Subj : MESO: Mesoscale Discussion 2202 To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 27 2023 23:43:32 ACUS11 KWNS 272343 SWOMCD SPC MCD 272343=20 KYZ000-INZ000-ILZ000-280145- Mesoscale Discussion 2202 NWS Storm Prediction Center Norman OK 0643 PM CDT Wed Sep 27 2023 Areas affected...Southern Illinois and southern Indiana into Kentucky Concerning...Severe potential...Watch possible=20 Valid 272343Z - 280145Z Probability of Watch Issuance...40 percent SUMMARY...Thunderstorms developing across southern Illinois are expected to intensify as they migrate east into the Ohio River Valley. Large hail and severe wind gusts will be possible with the more intense cells, but thunderstorm coverage and mode remains uncertain. Trends will be monitored for watch issuance. DISCUSSION...Over the past hour, a few transient attempts at convective initiation have been noted across southern IL ahead of a subtle mid-level impulse and in the vicinity of a decaying surface low. Additional attempts at CI are expected over the coming hours as isentropic ascent increases over a warm front draped from southern IL into the OH River Valley. Temperatures across the warm sector - which is bound to the east by a residual outflow boundary - have begun falling with the onset of nocturnal cooling. MLCAPE values have been falling due to this cooling, but MUCAPE values should remain near 1000 J/kg as saturation of the surface-850 mb layer increases. Additionally, weak south/southeasterly flow across the region with 30-35 knot flow aloft is supporting somewhat elongated hodographs with effective bulk shear values near 30-35 knots. Some veering in the lowest 1 km is noted in regional VWPs, which is supporting effective SRH values around 100-150 J/kg. This environment is favorable for organized convection, including the potential for a few supercells.=20 However, several modulating factors are noted. Deep-layer shear and storm motion vectors are forecast to be largely oriented along the warm front, which should favor a tendency for upscale growth. These factors may be offset by the isolated nature of storms given the relatively weak ascent over the region, so storm mode remains somewhat uncertain. Additionally, the noted nocturnal cooling may hinder the potential for surface-based convection, limiting the tornado potential and favor large hail and severe winds as the primary hazards. Trends will continue to be monitored for the needed for a watch issuance, which may be conditional on storm coverage and organization. ...Moore/Hart.. 09/27/2023 ....Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!_DkgSRAphOwZz8mZxpTTN7dtuHOmYlX05M8d3rtXQVzoL2AopFwjDMi2sFHsJzGsiKN8CxdeO= pdK_qpafQbw5SR2Y_4$ for graphic product... ATTN...WFO...LMK...IND...PAH...ILX...LSX... LAT...LON 38548523 38288487 37848482 37288516 36898588 36758649 37068764 37328846 37548904 37848943 38288944 38688888 38758804 38768588 38548523=20 =3D =3D =3D 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) .