Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 08 2025 16:00:11 FOUS30 KWBC 081559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1059 AM EST Sat Mar 8 2025 Day 1 Valid 16Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE EAST-CENTRAL GULF COAST ... ....16Z Update... Mosaic radar imagery from 1530Z showed ongoing showers and thunderstorms extending from southern Louisiana to northern Florida, tied to a low level convergence boundary which was partially associated with the leading edge of surface moisture=20 return in the Gulf as seen on layered PW imagery. This boundary,=20 along with a forecast cold front to drop southward through Alabama/Georgia later today along with an elevated convergence=20 axis aligned from west to east are likely to support heavy rain=20 later this evening and overnight over the Florida Panhandle,=20 and possibly southern Alabama/Georgia into northern Florida. The latest NWP continues to suggest the best potential for flash flooding will occur tonight, perhaps in the last 6 hours of the D1 period as better forcing arrives ahead of the shortwave mentioned below edges closer, combined with right-entrance region ascent related to a 150-170 kt upper level jet max over the northern Gulf Coast states. Rainfall rates of 1-2 in/hr will be possible from west to east training along the aforementioned boundary/boundaries. Otto ....previous discussion follows... There will be an increasing chance for showers and thunderstorms=20 capable of producing localized downpours later today and tonight=20 across portions of the central Gulf coast. There could be some=20 rainfall rates that exceed one inch per hour as a fairly potent=20 shortwave trough/upper low makes its way from the Southwest U.S.=20 into the Southern Plains by early Sunday morning. South to=20 southwesterly low level flow ahead of the mid- level energy will=20 start to draw moisture northward...with precipitable water values=20 increasing into the range between 1.50 and 1.75 inches by later=20 this afternoon...although model guidance still suggests that the=20 higher rainfall rates probably do not develop until the better=20 upper level support approaches and a well- defined cold front nears the coast later tonight/early Sunday morning, Given the Flash=20 Flood Guidance in the region...not expecting more than isolated=20 problems given the 08/00Z HREF neighborhood probabilities for=20 amounts exceeding an inch of accumulation in one hour. Bann Day 2 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.... Considerable spread remains in the numerical guidance in term of placement...but enough QPF along the path of a well-defined shortwave to keep a Marginal risk in place. The 08/00Z GFS started out in fairly good agreement with other models but becomes a northerly outlier as it gets drawn northward by northern stream energy...while the 08/00Z NAM continued to indicate heavier rainfall with a greater threat for flash flooding farther 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. In large part...there were few changes needed given good continuity with the WPC deterministic QPF and the consensus QPF of the non- NCEP guidance. Bann Day 3 Valid 12Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025 The probability of rainfall exceeding Flash Flood Guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5U6iaTHqPpTJ57iinxga0jArMYEAMu7X8UO5l1nf6bTT= ITK0lDWhNtIj5vIj1-xUNPRGD-7Dw7oQ8PG6ffvN6hF1DOk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5U6iaTHqPpTJ57iinxga0jArMYEAMu7X8UO5l1nf6bTT= ITK0lDWhNtIj5vIj1-xUNPRGD-7Dw7oQ8PG6ffvNIsVSOqY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5U6iaTHqPpTJ57iinxga0jArMYEAMu7X8UO5l1nf6bTT= ITK0lDWhNtIj5vIj1-xUNPRGD-7Dw7oQ8PG6ffvNIJ0mYfs$=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) .