Looking at the 1km radar data it would appear that the heaviest rainfall was
alligned with the eastern side of the Otter valley - with the western-side
of the valley being virtually free of heavy rain - the steering effects of
the surface are often overlooked.

Chris


"Will Hand" wrote in message
...
Hi Nick,

Awesome stuff indeed.
Here are some links to pictures
http://www.thisisexeter.co.uk/galler...l/gallery.html
http://www.bbc.co.uk/devon/content/i..._gallery.shtml

It's estimated that circa 120mm rain fell in storm centre allowing for
hail.

First I was aware of it was listening to Radio Devon on way to work at
0730 this morning, when they were going on about snow drifts and flooding.
Snow was, of course, hail. Apparently the hail floated on the water and
when it subsided huge chunks of ice 2 feet high were left in car parks
hemming in cars and there is still hail around.

What was the cause?

Occlusion slow moving oriented N-S across E. Devon with normal amounts of
rain associated with it. Low centre nearby. Potential vorticity filament
associated with jet streak to west of low in upper air tracked east and
helped de-stabilise the warm air part of the occlusion. Deep instability
released as air north of low was of Arctic origin and thunderstorms
spawned. But that was not all ... once the storms got going they became
trapped in the almost-calm centre of the low and could not go anywhere,
hence a local deluge with huge amounts of hail. Very localised and
unpredictable, even in hindsight. Exeter had circa 6mm rain, Ottery St
Mary 100mm. High resolution 1km radar imagery available at work showed
torrential rain and a widespread hail signal. Evidence of rotation and a
comma-like structure too. The investigation continues ...

What a day!

For those of us in the SW, the pictures on Spotlight are going to be
interesting!

Will (from a serenely quiet but very cold Haytor)
--

"Nick Gardner" wrote in message
...
Last night has got to be one of the most memorable 'weather' nights ever.
A thunderstorm of the intensity I have not witnessed since those summer
'biggies' from what now seems like a long time ago.

The lightning started around 23:45 but the rain did not really get going
until just after midnight, though it was a mixture of torrential rain and
hail. The road outside soon resembled a mini-glacier with hail floes
running everywhere.

The lightning was regular, frequent and overhead with amazing cloud-cloud
flickering and the occasional ground strike; the thunder was the house
foundation shaking type and at times truly deafening. The brightness of
the lightning was awe inspiring.

I have just checked the rain gauge and it was blocked by hailstones that
still had not melted but there was 63 mm of rain in there. The Davis AWS
recorded a total of 70 mm since midnight with 40 mm falling between 0:00
and 3:00. These rainfall figures are probably much lower than what
actually fell.

With reports that Ottery St Mary and many villages around here are
flooded and cut off, the A30 and part of the motorway at Junction 29
closed due to multiple accidents. There have been 'hail drifts' (not snow
as reported by some people) so deep that cars have been buried in them,
it certainly has been one of those nights to remember.
________________
Nick.
Otter Valley, Devon
83 m amsl
http://www.ottervalley.co.uk