Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 05 2023 16:01:55 AWUS01 KWNH 051601 FFGMPD INZ000-ILZ000-052200- Mesoscale Precipitation Discussion 0870 NWS Weather Prediction Center College Park MD 1200 PM EDT Sat Aug 05 2023 Areas affected...Portions of east-central IL...west-central IN Concerning...Heavy rainfall...Flash flooding likely Valid 051600Z - 052200Z Summary...Renewed deep convection with 1-3"/hr rainfall rates to lead to 4-6" localized totals. Isolated to scattered instances of flash flooding are considered likely. Discussion...An impressive surface to low-level vortex (extending as high as 700 mb) is decelerating as translates eastward across Illinois late this morning. The evolution of this vortex has been fascinating to observe via MRMS base reflectivity (BREF) since overnight, as it exhibited an eye-like structure for a couple of hours over west-central IL (with higher reflectivity wrapping around the low-level vortex). Farther up in the troposphere, a potent shortwave displaced just to the northeast (most evident on GOES-East upper-level water vapor imagery) is driving equally remarkable mesoscale features, inducing a 60-70 kt jet streak (at 250 mb) that is displaced to the southwest of the primary northern stream jet streak (centered near New England). Increasing divergence aloft (via localized right-entrance region effects of the jet streak) should assist with redevelopment of deep convective activity this afternoon, as instability increases to a diurnal maximum (MU CAPE reaching 1000-1500 J/kg). Precipitable water values along and ahead of the vortex range from 1.9-2.2" (with the 12z sounding at ILX recording a near record PWAT of 2.11" for the date) with deep layer (0-6 km) shear generally 30-40 kts. It is worth noting that the 12z ILX sounding recorded a near record PWAT for the date (2.1") with deep layer shear of 62 kts surpassing the prior record of 48 kts. The latest CAM guidance (12z HREF suite) continues to be very robust with QPF depictions through early to mid-afternoon, as the probability-matched mean (PMM) indicates the potential for localized totals of 4-8" through 22z (primarily driven by the NAM-nest and ARW members). Hourly runs of the HRRR have depicted similar localized totals (though usually capped closer to 6" totals), while the 06z run of the experimental RRFS is quite a bit lower with 3-4" totals. Given the mesoscale environment and range of CAM solutions, localized totals of 4-6" (over a period of 3-6 hours) seems probable, which would lead to isolated to scattered instances of flash flooding (given associated FFGs range from 2-4"). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9Cjp8zRAm87cLTyRpa_rSOI8pvM9JcJHDcE0d044iK1TW4d3y33g6UKqLzq1-IGRWf4b= Crpc8J1DiUc0mebuRvv4y-k$ for graphic product... ATTN...WFO...ILX...IND...IWX...LOT...LSX... ATTN...RFC...NCRFC...OHRFC...NWC... LAT...LON 41188825 40928679 39828633 38838760 38998888=20 39518976 39878962 40318926 40938898=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) .