Convective Outlook: Mon 05 Jul 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Mon 05 Jul 2021 - 05:59 UTC Tue 06 Jul 2021

ISSUED 06:04 UTC Mon 05 Jul 2021

ISSUED BY: null

Showery outbreaks of rain across Scotland, Northern Ireland, northern England, on the forward side of an upper trough slowly lifting northwards, will once again break up into heavy showers during Monday daytime. The most unstable environment will be across Scotland where a few thunderstorms will be possible, particularly across southern, central and western areas. Some directional shear is likely in the low-levels, otherwise most of the profiles here will exhibit fairly unidirectional winds with only a slight increase in speed with height. The net result is pulse-type convection, capable of producing locally high rainfall totals and hence the risk of local surface water flooding. These will tend to gradually ease through the evening hours. Additional showers are likely to develop over Ireland and northern England; convection is likely to be restricted to around 700mb in Ireland which coupled with weak shear suggests the risk of lightning is quite low. However, across northern England strong flow in the upper troposphere could result in, if convection can grow tall enough, up to 35kts cloud layer shear - which could produce an isolated but quite active cell, the main focus probably Yorkshire (but this is highly dependent on deep enough convection to utilise the stronger flow aloft).


Overnight, the attention turns to southern Britain where a deepening low beneath the left exit of a pronounced mid/upper-level jet will approach SW/Cen S England. Frontal rain will spill northwards well-ahead of the surface low across much of England and Wales on Monday night. An airmass of relatively high Theta will advect into SE Britain within the warm sector of this system, and this may provide the focus for a few isolated lightning strikes along the cold front - especially given the strongly-sheared environment with dry air aloft over-running moist low-levels, albeit with rather skinny/weak CAPE. However, confidence in much of the way of lightning is rather low. Also, close to the surface low centre bands of showery rain will likely be wrapped around; forecast profiles exhibit some medium-level instability and so again there will be a risk of a few lightning strikes. Should any convection in southern Britain became surface-based (and sustained) then this would present a tornado risk given the strong low-level shear - however, it seems most convective elements will tend to be elevated through this period.