Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 01 2023 23:52:41 FOUS30 KWBC 012352 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Wed Nov 01 2023 Day 1 Valid 01Z Thu Nov 02 2023 - 12Z Thu Nov 02 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR WESTERN WASHINGTON STATE AND NORTHWEST OREGON... Maintained the Marginal Risk area with no change from the 16Z Excessive Rainfall Outlook. Even though rainfall has been moving into parts of the Pacific Northwest during the late afternoon and early evening...rainfall rates have not been particular high and rainfall accumulations have not been of sufficient magnitude to warrant much concern. Expectation remains that there will be an increase in rates later this evening or overnight in a few hour window where problems from run off could still occur. HREF neighborhood probabilities remain low for rates of an inch per hour...but were in the 35 to 45 pct range for 3 inches per 12 hours in the southern Washington Cascades. Rainfall totals between 1-3" with localized 4-5" are forecast during the period with most of the rainfall not really starting until 02/05Z or 02/06 given the rates. The MRGL is maintained due to the risk of localized flooding and maintaining continuity with guidance and probabilistic fields generally unwavering. Bann Day 2 Valid 12Z Thu Nov 02 2023 - 12Z Fri Nov 03 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR NORTHWEST WASHINGTON AND THE CASCADES OF WASHINGTON AND OREGON... ....20Z Update... The main change in the period is the removal of the MRGL across the OR coast and tightening of the edges around the Cascades as the leeward portion of the range will likely miss out on the best precip potential given the downsloping pattern on the eastern side of the mountains. General 1-2" with local up to 3" is forecast for the front half of the forecast period with a degrading AR signature after 18z as the cold front moves inland and shuts off the moisture pipeline. The Cascades and Olympic Peninsula are very much favored for the continued heavy rain potential, although intensity wise will fall below the 1"/hr mark. The MRGL risk is primarily the compounding concerns of total rainfall with some localized flash flooding risks across the terrain influenced areas. This was one of the reasons to remove the coastal plain of Oregon from the current D2 MRGL. Forecast is otherwise still well on track with only minor variance in the guidance spread which is limited to noise at this range. Kleebauer ....Previous Discussion... The atmospheric river will be the most active during the 12Z Nov 2 to 00Z Nov 3 period across western Washington and Oregon with a notable southward shift of the main moisture flux anticipated with higher totals reflected along the northwest and central Oregon coast with some heavier rain expected along the central Oregon Cascades. The AR signal will decay the second half of the period. The WPC forecast has additional 1 to 2 inches falling over much of the same areas as the D1 period-- yielding 48 hour totals in the 2 to 4 inch range with isolated maximums nearing 6 inches. Minor adjustments were made to the inherited Marginal Risk area to reflect the latest trends and for the compounding effect from the initial surge of moisture at the back end of D2 with a continuation into D3 before rainfall subsides. Campbell Day 3 Valid 12Z Fri Nov 03 2023 - 12Z Sat Nov 04 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 =20 Campbell/Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6dh-IpC3t047ibDWaEtFssvhIpdhK0cymQCXXmTjg4oV= R2FsHRuKNou3hRI3isBYGMXg5rMoVkIAugD-N6fGbhkSFxI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6dh-IpC3t047ibDWaEtFssvhIpdhK0cymQCXXmTjg4oV= R2FsHRuKNou3hRI3isBYGMXg5rMoVkIAugD-N6fGftGAk4Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6dh-IpC3t047ibDWaEtFssvhIpdhK0cymQCXXmTjg4oV= R2FsHRuKNou3hRI3isBYGMXg5rMoVkIAugD-N6fGe0Tv3_E$=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) .