VALID 06:00 UTC Sat 16 Mar 2019 - 05:59 UTC Sun 17 Mar 2019
ISSUED 21:55 UTC Fri 15 Mar 2019
ISSUED BY: Dan
During Saturday daytime the bulk of any lightning potential (albeit very low) will be largely restricted to the Northern Isles, since a deepening surface low will move eastwards from Northern Ireland and across southern Scotland, bringing widespread dynamic rainfall to many areas.
However, the approaching upper trough and associated cooling aloft will steepen lapse rates and generate a few hundred J/kg CAPE across Ireland during the afternoon hours. Scattered showers here may produce a few sporadic lightning strikes, especially given the strongly-sheared environment. This favourable environment for deep convection will expand eastwards across the remainder of the British Isles through Saturday night, behind a southeastward-moving cold front. Sporadic lightning will continue to be possible from scattered showers, the risk generally highest in exposed western areas and over open seas here. Showers will be organised into more distinct bands at times courtesy of embedded shortwave troughs, these features then capable of pushing showers much further inland. Some small hail and gusty winds will be possible from the most intense cells.
Incidentally, the cold front will begin to develop elements of line convection during Saturday late afternoon / evening due to a combination of strong deep layer shear, a tongue of relatively warm, moist low-level air, marginal instability and forced ascent. This will develop initially across Wales / north Midlands / northern England, before moving southeastwards on Saturday night. A brief spell of very heavy rain and strong gusts of wind will be possible locally from this feature, embedded within a broader precipitation envelope. Weak instability and saturated profiles suggest lightning is rather unlikely.