Convective Outlook: Sun 22 Sep 2019
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sun 22 Sep 2019 - 05:59 UTC Mon 23 Sep 2019

ISSUED 21:09 UTC Sat 21 Sep 2019

ISSUED BY: Dan

A complex pattern on Sunday, with several areas of potential interest. An instability axis will straddle a line from SW Scotland - Midlands - SE England first thing on Sunday morning, associated with a tongue of relatively high Theta-W. This zone will continue to nudge northeastwards through the day, which combined with subtle forcing aloft will allow clusters of elevated showers to develop ahead of the cold front - some capable of producing sporadic lightning. However, confidence is not particularly high as to how much lightning activity may occur given marginal CAPE and fairly marginal mid-level lapse rates, and so this scenario is treated with a low-end SLGT over northern and eastern England.


The cold front will be marked by a zone of showery rain from Northern Ireland - Wales - SW England first thing on Sunday morning, and this too will nudge northeastwards through the day. However, its slow motion will eventually allow a favourable overlap with strong forcing aloft on the forward side of the approaching Atlantic upper trough, which combined with a marked dry intrusion in the mid-levels could lead to an increase in deep convection along the leading edge of the cold front by noon and through the afternoon hours. The risk of lightning will therefore affect similar areas to the earlier elevated showers already covered by a SLGT.

Behind the cold front, the main upper trough axis will cross Ireland and SW Britain during the afternoon hours. The associated cool air aloft atop warm seas and diurnal heating inland will encourage scattered showers to develop, some weakly-electrified. Two low-end SLGTs have been introduced to cater for this risk over SE Ireland and SW England / S Wales.