Omonous clouds like this one I captured yesterday will develop for many through this afternoon. (Photo courtesy of Mark Vogan)
Well it looks as though Sunday will follow in Saturday’s footsteps of a tame, quiet start BUT with that low over SW England which has a nice cold layer over mild and as the sun begins to heat the surface, so that contrast between warm surface and cold aloft grows larger. The larger the contrast and greater the vertical motion and with the low to the southwest of the UK, the combo of sun and air coming up from a warmer source region, the setup is perfect for some big thunderstorms to once again develop. The contrast between warmth and cold in the atmosphere is known as the lapse rate. Like yesterday, the abundant sunny start for many will allow temperatures to warm beautifully into the 19-22C range with the Southeast which may escape the showers till later into the PM hours, may see 24C but all the while, keep an eye on those cumulus clouds quickly popping and vertically building into the frigid higher reaches of the atmosphere. Eventually, those magnificant and towering cumulonimbus clouds will dominate the horizon and so, like, yesterday, the heavens will open for some, while others remain in the sunshine, perhaps just a few miles away. Underneath these cells, watch for a rapid torrential downpour which may produce flash flooding, very gusty winds, hail and plenty of lightning.
This was the scene at the Dumfries Agricultural Show yesterday which eventually had to be cancelled. (Photo courtesy of Kevin Logan)
Check out what the GFS precip forecast is showing through today, notice the lack of rain in the AM, then the coverage of heavy rain expands rapidly, like dropping a water ballon. This indicates how it sees those thunderstorms developing and just how much ground they will cover. A LOT will see thunderstorms today and a fair amount may see flooding. Also be aware whilst driving that you may all of a sudden drive into an area which just got hit by a storm and you may encounter flooding with little warning!
Here another good indicator that the model is seeing thunderstorms and not just showers. CAPE is a measure of convective energy (upward motion) within the atmosphere. Notice how the bright colours develop and become very widespread into the PM hours, showing how as the warmth builds at the surface, so the rate of upward motion increases and thunderstorms build. The atmosphere is well primed.
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