Convective Outlook: Sun 18 Jun 2017
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sun 18 Jun 2017 - 05:59 UTC Mon 19 Jun 2017

ISSUED 20:14 UTC Sat 17 Jun 2017


Under broad upper ridging on Sunday, strong surface heating will yield SBCAPE values of up to 1,000 Jkg-1 with dewpoints typically in the high teens Celsius. Forecast profiles are very dry, but given some sea breeze convergence one or two isolated heavy showers / thunderstorms may develop in the very late afternoon into evening hours (only 10-20% chance in any given location). Main risk will be local flash flooding given slow storm motion and PWAT of 30-35mm, suggesting 30-40mm may fall in a short space of time.

High-res models naturally vary with location of such showers, so not to be taken literally - however, general trend appears to favour Norfolk in particular, along a NE-SW convergence zone between Norfolk and London. There are also hints of a separate convergence zone from Lincs SW-wards to E Wales, though with less of a suggestion for showers to develop here - but may require a westwards extension to the LOW threat level if trends continue.