Convective Outlook: Fri 05 Jun 2020
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 05 Jun 2020 - 05:59 UTC Sat 06 Jun 2020

ISSUED 06:31 UTC Fri 05 Jun 2020

ISSUED BY: Dan

Negatively-tilted longwave trough continues to strengthen over the North Sea on Friday, evolving into a large, broad upper low. Mid-levels will continue to cool as a result, especially associated with a shortwave sliding across eastern England during the day where mid-level lapse rates will steepen substantially. A strip of shear vorticity will straddle Northern Ireland - north Wales - East Anglia along the northern periphery of a strong upper jet, slowly sinking southwards through the day. Strong deep layer shear will be present as a result of this jet, although shear will be much weaker north of the jet. In any case, convection will likely be restricted in height, moreso the further southwest you go, and so is unlikely to grow tall enough to utilise the strong flow aloft. Diurnal heating will yield 100-200 J/kg CAPE fairly widely in a broadly unstable airmass, but as high as 300-500 J/kg CAPE across eastern England into East Anglia. Here, a better overlap of CAPE, shear vorticity, steep mid-level lapse rates and some 20-30kts shear will occur (more especially East Anglia, where a narrow NW-SE zone of more enhanced shear could overlap favourably with cells to aid in organisation), and consequently it is this zone that is likely to see the deepest convection and greatest potential for some sporadic lightning, with ELTs potentially as low as -30C to -40C. A low-end SLGT (30%) has been issued to highlight the main area of interest. Elsewhere ELTs of -10C to -20C are more likely, limiting the lightning potential somewhat.

Showery rain across the Midlands and East Anglia will need to clear during the morning to allow sufficient surface heating to occur, to coincide with the passage of the shortwave from late morning into the afternoon hours. In general, shower coverage will increase across the British Isles courtesy of diurnal heating, but most convection will be relatively shallow in depth - the exception being primarily eastern England, and perhaps also SE Ireland. The strongest cells will likely produce gusts 40-50mph locally, and perhaps large quantities of small hail. This is more akin to an April showers day than early June! Many showers will likely fade through the evening and night hours, where the focus for showers and isolated lightning may shift close to the centre of low pressure approaching E Scotland / NE England.