Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 09 2023 08:22:35 FOUS30 KWBC 090822 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 421 AM EDT Wed Aug 09 2023 Day 1 Valid 12Z Wed Aug 09 2023 - 12Z Thu Aug 10 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF THE MID-MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS.... ....Southern Missouri/northern Arkansas into western Tennessee, northern Mississippi/Alabama... A mid-upper level shortwave will track ESE from the central High Plains this morning to KY/TN for Thursday morning, supporting the organization of a surface low near the KS/OK border with attendant cold/warm fronts. A slow moving warm front currently in place from near the Red River to LA/MS was associated with precipitable water values just shy of 2 inches per 00Z RAOBs and recent (07Z) GPS data. There is good agreement in recent HRRR runs and the 00Z CAMs that overrunning of the front will lead to elevated thunderstorms in the vicinity of southern MO/northern AR at the start of the outlook period, out ahead of ongoing (07Z) thunderstorms across the southern/central Plains. While individual cells with this initial round of thunderstorms should move steadily toward the east and southeast, repeating rounds and training will be possible with the potential for localized 2-4 inch totals prior to 21Z. As the anticipated first round of thunderstorms moves east into the OH/TN Valleys, a second round of storms is expected to develop near or just prior to 00Z over the Ozarks as the aforementioned shortwave approaches along with a ~100 kt upper level jet streak. Increased ascent within the entrance region of the upper level jet streak should aid in the development of an expanding area of thunderstorms between 00-03Z, just ahead of an approaching surface low, with the potential for multiple rounds of storms repeating over the same region overnight. There is some question as to the degree of overlap between the two expected rounds of heavy rain but there remains the potential for upgrading to a Moderate Risk with the 16Z update if there is better confidence in the two rounds overlapping with each other or with portions of the region that are more sensitive given recent heavy rain over the past week or so. However, current thinking is that the greatest potential for 3 to 5 inches through 12Z Thursday will set up along the MO/AR border, extending into western TN...or mainly south of more sensitive regions located in central/eastern MO and western KY. ....eastern Kansas, central/northern Missouri, southern Iowa into the Ohio Valley... Thunderstorms are likely to advance eastward from the central Plains this morning into the Midwest and OH Valley, out ahead of an upper level shortwave tracking eastward from the Plains. Increasing upper level jet divergence within the entrance region of a 110-130 kt speed max along with diffluent flow aloft should help to increase convective coverage through the late morning and afternoon. Elevated low level convergence focused at the nose of a 925-850 mb plume of moisture transport should focus convection from portions of northern MO, eastward into the OH Valley. Repeating and short term training of convection may lead to scattered areas of flash flooding with potential for 3 to 5 inches locally. Portions of MO into IL and IN have been wetter than average over the past 1-2 weeks, lowering FFG and increasing susceptibility to flash flooding. ....Arizona/New Mexico... Weakly anomalous moisture is expected to be in place across AZ (standardized precipitable water values of 1 to 1.5) this afternoon, while higher anomalies (+2 to +3) reside over the southern CA coast. While cloud cover during daytime heating remains a bit uncertain, it seems clouds will be more likely over CA during the early afternoon, associated with remnant moisture from former Hurricane Eugene in the eastern Pacific. Thunderstorms are expected to initiate along the Mogollon Rim with daytime heating (likely 18Z+) followed by additional convection over the higher terrain of southeastern AZ. Forecasts from a majority of the 00Z guidance suggest MLCAPE of 500-1500 J/kg during the afternoon with forecast soundings showing fairly moist low to mid level profiles. While storm motions don't appear overly slow overall, there is at least a low-end threat for isolated flash flooding with the convective peak later in the day. Otto Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5YY18OT1-hfSXaeFOhFJ_pt_P6sCxgmnMuPAfkJbhE0D= AftGPcLGKtJMF2F_FX41pvdzseiFHabX201rTpKT1iqpkyw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5YY18OT1-hfSXaeFOhFJ_pt_P6sCxgmnMuPAfkJbhE0D= AftGPcLGKtJMF2F_FX41pvdzseiFHabX201rTpKT1cjn9bo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5YY18OT1-hfSXaeFOhFJ_pt_P6sCxgmnMuPAfkJbhE0D= AftGPcLGKtJMF2F_FX41pvdzseiFHabX201rTpKT9tse_8k$=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) .