Convective Outlook: Thu 27 Apr 2023

LOW SLGT MDT HIGH SVR

What do these risk levels mean?

Convective Outlook

VALID 06:00 UTC Thu 27 Apr 2023 - 05:59 UTC Fri 28 Apr 2023

ISSUED 06:16 UTC Thu 27 Apr 2023

ISSUED BY: Dan

The main interest during this forecast period is linked to a developing low originating from the Azores, tracking across southern Ireland on Thursday afternoon and across northern England on Thursday night. While some warm advection will occur at low-levels, a substantial tongue of reasonably high Theta-W air aloft (>14C at 850hPa) will be associated with the warm sector, yielding some elevated instability in the 700-900hPa layer.  A substantial dry intrusion aloft will generally serve as a cap to deep convection in the post-cold frontal environment, and so there is a relatively narrow spatial window of opportunity for some deep elevated convection embedded within/near the frontal rain that tracks erratically northeastwards across the UK and Ireland, especially near the leading edge of this dry intrusion. Forecast profiles do suggest that, while CAPE will be very skinny, there may be scope to surpass a slight warm nose at ~700hPa and potentially develop some deep convection into the dry air aloft. This situation is highly sensitive to the exact thermodynamic profile, which varies slightly amongst NWP guidance, and therefore casts a lot of uncertainty over whether much lightning activity will actually occur. The lightning risk appears greatest over the Celtic and Irish Seas and adjacent portions of southern Ireland, Wales and perhaps SW England, with a second area of interest potentially Cen S Eng / M4 corridor into the London area during the evening hours - but in all cases confidence is not high and so for now have refrained from introducing a SLGT.