Convective Outlook: Thu 13 May 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 13 May 2021 - 05:59 UTC Fri 14 May 2021

ISSUED 06:47 UTC Thu 13 May 2021

ISSUED BY: Dan

There is an unusual amount of uncertainty about the exact location/shape of a surface low that is likely to linger near the English Channel or northern France on Thursday, and this will dictate the site-specific detail. Frontal rain is likely to affect Wales and SW England, with a cold front also straddling southern England in a general west-east line. The exact north/south location of this line will determine where the best potential for thunderstorm activity evolves by the afternoon and evening since residual moisture and convergence along/ahead of this front, combined with surface heating to the north, will likely provide the key ingredients for deep convection to develop later in the day. Have tentatively introduced a low-end SLGT where the best potential exists for forced ascent and hence sporadic lightning - but this will need monitoring through the day. Some concern exist over fairly moist profiles which may reduce the lightning potential but heighten the risk of flash flooding - it is possible very little lightning activity may occur despite locally torrential rain. Any strong convection that can develop close to the triple point will be in an environment with modest LLS and substantial veering of winds in the low-levels - suggesting the potential for an isolated tornado.

Elsewhere, scattered showers will develop in response to diurnal heating and low-level convergence/orographic forcing across portions of northern England, the north Midlands, Scotland and Ireland/Northern Ireland, and here a few lightning strikes will be possible - especially in Ireland/Northern Ireland where colder air aloft will allow for deeper convection and a greater potential for lightning. For the most part shear will be rather weak, although some directional shear is noted over Ireland in particular. In all cases, the general slack surface pattern and convergence may encourage a few funnel clouds to develop.