By Gary McManus, Oklahoma Climatological Survey:
More and more color showing up in the U.S. Drought Monitor map, and now we’re up to 45% of the state covered by drought, a rise from 38% last week. We saw moderate drought spread across southern Oklahoma and the non-drought status of “abnormally dry” also spread up into central Oklahoma, as well as northern Oklahoma. So the amount of the state covered by D0 (abnormally dry) to D4 (exceptional drought) rose from 60% to 74%.
What’s driving this? Well, that’s obvious, I reckon, and I’ve been tracking the current dry spell on the Ticker. But since August 18, almost no rain has fallen in the state.
I say “almost no rain” because the statewide average for that period was 0.07″, 1.81″ below normal (or about 4% of normal). That’s the driest August 18-September 5 since 1921. Southwestern Oklahoma has not recorded a drop of moisture during that time.
Southern Oklahoma has had a rough time even farther back, however. While the northern two-thirds of the state was getting decent rains during the first 17 days of August, the southern third was going largely without.
Temperatures have been mostly on the hot side since the rains went away on the 18th, especially on the high temps side. The statewide average temperature from the Mesonet since the August 18 was 80.6 degrees, 1.3 degrees above normal.
The maximum temperatures, however, averaged 93.6 degrees, 2 degrees above normal.
So you take the sudden but extended lack of rainfall coupled with above normal temperatures and you have the makings of a flash drought situation (i.e., rapidly developing drought). Now for those areas across the western third of the state, this is not a flash drought, it’s nearly the culmination of a three year drought episode, which can trace its beginnings back to October 2010. If we look at the 36th month period from August 2010-July 2013, southwestern Oklahoma has had an area averaged total of about 64 inches of rain, which is about 20 inches below normal for that three year period, and ranks as the 4th driest since 1895.
Things still look fairly dry for the next 7 days, especially for southern Oklahoma.
So we once again are dealing with a flash drought situation, which for parts of the state is building upon long-term drought.
Luckily, fall is just around the corner (well, technically, for us weather types it began Sept. 1). With that we’ll start to see more cold fronts, more chances for rain, and less water water stress.