Phew. After the unprecedented rainfall in Cumbria, it got me wondering. Rain
gauges used by amateur observers like your good selves, what is the maximum
they can record before being emptied/reset? Hearing on the news that 372mm
fell in 24 hours, I would have thought most gauges would have overflowed. I
assumed they could go up to about 300mm, since more than that in this
country is unheard of (well, it was up till now). Will this mean everyone
rushing out to buy larger gauges?
Thinks: possible investment opportunity here.

And along the same lines, what is the maximum wind velocity recordable on
amateur equipment?

jim, Northampton

On 20 Nov, 23:25, "jbm" wrote:
Phew. After the unprecedented rainfall in Cumbria, it got me wondering. Rain
gauges used by amateur observers like your good selves, what is the maximum
they can record before being emptied/reset? Hearing on the news that 372mm
fell in 24 hours, I would have thought most gauges would have overflowed. I
assumed they could go up to about 300mm, since more than that in this
country is unheard of (well, it was up till now). Will this mean everyone
rushing out to buy larger gauges?
Thinks: possible investment opportunity here.

And along the same lines, what is the maximum wind velocity recordable on
amateur equipment?

jim, Northampton

There's two variants of standard 'storage' raingauges as used to
derive 'standard' climatological rainfall totals - the Snowdon and the
Met Office MkII. Both are based upon designs in use for almost 150
years now. The latter has a splayed base and can hold more rain in its
overfow base than a Snowdon pattern, but even the Snowdon will hold
around 100 mm in its bottle and another 50 -60 mm in its outer can;
the MkIi can hold up to about 300 mm in all.

So the highest Cumbrian rainfalls in this most recent event would tax
the capacity of a daily-read gauge if the fall accumulated over the
rainday period. However, most of the gauges in the wettest locations
are not read daily and records from there are obtained from tipping-
bucket gauges, with 0.2 mm or 1 mm increments, and provided the gauge
itself does not fllood or malfunction there is no limit to the amount
of rainfall these gauges can record.

As for everyone rushing out to buy larger gauges: we're talking about
300 mm in 24 hours in a handful of the very wettest hillside
locations, and this is almost certainly the highest 24 h total in
comparable records (back 150 years) within the British Isles - see my
post on the Seathwaite totals. I'm not too worried about overflowing
becoming a problem on my trusty MkII just yet ... if we had 300 mm
within 24 h in Berkshire I think I'd have more to worry about than
fretting over whether my raingauge was clsoe to overflowing ...
although it is a pleasant thought!

As for the maximum wind velocity recordable on amateur equipment - a
Davis anemometer recorded something like 170 mph in Hurricane Andrew
in Florida in 1992. Providing the anemometer mast itself isn't blown
away or blown down by the winds, there's no reason why they shouldn't
record this level of wind speed. That particular anemometer was later
subjected to wind tunnel testing to determine the true gust speed, and
it was found reasonably accurate (within 10% or so, as I recall) and
provided useful information on teh fine structure of the eyewall as it
moved over land.

--

Stephen Burt
Stratfield Mortimer, Berkshire