Hot and dry is not just a cliche, it's a horrible reality in the summer of 2011, said Gary McManus of the Oklahoma Climatological Survey.
The ongoing drought throughout the Southern Plains is contributing to the heat wave, he said.
“Extreme heat and drought go hand in hand, as Oklahoma has seen in its past,” McManus explained. “The extreme droughts of the 1930s and 1950s produced many of Oklahoma's heat records.”
And it's true that even some summers in the last 15 years, such as 1996, 2000 or 2006, have produced a few really hot days. But this heat wave is different, and McManus talked Tuesday about the factors having contributed to a summer in which the Oklahoma Mesonet weather network has had a station reach at least 100 degrees 54 days so far this year.
The first 100-degree day was recorded April 3 at Mesonet sites in Altus, Mangum, Hollis, Retrop and Butler.
With the drought comes a lack of green vegetation and soil moisture. That leads to a majority of the sun's energy going toward heating the earth's surface instead of evaporating soil moisture or being absorbed by plants. During the summer, the sun's intensity is at its greatest and there is plenty of energy to be used for that heating.
The heat then depletes more soil moisture and withers more plants, so the heat and drought then begin to feed off each other in that destructive feedback loop.
How did it begin?
The drought began last fall. Since Oct. 1, 2010, the statewide average rainfall total is more than 12 inches below normal, the second-driest such period on record dating to 1921. For the western half of the state, it has been the driest on record.
A strong La Nina formed last summer, cooling equatorial Pacific waters and helping push the jet stream to the north through the spring, giving the drought a six-month head start. The La Nina has since faded, but it occurred just in time for the beginning of the normal summer heat and dryness.
The heat began in earnest during June when a ridge of high pressure camped over the Southern Plains. June ended as the second-warmest across the state since 1895. That was behind only 1953, and the heat has persisted since then.
“Thanks to the drought, we continue to face a summer on steroids,” McManus said. “The extreme heat will continue unabated until significant rains occur or fall arrives, whichever comes first.”