Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Nov 02 2023 23:40:36 FOUS30 KWBC 022340 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 739 PM EDT Thu Nov 02 2023 Day 1 Valid 01Z Fri Nov 03 2023 - 12Z Fri Nov 03 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 2 Valid 12Z Fri Nov 03 2023 - 12Z Sat Nov 04 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE OLYMPIC PENINSULA... Second AR within the last few days will bring heavy rainfall across NW Washington state and adjacent areas Friday evening through the end of the D2 period. Forecast integrated vapor transport (IVT) supports a low to medium scale AR event across the coastal sections of OR/WA with the highest impact zone favored from a latitude of Eugene, OR up through the Olympic Peninsula. The Olympics were the benefactor of this last AR event with general totals of 2.5-3.5" with localized 5" maximum on the southwest side of the Olympic terrain. A trend in recent guidance, backed by ML models are orienting the heaviest of the QPF field further north leading to a repeat of the same areas getting the most rainfall with this coming event as the one prior. Rates will still be an issue for higher impacts as less than 1"/hr rates will be common, less than 10% in the probabilistic realm, but the incessant nature of the precipitation over a 6-12 hr span being the primary concern for enhanced rainfall potential. Forecast totals over the Friday evening to early Saturday morning time frame range from 1.5-2.5" with local amounts over 3" possible within the terrain across the Olympics. The surrounding locales along the Skokomish River are also in a slightly higher impact potential due to river rises with the past rainfall adding a compounding setup for flood potential during the next event. With coordination from the Seattle WFO and agreement from impacted WFO's within the AR focus, have elected to shrink the previous MRGL forecast down to just include the NW corner of WA state with a focus over the Olympic Peninsula. =20 Kleebauer Day 3 Valid 12Z Sat Nov 04 2023 - 12Z Sun Nov 05 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE OLYMPIC PENINSULA... The back end of the next AR event will occur over the course of Saturday morning before quickly scaling back with the IVT signal across the PAC NW waning with the loss of a prominent 850-700mb moisture fetch off the Pacific. Continued locally moderate to heavy rainfall over an area that will be fairly water logged will occur through the front half of the D3 period with some localized flooding concerns continuing within the Olympic terrain and adjacent Skokomish river basin due to the compounding nature of all the rainfall. As a result, maintained a very similar orientation of the MRGL risk across the area compared to D2 with a slight modification over the NW corner of WA state.=20 Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_yCycEsYNAIyViiz95mXZ4BNv3PUsDiPzdVN1pNSEjtK= QS7Hn_yDNPqioq-fB9eRRoLb694X65wmdH80D6A3deZG-yk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_yCycEsYNAIyViiz95mXZ4BNv3PUsDiPzdVN1pNSEjtK= QS7Hn_yDNPqioq-fB9eRRoLb694X65wmdH80D6A3SfMXByw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_yCycEsYNAIyViiz95mXZ4BNv3PUsDiPzdVN1pNSEjtK= QS7Hn_yDNPqioq-fB9eRRoLb694X65wmdH80D6A3HHnuTOY$=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) .