Areas Affected:
Most of England and Wales (only focusing on UK areas)
Discussion:
Very tricky situation for Monday afternoon into Tuesday morning...
Overall set-up...Large upper trough located to the west of the British Isles over the Atlantic will dig in through the day, spreading areas of PVA across much of the country. Very warm to hot and humid surface air will be in place, particularly across southern/eastern Britain where temperatures could near or exceed 30C in places and dew-points could exceed 20C will provide some of the ingredients necessary for strong to potentially severe thunderstorms in the Severe & Thunderstorm warned area. A breakdown of the areas can be found below:
Severe area: (a portion of E England)...I will stress before I begin, the risk of afternoon thunderstorm development is particularly low, however if any do develop they could become severe...Some of the warmest surface temperatures will be located in this area upper 20s to near 30C possible. Along with dew-points in the low 20s this could produce CAPE values in the region of 2000j/kg. Deep layer shear values will be near 35-40kts in this region, enough to separate updraft/downdraft regions and potentially produce a few mesocylones/supercell thunderstorm IF afternoon, surface based convection can develop. Cap strength will likely be fairly strong as upper ridge is slow to clear the east of England. This will produce a dry/warm layer separating the hot humid surface air from the cooling upper level air above it. At the moment, both NAE and GFS are reluctant to break the cap and produce this surface based convection, so chances of it occurring are in the 20% realm, however if they do develop they would do so quickly and produce severe weather with the potential of large hail (up to 2.5cm), strong gusty winds, particularly given the drier mid-layers, frequent CGs and potentially a few isolated tornadoes. - Low level shear is in the range of 15-20kts and SSE to SSW surface convergence is possible in this region, indicated by the 12z NAE.
Thunderstorm Area: (S and E England) This area will be monitored for mid-level instability thunderstorms which are likely to develop across France during the afternoon and move northward across the area during the evening and overnight. Lightning (mostly in cloud), gusty winds and some hail could be associated with these elevated storm even into Tuesday morning in East Anglia and Eastern England.
