Convective Outlook: Fri 25 Jun 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 25 Jun 2021 - 05:59 UTC Sat 26 Jun 2021

ISSUED 07:06 UTC Fri 25 Jun 2021

ISSUED BY: Dan

An upper trough will disrupt over the UK/Ireland on Friday, with a cut-off upper low sliding southwards to be located over the Celtic Sea by 06z Saturday. At the surface, a humid airmass is present with dewpoints of 14-15C across East Anglia and SE England. Frontal rain associated with a cold front, initially over the Midlands / Cen S England, will migrate eastwards to East Anglia / SE England while fragmenting, the wrap-around occlusion providing a persistent area of rain over northern England, southern Scotland and north Wales. The potential for deep convection remains unclear, and appears tied strongly to the requirement for sufficient surface heating. Extensive cloud may inhibit this, while a marked dry intrusion will also spread across Wales, SW / Cen S England and the Midlands through the day - and this may act as a capping inversion if surface temperatures are unable to increase to near or above 20C. As a result, there is much uncertainty over how much deep convection can evolve, weaker capping over East Anglia / SE England but likely more extensive cloud limiting surface heating, while better clearance but potentially more capping in central/western Britain.

In either case, a notable jet streak will track eastwards through the day, particularly focussed over the Home Counties, E Midlands and then East Anglia and SE England. Forecast profiles reveal rather light winds with weak shear below 700mb, but a gradual increase in flow through the mid/upper troposphere, and hence potentially quite strong shear aloft. This, coupled with a rather moist boundary layer and very dry air in the mid-levels suggests that any deep convection that is able to develop and grow tall enough to utilise these various properties could become quite electrically active, but as stated this is uncertain. A blend of various model guidance would highlight two main areas of interest - first, the London/Kent area and adjacent counties into East Anglia, and portions of mid/north Wales into the West Midlands - but neither carries high confidence. Have tentatively introduced a couple of SLGTs, but it is plausible these may need adjusting depending on trends through the day.