Convective Outlook: Thu 17 Aug 2017
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 17 Aug 2017 - 05:59 UTC Fri 18 Aug 2017

ISSUED 21:48 UTC Wed 16 Aug 2017


Cool air aloft associated with a shortwave moving NE-wards on Thursday will generate several hundred Jkg-1 CAPE when combined with diurnal heating - however, probably slightly out of sync (too fast) with the diurnal cycle, with a peak in potential around early afternoon over eastern England, and reducing from mid afternoon for most areas except NE Scotland where the pivoting trough will clear slowest. Nonetheless, a few scattered showers are likely, perhaps weakly-electrified, focussed along areas of wind convergence (such as peninsula convergence from SW England - East Anglia) but probably fairly isolated given quite dry profiles.

Lightning potential increases further overnight as the main longwave trough swings eastwards, accompanied by much steeper lapse rates. SLGTs have been issued where an increase in deep convection is expected, with showers becoming numerous, some producing hail and lightning. Gusty winds will also be possible with the most intense cells.

SE England also needs monitoring for the potential for an upgrade to SLGT during the late evening hours as the approaching trough induces a wave along the old frontal boundary over France, perhaps allowing some elevated instability to move NE-wards over the English Channel and potentially get close to parts of SE England. Confidence is not high enough for an upgrade at present, but may be added if necessary in any later updates.