Weather math
Posted at 10:31 AM on January 27, 2012
by Bob Collins
(8 Comments)
Filed under: Weather
The National Weather Service has just issued a "heavy snow" warning for the Minneapolis Saint Paul Airport:
THE NATIONAL WEATHER SERVICE IN THE TWIN CITIESCHANHASSEN HAS
ISSUED AN AIRPORT WEATHER WARNING FOR...
MINNEAPOLISSAINT PAUL INTERNATIONAL AIRPORT MSP
* VALID FROM NOON TODAY TO 4 PM CST THIS AFTERNOON
FOR THE FOLLOWING THREATS...
* SNOW FALLING AT A RATE OF 34 INCH OR MORE PER HOUR
LIGHT SNOW WILL ENVELOP THE TWIN CITIES METRO AIRPORT SHORTLY BEFORE
THE NOON HOUR. SNOWFALL RATES OF UP TO THREE QUARTERS OF AN INCH
PER HOUR ARE LIKELY BETWEEN NOON AM AND 430 PM. SNOWFALL
ACCUMULATION OF NEAR AN INCH SHOULD BE EXPECTED.
This invites some math. If the rate of snowfall is "up to" 3/4 of an inch per hour, and the snow will last for four hours and the total accumulation is near an inch, for how long would the rate of snowfall be 3/4 of an inch per hour?
Comments (8)
Just because it falls at 3/4-in/hr does not mean it will ACCUMULATE at 3/4-in/hr.
Maybe it was suppose to say "3-4 inches," not "3/4."
I'm hoping they really meant 34" per hour. That would be a sight to behold.
That one looks like it was written by one of the chimps from the days of Soviet space launches.
They use the rate as a way to communicate what viability will look like at the hardest point. Much like a thunderstorm, you may get 3" an hour rate, but it might only occur for a couple minutes. The rest will be at lower rates. So in this case you might get 20 minutes at the 3/4" rate, the remaining at 1/4" an hour which will get you just over an inch.
@Eric,
Actually, with your example, you'd get less half an inch, not over an inch.
(3/4 inch/hour) * (1/3 hour) + (1/4 inch/hour) * (2/3 hour) = (5/12 inch)
Which is exactly the point that people get confused by fractions, rates and addition.
Doesn't this call for a rousing game of SNINGO!
They give a big range of time when it might happen, but it doesn't mean that it will occur the whole time. They might just be noting that it could happen in that time, but might not be the whole time, similar to a severe thunderstorm warning.
34 inches of snow an hour would be awesome to watch. Especially from a tropical climate or in a really sturdy building.
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