Subj : DAY1SVR: Marginal Risk To : All From : Mike Powell Date : Fri Oct 13 2023 09:12:00 ACUS01 KWNS 131241 SWODY1 SPC AC 131239 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0739 AM CDT Fri Oct 13 2023 Valid 131300Z - 141200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL IOWA TO NORTHERN/WESTERN ILLINOIS AND EASTERN MISSOURI... ....SUMMARY... A few severe storms will be possible this afternoon from central Iowa to northern/western Illinois and eastern Missouri. ....Synopsis... In mid/upper levels, a Rex pattern covering much of north-central/central North America will transition back toward an omega configuration, as: 1. An anticyclone persists over central Canada, and 2. A pronounced cyclone -- initially centered over NE -- travels eastward roughly along I-80 to the southern Lake Michigan shore region around 12Z tomorrow. By 00Z today, the 500-mb low should be near DSM. The corresponding surface low was analyzed at 11Z over northeastern NE near OFK, with cold front to near an STJ-CNU-SPS-FST line, and warm front across south-central/southeastern IA to southern IL. The low should shift across southern/central IA through the day, nearly in step with its nearby mid/upper-level counterpart, as the warm front moves slowly northeastward over eastern IA and western IL. By 00Z, the triple point should be over west-central/central IL, ahead of the low, with cold front across southeastern MO, southern AR, and east through south-central TX. A separate, quasistationary frontal zone across north-central FL should move little through most of the afternoon, then slowly southeastward in response to cyclogenesis near coastal SC. That development should be related to the advance of the mid/upper cyclone across the Midwest/Great Lakes, and shortwaves traversing the basal cyclonic flow. While isolated thunderstorms will be possible along and south of the FL front atop a richly moist boundary layer, severe potential there should be muted by lack of stronger shear, lapse rates and lift. ....IA/IL/MO region... Scattered thunderstorms should develop from midday through the afternoon in one or two arcs east through southeast of the surface low, near the occluded/cold fronts. Activity should form initially over western parts of the outlook area, then spread north through east over it. A marginal tornado threat exists, with any sustained supercell(s) being the main concern for that, along with isolated damaging gusts and low-end severe hail. With abundant clouds and precip areas ongoing over the region and only slowly shifting away through much of the morning, diurnal destabilization will be slow to occur, and much of the buoyancy may arise from a combination of weak warm advection/heating in low levels and the eastern fringes of cooling aloft preceding the progressive mid/upper low. Surface dewpoints commonly in the mid 50s to low 60s F (locally higher) will support a narrow corridor of MLCAPE in the 300-700 J/kg range immediately preceding the frontal arc, amidst 25-40-kt effective-shear magnitudes and effective SRH generally in the 150-250 J/kg range (maximized just east of the low). Instability, lift and low-level shear each should diminish southward over central/eastern portions of MO/IL. Convective organization should diminish with eastward extent and time this evening as well, due mainly to weakening instability. ...Edwards/Broyles.. 10/13/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .