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- Fort Smith, AR also set both its wettest May and wettest of any month records with a total of 19.85” in May 2015. The previous May record was 13.67” in 1943 and the previous wettest month record was 15.02” in June 1945.
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- May 2015 was a very wet month, with slightly below normal temperatures. Well above normal amounts of precipitation fell at all 4 of the climate sites (Tulsa (+8.86"), Fort Smith (+14.38"), Fayetteville (+6.97"), and McAlester (+17.81")). Temperatures at all 4 climate sites ran slightly below normal for the month, ranging between 0.1°F to 1.4°F below normal.
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- Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for May 2015 were 10” to 25” across most of the HSA. A portion of Osage, Pawnee, Washington (OK), Nowata, Benton, Carroll, northern Washington (AR), and northern Madison Counties were the low spots with *only* 6”-10” of rain this month. The entire area received above normal rainfall, with portions of eastern OK and west central AR getting 300%-600% of the normal May rain. The January 1 – May 31, 2015 total ranges from 15” in and around Osage County to 43” in southeast OK. This is 5” to over 20” above the normal year-to-date rainfall.
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- For the entire state of Oklahoma, the average rainfall for May 2015 was 14.06”, setting the new record for not only the wettest May, but for the wettest of any month on record. The previous record was 10.75” in October 1941. The entire state of Arkansas recorded its second wettest May on record with 10.35”.
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- An analysis by the NWS Hydrometeorological Design Studies Center determined that several areas along and south of I-40 in OK had precipitation totals with less than a 0.1% annual chance (1,000-year event) of occurring (Fig. 11). The highest rainfall total in the HSA this month occurred in Hartshorne 4ESE, OK (Pittsburg County) with 27.70”. The average 0.1% annual occurrence (1,000-year event) is 25.6” (but can range from 19.3”-32.2”; see https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=ok )
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- Widespread, devastating flooding occurred across eastern OK and northwest AR this month. Locations along and south of I-40 received nearly half a year’s worth of rainfall during a 3 week period. 7 fatalities occurred this month in eastern OK and northwest AR due to flooding. Several rounds of severe weather also occurred, with large hail, damaging winds, and a few tornadoes being reported.
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- For the month of May as a whole, the subtropical jet was abnormally strong across northern Mexico, with downstream troughing, resulting in abnormally strong southerly flow across the Southern Plains. Further, there was a broad region of abnormally strong upward motion for May across the Southern Plains and south Texas. Low-level moisture was abnormally high for the last two weeks of May along the corridor of heaviest flooding. The precipitable water anomalies for the month as a whole surprisingly did not show a strong signal. The abnormally low upper-level pressure across the southern California area favors a storm track from over the moisture rich Baja Peninsula Mexico, northeast into the Southern Plains. The anomalous ridge over the eastern U.S. promotes moisture rich flow from the Gulf of Mexico into the southern Plains. The significantly anomalous high pressure over the Gulf of Alaska and anomalous low pressure over southern California, combined, is indicative of a blocking pattern over the west coast/eastern Pacific Ocean, resulting in this persistent pattern of moisture rich flow into the Southern Plains.
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- Just in May alone, there were 36 river floods and 46 crests for 18 river forecast points (out of 33). Of these 46 crests, 8 were major, 27 were moderate, and 11 were minor. 9 floods continued into June, with one additional major flooding crest in June from the rain in May. Flooding occurred at the following locations: Verdigris River Basin: Polecat Creek near Sapulpa; Caney River near Ramona and Collinsville; Bird Creek near Sperry and Owasso Grand-Neosho River Basin: Neosho River near Commerce; Spring River near Quapaw Lower Arkansas River Basin: Illinois River near Watts and Tahlequah; Arkansas River near Muskogee, Van Buren, and Ozark Lock and Dam; Lee Creek near Van Buren; Poteau River near Poteau and Panama Canadian River Basin: Deep Fork River near Beggs Lower Red River Basin: Kiamichi River near Antlers; Red River near Arthur City
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- The Poteau River flooded 3 times in May 2015. The first flood led to moderate flooding near Poteau, but major flooding and one fatality near Panama. The third flood, which lasted 9 days near Poteau and 11 days near Panama, caused major flooding along the river downstream of Wister Lake, as measured by the gages at Poteau and Panama.
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- The Arkansas River at Van Buren exceeded flood stage 4 times in May. The river crested twice above major flood stage during the last, 11-day, flood of the month. Likewise, the Arkansas River at Ozark Lock and Dam exceeded flood stage 3 times in May, with two crests above major flood stage during the last flood, which lasted 12 days, at the end of May/beginning of June.
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- The Red River at Arthur City flooded twice in May, with two crests above major flood stage during the second flood that lasted 17 days.
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- The Kiamichi River near Antlers had three floods. The second flood lasted 8 days and included 4 crests, all above moderate flood stage.
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- The Kiamichi River near Antlers had three floods. The second flood lasted 8 days and included 4 crests, all above moderate flood stage.
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- According to the USACE, all of the major reservoirs in the HSA were operating well into their flood pools as of 5/31/2015, except for Skiatook Lake, which was at 81% of its conservation pool (but up from 53% at the end up April). The following lakes were operating in their flood control pools (percentage of flood pool listed) as of 5/31/15: Sardis Lake 158%, Wister Lake 122%, Hugo Lake 102%, Eufaula Lake 100%, Ft. Gibson Lake 96%, Grand/Pensacola Lake 96%, Hudson Lake 95%, Beaver Lake 94%, Keystone Lake 93%, Kaw Lake 89%, Oologah Lake 81%, Tenkiller Lake 74%, Hulah Lake 58%, Copan Lake 52%, Birch Lake 37%, Heyburn Lake 2%.
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- A couple of lakes set new pool records this month: Wister Lake 508.35’ (prev. record 508.22’) and Hugo Lake 440.11’ (prev. record 440.05’). By the early morning hours of the 12th, Eufaula Lake exceeded the top of its flood control pool and went into surcharge. The lake remained in surcharge until May 31. The highest lake elevation was 599.68’ (128% of flood pool) during the afternoon of the 26th. For reference, the record pool elevation for Eufaula Lake is 599.77’ and the top of the surcharge pool is 600.00’. Eufaula Dam was completed in 1964 and impounds one of the world’s largest man-made lakes (covering 102,500 acres).
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- According to the Drought Monitor from June 2, 2015, the entire drought that had been plaguing the area is gone due to the excessive rainfall this month. According to the Oklahoma Climatological Survey, “It's been … 239 straight weeks of having at least D1 (Moderate) drought somewhere within the state of Oklahoma's borders, all the way back to October 26, 2010, some 1673 days ago.”
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| Spring (March - April - May) 2015 |
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| Outlook |
- The Climate Prediction Center CPC outlook for June 2015 (issued May 31, 2015) indicates an enhanced chance for below normal temperatures across all of eastern OK and northwest AR. This outlook also calls for a slightly enhanced chance for above median rainfall across Choctaw County, with an equal chance for above, near, and below median precipitation elsewhere. This outlook is based on short- and extended-range computer models. The largest signal for below normal temperatures is centered over north TX and OK, where soil moisture currently exceeds the 90th percentile.
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- The CPC outlook for the 3-month period June-July-August 2015, CPC is forecasting an enhanced chance for below normal temperatures and above median precipitation across all of eastern OK and northwest AR (outlook issued May 21, 2015). This outlook is based on both statistical and dynamical forecast tools and considering El Niño conditions.
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- According to CPC, El Niño conditions continue to strengthen and are currently on the border line of weak to moderate strength. These conditions are favored to continue through at least the next few months and likely into the later part of the year. The coupling between the ocean and atmosphere remains strong over the tropical Pacific. However, El Niño impacts are generally most significant during the cold seasons. An El Niño Advisory is in effect.
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