Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Oct 31 2023 19:55:49 FOUS30 KWBC 311955 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 354 PM EDT Tue Oct 31 2023 Day 1 Valid 16Z Tue Oct 31 2023 - 12Z Wed Nov 01 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 =20 Campbell/Kleebauer Day 2 Valid 12Z Wed Nov 01 2023 - 12Z Thu Nov 02 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR WESTERN WASHINGTON STATE AND NORTHWEST OREGON... ....20Z Update... Very little deviation from the previous forecast as the atmospheric river signature is most prevalent across western WA into northwest OR with highest rainfall totals focused over the Cascades in WA/OR into the Columbia Gorge over northern OR. 12z HREF neighborhood probabilities of at least 3" of rainfall between 00-12z Thursday (Second half of the D2 period) are running very high (70-80%) within the southern Washington Cascades down into the valley west of Portland near Mount Hood. Rainfall intensity will mostly reside below the 1"/hr mark for a majority of the area, but a continuous 0.5-1"/hr rainfall rate over terrain will cause some localized flooding potential within smaller towns and more established urban settings. GFS/ECMWF combo has come into line with highest forecast Integrated Vapor Transport (IVT) centered over Northwest OR with extension into central WA state by the end of the forecast period. IVT indices point towards a borderline weak to moderate AR signal which correlates to the lower threshold of FFG exceedance potential within the impact zones. This helped maintain continuity in the previous forecast cycle. Kleebauer ....Previous Forecast... An atmospheric river will be making its way inland during this period, bringing beneficial moisture to western parts of Oregon while moderate-to-heavy rainfall for northwest Oregon and western Washington. Much of coastal Oregon and the Willamette Valley are experiencing lower than normal river levels, so the start of this first atmospheric river will largely be absorbed into the soil. Recent burn scars scattered about the Washington Cascades will increase the threat for localized flooding concerns with this anomalous plume of moisture. PW values of 1.5 inches will be nearly double the normal for early November by 00Z then another surge brings it to being tripled the average. The Marginal Risk area that was already in effect had minor adjustments made to reflect the latest trend in model guidance and WPC QPF. Campbell 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!-6q6Jb8JSdEL-a7_ABezdr5I1S_p6JajJD2eAYxySW5x= pP1PB88jcGfO18NYoZrPqPvNK-3BYKLGafJ6M5ipOiocEgc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-6q6Jb8JSdEL-a7_ABezdr5I1S_p6JajJD2eAYxySW5x= pP1PB88jcGfO18NYoZrPqPvNK-3BYKLGafJ6M5ipBlKJ4d4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-6q6Jb8JSdEL-a7_ABezdr5I1S_p6JajJD2eAYxySW5x= pP1PB88jcGfO18NYoZrPqPvNK-3BYKLGafJ6M5ip65XnQHs$=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) .