Convective Outlook: Wed 28 Jul 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 28 Jul 2021 - 05:59 UTC Thu 29 Jul 2021

ISSUED 06:27 UTC Wed 28 Jul 2021

ISSUED BY: Chris

A broad upper low will rotate eastwards across Scotland during Wednesday, with an eastward progressing trough extending southwards across England and Wales. A strong jet streak and associated left exit region combined with several shortwaves will ripple through the flow, with notable PVA moving from Ireland across Wales and central England during the day and into the evening. This set-up will be conducive to widespread showers and thunderstorms across these areas on Wednesday. 


An unstable airmass with CAPE values in the region of 500-1,000 J/kg will develop across parts of England and Wales through the day. Instability combined with an increasing westerly flow aloft associated with the strengthening jet stream will aid in the increase of deep layer shear by late afternoon and early evening (30-40kts across Wales and central and eastern England later) and 50kt across southern England. The most favourable environment for significant, organised convection will be located on the northern edge of the jet where the best overlap of shear and instability is expected. Convection will be increasingly shallower in depth further south towards southern England, but in a high shear environment.

Areas of interest: 

... CEN/N SCOTLAND ...
A slow-moving occluded front will persist across the are leading to some prolong periods of rain, however models indicate some embedded convection is possible (300-600 J/kg of CAPE) and therefore some sporadic lightning will be possible in the N and NE. 

... IRELAND / N ENGLAND ...
The highest instability, pockets of 700-1,000 J/kg of CAPE, will be present across these areas, although with generally limited shear. Convection and lightning should be fairly widespread, although messy in nature. 

... N MIDS / E ENG / N EAST ANGLIA ... 
The best overlap of instability and shear should occur in this region during the mid to late afternoon and evening with CAPE values of 500-1000 J/Kg possible along with DLS increasing to 30-40kts during the afternoon and early evening. This would be supportive of supercell thunderstorms capable of producing 2-4cm hail and gust of 50-60mph. LLS is rather weak, so the tornado risk may be limited, although cannot be ruled out. 

... CEN S ENG / S ENG ...
While instability is rather limited further south into England, shear will be increasing through the day and models indicate some showers and thunderstorms are possible as far as the Salisbury Plain. Given increasing shear profiles a few of these showers and thunderstorms may linger into the evening. 

Severe weather risk...

2-4cm hail
Outflow gusts in excess of 50mph
Low-end tornado risk
Flash flooding