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What would you consider 'heavy' rain?

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mcrossley
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What would you consider 'heavy' rain?

Post by mcrossley »

I'm thinking in the UK only!

So how many mm would you put on the following thresholds for daily rain?

light
medium
heavy
very heavy
exceptional

RayProudfoot
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Re: What would you consider 'heavy' rain?

Post by RayProudfoot »

Hmmm, this is a tricky one Mark. The highest rainfall in a day doesn't necessarily equate to it being the most intense.

Take my records as an example. The highest rain rate I've recorded is 9.76" (248mm) / hour but the total rain for that day was a mere 1.09" (27.7mm).

Compare that to a daily total of 2.06" (52.3mm) of which 1.1" (28mm) fell in one hour. Which is the higher record?

I've always thought that 1" (25.4mm) in 24 hours represents a wet day but that could come via a 20 minute cloudburst or constant rain over 24 hours.

What are you trying to determine?
Cheers,
Ray, Cheshire.

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mcrossley
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Re: What would you consider 'heavy' rain?

Post by mcrossley »

Hi Ray, I am not considering the rate, just the total for the day. Extreme is probably anything over 100mm? - given UK records seem to top out about 200mm/day.

My terms in the first post are probably a bit confusing as they imply a rate, so here is my first stab - in the absence of Google turning up any 'official' so far. The terms are not important other than as a general indicator, I'm looking for suitable ranges of values.

damp < 5mm
wet 5-10mm
rain 10-20mm
heavy rain 20-50mm
very heavy 50-100mm
extreme > 100mm

RayProudfoot
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Re: What would you consider 'heavy' rain?

Post by RayProudfoot »

Hi Mark,

Ah right, that clarifies things a bit. You do realise that anything we class as very wet or extreme will be mocked by those in warmer climes. :)

I'd say anything over 2" (50mm) in 24 hours is fairly rare for a given location away from hilly or mountainous areas in the UK. As for the rest...

Damp - up to 0.1" (2.5mm)
Wet - up to 1" (25mm)
Very Wet - up to 2" (50mm)
Extremely Wet - up to 3" (75mm)
Exceptionally Wet - over 3" (75mm)
Once in a lifetime - over 4" (100mm)

Back in August 1972 I can remember taking an exam in a glass-roofed building in Norwich and the noise was deafening. I had a rain gauge which recorded over 5" in 24 hours but some parts of the area had over 7". :shock:
Cheers,
Ray, Cheshire.

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nking
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Re: What would you consider 'heavy' rain?

Post by nking »

RayProudfoot wrote: Damp - up to 0.1" (2.5mm)
Wet - up to 1" (25mm)
Very Wet - up to 2" (50mm)
Extremely Wet - up to 3" (75mm)
Exceptionally Wet - over 3" (75mm)
Once in a lifetime - over 4" (100mm)

Back in August 1972 I can remember taking an exam in a glass-roofed building in Norwich and the noise was deafening. I had a rain gauge which recorded over 5" in 24 hours but some parts of the area had over 7". :shock:
I'm sure there will be quite a few variations but I think Ray's is pretty good apart from changes to the following

Exceptionally Wet - over 4" (100mm)
Once in a lifetime - over 5" (125mm) I note that Ray actually recorded over this in 1972 :)

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