Average July rain brings varying relief to the area


Published: Friday, August 1, 2008 at 6:01 a.m.
Last Modified: Friday, August 1, 2008 at 12:36 a.m.

Here's a word you can toss into the water cooler chats today if the subject of weather comes up: evapotranspiration.

It describes water that is lost by heat or taken up by vegetation, and it is the reason the flow of some area rivers remains at near-record lows despite an average July rainfall, forecasters say.

The Gainesville area got 5.61 inches of rain in July, just slightly below the average of 6.1 inches, according to National Weather Service meteorologist Phil Peterson.

Peterson said the area was about 6.25 inches behind average for the year at the end of July, and a year ago the rainfall deficit was around four inches.

Peterson and Suwannee River Water Management District hydrologist Megan Wetherington said it is important to remember that averages in Florida are based on specific rain gauge locations and can vary widely even within a mile or two.

"The rain has been hit and miss" around the North Florida district, Wetherington said in an e-mail.

According to district records, High Springs, in far-west Alachua County, received about 5.8 inches of rain in July. On the county's eastern edge, Lake Santa Fe got more than twice as much 11.65 inches. Bradford County got more than 10 inches of rain during the past month, improving the flow of the upper Santa Fe River in the Worthington Springs area. At the same time, the flow of the lower Santa Fe River near Fort White is at a near-record low for this point in the summer.

"In July, evapotranspiration can be in the neighborhood of two-thirds of normal precipitation, so rivers and groundwater don't get much bang for the buck from normal summer rainfall," Wetherington said. "The water level in a monitoring well near High Springs was below the fifth percentile, which means that 95 percent of the readings since the well was first measured in 1976 have been higher. Anything below the 10th percentile is considered extremely low."

Nonetheless, normal rain patterns and evapotranspiration make for happy state forestry officials. They mean the growth on forest floors and elsewhere is getting moister and becoming less of a threat to quickly ignite.

"We were very happy to see the summer pattern kick in, those regular afternoon rains," said Division of Forestry spokeswoman Ludie Bond. "This pattern did not set up for us very well last summer, but this year we noticed that it began in South Florida, moved up into Central and North Florida and now we need it to move into the Panhandle."

Forestry records show that the drought index in several area counties has dropped considerably.

The index has a range of 800 points, with 800 being the driest conditions and zero representing complete saturation. In Levy County, the index fell from 255 points to 78 points in July, while in Alachua County the index fell from 424 to 295 over the past month, Bond said.

Look for the chance of rain to peak at 70 percent Saturday, decline to 30 percent by Tuesday and continue at 30 percent for most of next week, according to Peterson.

Cloudy skies and rain should keep daytime high temperatures in the upper 80s over the weekend, but expect them to reach the 90s during the week as the rain chances decline.

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