Severe Storm Outlook Narrative (AC)
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Issued by NWS
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786 ACUS11 KWNS 212020 SWOMCD SPC MCD 212020 IAZ000-212145- Mesoscale Discussion 0875 NWS Storm Prediction Center Norman OK 0320 PM CDT Tue May 21 2024 Areas affected...Southwest/South-Central IA Concerning...Tornado Watch 277... Valid 212020Z - 212145Z The severe weather threat for Tornado Watch 277 continues. SUMMARY...A localized corridor favorable for strong tornadoes exists across southwest/south-central Iowa, including Des Moines vicinity. DISCUSSION...Pair of supercells on the southern end of the line of storms extending across western IA have recently shown notable intensification, with rotational velocity recently estimated around 50 to 55 kt within the southernmost cell. Strong southerly flow exists ahead of this storm, contributing to strong low-level shear, evidenced by recent 0-500m storm relative-helicity around 200 m2/s2 from DMX VAD. Robust deep-layer shear exists as well, with DMX VAD sampling 0-6 km bulk shear was over 60 kt. Recent mesoanalysis estimates effective-layer STP from 3 to 4 downstream. All of these factors suggest the downstream environment will remain conducive for supercell persistence. Storm motion for this southernmost storm is estimated to be northeasterly at around 45 kt, bring it into the Des Moines vicinity around 2130Z. ..Mosier.. 05/21/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...OAX... LAT...LON 40719467 41269501 41659451 41949347 41189288 40719467