Convective Outlook: Fri 29 May 2020
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 29 May 2020 - 05:59 UTC Sat 30 May 2020

ISSUED 20:07 UTC Thu 28 May 2020

ISSUED BY: Dan

Substantial upper ridging covers the British Isles on Friday, extending northeastwards towards Scandinavia. Meanwhile a disrupting upper trough over the Atlantic gradually approaches from the west. The net result is a strong southerly flow aloft across Ireland and western Scotland, with heights slowly falling during the forecast period. A plume of relatively high Theta-W will be drawn northwards, just to the west of Ireland, over the Atlantic. Subtle impulses embedded within the strong southerly flow aloft throughout this forecast period may engage with this plume, gradually moistening/cooling the mid-levels to increase mid-level instability, and potentially develop a few elevated showers/thunderstorms in a relatively narrow north-south line.

However, this appears very finely-balanced, and model guidance varies in extent (if any) of convective precipitation. The main focus will be offshore, but not by much - hence the inclusion of a LOW threat level - although the overall greatest risk of lightning will probably further north along similar latitudes to the Hebrides. The instability axis may drift a little closer to western Ireland for a time on Friday evening, before retreating back west again overnight. If confidence increases a little, we may consider introducing a SLGT for the extreme west coast perhaps.

Elsewhere, surface heating will yield some substantial SBCAPE over the NW Highlands on Friday afternoon - however, given a deeply mixed boundary layer and capping inversion around ~800mb, this is likely to inhibit deep convection. That said, some convective cloud may develop and an isolated shower cannot be ruled out but the risk of lightning is considered rather low.