Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Feb 21 2025 00:36:15 FOUS30 KWBC 210036 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 736 PM EST Thu Feb 20 2025 Day 1 Valid 01Z Fri Feb 21 2025 - 12Z Fri Feb 21 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 2 Valid 12Z Fri Feb 21 2025 - 12Z Sat Feb 22 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer/Wegman Day 3 Valid 12Z Sat Feb 22 2025 - 12Z Sun Feb 23 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN WASHINGTON STATE AND COASTAL OREGON... 20Z Update: No changes to the previous forecast as 12z guidance maintained continuity in both the location and magnitude of the incoming atmospheric river event. IVT anomalies around the order of +4 to +5 deviations will generate a significant deep moisture regime that will allow for steady moderate to locally heavy rainfall rates over the course of the Saturday afternoon and evening time frames, lingering into Sunday morning. QPF is currently estimated between 2-4" across the mountains with widespread 1-2.5" within the lower elevations, mainly the coastal plain of WA/OR. This is generally within the lower bounds of AR output for a 24 hr period, so the threat for flash flooding remains at the lower end of the MRGL risk threshold. Kleebauer ...Previous Discussion.. A pair of frontal disturbances are expected to move into the coast of the Pacific Northwest on Saturday. These disturbances will have peak integrated vapor transport (IVT) values around 700 kg/ms as they move ashore within a 130+ kt upper level jet. With that level of moisture advection off the Pacific, areas of heavy rain are expected, especially into the coastal ranges of Oregon and Washington as well as into the Cascades. Rain rates may reach up to a half inch per hour at times. Snow levels with these systems will be high enough (between 7,000 and 8,500 ft MSL) that much of the precipitation falling west of the Cascades will be in the form of rain. Colder air will remain in place further inland, especially into the higher elevations of Idaho and Montana so the flooding threat there will be near zero. West facing slopes will receive the greatest rainfall amounts Saturday and especially Saturday night, and it's along these slopes and their adjacent valleys where any isolated flash flooding may occur. Since most of the Marginal risk area is already very flood resistant, this is a lower-end Marginal Risk. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!476LinBN7WhIkR1V3FXIGttq9RVBSCE58KZmlEmZARTE= HFFMMiBxOJG0Hd55S-NIliBBBmiuxb9iIV5b6FCKc8Z-gjI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!476LinBN7WhIkR1V3FXIGttq9RVBSCE58KZmlEmZARTE= HFFMMiBxOJG0Hd55S-NIliBBBmiuxb9iIV5b6FCKveKDX8I$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!476LinBN7WhIkR1V3FXIGttq9RVBSCE58KZmlEmZARTE= HFFMMiBxOJG0Hd55S-NIliBBBmiuxb9iIV5b6FCKpuvIVGE$=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) .