tongue of moister airmass with mixing ratio around 12 g /kg will impinge on the coastline and in the strong flow will regenerate low-topped convection over the rich terrain. Lack of steep lapse rates will reduce the potential for abundant latent instability, but few hundreds J/kg should suffice for the threat of excessive precipitation as the numerous rounds of storms cross the region. Both strong DLS and LLS are forecast over the region during the late evening hours, but the lack of CAPE inland reduces the risk of tornadoes to some degree, making them less of a threat compared to heavy rain.

... Gulf of Lion ...

Increasing southerly flow will advect moisture from the Southern Mediterranean N-ward towards the Gulf. A convergence in the low-level flow is simulated in the models by the late evening and night hours, creating a strong lift with widespead stratiform precipitation. Some convective elements should be present within the stratiform rain shield as the marginal latent instability will be present in the tongue of moister airmass. At the same time, a strong low-level jet will have formed with 850 hPa windspeeds up to 25 m/s impinging on the coastline and supporting strong lift. Overall, this will be the beggining of a multi-day heavy rainfall period over the region. Because embedded convection may enhance the rainfall rates especially close to the coastline, Lvl 1 is introduced.

... Moldova, parts of Ukraine ...

Similar situation to S France will unfold also here. In the belt of a strong lower tropospheric flow, reaching around 20 m/s at 850 hPa flow, impinging on the coastline, a numerous rounds of storms will form. Due to the abundant moisture content and a strong low-level convergence supporting regenerating storms, excessive rainfall risk will be present, especially in the noon to afternoon hours.