BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Tue, 17 Mar 2026 23:48:32 +0000 ----------------------------------------------------------- FOUS30 KWBC 172348 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 748 PM EDT Tue Mar 17 2026 Day 1 Valid 01Z Wed Mar 18 2026 - 12Z Wed Mar 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... ...01Z Update... Once again...no change was made to the outlook area given the consistent signal for rainfall rates to increase and may reach greater than 0.5 inches per hour after 18/06Z. Remainder of the forecast reasoning below remains valid. Bann ...17/16Z update... No changes to the outlook area for this update as the 12Z hires models and the forecast reasoning below remains reasonable. The plume of IVT will remain focused across western Washington over the next 24 hours with some varying in latitude. The HREF members have varied a bit with 24 hr QPF magnitude over the past 2-3 cycles but have largely remained the same. 12Z HREF 40 km neighborhood probabilities for 0.5+ inches per hour remain negligible (outside of peaks such as Mt. Baker and Mt. Rainier) until 06-12Z for the northern Washington Cascades where values peak in the 30-40 percent range. All of the 12Z HREF members show 24 hr QPF of 3+ inches within the central/northern Washington Cascades with neighborhood probabilities for 5+ inches just over 40 percent east of Puget Sound. However, rain rates do not appear to be a significant driver of potential flooding. Otto ...previous discussion follows... Active pattern across the Gulf of Alaska will lead to another AR contribution into portions of the Pacific Northwest as the main IVT surge will adjust south into WA state after impacting neighboring British Columbia the past 24-48 hours. IVT forecast remains consistent within guidance as values between 500-700 kg/ms are expected across northwest WA state with the surge propagating far enough inland to impact the Northern Cascades. Rainfall amounts between 2-3" will be common in the hardest hit areas, mainly into the Olympic Peninsula, Chehalis River valley, as well as the Cascades to the east of Seattle. Latest 00z HREF neighborhood probabilities for >2" of rainfall over the course D1 are running between 50-70% across the Olympic Peninsula into the Chehalis River basin where Flood Watches have been issued for the upcoming AR. Probabilities for the Northern Cascades are more robust for the same 2" threshold, running between 70-90+% across the entire area from Mount Rainier up to the Canadian border. Greater than 3" probs are modest between 50-70% in those interior terrain areas, including the highest elevations of the Olympics. Snow levels are forecast to be around 8000ft MSL leading to a large portion of the mountain ranges to see ample rainfall and snow melt that will contribute to higher run off prospects. Rainfall rates will lack vigor to the point for a more substantial impact, so the threat is mainly due to prolonged moderate to locally heavy rain prospects falling over relatively moist soil layer present after being impacted for weeks leading in coupled with the expected snow melt. The previous MRGL risk was generally unchanged with the threat leaning towards the low to mid level of the risk threshold. Areal hydrologic concerns are still viable with river and small stream flooding the most notable potential impacts as forecasts around some of the major river basins, including the Chehalis River, are expected to reach into Action stage and even some minor river flood forecasts. Be sure to check into the latest forecasts from the local Seattle WFO and the National Water Center for the latest on the river flooding threat. Kleebauer Day 2 Valid 12Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Occluded low over the Gulf of Alaska and a strong mid-level ridge positioned across the Southwest U.S. will lead to a continued transport of modest IVT into WA state for the D2 period. AR dominated pattern will enhance rainfall prospects for the northern half of WA leading to cumulative rainfall totals breaching 4" in spots within the Northern Cascades, Olympics, and adjacent coastal areas of northwest WA. Real concern is the growing hydrologic factors with river flooding coupled with moderate rainfall posing a problem for areas around the main rivers and tributaries for the aforementioned areas. Flash flood threat remains lower end by definition due to the rates anticipated with the rainfall as hourly rainfall will remain <0.5"/hr for a majority of Wednesday. However, the coupling of the previous days rain and the already saturated soils will likely lead to some hydro concerns mid-week, especially for the Chehalis River basin and the rivers/stream connected with the Northern Cascades as they encounter the tandem of rainfall and snow melt. Maintained the previous MRGL risk inherited with no modifications necessary as the forecast remains on track. Kleebauer Day 3 Valid 12Z Thu Mar 19 2026 - 12Z Fri Mar 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Persistent onshore flow within a zone focused between a broad occluded cyclone in the Gulf of Alaska and a stout ridge axis focused over the Southwestern U.S. will lead to a prevailing moderate rain setup over much of the same areas impacted the previous periods. Total rainfall in the Northern Cascades over into the Olympic Peninsula will run between 4-7" with local amounts to 9" possible in the 72 hour time frame of the AR. The same impact scenarios apply with the focus being a compounding factor of rainfall, snow melt, and prolonged run off into local rivers and streams that could result in flooding prospects for multiple days as river levels reach action stage and minor to even moderate flood stages. It will be important to maintain awareness on local river conditions as the additional rain will exacerbate any receding potential within the river basins. Highest impacted zone will continue to be the Chehalis River basin where Flood Watches are in effect for multiple days due to the prolonged AR and river levels continue to run high after several weeks of rainfall. Additional watches are in effect over the Northern Cascades due to anticipated run off from rain and snow melt leading to newer hydro concerns as the event wears on. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6ZCrr4hRWmZkDduIWSs6RolOJtCu41gArCngVLxkVKv6= MP03SalZ-wdjJMT2dyfs2xTtwXStXqa2tq_2ukvAgJEm3_0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6ZCrr4hRWmZkDduIWSs6RolOJtCu41gArCngVLxkVKv6= MP03SalZ-wdjJMT2dyfs2xTtwXStXqa2tq_2ukvAAugpCCo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6ZCrr4hRWmZkDduIWSs6RolOJtCu41gArCngVLxkVKv6= MP03SalZ-wdjJMT2dyfs2xTtwXStXqa2tq_2ukvAzlHnzDI$=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]