Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 16 2025 20:00:19 FOUS30 KWBC 162000 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sun Mar 16 2025 Day 1 Valid 16Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA... ....20Z Special Update... In coordination with AKQ/Wakefield, VA forecast office, a Slight Risk upgrade was introduced with this update. The lines of storms approaching the Slight Risk area from the west are expected to slow and reform on the southern/western end of the line, resulting in some training of the storms. While the area has been dry, the urban areas within the Slight, namely the Hampton Roads area, could be=20 at particular risk for flash flooding as the storms will be capable of 1-2 inch per hour rates. With potential for training thunderstorms, these high rainfall rates could exceed flash flood guidance in the area, resulting in very rapid filling of storm=20 drains and drainage areas, resulting in localized flash and urban=20 flooding. A Flood Watch has been issued for areas at particular=20 risk. Wegman ....16Z Update... ....West Coast... No changes were needed to the ongoing Marginal Risk area. A long fetch of persistent southwest to westerly flow will continue to pump plentiful Pacific moisture into the west coast, with rates exceeding a half inch per hour at times. Any resultant flooding would likely be larger-scale river flooding since the rain rates don't necessarily support flash flooding, but rapid rises in streams and creeks could locally lead to out-of-bank flooding. Wegman ....Previous Discussion... ....East Coast... A progressive cold front and negatively tilted longwave trough will traverse much of the East Coast today, as the upper-level pattern becomes a bit less amplified (shortwave over the Southeast cutting off from northern/polar stream with ridging building over central CONUS). Convection in association with the front looks to generally result in areal average totals of 1.0-1.5" (per latest WPC QPF), but the latest CAMs (00z HREF suite) suggests relatively high odds (30-50%+) for localized totals in excessive of 2" (per 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 particularly high here). While this is a lower-end Marginal risk for most places, the risk is maximized over coastal NC where 3" exceedance probs are 40-60%. ....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. Wegman 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. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7LAd_si0ybsa7cnp24TsCrAgQQdGw8ejPpBzQO8I_5aN= 3akO_MYSw8BFdHMfugJxWQd20t3jzH6nMXKQu-v_lbw22Gc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7LAd_si0ybsa7cnp24TsCrAgQQdGw8ejPpBzQO8I_5aN= 3akO_MYSw8BFdHMfugJxWQd20t3jzH6nMXKQu-v_JpmRWNs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7LAd_si0ybsa7cnp24TsCrAgQQdGw8ejPpBzQO8I_5aN= 3akO_MYSw8BFdHMfugJxWQd20t3jzH6nMXKQu-v_xMP7GeE$=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) .