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Thursday, October 14, 2021

SPC Oct 14, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0220 PM CDT Thu Oct 14 2021 Valid 142000Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHERN ARKANSAS INTO THE LOWER OHIO VALLEY AS WELL AS OKLAHOMA... ...SUMMARY... A few strong/marginally severe thunderstorms are possible this afternoon from northeastern Arkansas to the lower Ohio Valley region, and later this evening across portions of Oklahoma. ...Discussion... No change was made to the previous convective outlook. ..Smith.. 10/14/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Oct 14 2021/ ...Arkansas through lower Ohio Valley region... No changes have been made to previous outlook. Widespread multi-layer clouds reside within a plume of subtropical moisture. However, some cloud breaks are evident on satellite imagery, which will promote pockets of diabatic heating of the moist boundary layer. Despite the presence of rich low-level moisture with upper 60s to around 70 F dewpoints, instability will remain marginal (500-1000 J/kg MLCAPE) due to weak mid-level lapse rates (~ 5 C/km in the 700-500 mb layer). Nevertheless, some increase in thunderstorm intensities is expected with activity developing along and just ahead of a cold front from AR through southern MO into the lower OH Valley. Strong effective bulk shear from 45-50 kt will support potential for storms to organize with embedded bowing segments as well as a conditional risk for some supercell structures. Damaging wind will be the main threat, but a brief tornado or two cannot be ruled out. However, veered near-surface winds should limit low-level hodograph size, with 0-1 km storm relative helicity generally below 150 m2/s2. ...Oklahoma... Capping may delay substantial thunderstorm initiation until after 00Z -- perhaps even as late as 03-06z. However, isolated to scattered thunderstorms this evening into tonight will promote a threat for hail and strong gusts. Large-scale lift should increase over the region this afternoon and tonight with the approach of the main mid/upper trough, reinforced by the digging shortwave perturbation. The returning warm sector has been altered somewhat unfavorably by extensive precip upstream to the south, yet still should contain enough theta-e to support strong/isolated severe potential as it is lifted along and over the surface front. Even with a shallow/near-surface stable layer apparent in forecast soundings, MLCAPE of 500-1200 J/kg appears possible in the warm sector, along with similar values of elevated MUCAPE within about 50-100 nm behind the boundary. 500-250-mb layer winds will strengthen over this area from late afternoon into tonight, contributing to 50-60-kt effective-shear magnitudes in support of supercells. Limiting factors for the severe threat will include lack of greater low- and middle-level lapse rates tonight, limiting buoyancy and near-surface acceleration potential for both updrafts and downdrafts. Read more LIVE: spc.noaa.gov