Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 03 2025 00:19:00 FOUS30 KWBC 030018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 718 PM EST Thu Jan 2 2025 Day 1 Valid 01Z Fri Jan 03 2025 - 12Z Fri Jan 03 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHWESTERN OREGON AND NORTHWESTERN CALIFORNIA... ....01Z update... Maintained the Marginal Risk area with the continuation of a relatively weak but long duration atmospheric river. Satellite imagery from late this afternoon supports short-range guidance idea of an uptick in rainfall rates given cooling cloud tops within a region of diffluent flow approaches from the eastern North=20 Pacific. The previous adjustments look good and the outlook area=20 remains largely unchanged. Bann ....16z update... Forecast remains on track though a few 12z Hi-Res CAM solutions suggest a slightly northward track of the longer warm advection showers into the central OR coast. As such, a small northward inclusion was made to the initial forecast risk area, while the southern portions across NW CA are sculpted to the favored terrain. Gallina A relatively weak, long duration atmospheric river will continue to impact portions of the Pacific Northwest coast today, shifting focus from northwest California into far southwest Oregon. While there is a distinct lack of instability to fuel rainfall rates beyond 0.25"/hr, tropospheric moisture is still rather elevated with precipitable water values of 1.0-1.2" (2.0-2.5+ standard deviations, near the 95th percentile). Two distinct rounds of precipitation (one from late this morning through mid afternoon, and another round from late evening through the overnight) are expected to bring additional rainfall of 3-5" (primarily for Del Norte county, CA and Curry county, OR). While rapid onset flooding is generally not expected (given the muted rainfall rates), these areas (and surroundings) have already received 1-2" over the past 24 hours with USGS streamflow data indicating widespread above normal to much above normal streamflows (with some even at record territory for the date), suggesting additional rainfall may lead to localized flooding impacts. Churchill Day 2 Valid 12Z Fri Jan 03 2025 - 12Z Sat Jan 04 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR FAR SOUTHWESTERN OREGON AND PORTIONS OF NORTHERN CALIFORNIA... ....2000 UTC Update... No changes made to the previous D2 Marginal Risk area, based on the latest (12Z) guidance, which now incorporates the full suite of high-res CAMs (including the elevated HREF probabilities of hourly rainfall rates of 0.50+). Hurley ....Previous discussion below...A strong shortwave and associated surface low will plow into the coast of California and Oregon on Friday. Locally heavy rain with rates around 1/2 inch per hour will be ongoing Friday morning along the coast. The shortwave and low will move into the coast Friday evening and through the overnight. This will shift the heaviest rains both southward and inland, bringing northern portions of the Sacramento Valley, which has been largely missed with the previous days' rains, into the potential for heavy rain and higher elevation snow. The Marginal Risk inherited was left unchanged with this issuance. The heaviest rains are likely to be Friday morning as the aforementioned shortwave and surface low approach. Once they move into the coast Friday evening and overnight, rainfall rates should diminish quite a bit as the associated moisture moves inland. Any flooding from the Day 2/Thursday period will likely continue into Friday morning along the Oregon and California coasts...with any minor flooding for the Sacramento Valley more likely Friday afternoon. Wegman Day 3 Valid 12Z Sat Jan 04 2025 - 12Z Sun Jan 05 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W= klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBFRQpeZ8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W= klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBGie6eOY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W= klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBxl9gGXY$=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) .