Convective Outlook
VALID 06:00 UTC Sat 10 Jul 2021 - 05:59 UTC Sun 11 Jul 2021
ISSUED 07:02 UTC Sat 10 Jul 2021
ISSUED BY: Dan
Weak upper low will drift eastwards across southern Britain on Saturday, followed by another disrupting upper trough approaching western Ireland later on Saturday night. In a broad sense, another fairly slack pressure pattern dominates across the UK/Ireland, and so yet another day of daytime-driven showers is expected but with subtle shifts in the upper and surface pattern resulting in the focus shifting to more northern and western areas compared with recent days. Showery outbreaks of rain may intensify over northern England and the north Midlands on Saturday morning as the remnants of overnight activity become engaged by the PVA lobe sliding east across southern Britain. Consequently there is a low risk of a few lightning strikes even during the morning associated with this showery rain.
By the afternoon the focus shifts to more typical scattered showers driven by diurnal heating of a moist airmass (dewpoints 14-16C), orographic forcing and low-level convergence. Slight cooling in the mid-levels will have occurred relative to Friday, and this suggests convection may be a little deeper - at least for a time, as gradual warming is expected from the west during the afternoon and evening. However, for the most part convection will tend to be restricted to the lowest ~5km with generally light easterly winds throughout the cloud-bearing layer suggesting weak shear and pulse-type mode. However, there may be an increase in directional shear across the Midlands and northern England later in the afternoon, which could perhaps aid cell longevity slightly. Either way, numerous heavy showers are likely to develop and their slow-moving nature will bring the risk of localised flash flooding. The extent of lightning activity is questionable for the reasons already mentioned, but as was the case on previous days the slack pattern with multiple convergence zones could aid in the development of several funnel clouds.
A tentative low-end SLGT has been introduced where a few lightning strikes are considered slightly more likely, although the odd one is also possible over Cumbria and SE Scotland, for example.
