May 2018 Climate and Hydrology Summary

Tulsa: May 2018 was the Record warmest (76.7°F, previous record 75.3°F in 1962; since 1905) and the 27th driest (2.89"; since 1888) May on record.

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

Fort Smith: May 2018 was the Record warmest (76.8°F, previous record 75.8°F in 2012, 1962; since 1883) and the 14th driest (2.00"; since 1883) May on record.

The record warm minimum temperature on May 31, 2018 in Fort Smith tied May 22, 1953 and May 31, 1918 as the warmest minimum temperature recorded for the entire month of May.

Fayetteville: May 2018 was the Record warmest (72.0°F, previous record 71.8°F in 1962; since 1950) and the 31st wettest (5.82"; since 1950) May on record.

Fayetteville: Daily records set or tied this month include record warm maximum temperatures.

May 2018 was the warmest May on record for the State of Oklahoma with an average temperature of 74.9°F, breaking the previous record of 74.0°F in 1962. This follows the second coldest April on record for Oklahoma.

May 2018 was the warmest May on record for the State of Arkansas with an average temperature of 74.8°F, breaking the previous record of 74.2°F in 1896.

May 2018 was the warmest May on record for the CONUS with an average temperature of 65.4°F, breaking the previous record of 64.7°F in 1934.

Oklahoma set a record for the latest first tornado of the year. The first tornado in Oklahoma in 2018 occurred on May 1 near Buffalo, breaking the previous record of April 26, 1962 as the latest first date of a tornado in the state.

3 tornadoes occurred in May 2018. An EF-1 tornado developed within a bow echo segment of a line of thunderstorms near Peter Pender in Franklin County Arkansas on May 3 and two EF-0 tornadoes occurred in Osage County on May 19. For more information on these events: https://arcg.is/1f5Ob4

Using the radar-derived estimated observed precipitation from the RFCs, rainfall totals for May 2018 ranged from around 2” to isolated amounts around 8” across eastern OK and northwest AR. This corresponds to 25-90% of the normal May rainfall for most of eastern OK and northwest AR. However, portions of McIntosh, Muskogee, Wagoner, Cherokee and northern Osage Counties, as well as small portions of other counties, received near normal to near 150% of the normal May rainfall.

Several rounds of showers and thunderstorms, some of which were severe, affected eastern OK and northwest AR from the evening of the 2nd through the late afternoon of the 3rd. The first line of storms moved into the area from the west during the evening of the 2nd and continued to progress eastward through the overnight hours. This activity moved out of western AR during the early morning hours of the 3rd, while additional storms moved into eastern OK from the west. By mid-morning of the 3rd, the 3rd line of storms pushed into eastern OK. By afternoon, this line moved into western AR. Part of the line began to accelerate forward as a bow echo as the storms moved into west central Arkansas. An EF-1 tornado developed within this bow echo segment near Peter Pender in Franklin County Arkansas. All of this activity came to an end by late afternoon. The three rounds of storms brought 0.75” to 3.5” to most of eastern OK and northwest AR, with some isolated totals to around 4”. However, far northwest Osage County only received 0.10”-0.30” of rain. This rainfall resulted in some flooding of roadways, as well as minor flooding along the Illinois River.

A supercell impacted far northwest Osage County during the evening of the 14th, bringing a small area of 2”-4” of rain. Additional storms moved south out of KS during the overnight hours, developing into a southeastward propagating MCS. The MCS weakened as it moved into western AR during the morning hours of the 15th. Convection also occurred over southeast OK during the early morning hours in response to an MCV (mesoscale convective vortex) from earlier storms in southwest OK. Rainfall totals generally ranged from 0.25” to 2”, with isolated pockets of 2”-3”.

Another MCV moved across eastern OK and northwest AR on the 16th, centered along an Okmulgee to Muskogee to Sallisaw path. Showers and thunderstorms rapidly developed during the late morning hours along and ahead of this feature and continued through the afternoon as the MCV shifted east. Some minor flooding was reported in the Muskogee and Bentonville areas. Additional thunderstorms affected Osage, Pawnee, Washington, and northern Tulsa Counties during the afternoon as well. All of the rain dissipated by mid evening. Rainfall totals were generally 0.25”-2”, with localized totals of 2”-3”.

Scattered showers and thunderstorms affected northeast OK, primarily along and north of I-44, during the morning hours of the 19th. This activity dissipated by around noon. Additional showers and thunderstorms developed along a cold front during the early afternoon across north central OK, which again moved across northeast OK affecting locations along and north of a Pawnee to Miami line. Damaging straight-line winds of 80-90 mph occurred near Fairfax in Osage County and Ralston in Pawnee County, and two brief EF-0 tornadoes occurred in Osage County. Shortly after midnight on the 20th, a third round of more widespread shower and thunderstorm activity in central OK moved east into eastern OK. These storms moved quickly northeast, exiting the region during the morning hours. All of this rainfall resulted in rainfall totals of 0.25” to 2” for most of the affected area, with higher totals of 2” to 4” falling over portions of Osage, Washington (OK), Nowata, and Craig Counties. These higher totals also occurred across the Neosho River basin in southeast KS, resulting in the Neosho River rising to about half a foot below flood stage.

According to the Drought Monitor from May 29, 2018, Severe (D2) Drought conditions were impacting western Osage and far northwest Pawnee Counties in eastern OK. Moderate (D1) drought conditions were present across portions of Osage, Pawnee, and eastern Kay Counties in eastern OK. Abnormally Dry (D0) but not in drought conditions encompassed portions of Pawnee, Creek, Osage, Washington, Tulsa, Rogers, Nowata, Ottawa, Delaware, Mayes, Craig, Latimer, Le Flore, and Choctaw Counties in eastern Oklahoma and far western Sebastian County in west central Arkansas.

According to the Oklahoma Climatological Survey, the last 30 days ending on May 31, 2018 was the 41st driest for northeast Oklahoma, the 46th drist for east central Oklahoma, and the 15th driest for southeast Oklahoma. Records go back to 1921. For the Year-to-Date period Jan. 1-May 31, 2018, northeast Oklahoma ranked as the 31st driest, east central Oklahoma was the 16th wettest, and southeast Oklahoma was the 25th wettest period. For the last 365 days (June 1, 2017-May 31, 2018), northeast Oklahoma was the 34th driest, east central Oklahoma was the 30th wettest, and southeast Oklahoma was the 27th wettest.

Spring (March-April-May) 2018

Tulsa: Spring 2018 was the 33rd warmest (61.3°F, tied 2001, 1972, 1908; since 1905) and the 19th driest (7.96"; since 1888) Spring on record.

Fort Smith: Spring 2018 was the 28th warmest (62.8°F, tied 2016; since 1883) and the 23rd driest (8.70"; since 1883) Spring on record.

Fayetteville: Spring 2018 was the 21st warmest (57.8°F, tied 2000, 1990; since 1950) and the 30th driest (12.76"; since 1950) Spring on record.