Convective Outlook: Fri 02 Jul 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 02 Jul 2021 - 05:59 UTC Sat 03 Jul 2021

ISSUED 21:32 UTC Thu 01 Jul 2021

ISSUED BY: Dan

A weak upper low will drift slowly westwards from the North Sea across northern Britain on Friday, eventually merging with an increasingly negatively-tilted longwave trough over the North Atlantic. A PV maxima will spread inland across central and southern Scotland from the North Sea, while a couple of other PV filaments will drift north across England and Wales. That said, forecast profiles reveal some substantially deep dry mid-level air which may inhibit deep convection somewhat (less pronounced further north), but if sufficient surface heating and moisture pooling can occur along low-level wind convergence then this may just be able to allow some deeper convection and a few lightning strikes to occur locally. The greatest risk of more widespread/sustained heavy showers appears to be the Pennines and Southern Uplands (drifting to the NE), perhaps also parts of northern and eastern Ireland (drifting to the N/NW). 

Overnight, as the mid-level flow gradually strengthens and backs slightly, advection of modest Theta-E will occur from France across the English Channel towards S/SE England. This coupled with cooling aloft and increasing forced ascent on the forward side of the approaching upper trough may encourage some elevated convection to occur over these areas during the night. Lightning activity remains uncertain given generally weak/skinny CAPE and increasingly moist profiles, but heavy, showery rain will be possible and the LOW threat area has been extended south of the M25 to cover this low risk overnight. Similarly, the odd isolated lightning strike cannot be ruled out in parts of S Ireland, S Wales and SW England during the night hours as pulses of showery rain with embedded weak elevated convection push northeastwards - but the overall risk of lightning in any one location is considered rather low.