Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 23 2024 15:40:17 FOUS30 KWBC 231540 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1140 AM EDT Fri Aug 23 2024 Day 1 Valid 16Z Fri Aug 23 2024 - 12Z Sat Aug 24 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE FOUR CORNERS REGION/INTERMOUNTAIN WEST AND PARTS OF THE SOUTHEAST US... ....Florida and far southeast Georgia...=20 The primary change for the 16 UTC outlook update was to connect the two Marginal Risk areas to introduce a Marginal Risk across parts of central Florida. There is enough signal in the 12Z HREF that indicates potential for localized rainfall maxima in excess of 4 inches, and some small probabilities of exceeding 3 hour FFG, both in C FL and the existing risk areas. Some HREF members are=20 relatively dry today, but there does seem to be strong instability=20 and precipitable waters near 2 inches, which would support heavy=20 rain rates in any convection that does manage to develop, and weak=20 flow should keep the storms relatively slow-moving. ....Southwest US... 16 UTC update: no changes were made to the risk area in the Southwest U.S. The forecast reasoning from before remains the same and is included below. Moisture feeding northward into the Southwest US will begin to be=20 channeled into a more narrow corridor disrupted today...leading to=20 a somewhat smaller coverage of late day and evening convection=20 capable of producing heavy rainfall. A secondary focus across the=20 terrain in Southeast AZ over into the NM Bootheel will also be an=20 area that could see some scattered heavy rain signals with some=20 support from global deterministic and ensemble members. Current QPF signal is modest with areal averages and the setup is more benign=20 in the grand scheme, especially considering the previous active=20 periods. Lamers/Bann Day 2 Valid 12Z Sat Aug 24 2024 - 12Z Sun Aug 25 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST/FOUR CORNERS AND SOUTH FLORIDA... ....Southwest and Four Corners... Lingering moisture and relative instability coupled with progressive shortwaves cutting through the Interior Mountain West will set up another round of isolated convection during the afternoon and early evening hours on Saturday before a gradual dissipation with the loss of diurnal heating. Pockets of heavy rainfall are still forecast across a similar corridor as on Day 1, so there is some concern that the antecedent conditions could be favorable for greater impacts pending what occurs leading up to the start of the forecast period on Saturday morning. Overall ensemble QPF footprint still indicates a max of 1-2", at best, within the strongest cores. This is still enough for flash flooding within complex terrain and especially around any burn scars. The previous MRGL risk was relatively unchanged. ....South Florida.. Incoming moisture flux with roots from the Caribbean will make headway into South Florida on Saturday with area precipitable water anomalies approaching 2 deviations above normal. The increasing moisture will be in proximity to a quasi-stationary front to the north...with a sharp delineation point of where the moisture pooling will reside. A Marginal risk area was maintained across the Southern FL Peninsula. Bann Day 3 Valid 12Z Sun Aug 25 2024 - 12Z Mon Aug 26 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST/FOUR CORNERS AND SOUTH FLORIDA... As an upper high over the Southern Plains begins to move eastward and away from the Southwest...another push of moisture and shortwave energy will move northward. This will sett up another round of isolated to widely scattered thunderstorms capable of producing flash flooding or run off problems within complex terrain and especially around any burn scars. Given the fetch of moisture from the southeast...the areal coverage was expanded somewhat compared with the size of the Marginal risk area on Dy 2. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7R3l223bS2LxOgAFcrqDGEHCsM3klqOHidfeESizzkPJ= vKp-1GZRmn9n46LHQezd61aIxe7MBr6tpTnn24xvYg4ZAEk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7R3l223bS2LxOgAFcrqDGEHCsM3klqOHidfeESizzkPJ= vKp-1GZRmn9n46LHQezd61aIxe7MBr6tpTnn24xv9720lCI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7R3l223bS2LxOgAFcrqDGEHCsM3klqOHidfeESizzkPJ= vKp-1GZRmn9n46LHQezd61aIxe7MBr6tpTnn24xvspPVwU8$=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) .