Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 16 2025 08:26:00 FOUS30 KWBC 160825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 425 AM EDT Sun Mar 16 2025 Day 1 Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE EAST COAST FROM SOUTH CAROLINA THROUGH SOUTHERN NEW ENGLAND,=20 AND FOR PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON... ....East Coast... A progressive cold front and negatively tilted longwave trough=20 will traverse much of the East Coast today, as the upper-level=20 pattern becomes a bit less amplified (shortwave over the Southeast=20 cutting off from northern/polar stream with ridging building over=20 central CONUS). Convection in association with the front looks to=20 generally result in areal average totals of 1.0-1.5" (per latest=20 WPC QPF), but the latest CAMs (00z HREF suite) suggests relatively=20 high odds (30-50%+) for localized totals in excessive of 2" (per=20 40-km neighborhood probabilities). The inherited Marginal risk area was expanded a bit to generally encompass where 2" exceedance probs are 30%+ (but excluding FL and much of southeast GA, as FFGs are=20 particularly high here). While this is a lower-end Marginal risk=20 for most places, the risk is maximized over coastal NC where 3"=20 exceedance probs are 40-60%.=20 ....Southwest Oregon into Northern California... A relatively weak and narrow atmospheric river (AR) will continue to bring moderate to heavy rainfall to the OR/CA coastal border region with additional forecast localized totals today of 2-5". Most of this rainfall will be spread out over a 12-18 hour period with peak rates staying under 1"/hr due to a lack of instability (though 1"/hr rates may be reached for a brief period near the CA/OR border along the coast where the HREF indicates MU CAPE up to nearly 500 J/kg). Maintained the inherited Marginal risk, though a future targeted upgrade to Slight risk remains possible (depending on the evolution of rainfall this morning and any upticks in QPF in the 12z HREF suite). Churchill Day 2 Valid 12Z Mon Mar 17 2025 - 12Z Tue Mar 18 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 3 Valid 12Z Tue Mar 18 2025 - 12Z Wed Mar 19 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_E215qJVJD0nfnpZo2yNrpfOp15W3GCdbPAZ-yN3Ix7H= vy5vz0ZR3Y8GgUI8yG_DCYUkzwNK3MUyCUwYihYKSwqM4lI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_E215qJVJD0nfnpZo2yNrpfOp15W3GCdbPAZ-yN3Ix7H= vy5vz0ZR3Y8GgUI8yG_DCYUkzwNK3MUyCUwYihYKaUCZqDo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_E215qJVJD0nfnpZo2yNrpfOp15W3GCdbPAZ-yN3Ix7H= vy5vz0ZR3Y8GgUI8yG_DCYUkzwNK3MUyCUwYihYKJaOI3Og$=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) .