SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Mon Aug 23 2021 Valid 231630Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE CENTRAL AND NORTHERN PLAINS FOR LATE THIS AFTERNOON INTO TONIGHT... ...SUMMARY... Isolated severe thunderstorms are possible across parts of the central and northern Plains to mid/upper Mississippi Valley through tonight. A marginal tornado threat exists over parts of southern New England. ...Central and Northern Plains... The atmosphere will destabilize northward through the central Plains south of a warm front that will advance through northern NE into SD today. Low-level dewpoints in the mid to upper 60s F beneath steep (7.5-8.5 C/km) mid level lapse rates will contribute to 3000-3500 J/kg MLCAPE. However, capping associated with warm air at the base of an elevated mixed layer will be present most of the day. Primary uncertainty is how many storms can develop in this environment given relatively weak forcing in the presence of a low-amplitude upper ridge. However, water vapor imagery and RAP analysis imply a vort max across northern CO that will move east northeast into the Plains this afternoon. At least isolated high-based storms will probably develop along evolving dryline across western SD into western ND late this afternoon. This activity will spread east, and if storms can survive into the higher CAPE environment, they will likely become severe given strong instability and 35-40 kt effective bulk shear. Therefore a conditional threat exists for a couple of supercells capable of large to very large hail and isolated damaging wind late this afternoon into the evening. Higher confidence exists that elevated storms will develop late tonight, most likely within evolving warm advection regime across a portion of ND as the atmosphere destabilizes. Effective bulk shear of 30-40 kt and up to 2500 J/kg MUCAPE will support potential for elevated supercells, before storms congeal into an MCS. A SLGT risk upgrade will be considered for this area in later updates. ...Southern New England... Low-topped convection / showers within convergence bands associated with the remnants of Henry will persist across southern New England today. Low-level shear with storm relative helicity from 140 m2/s2 to 160 m2/s2 will remain sufficient for a marginal risk of a brief tornado or two. However, very weak instability will remain the primary limiting factor. ..Dial/Jewell.. 08/23/2021 Read more LIVE: spc.noaa.gov
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