Day 1 Convective Outlook
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Summary
Severe thunderstorms capable of producing large hail and damaging wind gusts are possible this afternoon and evening across parts of Oklahoma, eastern Colorado, and western Kansas. Isolated severe wind gusts and hail may also occur across the southern Plains and from the Ozarks into the Ohio Valley.
Product Text
000 ACUS01 KWNS 200521 SWODY1 SPC AC 200519 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1219 AM CDT Sun Sep 20 2026 Valid 201200Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF OKLAHOMA AND FROM EASTERN COLORADO INTO FAR WESTERN KANSAS... ...SUMMARY... Thunderstorms with severe wind gusts and large hail will be possible this afternoon and evening across parts of Oklahoma and from eastern Colorado into far western Kansas. Isolated severe gusts and hail will also be possible in parts of the southern Plains, and from the Ozarks eastward into the Ohio Valley. ...Southern Plains... At mid-levels, southwesterly flow will be in place today over much of the central U.S. A shortwave trough is forecast to move into Kansas and Oklahoma this afternoon. At the surface, a low will deepen over southwest Oklahoma today, as a cold front advances southward into central Oklahoma. Near the front, surface dewpoints will be in the mid to upper 60s F, which will allow moderate instability to develop by afternoon. MLCAPE is forecast to peak in the 2000 to 3000 J/kg range in much of central and eastern Oklahoma. As surface temperatures warm and low-level convergence increases, scattered thunderstorms are expected to develop in the afternoon, with storms moving from the Low Rolling Plains and Red River Valley northeastward into central and eastern Oklahoma. RAP forecast soundings at 00Z near the instability axis in central Oklahoma have MLCAPE around 3000 J/kg with 0-6 km shear near 30 knots, and 700-500 mb lapse rates in the 7 to 7.5 C/km range. Although a mixed mode is expected, the environment will likely support supercell development in areas that become locally favorable. Large hail and severe wind gusts will be possible with supercells. The potential for supercells may continue into the early evening over east-central Oklahoma, but a gradual transition to linear mode is expected to take place. The wind-damage threat could become maximized in the early evening, if an organized line segment can develop. ...Central High Plains... A mid-level shortwave trough will move into the central High Plains today. Ahead of this feature, a lee surface trough will deepen during the day from northeast New Mexico into eastern Colorado. Surface dewpoints near the surface trough will be in the 50s F, which will enable moderate destabilization by afternoon. As surface temperatures warm, convection will initiate in the higher terrain during the early afternoon and move eastward into the lower elevations. A small complex of storms will likely develop from this convection over the central High Plains. RAP forecast soundings near the instability axis in eastern Colorado at 00Z have MLCAPE near 1500 J/kg with 0-6 km around 40 knots, and 700-500 mb lapse rates near 7.5 C/km. This environment should be capable of producing supercells with large hail and severe wind gusts. ...Ozarks/Mid Mississippi and Ohio Valleys... At mid-levels, a subtle anticyclonic flow pattern will be in place from the Ozarks eastward into the Ohio Valley. At the surface, an axis of moisture and instability will be located from central Missouri eastward into southern Indiana and southern Ohio, along which surface dewpoints will be in the 70s F. By mid to late afternoon, MLCAPE is forecast to peak in the 2000 to 3000 J/kg range along much of this corridor. Although large-scale ascent will remain relatively limited, increasing low-level convergence near the moist axis will result in isolated convective initiation. Any small cluster that can develop and persist in the late afternoon and early evening could produce isolated severe wind gusts. ..Broyles/Thornton.. 09/20/2026 $$