Convective Outlook: Fri 08 May 2020
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 08 May 2020 - 05:59 UTC Sat 09 May 2020

ISSUED 06:20 UTC Fri 08 May 2020

ISSUED BY: Dan

In a broad sense, an upper ridge will cover much of the British Isles during Friday, albeit heights slowly falling through the day. Weak impulses will crest the northern flank of the ridge, and may in-part aid in convective development. However, aside from Friday morning where some elevated convection may be occurring over Devon and Cornwall (with an attendant risk of lightning, albeit fairly low), the more significant factor for forced ascent will be a combination of diurnal heating, low-level wind convergence and orographic forcing.

Isolated to well-scattered showers are possible, and CAM guidance suggests surface-based convection may begin to develop from around 1pm BST onwards, although both 00z soundings and forecast profiles are quite warm aloft which may restrict the potential depth of convection (generally below 500mb / ELTs -17C), despite 300-700 J/kg CAPE. 00z Nottingham and Albermarle soundings suggest convection may be able to grow slightly taller than offered on the Camborne ascent, albeit very dry aloft, while Hertstmonceux offers only limited shallow convection and very unlikely to yield deep convection.

Eventually, towards late afternoon/early evening, a few showers may gain sufficient height to produce a few isolated lightning strikes. It is difficult to pin-point specifically where this may occur, given a fairly broad risk area. Perhaps the risk is somewhat higher over east Wales / west Midlands, and East Anglia, where a low-end SLGT (30%) has been introduced - but confidence on much in the way of lightning is fairly low. Showers will gradually decay through the evening and night as diurnal heating subsides.