What Was Normal Weather Then isn't Normal Now

The National Weather Service updated its 30-year normal temperatures and rainfall levels.

What on Sunday was considered typical weather has changed in a small way as the National Weather Service revamped its normal temperatures and rainfall.

The weather service does this every 10 years across the country, lopping off the earliest decade in 30 years of measurements and adding the latest.

So on Monday, temperature and rain from 1971 to 1980 were erased from the three decades of statistics, and records from 2000 to 2010 were tacked on.

The weather service does this to keep the data fresh and include environmental changes, large or small.

The differences weren’t much, but overall winter in West Central Florida got slightly cooler while the spring and summer grew a bit warmer.

Also, the Tampa Bay region got slightly wetter.

Some of the changes emerge from tossing out statistical peaks and valleys from the 1970s, the weather service says. A shift in instrument locations could explain more change.

And the continued development around Tampa International Airport and Tampa in general could account for some of the warmer nights that helped push average temperatures higher for April through August.

A slight shift in equipment location at Tampa International Airport could also influence the low morning readings, the weather service says.

Or, the overall reason also could be changes in global climate, but that’s impossible to determine from readings at one location, the weather service says.

Changes in monthly temperatures weren’t large, though the average temperature for May went up .8 of a degree and June was up .7.

On the other end, November through January grew slightly colder with January chilling by an average of a half degree a day. February got warmer, and then March got cooler.

This change could be partly statistical. The new readings included serious winter blasts in January and December of 2010, dropping two very warm Januaries and eliminating February of 1978, the coldest on record, the weather service says.

The change in rainfall, from an average 44.77 inches to 46.3 doesn’t have quite as solid an explanation. Summer rain increased while averages for the dry months remained the same.

The exception was May that got a lot drier, going from the fifth wettest month in the year to the third driest, trailing November and April.

The average rain in May changed from 2.85 inches to 2.1 inches.

Some of that again could be statistics, the weather service points out. The new normal range erased May 1979, the wettest on record with 17 inches.

Except for the shift of May, the new statistics don’t alter the monthly standings.

November is still the driest month with 1.55 inches and August is the wettest with 7.77 inches.

January remains the coldest at 60.8 degrees average and August is the hottest at 83.2 degrees.

The weather service also says the normals are more than just numbers. Power companies use them to help forecast how much electricity people will want. They are guidelines for agriculture.

And without normals, TV weather broadcasters would have nothing to compare today’s temperature with.


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