Convective Outlook: Thu 16 Jun 2016
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 16 Jun 2016 - 05:59 UTC Fri 17 Jun 2016

ISSUED 17:50 UTC Wed 15 Jun 2016

ISSUED BY: Dan

Once again, large upper trough sits over the British Isles, continuing to dig southwards across Iberia. At the surface, a slack pressure pattern results in areas of frictional convergence due to a small low centre. These convergence zones offer the best forcing for deep convection to generate heavy showers and a few thunderstorms, primarily pulse-type given very little shear, but as has been the case in recent days zones of more pronounced convergence can create a favourable environment, given 500-700 Jkg-1 MLCAPE, for more active thunderstorms with frequent lightning, at least for a time. 

High-resolution NWP output struggle to agree where such boundaries may lie, and in either case these are likely to shift during Thursday as well - it is likely that multiple convergence boundaries will set up, providing several zones of better thunderstorm potential.

A broad SLGT has been issued as a result, although worth noting that once again there may be quite a few areas within the SLGT that remain dry and lightning-free. There does appear to be a trend in most models for an area of relative minima in terms of convection (and hence lightning potential) bound within a circle that connects Cambridge / Peterborough / Northampton / Luton - not to be taken too literally of course, but an interesting trend that might warrant a downgrade to sub-SLGT for this area.

Otherwise, once again the ongoing threat of local flash flooding remains given prolonged torrential downpours, especially when falling on increasingly saturated ground. Low cloud bases near convergence zones will produce the greatest opportunities for a few funnel clouds or a weak tornado.