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"Ask Allison" What does a 60% chance of rain mean? - 04/08/14

60% Chance of Rain?  Means there's a 40% chance we won't see anything...well that's not entirely true.

One of the more common questions that people ask me is, 'What does a __% chance of rain mean?'  This question was most recently submitted by KEYE-TV viewer, Anya.

Well, that's a simple yet complicated answer.  For 60%, it means there's there is a 60% chance of precipitation occurring at any point in the selected area.  The selected area for KEYE-TV meaning Fredericksburg to La Grange, San Marcos to Georgetown.

To break it down, we're talking about our confidence of rain and the actual rain coverage.  So if we say, there's a 70% chance that rain will occur somewhere in our 'area' and it will produce measurable rain over 80% of that area.  Then, the percentage will arrive at is .7x.8 which equals .5 or 60%

This is helpful when covering a large area.  As a Meteorologist, I like to add additional information to aid to the percentage we give.
So, if I say there's a 60% chance of showers today.  For example, I'll add that the rain will begin in the Hill Country in the morning and increase towards Austin by the afternoon.  We're likely to see only 0.25" of rain for parts of the Hill Country and closer to 1" around Austin.


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