BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Fri, 13 Mar 2026 18:02:48 +0000 ----------------------------------------------------------- FOUS30 KWBC 131802 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 202 PM EDT Fri Mar 13 2026 Day 1 Valid 16Z Fri Mar 13 2026 - 12Z Sat Mar 14 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE PACIFIC NORTHWEST... 16Z Update... Generally no change to the previous thinking concerning the long- duration atmospheric river impacting the Pacific Northwest. However, we did proceed with adding a second Marginal Risk area to portions of southeast WA, northeast OR and west-central ID to account for heavy rains persisting at some of the lower elevations across these areas since the inland core of stronger IVT magnitudes continue to impact this region. Antecedent conditions across these areas have become increasingly sensitive with the rainfall of the past couple days, and given high streamflows, the additional rains here may encourage some localized flooding concerns. Orrison Previous discussion... Final day of impact from a continuous AR regime that has doused the Pacific Northwest with several inches of precipitation the last 72+ hours. Continued fetch off the Pacific will maintain its composition for another period with a slow shift south in the primary moisture advection regime as the approach of a final, yet potent shortwave helps press against the prevailing height field situated across the Pacific Northwest into British Columbia. A modest 600-800 kg/ms IVT signature has been persistent within a zone oriented from Olympia down towards the WA/OR border. Expectation is for the IVT advection pattern to pivot south to include more of northwest OR extending inland into the southern WA and northern OR Cascades leading to an extended moderate precipitation band through Friday into early Saturday. Current rates are still subject to be focused between 0.25-0.5"/hr at peak intensity with perhaps a few localized areas within the upslope regions of the Cascades to breach closer to 0.6-0.75/hr at times. This alone falls below the FFG criteria for the region, however its the longevity and recent priming that would tip the scales towards a low-end flash flood scenario, especially within the confines of any urbanized zones. Downsloping into the Willamette Valley should cause a regional min with this setup leading to lower probabilities of any flood concerns in the shadowed zone. City of Portland remains right on edge of persistent rain bands and waves of moderate rainfall with the heaviest likely to focus closer to Astoria and over into the adjacent Cascades thanks to the upslope component. D1 QPF indicates the sharp delineation in the split maxima with Portland proper right on the edge of the higher totals. Considering a solid run-to-run continuity across guidance the past 24-36 hours, there wasn't really any reason to deviate from the previous MRGL risk inheritance as 2-4" of rainfall with local maxima of 6" possible in the Cascades are enough to warrant at least a low-end risk. Kleebauer Day 2 Valid 12Z Sat Mar 14 2026 - 12Z Sun Mar 15 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Chenard Day 3 Valid 12Z Sun Mar 15 2026 - 12Z Mon Mar 16 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Some consideration was given to a Marginal risk across portions of the OH and TN valley where strong to severe convection is likely Sunday afternoon into the overnight. Working against a flash flood risk is the quick movement of the cold front and expected short duration of heavier rain rates. Experimental MPAS runs generally support hourly rainfall peaking around 1", which is below FFG. Given the intense nature of convection, it will only take some brief training or cell mergers to get rainfall towards 2", which would be enough for localized flash flooding. We will continue to=20 monitor, but for now will keep no areas in the ERO with the risk still considered below 5 percent. Chenard Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-hH2OX_vMiSekAU4Hc77zSB2An2ioPOEnc9UqA02NqRw= jqn1sSZJj1iZ3XcWUCXDKxgY1ZE1VBphOaq9NYmeaQRu_Wo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-hH2OX_vMiSekAU4Hc77zSB2An2ioPOEnc9UqA02NqRw= jqn1sSZJj1iZ3XcWUCXDKxgY1ZE1VBphOaq9NYmepKfgHF0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-hH2OX_vMiSekAU4Hc77zSB2An2ioPOEnc9UqA02NqRw= jqn1sSZJj1iZ3XcWUCXDKxgY1ZE1VBphOaq9NYmeDLgfjic$=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 3.28-Linux * Origin: Capitol City Online (1:2320/107) ----------------------------------------------------------- [Voltar]