Beyond Words

Words, Wit and Wisdom for Today's Style and Decision Makers

Tuesday’s Tip: Chances of Rain September 23, 2014

Filed under: Uncategorized — carlawordsmithblog @ 10:48 pm

umbrella beach


Happy first day of fall! I just love autumn; it’s probably my favorite season.  I love the colors, the clothing, the football, and the weather.  Oh, the weather.  How it can change on a dime.


Last week in Austin we had rain nearly every day, leading to flash flooding.  Before that we were suffering through those dreaded end-of-summer high 90s, so with the rain came not only flood waters but nearly unbearable humidity too.  This week we are back to dry skies and only upper 80s.   Yay us!


I’ve always said I love rain, particularly those day-long thunderstorms. Curl up with my dog, some decaf, and a good book and I’m a happy clam.  I think I like rain so much because it’s really the only “weather” we get in Austin.  To me, it’s a nice break from the heat and the sun.  Needless to say I get downright giddy when the weather forecast calls for a chance of showers.


What exactly does that “80 percent chance of rain” really mean though? Does it mean there’s an 80 percent chance of rain that it will rain at my house?  Will it rain 80 percent of the day?  Will it rain only over 80 percent of the city where I live?  Do I need an umbrella today?  The answer:  maybe, maybe, maybe, and maybe.


A meteorologist I am not, but I’ve researched it all for you and have learned that what a real meteorologist does when forecasting rain is use a formula that combines “degree of confidence” and “area coverage.” How confident is Willie the Weatherman that it’s going to rain in a certain area of town?


According to the National Weather Service, “chance of rain 40 percent” means there is a 40 percent chance that rain will occur at any given point in the “viewing area,” the households that receive a particular TV channel that’s broadcasting the weather forecast.


How do forecasters get there? By using math with their handy dandy “Probability of Precipitation” method, which describes the chance of precipitation occurring at any point you select in any given area.  In short,  PoP = C x A (“C” being the confidence that precipitation will occur and “A” being the percent of the area that will receive measureable precipitation.)  That’s in the perfect weather world though. In most cases, forecasters use a combination of degree of confidence and area coverage.


Here’s how it works: if Molly the Meteorologist is only 50 percent sure that precipitation will occur and expects it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40 percent. (.5 x .8 = .4 or 40 %.)


Confused? Well, it gets even more confusing.


If you hear there’s a 20 percent chance of rain, it could mean the weather gurus are 50 percent sure it will rain in 40 percent of the viewing area OR, they could be 90 percent sure it’s going to rain in 20 percent of the area.


Okay, maybe that’s why my degree is news reporting and not a weather forecasting. Too much math!


In any event, perhaps the best way to interpret the forecast is to remember that a 40 percent chance of rain means there is a 40 percent chance that it will rain in the city or town where you live. When all else fails, just always keep an umbrella handy!



evacuation route


Hurricane? Cyclone?  Typhoon?

Last week’s rain in Austin was thanks to the remnants of Hurricane Odile, which brought heavy rains to the West Coast after hitting Baja Mexico with hurricane force winds. In sticking with today’s weather theme, I thought I’d explain the difference between a hurricane, a cyclone, and a typhoon.


Basically they are all the same things. Different parts of the world use different terms though.  “Hurricane” is used is the Atlantic Ocean, Caribbean Sea, central and northeast Pacific.  In the northwest Pacific, they are called typhoons; while in the Bay of Bengal and the Arabian Sea they are called cyclones.












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