April 2011 Climate and Hydrology Summary

Very heavy rainfall and catastrophic flooding affected eastern Oklahoma and northwest Arkansas during the last half of April 2011 after many months of below normal rainfall and expanding drought conditions.

Tulsa: April 2011 was 23rd warmest (63.4°F, since 1905) and the 31st wettet (5.41"; since 1888) April on record.

Tulsa: Daily records set this month include record warm max temperatures and record warm mean temperatur es on 4/3/11, 4/8/2011, and 4/9/11; a record warm min temperatur e on 4/9/2011; and record rainfall on 4/24/11.

Fort Smith: April 2011 was the 20th warmest (64.5°F, tied with 2010) and the 3rd wettest (9.55") April since records began in 1883. Fort Smith went from the 5th driest March on record to the 3rd wettest April on record!

Fort Smith: Daily records set this month include record warm max temperatures on 4/3/11, 4/8/11, and 4/9/11 and record warm mean temperatur es on 4/9/11 and 4/10/11.

McAlester: Daily records set this month include a record cool max temperature on 4/27/11; a record warm min temperature on 4/9/11; record min temperatures on 4/4/11 and 4/5/11; record warm mean temperatur es on 4/8/11 and 4/9/11; a record cool mean temperature on 4/27/11; and record rainfall on 4/14/11.

Fayetteville: Daily records set this month include record warm max temperatures on 4/3/11, 4/8/11, 4/9/11, and 4/10/11, and a record warm min temperature on 4/3/11.

Rainfall totals for April 2011 ranged from around 1.5” in western Pawnee and western Osage Counties to over 15” in portions of Adair County in OK and Benton, Washington, Carroll, and Madison Counties in AR. The highest values of 10” to over 15” correspond to 300% to 500% of the normal April rainfall. A large portion of the area received 5” to over 10” of rain this month, which equates to 150% to over 300% of the normal April rainfall. While most of eastern OK and northwest AR received near to above normal rainfall this month, portions of Pawnee and Osage Counties received only 25% to 75% of the normal April rainfall

Most of the rainfall this month fell between April 21-27, which lead to extensive flash flooding and record river flooding. Several locations across northwest Arkansas and east central Oklahoma measured over 5" of rain in one day, including: Haskell, OK 6.77" (4/24 OK mesonet), Okmulgee, OK 6.76" (4/24 OK mesonet), Prairie Grove, AR 6.07" (4/25, COOP), Hectorville, OK 5.74" (4/24, OK mesonet), Porter, OK 5.51" (4/24, OK mesonet), Muskogee Davis Field, OK 5.19" (4/24, ASOS), and Hindsville, AR 10E 5.10" (4/24, COOP). In addition, many locations in this area received 3+ inches of rainfall for 3 days in a row (rain that fell on April 23-25). Click here for more information about this event.

The April 21-27 widespread flash flooding unfortunately led to 5 fatalities in northwest Arkansas when 3 vehicles were swept away or stalled in high water. Dozens of water rescues occurred during the multi-day event across east central OK and northwest AR. So many roads were flooded that emergency management officials in Adair County, OK and Washington County, AR issued emergency requests discouraging travel throughout and into the counties.

New record stages were set at the Illinois River near Watts, OK and the Baron Fork at Eldon, OK. Major flooding occurred along the Kings River near Berryville, AR and the Illinois River near Tahlequah, OK. Additionally, moderate and minor flooding affected areas along the Arkansas River at Van Buren, AR; Lee Creek near Van Buren, AR; the Poteau River near Poteau, OK and Panama, OK; Flint Creek near Kansas, OK; the Deep Fork River near Beggs, OK; the Neosho River near Commerce; the Spring River near Quapaw, OK, and Polecat Creek near Sapulpa, OK.

April 2011 set the record for the most tornadoes in a month in the NWS Tulsa forecast area. There were 42 tornadoes in April, all of which occurred in a 12-day period. The previous record was 39 tornadoes in May 2010. April 14, 2011 also broke the calendar day record for tornadoes, with 25 confirmed tornadoes. The previous forecast area record was 22 tornadoes on May 10, 2010.

According to the Drought Monitor from April 26, 2011, significant improvements have occurred this month due to the heavy rain and flooding event during the last couple of weeks in April. Severe (D2) drought conditions were still affecting Choctaw and southern Pushmataha Counties, where extreme (D3) conditions existed last month and the heaviest rainfall this month remained just to the north of this area. Moderate (D1) drought conditions remained over Pushmataha, Pawnee, and portions of Creek and Okfuskee Counties. Abnormally dry (D0) conditions were affecting all or portions of Osage, Tulsa, Creek, Okmulgee, Okfuskee, Pittsburg, Haskell, Latimer, Le Flore, Sequoyah, Crawford, Sebastian, and Franklin Counties.

According to the Oklahoma Climatological Survey (OCS) for April2011, northeast OK ranked as the 20th wettest, east central OK ranked as the 5th wettest, and southeast OK ranked as the 11th wettest April since records began in 1921. For the water year so far (October 1, 2010 - April 30, 2011), northeast OK ranked as the 18th driest, east central OK ranked as the 27th driest, and southeast OK ranked as the 12th driest water year on record. Southeast OK went from the driest March on record to the 11th wettest April on record, and east central OK went from the 6th driest March to the 5th wettest April!

Outlook

The Climate Prediction Center (CPC) outlook for May 2011 (issued April 30, 2011) indicates a slightly enhanced chance for above average temperatures south of a Tulsa to Fort Smith line and an equal chance for above, near, and below average temperatures elsewhere. The May 2011 outlook also calls for a slightly enhanced chance for below median precipitation northwest of I-44, and a slightly enhanced chance for above median precipitation southeast of a McAlester to Bentonville line. Equal chances for above, near, and below median precipitation are projected in between these areas.

For the 3-month period May-Jun-Jul 2011, CPC is forecasting an equal chance for above, near, and below average temperatures across eastern OK and northwest AR. This outlook also calls for a slightly enhanced chance for above median precipitation across far northeast OK and far northwest AR, with an equal chance for above, near, and below median precipitation elsewhere (outlook issued April 21, 2011).

According to CPC, the direct impact of La Niña is expected to be minimal on the U.S. in May. Current computer models indicate that La Niña conditions will continue to diminish through the remainder of spring 2011, with ENSO-neutral conditions likely by June 2011. A La Niña Advisory continues, meaning La Niña conditions have been observed and are expected to continue.