Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 19 2023 12:47:57 ACUS01 KWNS 191247 SWODY1 SPC AC 191246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Sat Aug 19 2023 Valid 191300Z - 201200Z ....NO SEVERE THUNDERSTORM AREAS FORECAST... ....SUMMARY... The risk for severe thunderstorms appears limited across the U.S. today. ....Synopsis... In mid/upper levels, a strong high is initially located over northwestern OK. The associated anticyclone is expected to enlarge and intensify further through the period, with some eastward to northeastward drift possible, and net height rises over the central/northern Plains, Mississippi Valley, and Great Lakes. This will occur as a cyclone -- now over the St. Lawrence Valley of southern QC -- moves slowly northeastward toward the Gulf of St. Lawrence. West of the high, a persistent/cut-off low is apparent in moisture-channel imagery offshore from south-central CA. That low should drift erratically through the period as the core region of Hurricane Hilary proceeds northward toward and over the western Baja coastline and adjacent waters. See NHC advisories for tropical watches/warnings and track intensity guidance on Hilary. At the surface, 11Z analysis showed a cold front offshore from NC, becoming quasistationary southwestward across southern GA and westward over coastal AL/MS, then a warm front over northeast TX and southwestern OK. The warm front will move northeastward and become diffuse today, with warm/moist advection common ahead of the next cold front. The latter front -- analyzed initially from northwestern MN across central/southwestern SD and northeastern WY -- is forecast to cross the remainder of the northern Plains and much of the Upper Midwest through the period. By 12Z tomorrow, this front should reach central/eastern Upper MI, southern WI, southeastern IA, the central/western KS/NE border area, and northeastern CO. Though moisture and instability will increase throughout the day ahead of this front across the upper Mississippi Valley into eastern NE, EML-related capping still appears too stout to support sustained convective development this afternoon. ....Western CONUS... Isolated to scattered thunderstorms are possible this afternoon and evening over a large part of the western CONUS, and throughout the period over the lower Colorado River Valley, Imperial Valley, and Mojave/Sonoran deserts. The latter area of convection, for much of the period, will be only indirectly associated with Hilary, via continued/intensifying fetch of moisture advection/transport in low levels well to its north. With abundant cloud cover and modest deep-layer lapse rates, buoyancy will be limited in this plume, though coverage may be locally dense due to weak inhibition and persistent orographic forcing. The anomalously moist thermodynamic profile and increasing gradient flow may support an occasional strong, water-loaded downdraft gust. The main hazard, by far, will be from heavy rain; see WPC excessive-rainfall discussions for more details. Surrounding that plume this afternoon -- from interior northern CA/OR across much of the northern/eastern Great Basin to the central/northern Rockies and Colorado Plateau -- diurnal heating of a less-moist boundary layer will result in steeper low-level lapse rates and common inverted-v thermodynamic profiles. Convection moving over well-mixed, deep boundary layers could produce intense downdrafts locally, almost anywhere over a vast area. At this time, potential appears too isolated and nebulously focused for an unconditional severe-wind area. Low-level hodographs should start to enlarge near the international border, during the last few hours of the period. This should occur as the strengthening low/middle-level gradient influences of what now is Hurricane Hilary enhance antecedent/ambient gradient flow between the cold-core/cutoff low and the central CONUS high. Given the weak overall instability and lack of low-level lapse rates at those hours, tornado potential appears too conditional and speculative to introduce for the end of the period. However, the NHC forecast track already has been sped up some, and any faster shift of the TC and its northeastern-quadrant, low-level wind fields may result in a less-conditional threat beginning before 12Z. This will be monitored for succeeding outlooks. ...Edwards/Jewell.. 08/19/2023 $$ = = = 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) .