Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 08 2025 00:45:50 FOUS30 KWBC 080045 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 745 PM EST Fri Mar 7 2025 Day 1 Valid 01Z Sat Mar 08 2025 - 12Z Sat Mar 08 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 2 Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE CENTRAL GULF COAST... 19Z Update... No significant changes were made to the previous outlook area. Previous discussion... There will be an increasing chance for showers and thunderstorms to organize and become capable of producing rainfall rates in the 1 to 2 inch per hour range along portions of the central Gulf coast on Saturday and Saturday night. A fairly potent upper low will be making its way from the Southwest U.S. into the Southern Plains by early Sunday morning. South to southwesterly low level flow ahead of the mid- level energy will start to draw moisture northward...with precipitable water values increasing into the range between 1.50 and 1.75 inches by Saturday afternoon...although present indications are that the higher rainfall rates probably do not develop until the better upper level support arrives and a well- defined cold front makes approaches the coast later in the day. The 07/00Z suite of QPF guidance still focused parts of the Gulf coast for mainly a low-end risk of excessive rainfall...which mirrored the WPC deterministic QPF preference which gave least consideration to the more northerly position of the GFS QPF compared with other operational model runs...and offered strong support to the placement of yesterday's Day 3 ERO. Consequently...only minor changes were needed. Pereira/Bann Day 3 Valid 12Z Sun Mar 09 2025 - 12Z Mon Mar 10 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEAST U.S.... 19Z Update... Made minor adjustments to the previous outlook, including a slight extension north, but not the degree that the NAM or GFS might suggest. There was notable spread in the 12Z guidance with respect to the axis of heavier precipitation. The NAM, and to a lesser degree the GFS, indicate heavier precipitation, and a greater threat for flash flooding further to the north. Less weight for now was given to these solutions, keeping the deterministic QPF and the Marginal Risk for excessive rainfall more in line with the more southerly ECMWF, CMC, and UKMET guidance. Previous Discussion... The potent shortwave trough that brings the risk of excessive rainfall along the Gulf coast on Day 2 will continue tracking eastward from the Southern Plains towards the Florida panhandle or southern Alabama by early Monday morning.. Moist southwesterly flow ahead of the system will have drawn an airmass with precipitable water values in excess of 1.5 inches over portions of the northern Florida peninsula and adjacent parts of Georgia. The WPC deterministic QPF forecaster still gave less weight to the GFS...resulting in little need to make more than some cosmetic changes to the placement of yesterday's Day 4...before the bulk of the rainfall from this system moves offshore. Pereira/Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-KUyhPC9G34twpAgxpHaFtx6jijoLwih78wD4rTtrX50= fr3aLlsyuS4OlMN5ww3Vi-6wC5-Zmb9FoV1pgj0ourR5y6U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-KUyhPC9G34twpAgxpHaFtx6jijoLwih78wD4rTtrX50= fr3aLlsyuS4OlMN5ww3Vi-6wC5-Zmb9FoV1pgj0oyL5LkYc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-KUyhPC9G34twpAgxpHaFtx6jijoLwih78wD4rTtrX50= fr3aLlsyuS4OlMN5ww3Vi-6wC5-Zmb9FoV1pgj0oG0ThfY4$=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) .