September 2015 Climate and Hydrology Summary

Tulsa: September 2015 was the 21st warmest (76.4°F, tied 2013; since 1905) and the 58th driest (2.93"; since 1888) September on record.

Fort Smith: September 2015 was the 29th warmest (76.7°F; since 1882) and the 55th driest (2.57"; since 1882) September on record.

Fayetteville: September 2015 was the 26th warmest (70.4°F, tied 1953; since 1949) and the 13th driest (1.75"; since 1949) September on record.

Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for September 2015 ranged from around 1” to around 8”. Most of eastern OK and northwest AR received 1.5”-3” of rain this September. This corresponds to 25%-75% of the normal September rain across the majority of eastern OK and northwest AR. The exceptions were in northern Creek, southern McIntosh, southern Pittsburg, and southern Latimer Counties, where localized heavy rain yielded 110% to near 250% of the normal September rainfall.

With the exception of a few isolated locations, eastern OK and northwest AR saw above normal temperatures and below normal rainfall during September 2015.

According to the Drought Monitor from September 29, 2015, Severe (D2) drought remained across Choctaw and southern Pushmataha Counties in southeast OK. Moderate (D1) drought was occurring over most of Pushmataha County. Abnormally dry (D0), but not in drought, conditions were located across far northern Pushmataha Co. and the southern portion Le Flore Co. in southeast OK, and the southeast half of Sebastian Co. in west central AR.

According to the Oklahoma Climatological Survey, September 2015 was the 23rd driest for northeast Oklahoma, the 35th driest for east central Oklahoma, and the 31st driest for southeast Oklahoma. Records go back to 1921. For the 60-day period August 2-September 30, 2015, northeast Oklahoma ranked as the 47th wettest, east central Oklahoma was the 42nd driest, and southeast Oklahoma was the 19th driest period. For Water Year 2015 (October 1, 2014-September 30, 2015), northeast Oklahoma ranked as the 16th wettest, east central Oklahoma was the 2nd wettest, and southeast Oklahoma was the 16th wettest Water Year.

Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for Water Year 2015 ranged from around 40” to 80” across all of eastern OK and northwest AR, expect for Osage and Pawnee Counties where totals were 30”-50”. The highest rainfall of around 70” occurred primarily in east central OK. According the OCS, Water Year 2015 was the 2nd wettest on record (since 1921) for east central OK, with 66.57” (20.43” above normal; record 69.78” in 1944-45). These high rainfall totals equate to 110%-200% of the normal Water Year rain across the majority of eastern OK and northwest AR. The exceptions were in Osage, Pawnee, Choctaw, Pushmataha, and Mayes Counties, where rainfall ranged from near normal to 25% below normal for the water year.

In Tulsa, OK, Water Year 2014-15 ranked as the 42nd warmest Water Year (61.0°F, tied 1952-53, 1945-46, 1936-37; since records began in 1906-07) and the 10th wettest Water Year (53.37”; since records began in 1893-94).

Fort Smith, AR had the 53rd warmest Water Year (61.8°F, tied 1994-95, 1986-87, 1945-46, 1944-45; since records began in 1882-83) and the 3rd wettest Water Year (63.96”; since records began in 1882-83). The wettest Water Year on record in Fort Smith is 79.11” in 1944-45, followed by 64.94” in 2007-08.

Fayetteville, AR had the 17th coldest (56.7°F, tied 1996-97, 1993-94, 1976-77) and the 10th wettest (56.81”) Water Year since records began in 1949-50.

Outlook

The Climate Prediction Center (CPC) outlook October 2015 (issued September 30, 2015) indicates a slightly enhanced chance for above median precipitation across far southeast OK, and equal chances for above, near, and below median precipitation elsewhere. The outlook also calls for an equal chance of above, near, or below normal temperatures across all of eastern OK and northwest AR. This outlook is based on both short- and extended range weather forecasts. The precipitation outlook also considers El Niño influences.

For the 3-month period October-November-December 2015, CPC is forecasting an equal chance for above, near, and below normal temperatures and an enhanced chance for above median precipitation across all of eastern OK and northwest AR (outlook issued September 17, 2015). This outlook is based primarily on both statistical and dynamical forecast tools, as well as typical impacts resulting from El Niño conditions.

According to CPC, weekly El Niño conditions are currently of strong strength. The ongoing El Niño is expected to peak in strength in the late autumn or early winter. There are indications that this event could peak as a very strong (sometimes referred to as a “super”) El Niño, with sea surface temperature anomalies greater than +2.0°C. There is a 95% chance for El Niño to continue through the upcoming winter and it is expected to persist through spring 2016.El Niño impacts are generally most significant in the Southern Plains during the cold season. An El Niño Advisory is in effect.