Convective Outlook: Sun 08 Aug 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sun 08 Aug 2021 - 05:59 UTC Mon 09 Aug 2021

ISSUED 06:42 UTC Sun 08 Aug 2021

ISSUED BY: Dan

An upper low continues to cover the UK/Ireland on Sunday, generally centred over Scotland while slowly filling. Multiple PV anomalies / shortwaves will rotate anticlockwise around the upper low through the forecast period. One such feature will drive an area of showery rain, with some embedded lightning, northwestwards over the North Sea towards Orkney and Shetland - although possibly with a weakening trend towards arrival. Elsewhere, outbreaks of rain are likely to affect parts of Scotland, England, Wales and Northern Ireland initially, but will probably break up into heavy showers by the afternoon. Diurnal heating will lead to 400-800 J/kg CAPE, and a number of heavy showers are expected to develop - particularly across Cen S / SE England and East Anglia coinciding with a minor shortwave trough in the afternoon, but also over/to the east of the Pennines and within the slacker regime in central/southern Scotland. Here, the light steering winds could lead to localised surface water flooding, while stronger flow further south across England will enable individual cells to move quicker to the ENE with a greater chance of hail and gusty winds. As was the case on Saturday, fairly tall, skinny CAPE profiles with weak shear (mostly 5-10kts, locally higher) will tend to limit the amount of lightning activity while still producing heavy downpours.

Any cells lingering across southern England during the evening hours may be able to utilise the strengthening mid-level flow. There is a risk of a few lightning strikes in NE Northern Ireland too, but cloud cover and outbreaks of rain casts too much uncertainty to introduce a SLGT. During the evening and and overnight period, the next PV anomaly will swing from SW Ireland across the Celtic Sea towards SW England / English Channel. This will lead to an increase in shower activity spreading eastwards with time, and while a few isolated lightning strikes may be possible in S Wales / Bristol Channel / SW England / English Channel and adjacent coasts, the risk in any one location is considered generally too low to warrant specific SLGT areas - the only exception is S Wales where a low-end SLGT has been introduced when considering climatology in similar setups, however confidence that lightning will occur is rather low. Nonetheless, the strongest cells could produce some hail and gusty winds.