Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Wed Nov 01 2023 08:28:00 FOUS30 KWBC 010819 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Wed Nov 01 2023 Day 1 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... The latest guidance is persistent with the atmospheric river across western Washington and into northwest Oregon with the highest rainfall focused over the Cascades in Washington and Oregon into the Columbia Gorge over northern Oregon. Rain intensity ramps up around 00Z Nov 2 and maintains a continuous 0.5-1"/hr rainfall rate over terrain through 12Z. Rainfall intensity will mostly reside below the 1"/hr mark for a majority of the area, but will cause some localized flooding potential within smaller towns and more established urban settings, especially for recent burn scars and other sensitive areas. Areal averages are still expected to be in the 1 to 3 inch range with very localized maxes up to 4 inches certainly possible. The 12z HREF neighborhood probabilities of at least 3" of rainfall between 00-12z Thursday (Second half of the D1 period) is running very high (70-90%) within the southern Washington Cascades down into the valley west of Portland near Mount Hood. The Marginal Risk area was maintained with some minor adjustments to reflect the latest trend in model guidance and WPC QPF. Campbell Day 2 Valid 12Z Thu Nov 02 2023 - 12Z Fri Nov 03 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR WESTERN WASHINGTON AND OREGON... 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. During this period a resurgence of anomalous moisture will stream onshore further south than the most recent atmospheric river, focusing over southern Oregon and northern/central California. These areas largely were not impacted by the recent moderate/heavy rainfall event thus being able to absorb at least a couple of inches without notable hazardous impacts to the region. The area to watch for soils reaching saturation, or possibly exceeding saturation, will likely be northern/central California where the PW anomalies reach triple the average for early November. The WPC forecast has much of the Pacific Northwest and northern California less than 1 with a concentration of 2/2.25 inches near the far southwest corner of Oregon/Northwest California. Campbell $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .