Convective Outlook: Wed 04 May 2022
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 04 May 2022 - 05:59 UTC Thu 05 May 2022

ISSUED 06:25 UTC Wed 04 May 2022

ISSUED BY: Dan

A PV anomaly will slide southeastwards across Britain during Wednesday daytime, with heights falling temporarily and cooling in the mid/upper troposphere coinciding with peak diurnal heating. The net result is the potential for much deeper convection than on Tuesday. Fairly extensive cloud during the morning, and areas of showery rain, will gradually break due to convective overturning, with an increasing risk of heavy showers evolving/developing across central and eastern England from around noon and through the afternoon and early evening. Surface temperatures of 15-17C and dewpoints 10-12C will likely yield 400-600 J/kg CAPE in a relatively narrow corridor (spatially) that will shift gradually southeastwards through the afternoon. Forecast profiles reveal skinny CAPE within a modestly sheared environment of 20-30kts as northwesterly flow aloft strengthens from the west on the rear side of the upper trough; a combination of both speed shear, as flow strengthens with height, and also some directional shear with NW-ly winds aloft and backed W or even WSW surface winds.

Some concerns exist over just how cool the mid troposphere can become, with some evidence of a slight warm bulge at 500-550hPa which may inhibit air parcels passing this point (and therefore stunt convective cloud growth and reduce the lightning risk), or at the least lead to slower parcel accelerations. Assuming convection can grow tall enough, then a few cells may become somewhat organised and longer lasting with some sporadic lightning and sub-severe hail - and as such, a low-end SLGT has been issued. But it is plausible many of the showers may be void of much in the way of lightning. Showers/thunderstorms will gradually decay and clear eastwards during the evening hours.