Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 11 2024 15:51:47 FOUS30 KWBC 111551 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Sun Aug 11 2024 Day 1 Valid 16Z Sun Aug 11 2024 - 12Z Mon Aug 12 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR CENTRAL UTAH THROUGH NORTHWESTERN ARIZONA, PORTIONS OF THE OZARKS AND CENTRAL PLAINS, AND FOR THE COASTAL CAROLINAS... ....16Z Update Summary... Some minor adjustments were made to the SLGT risk areas across the Plains and Ozarks with very little change to the other SLGT risk areas out west and across the Carolinas. More details for each setup can be found in the correlating sub-headings below.... Kleebauer ....Central Utah through Northwestern Arizona... 16Z Update: Not much change within the suite of CAMs and global deterministic so far this morning with the HREF blended mean QPF relatively unchanged compared to the recent 00/06z runs. Shortwave is analyzed across Central NV this morning with eastward movement that will eventually help ignite the enhanced convective concerns across parts of the Great Basin. General totals of 0.5-1" will be common as far an areal average, but pockets of 1-2+" will be plausible given the increasing PWATs and elevated theta-E's advecting northward through Northwest AZ into Southern UT. SBCAPE between 2000-3000 J/kg will be situated within the current SLGT risk forecast implying a very suitable instability axis that will aid in the heavier convective cores this afternoon and evening. Considering variables at hand, there was little need to deviate from the previous forecast, so continuity was maintained.=20 Kleebauer ...Previous Discussion.. Monsoonal moisture will continue to draw northward across the Four Corners region today. The jet stream and an upper level jet streak will be set up across northern Utah today. PWATs increasing above 0.75 inches will boost portions of southern Utah to 2.5 sigma above normal. With moisture and forcing in place, expect a renewed round of afternoon convection across this area. With previous days' storms having soaked the soils in some areas, the flash flooding threat will be higher today as compared to previous days across Utah and portions of northwestern Arizona. The Slight risk area was expanded southward with this update to include much of the Grand Canyon and points north, including Glen Canyon. ....Portions of the Ozarks and Central Plains... A pretty stout MCS is currently within the final stages of its life-cycle this morning after dropping a barrage of rainfall across Central OK with totals across the OKC metro and surrounding locales coming in between 4-7" based on recent obs. There's been some warming within the cloud tops in recent IR satellite scans meaning the complex will be decaying gradually as move into the afternoon hours. There was thought in removing the current SLGT risk over Central OK, but with rain ongoing and Flash Flood Warnings in effect, maintained continuity across the region to account for the current rainfall. Expect that area to be removed in the next 01z update as the rainfall expected this period is focused through this morning with a quieter night anticipated.=20 Further north and northeast will be another story as the next complex will develop late this evening as a the leading edge of a 30-50kt LLJ will nose into the Four State area (MO/KS/AR/OK) a shortwave bisecting the region as it ejects out of KS. The setup is driven by a strong focus of elevated instability with MUCAPE between 1000-2000 J/kg across the above region within an axis of +1 to +2 deviation PWATs positioned across Central Plains to the western half of the Mid-Mississippi Valley. There's some uncertainty on the exact placement of the highest QPF axis with guidance jockeying on how the mid-level evolution will come to fruition which plays a significant role in the timing of initiation of convection, as well as the magnitude of convection that does develop over the area. The strongest probabilities for heavy precip are located over Southeast KS into Southeast MO for the second round of heavy precip within the current SLGT risk forecast. There was enough consensus to pull away from the Kansas City area, although another potential complex of thunderstorms will be passing to the north, putting the metro in a "squeeze" of sorts when it comes to relevant QPF maxima. In any case, the forecast SLGT was maintained for the threat with the best potential likely lying within urbanized areas given the antecedent conditions surrounding the forecasted zone of impact. The highest probabilities for flash flooding concerns lies near Tulsa thanks to the ongoing situation with the MCS with some guidance also bring in the southern flank of the second round overhead towards the very end of the forecast period. A tricky forecast overall, but the low-end SLGT risk remains.=20 Kleebauer ....Coastal Carolinas... 16Z Update: The setup from the last few days will be on repeat once again with scattered to widespread convection developing across the Carolinas thanks to lingering buoyancy, elevated moisture tied near and east of the stationary front, and afternoon destabilization allowing for a priming of the environment with eventual cell initiation. The probability fields are basically a carbon copy from yesterday with neighborhood probs for >3" settled between 45-80% over a large area with the highest probabilities positioned just inland from Morehead city down to Wilmington. This area has been hit incessantly for several days leading to very low FFGs and continued flooding that will only be exacerbated with any additional rainfall. Considering the relevant probabilities and consistent CAMs depiction of scattered heavy thunderstorms this afternoon and early evening, the SLGT risk remains with little variance from the previous forecast. Kleebauer ...Previous Discussion.. Guidance has been gradually shifting south and east/closer to the coast with the axis of the heaviest rain with the afternoon convection expected tonight. Thus, the Slight and surrounding Marginal risk areas have been shrunk to the southeast accordingly. Nonetheless antecedent conditions along the coast remain very favorable in the recovery post-Debby. Expect similar coverage of flash flood warnings as today's storms, but are likely to occur further east. Given the uncertainty as to where the storms will form, the Marginal risk still extends into central NC and western SC for the potential for more widely scattered storms, as well as across eastern Georgia. Wegman Day 2 Valid 12Z Mon Aug 12 2024 - 12Z Tue Aug 13 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE FOUR CORNERS REGION EAST TO THE MID-MISSISSIPPI VALLEY AS WELL AS FOR PORTIONS OF THE COASTAL CAROLINAS... ....Four Corners Region to the Mid-Mississippi Valley... Concern continues to increase with potential heavy rain and subsequent flash flooding in various areas. For the Four Corners, no major changes are expected, but with the greatest moisture having shifted east, convective coverage should be lesser on Monday as compared to today. Meanwhile, the signal for heavy rain remains strong from eastern Colorado into western Kansas. Easterly flow north of an ejecting low will draw plentiful Gulf moisture into the High Plains of Colorado. Meanwhile, a stalled front to the north will supply lower level forcing. The result will be an area of heavy rain caused by training storms moving east along the front, as moisture flowing northwestward on the warm side of the front supports backbuilding. There remains some uncertainty both with the placement of the heaviest rains, and for Kansas, the development of drought conditions potentially resulting in less flooding. However, it appears likely a Slight will be needed as plentiful moisture will support storms capable of rates to 2 inches per hour, which in areas of training storms should overcome otherwise high FFGs. Further east into Missouri, lingering storms from tonight will continue into Monday morning. Then, the stalled out front over the area will begin to reorient, but pivoting over Missouri. This should reduce the overall coverage of rainfall over Missouri for the day, but will keep the area in the crosshairs for heavy=20 rainfall going forward. ....Coastal Carolinas... Some lingering storms are possible along the coast Monday afternoon as the front over the area dissipates. With much reduced storm coverage, the Marginal remains over the area for the potential for isolated instances of flash flooding. This would likely be the result of sea breeze interactions. Wegman Day 3 Valid 12Z Tue Aug 13 2024 - 12Z Wed Aug 14 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE FOUR CORNERS REGION TO THE MID-MISSISSIPPI VALLEY, AS WELL AS FOR EASTERN NORTH CAROLINA... ....Missouri... A renewed push of Gulf moisture with the LLJ will impact a persistent front across Missouri today. This will likely result in an area of training thunderstorms capable of localized flash flooding. The area is likely to be upgraded to a Slight with future updates and higher confidence, but given the counter flow out of the northeast on the dry side of the front over the Midwest, it's likely that training storms are likely to impact a narrow corridor over Missouri along the front. There is potential that the St. Louis metro may be part of the heavy rain corridor. ....Eastern North Carolina... A bit stronger moisture push off the Atlantic may result in more widespread showers and storms a bit further inland into North Carolina. With little to organize the convection however, the flash flooding threat remains isolated. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!45Fwd5Z3_8VQg3VuaOSKQ4A6QYOLSWZ5o5dtduymbSPn= UA7u17ylyv6Cdq2CneN9KHY7Vt2OB873HOaQwzUbK4vO-J8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!45Fwd5Z3_8VQg3VuaOSKQ4A6QYOLSWZ5o5dtduymbSPn= UA7u17ylyv6Cdq2CneN9KHY7Vt2OB873HOaQwzUbjKEqaqs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!45Fwd5Z3_8VQg3VuaOSKQ4A6QYOLSWZ5o5dtduymbSPn= UA7u17ylyv6Cdq2CneN9KHY7Vt2OB873HOaQwzUb2WLRFBI$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .