Administrators NorthGeorgiaWX Posted July 28 Administrators Posted July 28 MD 1720 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTH DAKOTA Mesoscale Discussion 1720 NWS Storm Prediction Center Norman OK 0231 PM CDT Sun Jul 28 2024 Areas affected...South Dakota Concerning...Severe potential...Watch possible Valid 281931Z - 282230Z Probability of Watch Issuance...40 percent SUMMARY...Thunderstorm coverage is beginning to increase across western to northern South Dakota with scattered strong to severe storms probable by late afternoon and early evening. Watch issuance is possible this afternoon, but timing is uncertain. DISCUSSION...Latest GOES imagery shows steady deepening of convection along a cold front draped from northeast to western SD as well as within the Black Hills. 19 UTC surface observations along and south of the front report temperatures in the low 90s - considerably warmer than anticipated by recent guidance by this time, which implies that boundary-layer mixing (and an accompanying erosion of MLCIN) is progressing more rapidly than expected. As such, the recent convective trends should continue with additional thunderstorm development probable in the coming hours. Although moisture quality degrades with westward extent, easterly low-level winds on the northern periphery of a surface low are elongating hodographs with effective bulk shear values approaching 30-40 knots. This will support a window for a supercell or two as initially discrete cells develop over the Black Hills and/or along the front across western SD. With time, a combination of storm motions largely along the front and a 1-2 km deep boundary layer with nearly dry adiabatic lapse rates will promote consolidating cold pools and upscale growth into one or more clusters as convection propagates to the east and into a more moist/buoyant air mass. An organized MCS may emerge out of this activity this evening with the potential for severe winds, possibly up to 75 mph. Somewhat weak synoptic-scale forcing for ascent casts some uncertainty onto overall storm coverage, which may favor more isolated cells with limited potential for upscale growth and a more localized severe threat. Convective trends will be monitored for the need for watch issuance this afternoon/evening. ..Moore/Gleason.. 07/28/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FSD...ABR...UNR... LAT...LON 43550362 43860394 44210404 44410372 44570285 45150051 45280017 45419983 45459930 45429838 45359777 45279764 45069753 44829756 44459780 44219801 43939844 43689893 43509946 43419997 43330052 43270099 43280166 43270224 43420309 43550362 Read more View the full article Quote
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