On May 31, 2013, a prominent mid-to-upper level trough and closed mid-level low pressure area moved east-northeastward, with a lead upper low pivoting over the Dakotas and Upper Midwest region.
A moderately strong polar jet moved east-northeastward over the southern Rocky Mountains to the southern Great Plains.
With a broad influence of moderately strong cyclonic flow aloft, the air mass was expected to become unstable across much of the southern Great Plains, through the Upper Midwest and Mississippi Valley, by the afternoon.

Dewpoint values had ranged from the upper 60s °F (20 °C) to the lower 70s °F (20–22 °C), with temperatures in the low to mid-80s °F (27–30 °C), and CAPE (a meteorological concept used to predict the force and power of potential storms and tornadoes) predicting referring to values ranging from 3500 to 5000 J/kg.
Deep layer wind shear speeds of 45–55 kn (52–63 mph) would enhance storm organization and intensity.
These factors, along with CAPE values in excess of 4000 J/kg and an embedded speed maxima rotating around the southern periphery of the low, made the threat of significant severe thunderstorms increasingly likely.
These ingredients were present ahead of a cold front extending from the low from the eastern Dakotas southwestward to western Oklahoma, and ahead of a dry line extending from western Oklahoma southward into western north and west-central Texas.
The most intense severe weather activity was expected across the southern Great Plains, specifically central and eastern Oklahoma, during the afternoon hours.
As such, the Storm Prediction Center (SPC) issued a moderate risk of severe thunderstorms during the early morning hours of May 31 from southeastern Missouri to southwestern Oklahoma.
The degree of wind shear, moisture and instability within the warm sector favored the development of discrete supercells.
Very large hail and tornadoes were expected with the supercells, with the possibility of a few strong to violent tornadoes.

At 3:30 p.m. Central Daylight Time (CDT) early that afternoon, the SPC issued a Particularly Dangerous Situation Tornado Watch from southwestern through northeastern Oklahoma, surrounding the Interstate 44 corridor.
On May 31, 2013, a prominent mid-to-upper level trough and closed mid-level low pressure area moved east-northeastward, with a lead upper low pivoting over the Dakotas and Upper Midwest region. A moderately strong polar jet moved east-northeastward over the southern Rocky Mountains to the southern Great Plains. With a broad influence of moderately strong cyclonic flow aloft, the air mass was expected to become unstable across much of the southern Great Plains, through the Upper Midwest and Mississippi Valley, by the afternoon.
Dewpoint values had ranged from the upper 60s °F (20 °C) to the lower 70s °F (20–22 °C), with temperatures in the low to mid-80s °F (27–30 °C), and CAPE (a meteorological concept used to predict the force and power of potential storms and tornadoes) predicting referring to values ranging from 3500 to 5000 J/kg. Deep layer wind shear speeds of 45–55 kn (52–63 mph) would enhance storm organization and intensity. These factors, along with CAPE values in excess of 4000 J/kg and an embedded speed maxima rotating around the southern periphery of the low, made the threat of significant severe thunderstorms increasingly likely. These ingredients were present ahead of a cold front extending from the low from the eastern Dakotas southwestward to western Oklahoma, and ahead of a dry line extending from western Oklahoma southward into western north and west-central Texas. The most intense severe weather activity was expected across the southern Great Plains, specifically central and eastern Oklahoma, during the afternoon hours. As such, the Storm Prediction Center (SPC) issued a moderate risk of severe thunderstorms during the early morning hours of May 31 from southeastern Missouri to southwestern Oklahoma. The degree of wind shear, moisture and instability within the warm sector favored the development of discrete supercells. Very large hail and tornadoes were expected with the supercells, with the possibility of a few strong to violent tornadoes.
At 3:30 p.m. Central Daylight Time (CDT) early that afternoon, the SPC issued a Particularly Dangerous Situation Tornado Watch from southwestern through northeastern Oklahoma, surrounding the Interstate 44 corridor.
2013 El Reno tornado