The dry, cool weather conditions that started at the beginning of the month have continued across the southeast for the past two weeks. As a result, the risk for the spread of wildfires has continued to grow (Fig. 1).
At Montgomery, AL, for example, precipitation for the year is well above average; however, since March 1, the rainfall deficit has been 1.35 inches.
It’s been unseasonably chilly too. Montgomery has averaged more than 5 degrees below seasonal values since March 1, with almost every day being below average.
The pattern has been even more dramatic across south Florida. Fort Myers has reported temperatures running 7.4 degrees below average since March 1, along with rainfall deficits of one inch. All but two days this month have seen below average temperature readings.
At Naples, the rainfall deficit since March 1 is 0.78 inches. Each day this month has seen chillier than average temperature readings.
For south Florida, substantial precipitation has been limited since February 14, when about half of this year’s rainfall was reported.
Not surprisingly, at least in Florida, the Keetch-Byram Drought Index (a measure of soil and ground level organic matter dryness) has soared across much of the peninsula. In Lee County, for example, values on a scale of 0 to 800 are now in the upper 500’s. In many central Florida counties and also in Miami-Dade County, values are well up into the upper 600’s (Fig. 2).
These values don’t mean that fires are going to occur. Rather they signal that IF and WHEN they occur, their spread can be dramatic.
The National Weather Service (NWS) conveys this dry weather risk to the public and local emergency management officials via “red flag warnings.” These mean that critical fire weather conditions are either already occurring or are likely to occur shortly. In most locales (although the criteria can be adjusted locally), this means a combination of strong winds (usually 20 miles per hour or greater), low relative humidity (typically 25% or less for at least 3 hours) and/or warm temperatures.
For the next week, at least, precipitation chances for much of the Sunshine state are slim to none.
For the next several months, NOAA’s Climate Prediction Center is forecasting below average rainfall for much of the southeast and all of Florida (Fig. 3). This longer term forecast is due to be updated in about a week.
© 2013 H. Michael Mogil