We've had this conversation before about what constitutes a warning. In my opinion the original warning area didn't extend far enough south, so the update when it came at 0820 UTC was too late to be called a warning because the event had already started. They were simply issuing its laid down in the procedures that they should. As it happened it snowed for an hour or two across most of southern England and the southeast but only put down 3 or 4 cm as far as I can see from th SYNOPs. A very similar thing occurred on the 11th of December 2017 when High Wycombe had 17 cm of snow, this time the warm air saved their blushes.
The Combe Martin area is comprised of "fast response" rivers that typically flood quite quickly and die down equally quickly. If Exmoor has already experienced heavy rain in the preceeding few days then the response is even quicker and more marked. Having said all that, the radar does look quite uninspiring, so maybe the local radar was unfortunately off the air at the time.
For the KIngston area and adjacent north Surrey close to the Thames, heavy sleet only - just verging on proper snow briefly around 11am - was as exciting as it became. Now raining, as Richard said. Now the third snow event this winter which has affected Herts, Essex, Bucks but not the lowest lying areas of west London / Thames valley. Here in Molesey, no hint of snow lying so far this winter.The road weather sensors in much of Scotland show much midday ploughing and gritting going on - as well as impressive snow depths, though much of it has been on the ground for 3-4 days of course up there. Gritter drivers and highways staff will be grateful for a rest in a few days as the milder weather arrives, a well-deserved break.
Bit late to this but I experienced yesterday's snow in an area from Leavesden, near Watford, to Wanstead. At Leavesden, site of the Warner Brothers Harry Potter studio, the snow began to fall lightly at first at 10.30am before coming down in thick flakes. When I saw it falling on Privet Drive through the cafe window I initially thought it was the studio's special effects. It gradually got heavier and started covering all surfaces, leaving a layer of slush on local roads, I approached a local petrol station a bit too fast and had to take evasive action when my wheels locked - I think the local gritters must have been caught out. The snow gradually turned to pellets, sleet and then rain. By the time I reached Wanstead at 1.30pm there was just a thin layer of slush on car windscreens.
I wrote that SYNOP plotting software in 1998 when I was a programmer with the Met Office, I download and parse the obs from OGIMET. I can go back 6 hourly to 1973 and plot a chart for just about anywhere.
If you look at the OS map that I included in my blog the stream that runs through Combe Martin doesn't originate on Exmoor as far as I can see...
Swimbridge and Muddiford were two other places in N Devon that were affected by flooding.