Historic rains during May virtually eliminated the drought that had plagued Oklahoma for much of the past five years. The storms that brought that relief came with a cost, however, spawning more than 60 tornadoes, catastrophic flooding, and the highest price of all, 11 fatalities. The rains began during the first week of May and by the end of the month the state had seen the most rainfall on record for any month in its history. The statewide average, as measured by the Oklahoma Mesonet, finished at 14.40 inches, 9.58 inches above normal. That mark claims the top spot as the wettest month ever for Oklahoma, eclipsing October 1941’s tally of 10.75 inches. Those records date back to 1895. While the entire state saw much above normal rainfall, the southern half of the state bore the brunt of the excessive moisture with widespread amounts of 15-25 inches. Many individual locations shattered marks for their wettest month on record. The Norman Mesonet site recorded a total of 23.4 inches, obliterating their previous high monthly mark of 16.5 inches from October 1983. Oklahoma City claimed the same prize with 19.48 inches, besting June 1989’s 14.66 inches. That Oklahoma City total was 14.83 inches above normal. Of the Oklahoma Mesonet sites, Lane led the way with 28.17 inches. Twenty-two Mesonet stations recorded at least 20 inches of rain, and 54 recorded at least 15 inches. Buffalo had the lowest total with 5.91 inches, but even that total was more than 2 inches above normal. Climatological spring (March-May) ended as the second wettest in state history with a statewide average of 21.62 inches, 10.5 inches above normal. The first five months of the year were the third wettest on record with an average of 24 inches, 9.49 inches above normal. That's compared to 2014's January-May total of 7.39 inches, the fourth driest on record.
With all the rain and associated cloudiness obscuring the sun for much of the month, it's not a surprise that May was on the cool side. The statewide average of 65.6 degrees was 2.6 degrees below normal, the 15th coolest on record. The Mesonet recorded temperatures of 90 degrees only five times during May, with the highest being 91 degrees at Beaver and Hooker on the third and Altus on the 18th. The average spring temperature was near normal at 59.4 degrees. The January-May temperature remained below normal by 0.7 degrees with a statewide average of 51 degrees, although that only ranks as the 58th coolest on record.
Multiple bouts of flooding occurred in nearly every region of the state. According to the Oklahoma Department of Emergency Management, 10 residents died in May as a result of flooding. A Claremore firefighter attempting a water rescue was one of those killed. In addition, one person died in Bryan County as a result of a tornado. At least 49 injuries were reported due to storms during May as well. After a record low year with 16 tornadoes during all of 2014, May 2015 saw at least 60 confirmed tornadoes by month's end according to National Weather Service (NWS) numbers, with that number expected to rise as more possible twisters are investigated.
The extraordinary rains blasted the 2010-15 drought from existence, with the only vestiges remaining across the far western Panhandle. The U.S. Drought Monitor showed 59 percent of the state in drought at the beginning of the month, but that area had shrunk to only 3 percent by the end of May. That's the lowest percentage of drought indicated for Oklahoma by the Drought Monitor since Oct. 26, 2010, when the drought was in its beginning stages. Dwindling reservoirs and dry farm ponds swelled with excess water as the torrential rains continued to add to their coffers. Lake Tom Steed in southwest Oklahoma, the main water supply for Altus, rose 18 feet during the month. Lake Texoma had risen to the highest level in its history on May 29. Several lakes still had some catching up to do, however. The reservoirs at Canton, Foss and Skiatook remained well below normal despite the generous moisture. Canton Lake was 9 feet below normal, or 39 percent of capacity, at the end of May.
Short-term forecasts call for a relatively dry first week of June. The NWS' Climate Prediction Center (CPC) show increased odds for above normal precipitation across far western and southern Oklahoma for June and across the entire state during the June-August period. The CPC's temperature outlooks for both periods indicate increased odds of below normal temperatures. CPC's Monthly Drought Outlook for June shows no signs of a return to drought during that month.