September 2010 Climate and Hydrology Summary

September 2010

Tulsa: September 2010 was 37th warmest (75.1°F, since 1905) and the 53rd driest (2.85", since 1888) September on record.

Fort Smith: September 2010 was the 34th warmest (76.0°F) and 21st wettest (5.79") September since records began in 1882.

Daily temperature records were set this September in McAlester and Fayetteville, with a daily rainfall record also set in McAlester.

Number of days with temperatures >=100°F for the warm season (April - September): Tulsa 17, Fort Smith 22, Fayetteville 4, Bartlesville 12, McAlester 18 (tied as 11th greatest number of days on record)

The big weather maker this month was the remnants of Tropical Storm Hermine, which brought copious rainfall and flash flooding to the region September 7-9. Widespread rainfall totals of over 10" occurred across east central Oklahoma and west central Arkansas, with the highest measurement of 13.42" in Whitefield, OK. An event summary, including rainfall totals from across the region, can be found here.

Hermine helped to improve the drought conditions across east central OK and northwest AR. According to the Drought Monitor, portions of Pushmataha, Latimer, Le Flore, and Sebastian Counties were still experiencing abnormally dry to moderate drought conditions by the end of September. Abnormally dry conditions had also developed across Pawnee County this month.

According to the Oklahoma Climatological Survey (OCS), east central OK ranked as the 8th wettest September, northeast OK ranked as the 27th wettest, and southeast OK ranked as the 22nd wettest since records began in 1921. Interestingly, east central OK went from the 5th driest August to the 8th wettest September due to Hermine.

The Arkansas River near Van Buren briefly exceeded flood stage due to Hermine this month.

The end of September 2010 marks the end of Water Year 2010 (October 1, 2009 - September 30, 2010). From CoCoRaHS, "hydrologists and climatologists ofter use the "Water Year" calendar for tracking water resources. Then comes spring with its accompanying snow melt and high runoff from mountainous regions and higher latitudes. The summer months bring high evaporation rates. Precipitation (much from thunderstorms) becomes much more localized. Soil moisture may be gradually depleted during summer as vegetation uses large volumes of water. Streams run slower and clearer.” According to OCS, northeast OK ranked as the 24th wettest, east central OK ranked as the 32nd wettest, and southeast OK ranked as the 43rd driest Water Year since records began in 1921.

Rainfall totals for Water Year 2010 ranged from 35" to 60" across eastern OK and northwest AR. This corresponds to +/- 25% of the normal rainfall for this time period. The only exception was across a few areas of northern Osage and northern Washington Counties in northeast OK, where between 125% and 150% of normal Water Year rainfall occurred.

Outlook

The Climate Prediction Center (CPC) outlook for October 2010 (issued September 30, 2010) indicates an enhanced chance for above average temperatures and an enhanced chance for below median precipitation. For the 3-month period Oct-Nov-Dec 2010, CPC is forecasting an enhanced chance for above average temperatures and an enhanced chance for below median precipitation (outlook issued September 16, 2010). The enhanced chance for above average temperatures and below median precipitation for the 1- and 3-month outlooks are consistent with a La Niña impacts across the southern Plains.

Sea-surface temperatures in the equatorial Pacific continued to decrease this month. According to CPC, La Niña conditions strengthened during August and early September. These conditions are expected to strengthen and at least last through winter 2010-11, though are very likely to continue into the spring. A La Niña Advisory remains in effect, meaning that La Niña conditions are observed and expected to continue.