Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 26 2023 19:55:54 ACUS01 KWNS 261955 SWODY1 SPC AC 261954 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Tue Sep 26 2023 Valid 262000Z - 271200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MS AND UPPER OH VALLEY...NM AND WEST TX...AND NORTHERN FL... ....SUMMARY... Isolated severe thunderstorms are possible today across parts of the Midwest, across parts of New Mexico into west Texas, and possibly northern Florida. ....20Z Update... ....Mid MS Valley into the Lower OH Valley... Visible satellite imagery shows a cumulus field from IA across IL into IN, with some recent building cumulus across eastern MO as well. All of this is occurring in the vicinity of an upper low centered over eastern IA. MCD #2198 was recently issued addressing the severe potential in this area. As mentioned in that discussion, cold mid-level temperatures and steep low-level lapse rates, and resulting modest buoyancy, in the presence of low-level vorticity may result in isolated instances of hail and perhaps a brief tornado this afternoon. An associated occluded surface low is centered below this upper low, linked to another surface low over northeast IL by a weak surface trough. A cold front extends from arc second low southward into southern IL and then back westward into west-central MO. As mentioned in MCD #2200, pulse-cells and multicell storms have been increasing in coverage and intensity along this boundary. A couple instances of hail are possible with the stronger storms this afternoon. Building cumulus across far southwest MO suggests thunderstorm initiation will occur in that region as well, and marginal hail and wind probabilities were extended accordingly. ....Elsewhere... Isolated thunderstorms capable of hail and damaging gusts remain possible across NM and West TX. A strong storm or two is also possible across northern FL, as mentioned in MCD #2199. ...Mosier.. 09/26/2023 ..PREV DISCUSSION... /ISSUED 1136 AM CDT Tue Sep 26 2023/ ....Midwest including Illinois/Indiana/Missouri... An upper low (-16C at 500mb) centered over eastern Iowa this morning will continue to drift east-southeastward toward and across northern Illinois through tonight. A semi-moist environment, with surface dewpoints in the upper 50s/low 60s F, will diurnally persist near/northeast of a weak surface low and occluded front/wind shift that will generally extend southeastward from the surface low. While deep-layer wind profiles will generally be weak (15-20 kt effective shear), ample CAPE with respect to low-topped storms will support the possibility of hail with the stronger pulse-type cells. Funnels appear quite plausible across areas including eastern Iowa, southern Wisconsin and northern/central Illinois, and sufficient low-level CAPE/ambient vorticity near the boundary could yield a brief tornado risk. Farther to the southwest, there is some potential that some strong to severe thunderstorms could develop near the front across central/eastern Missouri late this afternoon into tonight. MLCAPE could reach 1000-1500 J/kg MLCAPE near/south of the front, and wind profiles will be moderately strong, influenced by increasingly strong cyclonically curved westerlies in the base of the Upper Midwest shortwave trough. Thermodynamic/kinematic profiles could conditionally support some high-based supercells aside from multicellular clusters if/where storms develop. While near-frontal convergence will be modest, and the likelihood and extent of sustained deep convection may remain limited, there will be additional late night opportunities for convective development as warm advection/moisture transport increase, and some of these storms could also be strong. This region will be closely reevaluated in subsequent outlooks for a potential reintroduction of severe probabilities. ....New Mexico/West Texas... Within the weaker southern branch of westerlies, a weak shortwave trough is expected to move southeastward across the Four Corners vicinity through tonight. As it does, associated forcing for ascent should augment convective development, particularly storms initiating in response to heating across the mountains of southern/central New Mexico by early afternoon. It appears that moisture across this region will be sufficient to support initially sizable CAPE, beneath modest westerly to northwesterly flow, at least in upper levels. Stronger storms may become capable of producing marginally severe hail, then a few strong to severe gusts while propagating southeastward off the higher terrain into an unstable and more deeply mixed boundary-layer through early this evening. ....Florida Peninsula... Low severe probabilities have been introduced for the northern Florida Peninsula where storms are expected to increase/develop east-northeastward across the region, all while deep-layer shear modestly increases. High precipitable water content will support heavy precipitation loading and some potential for locally strong surface gusts. ....Coastal Oregon... Forcing for ascent within the exit region of a strong jet streak (including 70-90 kt around 500 mb) may contribute to an organized, vigorous pre-frontal convective band, associated with the surface cyclone approaching the Pacific Northwest. However, with the cyclone forecast to occlude prior to reaching the coast near/after 27/06Z, appreciable inland boundary-layer destabilization appears unlikely, and stable near-surface lapse rates may tend to mitigate the potential for downward mixing of severe surface gusts as the convective line progresses inland. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .