BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Wed, 18 Mar 2026 18:30:19 +0000 ----------------------------------------------------------- FOUS30 KWBC 181827 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 227 PM EDT Wed Mar 18 2026 Day 1 Valid 16Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... ...16Z update... A long duration, multi-day, AR event will continue today/tonight with a fairly steady axis of moisture transport into western Washington. IVT values along the coast have been, and will continue to be, between 500 and 600 kg/m/s through Thursday morning (locally higher on occasion). Selected gauge observations within the Washington Cascades showed peak rain values in the 0.4 to 0.5 in/hr range earlier this morning but these higher rates have been localized within the Cascades east of the Puget Sound and surrounding higher observations have been between 0.1 and 0.3 in/hr. With little change to the synoptic scale setup forecast through Thursday morning, it will be mesoscale impulses within the southwesterly flow aloft that will bring about fluctuations in rainfall intensity and location, but otherwise things look fairly steady state today. The latest 12Z HREF is in pretty good agreement with previous cycles with minor mesoscale differences in location/magnitude, highlighting the greatest 24 hour totals across the Olympic Peninsula into the Cascades (north of I-90). 24 hour QPF values should average in the 1 to 3 inch across these locations with locally higher values near 4 inches expected, perhaps an isolated spot near 5 inches through Thursday morning. No changes were made to the Marginal Risk area and the previous forecast discussion remains on track. Otto ...Previous discussion follows... Persistent AR across WA state will lead to bouts of moderate to occasionally heavy rainfall across the Olympic Peninsula into the Northern Cascades. Down-sloping will reflect a general min across the Seattle area, but the terrain will be susceptible to ongoing 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 factor to the hydrologic responses anticipated across the River basins within northwest WA. High snow levels ~8000ft MSL will lead to snow melt across the higher elevations within the Northern Cascades and Olympic Mountain ranges to couple with the rainfall. This excessive run off will be another factor in the additional water sources that will drain into nearby streams and rivers that will induce at least several action stage responses and some minor to borderline moderate river flooding across the region. The primary river of impact will continue to be the Chehalis River where minor flooding is already occurring and additional elevated stream flows and run off entering into the tributaries will eventually cause the crests of the river to slowly rise. Flood Watches are in effect across portions of northwest WA state, including Mason county where the greatest focus of flooding will occur around the Chehalis River. Considering the hydrologic factors at play despite rates only topping out around 0.5"/hr at peak intensity, a MRGL risk was carried over for the period with little 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... ...1830Z update... No changes to the Day 2 ERO based on the latest guidance,=20 including the 12Z HREF exceedance probabilities. Hurley ...Previous discussion follows... There are no changes from the prior forecast as the overall synoptic pattern remains consistent in run-to-run continuity. Prevailing 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 even into D3 (see below) due to the prolonged AR and river levels continuing 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. The previous MRGL risk inherited was unchanged given the continuity. 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... ...1830Z update... Minor tweaks to the Day 3 Marginal Risk was made to essentially mirror the Day 2 ERO, since it's essentially the same 'event', which as per the discussion below, will be be waning during the day Friday as the plume of highest TPW (1.0+ inches) and IVT (600-700+ kg/m/s) push south of Washington and dissipate with time. Hurley ...Previous discussion follows... Final day of impact for the current AR event over WA state will 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 passage signaling the end to the threat. Additional 1-2 inches of rainfall across northwest WA will bring final event totals to the 5-10 inch range over the span of 4 days which will ultimately contribute to persistent river flood concerns thanks to the snow melt coupled with rainfall to drain into the basins surrounding the Olympic Peninsula and Northern Cascades. The last wave of precip will be relatively heavy compared to the prior period as the shortwave addition will add a bit more vigor in the ascent pattern along with IVT and PWAT advection anomalies pushing 3-4 standard deviations above normal, respectively. Thankfully, this last push will materialize and end fairly quickly as the fast flow provided by a stout 165kt upper jet max will advance the final wave/disturbance eastward into southern British Columbia dragging the cold front swiftly through the region between 18-00z Fri/Sat. Flood Watches for the Cascades and portions of the Olympic Peninsula, with a focus on the Chehalis River remain in effect until Friday afternoon local time. The previous MRGL risk was generally unchanged as the pattern remains locked-in across various guidance. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7ZRyDZuD7smE1kXYzV2y57c2U-nVj5kcPn46tNg7eMvf= H1XuWJtCRXqONkZAD-9K88MPfjlDQO-ix3JClRuA3UhRqFw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7ZRyDZuD7smE1kXYzV2y57c2U-nVj5kcPn46tNg7eMvf= H1XuWJtCRXqONkZAD-9K88MPfjlDQO-ix3JClRuAdFFS_5Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7ZRyDZuD7smE1kXYzV2y57c2U-nVj5kcPn46tNg7eMvf= H1XuWJtCRXqONkZAD-9K88MPfjlDQO-ix3JClRuASX0Il3A$=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]