Convective Outlook: Mon 19 Jul 2021
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Mon 19 Jul 2021 - 05:59 UTC Tue 20 Jul 2021

ISSUED 06:44 UTC Mon 19 Jul 2021


Upper ridging generally dominates through Monday, however an upper trough will slide down the North Sea, the western edge passing close to East Anglia and SE England during the morning. The phasing of this feature is faster than peak daytime heating, but the associated cooling aloft may provide a slightly more favourable thermodynamic profile than was the case on Sunday. In either case, diurnal heating will yield substantial SBCAPE (>1,000 J/kg), however forecast profiles are rather dry once again with evidence of some warm noses, and this casts uncertainty as to how tall convective cloud may be able to grow. Initiation will likely be strongly tied to low-level convergence and orographic forcing. A deeply-mixed boundary layer will result in fairly high cloud bases, but if convection is able to grow tall enough it may be able to utilise slightly stronger northwesterly flow aloft.

For the most part, any showers that do develop will probably struggle to maintain themselves for any length of time - with the exception of SE England where the environment overall appears slightly more favourable for deeper convection and therefore potential for some lightning activity. Given the timing of the upper trough passage, this may perhaps be more of an afternoon event than an evening one. If a couple of heavy showers or thunderstorms develop, local flash flooding could be a concern. Depending on how sustained/organised, any thunderstorms could also pose the risk of some large hail. A low-end SLGT has been introduced where the risk is considered greatest.
Instability will only slowly weaken overnight, and so additional showers may continue to develop over the Midlands towards the northern Home Counties during the overnight period.