Convective Outlook: Mon 09 Apr 2018
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Mon 09 Apr 2018 - 05:59 UTC Tue 10 Apr 2018

ISSUED 20:14 UTC Mon 09 Apr 2018


UPDATE 20:14 UTC SLGT removed given latest trends - some mid-level instability release is still possible from Benelux and out across the North Sea tonight, but given marginal instability it is questionable as to how much lightning activity may occur, and then whether any makes it close to north and east Norfolk later tonight

UPDATE 10:31 UTC SLGT reduced in size given decreasing risk of lightning tonight - primarily focussed on Norfolk, but perhaps even staying offshore to the NE of Norfolk

UPDATE 07:42 UTC No changes to the map for now, but trends in guidance over past 12 hours would reduce the risk of lightning somewhat tonight due to a much later arrival, and tending to restrict it more to N + E Norfolk, or even offshore from there. Adjustments may be required to the SLGT area if these trends continue through today

Upper low to the west of Ireland will slide SE-wards, eventually merging with an upper low over northern Iberia / southern France by Monday night. Diurnal heating over Ireland in particular will lead to a few scattered showers developing during the afternoon, though with unimpressive mid-level lapse rates and warming aloft this will tend to limit convective depth - so a few locally heavy showers are possible, but lightning will be isolated (if any).

Instability will build over The Netherlands, Belgium and NE France on Monday afternoon. A shortwave is expected to lead to destabilisation here on Monday evening, and with the approach of the Iberian upper trough merging with the Atlantic upper low ultimately backing the flow across central and southern Britain, any thunderstorms that do develop over the nearby Continent associated with moisture plume will begin to drift west or northwestwards across the North Sea. 

At this stage there is some spread as to the exact track of these thunderstorms - general consensus would put the risk higher over East Anglia and perhaps NE Kent, but some model guidance offers a more southerly option, even as far south as Sussex (and a minority of models keep any deep convection offshore to the NE of East Anglia). In either case, it is questionable as to how much lightning will actually occur over land (assuming deep convection does move inland) given the gradual reduction of instability through the evening/night. The risk (albeit lowering) will continue to migrate NW-wards along eastern coasts of England through the early hours of Tuesday.
For now, a low-end SLGT has been issued to cover the threat of weakening thunderstorms arriving late Monday evening / early hours of Tuesday over East Anglia / Kent, but it is certainly possible this SLGT area may need to be altered or perhaps even removed, depending on trends during Monday.