Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 03 2023 08:29:01 FOUS30 KWBC 030828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 AM EST Sun Dec 03 2023 Day 1 Valid 12Z Sun Dec 03 2023 - 12Z Mon Dec 04 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR ALL OF THE OREGON COAST RANGES AND MUCH OF THE OREGON CASCADES... A moderately-strong atmospheric river, centered on OR, will continue to push into the coast today through this evening. A brief reprieve from the rain is expected tonight between impulses of energy. On top of the rain that's already fallen, expect another 2 to 4 inches of rain through this evening, with local amounts as high as 6 inches for the day. More widely scattered flash flooding impacts are likely today due to so much rain falling in a short amount of time. NASA Sport imagery shows soil moisture profiles about normal for this time of year across western OR, or about 75% saturated. The additional rainfall today should take less time than yesterday to cause flash flooding impacts since there's rain ongoing and soil moisture levels continue to increase. The ERO risk areas today remain largely the same, with the only change of note to extend the Slight Risk into the northwest corner of CA, from Crescent City northward as the coastal ranges in that area may see 2 to 4 inches of rain through this evening. The Slight Risk remains in effect for much of the OR Cascades, as rising snow levels will allow for snowmelt to contribute to rising river levels on the west side of the range, along with most to all of the precipitation on the foothills of the Cascades falling as rain. Much lighter amounts of rain are expected from central WA north today as the focus says largely over OR, with only 1 to 2 inches of rain expected. Since this too will be added to previous' days rains, an isolated flash flooding instance can't be ruled out, and the Marginal remains unchanged. Wegman Day 2 Valid 12Z Mon Dec 04 2023 - 12Z Tue Dec 05 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE WASHINGTON STATE AND NORTHERN OREGON COAST RANGES AND CASCADES... A strong cold front associated with a 964 mb low in the Gulf of Alaska will move into the coast of WA and northern OR, and stall out there by Monday night. Moisture riding along and ahead of the front will move northeastward into the coast, allowing heavy rain to impact the Willamette Valley and Puget Sound regions between the coastal/Olympic ranges and the Cascades. As far as timing goes, light shower activity is expected for much of the day Monday, with the main rainfall expected overnight Monday night...spreading southward down the coast with time. For the valleys, expect the front to produce 1 to 3 inches of rain with locally higher amounts through early Tuesday morning. For the Cascades and coastal ranges, expect 3 to 5 inches of rain with locally higher amounts to 7 inches. The northeastward movement of the moisture plume will allow for some of the moisture to cross the Cascades crest and onto the lee side of the mountains. Much warmer air moving in with the moisture will also raise snow levels to the summits, so in addition to the heavy rain, some snowmelt will also contribute to rising river levels and potential flash flooding. The most impressive rainfall totals are likely to be on the west facing slopes of the Olympics, where there's good agreement that rainfall totals of 5 to 7 inches with local amounts to 9 inches expected. Once again the bulk of the heaviest rainfall will be from Monday evening through Monday night when the front both stalls out and rainfall rates are boosted by the approach of a strong shortwave trough. Thus, many of the day's expected flooding impacts are expected overnight when they're more dangerous. This amount of rain in a relatively short amount of time is likely to cause flash flooding concerns in the Olympics and surrounding plains, and the Slight Risk remains a higher end concern for the Olympics and south/west facing slopes. No significant changes were made to the ERO risk areas. Despite some small increases in rainfall amounts, particularly in the Olympics, the timing and evolution of the atmospheric river event remains largely unchanged from previous days and forecast confidence remains high. Wegman Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-X8G1rSJkAwVDhv3qBW9wGLvaRa0YOojJGy4SH776xT2= uTf6uCXZHUK6R7PREPnjrDD0AafyUtK3Qh_hjPuPxCgXius$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-X8G1rSJkAwVDhv3qBW9wGLvaRa0YOojJGy4SH776xT2= uTf6uCXZHUK6R7PREPnjrDD0AafyUtK3Qh_hjPuP6DhYoUM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-X8G1rSJkAwVDhv3qBW9wGLvaRa0YOojJGy4SH776xT2= uTf6uCXZHUK6R7PREPnjrDD0AafyUtK3Qh_hjPuPGwD5RAQ$=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) .