May 2011 Climate and Hydrology Summary

Very heavy rainfall and major flooding affected eastern Oklahoma and northwest Arkansas again during May 2011 after record breaking flooding in April.

Tulsa: May 2011 was the 48th coldest (68.6°F, since 1905) and the 36th driest (3.58"; since 1888) May on record.

Tulsa: Daily records set this month include a record cold mean temperature on 5/2/11 and record warm min temperatures on 5/10/11 and 5/29/11.

Tulsa: The record warm min temperature of 77°F set on 5/19/2011 ties with 5/22/1953 and 5/31/1991 as the warmest low temperature recorded in the month of May.

Fort Smith: May 2011 was the 53rd coldest (69.1°F) and the 4th wettest (11.91") May since records began in 1883. Fort Smith went from the 5th driest March on record to the 3rd wettest April on record to the 4th wettest May on record!

Fort Smith: Daily records set or tied this month include a record warm max temperature on 5/9/11; a record warm min temperature on 5/10/11; a record min temperature on 5/3/11; record cold mean temperatures on 5/2/11 and 5/14/11; and record rainfall on 5/1/11 and 5/12/11.

Fort Smith: The record cold mean temperature of 46°F set on 5/2/2011is the coldest mean temperature recorded in the month of May. The record rainfall of 4.71" set on 5/12/2011 is the highest calendar day rainfall recorded in the month of May (however it is not the greatest 24-hr rainfall).

McAlester: Daily records set or tied this month include record cold max temperatures on 5/2/11 and 5/13/11; a record warm min temperature on 5/10/11; record min temperatures on 5/2/11 and 5/3/11; record warm mean temperatures on 5/9/11 and 5/28/11; and a record cool mean temperature on 5/2/11.

McAlester: The record cold max temperature of 48°F set on 5/2/2011 ties with 5/4/1954 as the coldest max temperature recorded in the month of May. The record min temperature of 34°F set on 5/3/2011 ties with 5/4/1954 as the coldest temperature recorded in the month of May. The record cold mean temperature of 43°F set on 5/2/2011 is the coldest mean temperature recorded in the month of May.

Fayetteville: Daily records set this month include a record max temperature on 5/9/11; record cool max temperatures on 5/2/11, 5/14/11, and 5/15/11; record warm min temperatures on 5/10/11, 5/29/11, and 5/30/11; and a record min temperature on 5/17/11.

Fayetteville: The record cold max temperature of 45°F set on 5/2/2011 is the coldest max temperature recorded in the month of May.

Muskogee: The record min temperature of 34°F set on 5/3/2011 ties with 1981 as the coldest temperature recorded in the month of May.

Rainfall totals for May 2011 ranged from around 2” across the western portion of the forecast area to over 10” across portions of southeast OK and northwest AR. Most of the forecast area east of the Hwy 75 corridor received 5” to over 10” of rain this month, which equates to 125% to near 300% of the normal May rainfall. However, locations along and west of Hwy 75 received 50% to 90% of the normal May rainfall.

A significant tornado and severe weather event occurred on May 22, 2011. Rotating supercells produced large hail (tennis ball to baseball sized hail occurred at the NWS office in Tulsa), wind damage, and tornadoes as they tracked east across eastern Oklahoma and northwest Arkansas (this system was responsible for the EF5 Joplin, MO tornado). An EF2 tornado severely damaged homes in the Fiddlers Bend area on the Illinois River, which only one month prior experienced record flooding. Later in the evening, additional severe thunderstorms developed along outflow boundaries that had been produced by the early storms. Flash flooding occurred across northwest AR where the highest rainfall totals were 1” to 4".

An outflow boundary from the storms on the 22nd lingered across northeast OK and northwest AR on the 23rd. Training of thunderstorms along and north of this boundary led to very heavy rainfall and extreme flash flooding. These storms eventually developed in a MCS. This complex moved through east central OK and west central AR and produced wind damage along its path. Rainfall totals for Nowata, Craig, and Ottawa Counties were 3” to 10” . The mesonet site in Vinita measured 7.48” of rain in only 5 hours! All of this rainfall led to river flooding as well, including major flooding along the Illinois River.

Just 2 days later, on May 24, 2011, a significant and deadly tornado outbreak occurred as a powerful upper-level storm system moved into the central plains. Severe thunderstorms rapidly developed along a dryline in western and central Oklahoma during the afternoon of the 24th and moved east into eastern Oklahoma by early evening. Large tornadoes occurred with the initial supercells in central Oklahoma (including an EF5 tornado in Binger/Guthrie), then continued into eastern Oklahoma and west central Arkansas overnight with several tornadoes reported. Damaging straight-line winds also occurred with some of the stronger bow segments. Several Oklahoma Mesonet sites measured wind speeds in excess of 65 mph. As the storms moved into western AR during the late night hours, a large EF4 tornado struck the Etna and Denning, AR area of southeast Franklin County , killing 2 people (at the time of this writing).

Major flooding occurred this May at the Illinois River near Watts, OK and Tahlequah, OK. Additionally, moderate and minor flooding affected areas along the Baron Fork at Eldon, OK, the Arkansas River at Van Buren, AR; Lee Creek near Van Buren, AR; the Poteau River near Panama, OK; the Neosho River near Commerce; and the Spring River near Quapaw, OK.

With the additional tornadoes that occurred this May, the tornado total for eastern OK and northwest AR through May already exceeds the highest annual number of tornadoes on record for this area.

According to the Drought Monitor from from May 31, 2011, all but the far western portion of the area was drought free this month due to the heavy rain and flooding in May. Abnormally dry (D0) conditions still lingered across far western Osage, Pawnee, Creek, and western Okfuskee Counties. Interestingly, drought conditions go from the highest category of exceptional drought to no drought conditions as one moves from west to east across the state of Oklahoma. While in the east, people are begging for the rain to stop, those living in the west are praying for rain.

According to the Oklahoma Climatological Survey (OCS) for May 2011, northeast OK ranked as the 26th wettest, east central OK ranked as the 32nd wettest, and southeast OK ranked as the 19th wettest May since records began in 1921. For the water year so far (October 1, 2010 - May 31, 2011), northeast OK ranked as the 30th driest, east central OK ranked as the 35th driest, and southeast OK ranked as the 24th driest water year on record.

Spring 2011

Tulsa: Spring 2011 was the 23rd warmest (61.5°F, tied with 1967, 1933, 1930, 1929; since 1905) and the 38th driest (9.99"; since 1888) Spring on record.

Fort Smith: Spring 2011 was the 16th warmest (63.3°F) and the 6th wettest (22.26") Spring since records began in 1883. Fort Smith went from the 5th driest March on record to the 3rd wettest April on record to the 4 wettest May on record!

According to the Oklahoma Climatological Survey (OCS) for May 2011, northeast OK ranked as the 27th wettest, east central OK ranked as the 13th wettest, and southeast OK ranked as the 24th wettest Spring since records began in 1921.

So far this year, there have been 68 confirmed tornadoes (with another two under investigation) across eastern Oklahoma and northwest Arkansas. This area averages around 20 tornadoes per year, and the record annual number of tornadoes for eastern Oklahoma and northwest Arkansas up until this year was 53, in both 1999 and 2008.

Outlook

The Climate Prediction Center CPC outlook for June 2011 (issued May 31, 2011) indicates a slightly enhanced chance for above average temperatures and an equal chance for above, near, and below median precipitation across eastern OK and northwest AR. According to CPC, La Niña conditions continue to weaken and ENSO neutral conditions were observed at the end of May as negative sea surface temperature anomalies continued to warm in parts of the Pacific Ocean. The direct impact of La Niña is expected to be minimal on the U.S. in June as residual atmospheric effects continue for the next few weeks. Current computer models indicate ENSO-neutral conditions by the end June 2011.

For the 3-month period Jun-Jul-Aug 2011, CPC is forecasting an equal chance for above, near, and below average temperatures and equal chances for above, near, and below median precipitation across eastern OK and northwest AR (outlook issued May 19, 2011).

According to CPC, La Niña conditions continue to weaken and ENSO neutral conditions were observed at the end of May as negative sea surface temperature anomalies continued to warm in parts of the Pacific Ocean. The direct impact of La Niña is expected to be minimal on the U.S. in June as residual atmospheric effects continue for the next few weeks. Current computer models indicate ENSO-neutral conditions by the end June 2011.