September 2012 Climate and Hydrology Summary

September & Water Year 2012

Tulsa: September 2012 was the 27th warmest (75.9°F, tied with 1920; since 1905) and the 33rd driest (1.78"; since 1888) September on record.

Tulsa had 5 days at or above 100°F in September 2012, ranking as the 11th most number of days at or above 100° for September, tied with 1913, 1978, and 1998, since records began in 1905. For the entire warm season of 2012, Tulsa recorded 38 days at or above 100°F, which ranks as the 10th highest number of days, tied with 1956 and 1978, in a single year since records began.

Fort Smith: September 2012 was the 19th warmest (77.3°F; since 1882) and the 35th driest (1.79"; since 1882) September on record.

Fort Smith had 6 days at or above 100°F in September 2012, ranking as the 3rd most number of days at or above 100° for September, tied with 1925 and 2000, since records began in 1882. For the entire warm season of 2012, Fort Smith recorded 42 days at or above 100°F, which ranks as the 5th highest number of days in a single year since records began.

Fayetteville: Daily records set or tied this month include a record warm mean temperature.

Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for September 2012 ranged from around 1” in a few spots of northeast OK to around 8” in isolated areas of eastern OK and west central AR. Most of the HSA received 1.5” to 4” of rain this month. Western Okfuskee and most of Franklin Counties received above normal rainfall this September, while the remainder of the area only saw 25%-75% of the normal rainfall for September. Portions of Osage and Washington Counties in northeast OK were very dry, only getting 10%-25% of the normal rainfall this month.

According to the Drought Monitor from September 25, 2012, all of eastern OK and northwest AR was in severe to Exceptional drought. Severe (D2) drought was present across Choctaw and western Pushmataha Counties. Exceptional (D4) drought was occurring over portions of Osage and northern Pawnee Counties in eastern OK and eastern Benton, eastern Washington, Carroll, and Madison Counties in northwest AR. Extreme drought (D3) conditions existed across the remainder of the area.

Water Year 2012 (October 1, 2011 - September 30, 2012)

Tulsa: Water Year 2012 was the RECORD warmest (64.7°F; since 1905; previous record was 63.6°F in 1925, 1932) and the 31st driest (32.72"; since 1888) Water Year on record.

Fort Smith: Water Year 2012 was the RECORD warmest (66.4°F; since 1882; previous record was 64.0°F in 2011) and the 58th wettest (42.60"; since 1882) Water Year on record.

There was generally a northwest to southeast rainfall gradient across eastern OK and northwest AR for Water Year 2012, with amounts ranging from around 25” to around 60”. For most of the HSA, these totals represented 10%-50% below normal rainfall for the water year. The largest rainfall deficits occurred over northeast OK and northwest AR, where the water year rainfall total was 8” to around 16” below normal.

Outlook

The Climate Prediction Center CPC outlook for October 2012 (issued September 30, 2012) indicates a slightly enhanced chance for below normal temperatures and equal chances for above, near, and below median precipitation across all of eastern OK and northwest AR. The temperature outlook is based on consistent signatures from the various extended range dynamical computer models, which set up a blocking pattern in the Gulf of Alaska with a downstream trough over North America. However, there conflicting signals in the computer models regarding the rainfall pattern

For the 3-month period Oct-Nov-Dec 2012, CPC CPC is forecasting a slightly enhanced chance for above average temperatures across northeast OK and northwest AR and equal chances for above, near, and below normal temperatures elsewhere. This outlook also calls for equal chances of above, near, and below median precipitation across the region (outlook issued September 20, 2012). This outlook is based on dynamic computer model output and long term trends.

According to CPC, ENSO neutral conditions continued through September, but El Niño conditions should develop this fall. The latest computer models are indicating a weaker El Nino in place by the end of the year compared to model runs over the last 2 months. Therefore, it seems unlikely that strong El Niño conditions will occur. An El Niño Watch remains in effect.