how heavy is 10mm in 12h rain?

[shmoo]

We've off on summer cruise weekend after next and looking at wetterzentrale 15 day forcast maps it looks a bit wet in the channel and round the end of brittainy.

The 12h Niederschlag chart spends a lot of time in the 10-15mm range - is that gentle drizzle or a real downpour?

 

[sarabande]

That dumps one litre onto every square metre of ground in 12 hours; that's one kilo. Roughly equivalent to 0.8 inches of rain in 24 hours; that's no drizzle.

 

[Twister_Ken]

Mod heavy, considering avg rainfall in Southern England is about 30 inches (762 mm) per annum.

 

[Aja]

That's nuthin'. Midgies are still able to fly in that stuff....

Donald

 

[2Tizwoz]

Its far worse than that
in Somerset

 

[Bergman]

Worst I've seen was said to be 36mm in 20 minutes.

That was really wet!

 

[peterb]

[ QUOTE ]
That dumps one litre onto every square metre of ground in 12 hours; that's one kilo. Roughly equivalent to 0.8 inches of rain in 24 hours; that's no drizzle.

[/ QUOTE ]

You've got your decimal point wrong; 1mm over 1 sq m is a litre, 10 mm gives 10 litres. Remember that 1 cubic metre = 1 tonne = 1000 litres; 1 mm of rain gives a thousandth of a cubic metre on every square metre.

 

[sarabande]

gimme break ! /forums/images/graemlins/grin.gif I have only got ten fingers !


OOOooooops ! /forums/images/graemlins/blush.gif

 

[Vara]

We had 50mm in 3 hrs last night and it was very very heavy, verging on the distinctly unpleasant . Does that help?

 

[shmoo]

Thanks all.

The one I can releat best to:
[ QUOTE ]

We had 50mm in 3 hrs last night and it was very very heavy, verging on the distinctly unpleasant . Does that help?


[/ QUOTE ]

leads me to:

if 10mm fell in 3 hrs (20% of very very heavy) that might be classed as mearly "heavy" or

if 10mm fell in 12 hrs ( ie 25% of "heavy", or 5% of very very heavy) that sounds like - kind of - light?

There needs to be a Beufort scale of rain heavyness.

 

[Twister_Ken]

Puts on moth-eaten arithmetic hat.

10 mm in 12 hours = .83 mm per hour = .83 litres per hour per square metre. If a sq m is roughly the floor area of a big cockpit, then it's like someone slowly emptying a not-quite-litre of water per hour into you cockpit, through a shower head. Or has my decimal point moved one place forward?

Wet, but not outrageous.

Depressing for 12 hours? You bet!

 

[shmoo]

Problem solved. Just found academic paper Automating the Observation of Drizzle (full ref on request) that defines heavy drizzle as 0.02 inches/h (it being US)

so 0.02 * 12 * 25 = 6mm in 12 h

so my 10-15mm in 12h is about twice as heavy as heavy drizzle.

I can live with that. So we plan to go...