Convective Outlook: Mon 01 Apr 2019
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Mon 01 Apr 2019 - 05:59 UTC Tue 02 Apr 2019

ISSUED 07:32 UTC Mon 01 Apr 2019

ISSUED BY: Dan

UPDATE 07:32 UTC LOW threat area shrunk in size over SE England in response to latest guidance. Development of elevated showers looks likely to occur farther east and perhaps slightly later than earlier guidance, and hence most activity may occur offshore to the east

... SE ENGLAND MONDAY NIGHT ...
Upper ridging initially over the British Isles on Monday will relax away to the east as a sharpening Atlantic upper trough approaches from the west. The net result is the flow aloft will begin to veer from an easterly to a southerly quadrant, allowing advection of a relatively high ThetaE airmass to occur on Monday evening/night from France into SE England. This airmass will have been diurnally-heated during Monday daytime, then lifted from the surface as it moves northwards above a notably cool boundary layer.

This isentropic upglide, combined with increased forcing aloft from the approaching upper trough, will result in increasing mid-level instability over SE England on Monday night. There is reasonable multi-model support to suggest the potential for elevated showers to develop over the eastern English Channel and / or SE England during the late evening, these then drifting NE-wards and expanding in coverage across East Anglia during the early hours of Tuesday.

Lightning activity is questionable given marginal instability (a few hundred J/kg CAPE and somewhat meagre shear), but some sporadic lightning seems plausible given forecast profiles. If confidence improves an upgrade to SLGT may be required - more especially for the eastern half of the existing LOW threat area.

... W SCOTLAND / NW IRELAND MONDAY NIGHT ...
Behind the cold front, the aforementioned upper trough will dig southwards across these areas, the associated cold air aloft atop relatively warm seas helping to contribute to increasingly steep mid-level lapse rates and a few hundred J/kg CAPE during the early hours of Tuesday. Numerous showers will affect the area, with some sporadic lightning and small hail in the most intense cells.