Convective Outlook: Tue 27 Aug 2019
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Tue 27 Aug 2019 - 05:59 UTC Wed 28 Aug 2019

ISSUED 08:05 UTC Tue 27 Aug 2019

ISSUED BY: Chris/Dan

UPDATE 08:05 UTC MDT introduced across eastern England, minor adjustments made to the SLGT.

A sharp upper trough will approach the British Isles from the Atlantic, as a frontal boundary moves into Ireland. A shortwave trough will also move northwards across Britain during day and this will help to trigger scattered thunderstorms by mid-to-late Tuesday afternoon and into the evening. 

Elevated morning convection may still be ongoing across southwestern portions of England and Wales at 0600 although this should weaken through the morning before the diurnally driven showers and thunderstorms re-develop. 

High surface temperatures (in excess of 30C in places) across central and eastern Britain will help to generate up to 1000 J/kg of CAPE by the afternoon. Steep lapse rates will also be present, although the main area of instability will be displaced slightly east of the shortwave that will move northeastwards across the Midlands by mid-afternoon. Deep layer shear through early afternoon will be around 30kts (although decreasing into the late afternoon and evening). The combination of shear and instability may trigger some severe weather during the early phase of the thunderstorm development. A supercell or two could be possible for a time producing hail up to 2cm in diameter.

The deep, rather high based convection (due in part to the surface temp and dew-point separation) is being triggered in the high res models around 1300-1400 in southern and western portions of the SLIGHT risk area before growing upscale as it moves northeastwards into a small MCS. The remnants of the MCS will move off the coast of NE England / SE Scotland around or just after midnight. 

A MODERATE risk will be considered for subsequent updates primarily for parts of Cambridgeshire, Lincolnshire and south Yorkshire providing model consensus improves.