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Tuesday, October 26, 2021

SPC Oct 26, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Tue Oct 26 2021 Valid 262000Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT FROM PARTS OF NORTH TEXAS ACROSS WESTERN/CENTRAL OKLAHOMA AND SOUTHWESTERN KANSAS... ...SUMMARY... Scattered severe thunderstorms capable of producing large hail, wind damage, and isolated tornadoes are expected across portions of Kansas, Oklahoma, and north/central Texas late this afternoon through the evening, and continuing into the overnight hours. ...20Z Update... No major changes have been made to the ongoing forecast. Pronounced ascent associated with an approaching upper trough is evident with clouds and low-topped convection that have developed over southern CO and NM this afternoon. Clearing of the stratus deck that was prevalent this morning has occurred across much of western north TX, western OK, and south-central KS ahead of a surface dryline. Low-level moisture characterized by generally mid 60s surface dewpoints continues to stream northward across the southern Plains and into KS. A very strong cap centered around 850 mb and shown in 12Z observed soundings from AMA, DDC, and LMN should continue to inhibit convective development through most of the rest of the afternoon. By early evening (23-01Z/6-8 PM CDT), the ascent and cooler mid-level temperatures associated with the upper trough are expected to aid storm initiation along the dryline. Any supercells that form in this environment will initially pose a threat for very large hail and isolated tornadoes given the favorable low-level shear and very steep mid-level lapse rates that will be present. Some recent high-resolution guidance suggests that two areas may be favored for initial storm development: northwestern OK into south-central KS, and parts of western north TX. Regardless, these storms will likely grow upscale into one or more bowing lines this evening and tonight in tandem with a strengthening southerly low-level jet, while continuing to pose a threat for severe/damaging winds and a couple of tornadoes as they spread eastward across south-central KS, OK, and north/central TX through early Wednesday morning. ..Gleason.. 10/26/2021 .PREV DISCUSSION... /ISSUED 1124 AM CDT Tue Oct 26 2021/ ...Central/southern Plains late this afternoon into tonight... A midlevel shortwave trough near the AZ/NM border will progress eastward to the TX Panhandle by late evening, as an associated lee cyclone deepens across northeast CO, and a trailing lee trough/dryline sharpens across the TX Panhandle into southwest KS. Boundary-layer dewpoints in the mid-upper 60s will spread northward today to the east of the developing dryline. The returning moist layer is a bit shallow based on 12z soundings across TX, but is sufficient for stratus formation across central/western OK. The stratus could persist during the day from western OK into KS as the moisture return replaces a relatively cool air mass, and the clouds may tend to restrict the stronger surface heating to a narrow zone along the dryline. The net result will be a narrow corridor of moderate buoyancy immediately east of the dryline, with cooler temperatures and a stronger cap to the east and northeast. The primary band of ascent with the shortwave trough extrapolates to the expected dryline location by 00-03z, by which time storm initiation is probable. The questions about moisture depth and potentially narrow width of the unstable/relatively uncapped warm sector cast some doubt on storm coverage/intensity this evening along the dryline, and uncertainty is larger than usual for the initiation of dryline storms. Still, deep-layer vertical shear and low-level hodograph curvature will be favorable for a window of opportunity for surface-based supercells capable of producing a couple of tornadoes, large hail, and damaging winds. Any dryline storms may tend to evolve into clusters/line segments after dark while spreading northeastward across KS and northwest OK. Later tonight, storm coverage is expected to increase in a band as ascent preceding a cold front aloft comes into phase with richer moisture profiles across northwest/central TX into central OK, likely a little east of the surface Pacific cold front. Occasional damaging gusts and isolated large hail will be the main threats, though a tornado or two may also occur with embedded circulations. Read more LIVE: spc.noaa.gov
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