Convective Outlook: Tue 19 Jul 2022
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Tue 19 Jul 2022 - 05:59 UTC Wed 20 Jul 2022

ISSUED 06:12 UTC Tue 19 Jul 2022

ISSUED BY: Dan

An incredibly hot, dry airmass continues to cover Britain on Tuesday associated with a deep well-mixed layer generally suppressing surface-based convection. Above this mixed layer scattered elevated showers and thunderstorms are possible in the morning over SW England and into Wales and perhaps SE Ireland along a NW-SE aligned instability axis drifting gradually eastwards through the day on the forward side of an upper low over Biscay. Most model guidance suggests activity along this zone will wane by the afternoon hours, however the instability axis remains as it tracks eastwards across England through the afternoon and evening and any subtle forcing/moistening may be sufficient for additional elevated showers/thunderstorms to develop. However, confidence is rather low on exactly when and where - a blend of guidance suggests there may be an uptick in activity across SE England, East Anglia and the E Midlands during the evening hours. Meanwhile, ahead of this feature the UKV (and to a lesser extent the ECMWF) continues to flag the potential for a few scattered showers/thunderstorms over Cen N and NE England and SE Scotland during the afternoon and early evening hours, exiting to the North Sea. In the model world these have a surface-based look to them forming within the surface trough axis, but in reality their bases would be incredibly high (same level as elevated convection essentially) and given the incredibly deep hot, dry layer such surface-based convection would likely struggle for moisture. Therefore this scenario is deemed rather unlikely, with elevated convection probably the more favoured mode (if anything does indeed develop). Any strong, isolated elevated convection that does develop at any point during this forecast period poses the risk of starting a fire given potential for dry thunderstorms and tinder dry vegetation, and perhaps also some heat bursts. Thunderstorms could produce quite frequent lightning given the magnitude of instability above the EML.

Perhaps better consensus is for an active complex of thunderstorms to quickly develop over parts of northern Scotland and the Moray Firth during the late afternoon and early evening hours, on the leading edge of the approaching cold front as PVA arrives from the southwest. This may become messy given a mixture of convective and dynamic precipitation, but could be rather active for a few hours before weakening on approach to Shetland. Overnight, there may also be an increase in elevated shower/thunderstorm activity in the vicinity of the Celtic Sea and portions of Wales/SW England (perhaps W Midlands/W Country) on the northern periphery of the approaching Biscay upper low.