Storm Forecast
Valid: Sun 10 May 2015 06:00 to Mon 11 May 2015 06:00 UTC
Issued: Sat 09 May 2015 20:49
Forecaster: TASZAREK
A level 1 was issued for E Hungary, SW Romania, E Serbia and W Bulgaria mainly for the large hail and in lesser extent for excessive precipitation.
A level 1 was issued for parts of Italy, Slovenia, and NW Croatia, mainly for severe wind gusts
A level 1 was issued for N United Kingdom and Ireland mainly for severe wind gusts and tornadoes.
SYNOPSIS
Weather in Europe on Sunday will be under influence of wide, but weakly waved geopotential wave extending from North Atlantic, through British Isles, southern Scandinavia and NW Russia. Jet stream within this border will separate cold air of polar origin in the north and warm and humid air of polar and tropical origin in the south. SW Europe will stay under high centered over Balearic Island and convection in this region will be unlikely. Lowered pressure field with the presence of thermodynamic instability will cover most of the SE Europe creating good conditions for internal air mass thunderstorms in weakly sheared environment. Favorable conditions for thunderstorms will also occur within the small geopotential wave with the axis extending from S Sweden to E Poland where the converging winds are forecast to occur.
DISCUSSION
...E Hungary, SW Romania, E Serbia and W Bulgaria...
Due to low kinematic field (DLS < 10-15 m/s) and moderate CAPE (up to 1200 J/kg), convection in most of the regions should not organize into multicells or supercells and should remain ordinary. The highest activity should fall on the late afternoon hours when daytime heating will provide the highest thermodynamic instability. Good overlap of high boundary layer's moisture content (average mixing ratio 10 g/kg) and steep lapse rates in the lvl. 1 area may be conducive for producing locally large hail up to 2-3cm. It also cannot be ruled out that low motion of the convective cells in the environment of PW values exceeding 25mm may locally produce threat for excessive precipitation. Thunderstorm activity should fall down in the evening hours.
...parts of Italy, Slovenia, and NW Croatia...
The area of thermodynamic instability up to 300-400 J/kg is predicted to overlap in the late afternoon hours with stronger air flow in mid and high levels. DLS over 20 m/s with locally favorable QG-forcing and moderate vertical directional wind shear in the low levels (SRH 0-3km ~ 100-200 m2/s2) create risk that ordinary cells may evolve into few supercells. Within such environment severe wind gusts of convective origin and large hail cannot be ruled out. The highest threat for severe weather phenomena will fall in the late afternoon and evening hours.
...N United Kingdom and Ireland...
Within trough approaching into Scotland and advection of cold air of polar origin in its rear flank, thermodynamic instability resulting from steep lapse rates (> 7C/km) and humid boundary layer (average mixing ratios ~ 7 g/kg) will reach 100-200 J/kg. Although free convective layer will be shallow (3-4 km), impressive mid and low level airflow will pose high threat for severe wind gusts of convective origin. Linearly organized convection within such environment cannot be also ruled out. High values of LLS (~ 10-15 m/s) overlapping with SRH 0-1 km ~ 150 m2/s2 will also pose a risk for tornado occurrence. Convection in this region is expected during the night and in the end of the forecast period. The highest threat for severe weather phenomena will fall on the passage of the cold atmospheric front (0300-0600 UTC). Due to relatively low and uncertain thermodynamic instability, the confidence of the forecast seems to be low.
