Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 19 2024 20:27:38 FOUS30 KWBC 192027 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 326 PM EST Fri Jan 19 2024 Day 1 Valid 16Z Fri Jan 19 2024 - 12Z Sat Jan 20 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 2 Valid 12Z Sat Jan 20 2024 - 12Z Sun Jan 21 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON... 21Z update: There's good model agreement with the deamplifying closed 500 mb low/trough moving into the Pacific Northwest early Saturday morning and areas of moderate to heavy rain ongoing across the northern California coast at 12Z Saturday. Rainfall rates of 0.25 to 0.50 (localized 0.5+ in/hr rates) are expected to impact portions of the northern California coast (with a focus from northern Sonoma County to Cape Mendocino) through 00Z as heavier rainfall shifts northward into far northern CA and southwestern Oregon. While precipitable water values from northwestern California into southwestern Oregon may struggle to reach 1 inch, persistent rainfall through the period is expected to allow for localized 3-5 inch totals for the 24 hour period ending 12Z Sunday. Given 200 to 400 percent of average rainfall for much of the region over the past week, some flooding concerns may be realized with a continuation of the previous Slight Risk with no significant changes. Otto Guidance has remained consistently wet now over the past few runs across portions of northern California and southwestern Oregon.=20 Precipitation is expected to develop across much of the region prior to Day 2 as a negatively-tilted mid-to-upper level trough and its associated frontal band move into the region Friday night. The models have been consistent in showing a weakening IVT plume as it moves onshore late Friday into early Saturday. However, westerly flow south of the parent low is expected to tap a secondary surge of deeper moisture and direct into the region as it lifts northeast along the northern California to southern Oregon coasts on Saturday. This moisture along with sufficient large-scale lift is expected to support an increase in rainfall rates with moderate to heavy amounts expected beginning Saturday morning. The general consensus of the deterministic models over past few runs suggests amounts of 1-3 inches, with locally heavier accumulations are likely across the region, with the heaviest amounts most likely in the upslope regions of the coastal ranges and the northern Sierra and southern Shasta foothills. HREF probabilities suggest that much of this may occur in the first 12 hours, showing high neighborhood probabilities for accumulations of 2 inches or more from 12Z Sat - 00Z Sun across parts of the area. Given the wet antecedent conditions and the move in the models toward a wetter solution, opted to upgrade this area to a Slight Risk.=20=20=20 Pereira Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!43SltJnw9hE9CEV_FLjoZyLrKj7Mdd8277nnUe8-PxWA= YHN05VNpVMuarPsVOYcKExnQG1IdtFSwqIZjXAYtC8uwciw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!43SltJnw9hE9CEV_FLjoZyLrKj7Mdd8277nnUe8-PxWA= YHN05VNpVMuarPsVOYcKExnQG1IdtFSwqIZjXAYtonIqPRc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!43SltJnw9hE9CEV_FLjoZyLrKj7Mdd8277nnUe8-PxWA= YHN05VNpVMuarPsVOYcKExnQG1IdtFSwqIZjXAYts4ynhso$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .