Storm Forecast
Valid: Wed 10 Oct 2018 06:00 to Thu 11 Oct 2018 06:00 UTC
Issued: Tue 09 Oct 2018 21:25
Forecaster: PUCIK
A level 2 was issued across Gulf of Lyon and SE France mainly for excessive rainfall and to the lesser degree for tornadoes.
A level 2 was issued for E coastlines of Corsica and Sardegna mainly for excessive rainfall.
A level 1 was issued for the Balearic Sea, NE Spain and NW Italy mainly for excessive rainfall.
A level 1 was issued for S to SW France mainly for large hail, excessive rainfall and to the lesser degree tornadoes.
A level 1 was issued for SE Turkey and NE Syria mainly for large hail and severe wind gusts.
A level x was issued across (areas) for (hail|tornadoes|wind gusts|extreme rainfall). (repeat for each level area)
SYNOPSIS
An extensive high pressure system is covering most of Central and E Europe, with stable and dry conditions over majority of the continent. More active weather pattern is forecast to the north of the high, in a belt from W UK throughout Scandinavia towards N Russia. However, here, DMC chances will be limited by a lack of abundant lower tropospheric moisture.
Over southern Europe, a cyclonic vortex will slowly lift across Iberia towards the Bay of Biscay during the forecast period. On its forward flank, strong S to SE-ly flow in the lower troposphere advects moisture N-wards towards Gulf of Lyon and further inland. In response, scattered to widespread DMC activity is forecast over the W Mediterranean, parts of France and Spain. Another vortex resides, quasistationary, over Turkey and the Aegean Sea.
DISCUSSION
... S to SW France ...
A tongue of moister airmass will advect over the region and combined with a plume of steeper lapse rates, associated with the vortex, will allow for CAPE values on the order of hundreds J/kg, up to around 1000 J/kg. Forecast hodographs suggest around 15 - 20 m/s of DLS and 10 m/s LLS with limited SRH in a messy looking wind profiles. Some well organized multicells, and perhaps brief supercells are forecast in this environment. Storms will initiate particularly along the N-ward advancing, ill-defined, warm front.
Primary threats will be several large hail, limited by the lack of steep lapse rates, and excessive rainfall events. Tornado threat may be elevated in the storms forming close to the warm front, where enhanced SRH and low LCLs are simulated.
... Gulf of Lyon ...
Long-lasting precipitation event is forecast for the area with a convergent, moist, lower tropospheric flow impinging upon the coastline. Forecast soundings reveal skinny CAPE profile, significant warm cloud layer depth and high RH in the low to mid-troposphere. Such conditions will promote heavy rainfall within individual cells while an MCS may become anchored to the local terrain. The threat of excessive precipitation will shift from NE Spain towards E and NE during the day. Tornadoes are not ruled out given around 10 m/s of LLS and low cloud bases.
... Eastern coastline of Corsica and Sardegna ...
Southeasterly flow will advect moister airmass towards the island. Upslope flow along the steep coastlines will easily initiate convection in an unstable airmass characterized by low LFCs. Towards the late evening and night hours, forecast profiles trend towards lower LCLs, high RH throughout the troposphere and skinny CAPE, again pointing at heavy rainfall risk with any developing cells. Combination of 5 - 10 m/s of SE-ly lower tropospheric flow changing to up to 10 m/s of SW-ly flow aloft suggests very slow moving convection, which will get easily anchored to the local terrain. Some of the NWP suggests hours long lasting convective rainfall along the coastlines, which is reasonable given to continuous inflow of moist airmass from SE. Overall heavy rainfall threat warrants Lvl 2.
... SE Turkey, NE Syria ...
On the SE flank of the mid-tropospheric vortex, NWP agrees on 20+ m/s of DLS and straight hodographs, conditions, which would favor well-organized convection likely in form of splitting supercells. Such storms would be capable of large hail and severe wind gusts. Lvl 2 was considered for this area, but uncertainty regarding the lower tropospheric moisture, and subsequently CAPE values, remains large among the NWP outcome. For this reason Lvl 1 seems sufficient at the moment.
