BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Wed, 18 Mar 2026 07:39:53 +0000 ----------------------------------------------------------- FOUS30 KWBC 180739 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 339 AM EDT Wed Mar 18 2026 Day 1 Valid 12Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Persistent AR across WA state will lead to bouts of moderate to=20 occasionally heavy rainfall across the Olympic Peninsula into the=20 Northern Cascades. Down-sloping will reflect a general min across=20 the Seattle area, but the terrain will be susceptible to ongoing=20 rain prospects and totals between 1-3" for the day. This is an ongoing threat that will carry on beyond the period adding a compounding=20 factor to the hydrologic responses anticipated across the River=20 basins within northwest WA. High snow levels ~8000ft MSL will lead=20 to snow melt across the higher elevations within the Northern=20 Cascades and Olympic Mountain ranges to couple with the rainfall.=20 This excessive run off will be another factor in the additional=20 water sources that will drain into nearby streams and rivers that=20 will induce at least several action stage responses and some minor=20 to borderline moderate river flooding across the region. The=20 primary river of impact will continue to be the Chehalis River=20 where minor flooding is already occurring and additional elevated=20 stream flows and run off entering into the tributaries will=20 eventually cause the crests of the river to slowly rise. Flood=20 Watches are in effect across portions of northwest WA state,=20 including Mason county where the greatest focus of flooding will=20 occur around the Chehalis River. Considering the hydrologic factors at play despite rates only topping out around 0.5"/hr at peak=20 intensity, a MRGL risk was carried over for the period with little=20 to no change from the previous risk issuance. Kleebauer Day 2 Valid 12Z Thu Mar 19 2026 - 12Z Fri Mar 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... There are no changes from the prior forecast as the overall synoptic=20 pattern remains consistent in run-to-run continuity. Prevailing=20 onshore flow within a zone focused between a broad occluded cyclone=20 in the Gulf of Alaska and a stout ridge axis focused over the=20 Southwestern U.S. will lead to a prevailing moderate rain setup over=20 much of the same areas impacted the previous periods. Total rainfall=20 in the Northern Cascades over into the Olympic Peninsula will run=20 between 4-7" with local amounts to 9" possible in the 72 hour time=20 frame of the AR. The same impact scenarios apply with the focus=20 being a compounding factor of rainfall, snow melt, and prolonged run=20 off into local rivers and streams that could result in flooding=20 prospects for multiple days as river levels reach action stage and=20 minor to even moderate flood stages. It will be important to=20 maintain awareness on local river conditions as the additional rain=20 will exacerbate any receding potential within the river basins.=20 Highest impacted zone will continue to be the Chehalis River basin=20 where Flood Watches are in effect even into D3 (see below) due to=20 the prolonged AR and river levels continuing to run high after=20 several weeks of rainfall. Additional watches are in effect over the=20 Northern Cascades due to anticipated run off from rain and snow melt=20 leading to newer hydro concerns as the event wears on. The previous=20 MRGL risk inherited was unchanged given the continuity.=20 Kleebauer Day 3 Valid 12Z Fri Mar 20 2026 - 12Z Sat Mar 21 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Final day of impact for the current AR event over WA state will=20 occur within the D3 period with much of any rainfall expected to occur in the first half Friday before the event finally comes to a close a strong shortwave trough exits the Pacific with a cold front=20 passage signaling the end to the threat. Additional 1-2 inches of=20 rainfall across northwest WA will bring final event totals to the=20 5-10 inch range over the span of 4 days which will ultimately=20 contribute to persistent river flood concerns thanks to the snow=20 melt coupled with rainfall to drain into the basins surrounding the Olympic Peninsula and Northern Cascades. The last wave of precip=20 will be relatively heavy compared to the prior period as the=20 shortwave addition will add a bit more vigor in the ascent pattern=20 along with IVT and PWAT advection anomalies pushing 3-4 standard=20 deviations above normal, respectively. Thankfully, this last push=20 will materialize and end fairly quickly as the fast flow provided=20 by a stout 165kt upper jet max will advance the final=20 wave/disturbance eastward into southern British Columbia dragging=20 the cold front swiftly through the region between 18-00z Fri/Sat.=20 Flood Watches for the Cascades and portions of the Olympic=20 Peninsula, with a focus on the Chehalis River remain in effect=20 until Friday afternoon local time. The previous MRGL risk was=20 generally unchanged as the pattern remains locked-in across various guidance.=20 Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-EIKDveHWcdYPNLMDtWh2p-tZR9P_OC2M-_Bbj0y2y6L= Tu6ZM0iZRhghZFoy4QxixeCh30v7QI6HtY5vTIQ6wMP1xSc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-EIKDveHWcdYPNLMDtWh2p-tZR9P_OC2M-_Bbj0y2y6L= Tu6ZM0iZRhghZFoy4QxixeCh30v7QI6HtY5vTIQ6fHQ0UA0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-EIKDveHWcdYPNLMDtWh2p-tZR9P_OC2M-_Bbj0y2y6L= Tu6ZM0iZRhghZFoy4QxixeCh30v7QI6HtY5vTIQ6IA-zzYk$=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. 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