Start
October 23, 2020 - 3:00 pm
End
October 23, 2020 - 3:00 pm
Categories
Convective Meteorology (Mesoscale Dynamics)Convective Meteorology (Mesoscale Dynamics) Seminar
Factors Inhibiting Widespread Warm Sector Supercells in Central Oklahoma on 20 May 2019
Thomas J. Galarneau
Friday, October 23, 2020
3 pm
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During the evening and overnight hours of 20–21 May 2019, a line of severe thunderstorms moved from the Texas Panhandle through Oklahoma and produced numerous tornado, wind and hail reports. Most of these reports occurred in the Texas Panhandle on the afternoon of 20 May and in central and northeast Oklahoma during the overnight hours. This severe weather event occurred in an environment characterized by strong synoptic-scale forcing for ascent with high convective available potential energy and vertical wind shear. A dryline was positioned in the Texas Panhandle and intersected a warm front that extended northeast through north-central Oklahoma. Supercells developed along the dryline in Texas and moved into southwest Oklahoma in the late afternoon. Widespread rain with embedded severe thunderstorms persisted throughout the day on 20 May on the north side of the warm front. A second round of thunderstorms developed along the retreating dryline in the evening hours and surged eastward through Oklahoma during the overnight hours as a tornadic quasi-linear convective system.
This case presents a difficult forecast challenge: would tornadic supercells form in the warm sector in central Oklahoma on the afternoon and evening of 20 May? Short-term convection-allowing model (CAM) guidance initialized from 0000 UTC through about 1800 UTC 20 May indicated that numerous supercells would occur in the warm sector. Forecasts initialized after 1800 UTC shifted to a more suppressed warm sector with supercell coverage limited to near the dryline. In the real atmosphere’s warm sector, a supercell formed west of Oklahoma City at ~2000 UTC and produced a tornado near Kingfisher before merging with the warm front and dissipating in north-central Oklahoma. The warm sector was suppressed thereafter, representing a stark contrast to the earlier CAM solutions. In this presentation, we will put on our thinking “caps” and explore what factors determined whether the CAM guidance produced warm sector supercells or not. The NSSL Warn-on-Forecast System will be used for the very short term (0–3 hour) forecast leads and operational High-Resolution Rapid Refresh for the short term (3–18 hour) forecast leads. We will “cap” things off by examining other warm sector situations in the southern Plains in 2019 and 2020 to determine if a similar behavior of CAM solutions occurred.