Latest update from the Portland Office of the National Weather Service 11/17/24:
Multiple Weather Systems to Bring Heavy Cascade Snow and a Potential Atmospheric River and Flooding Event this Week, plus Hazardous Seas, Tidal Overflow Flooding, and Breezy Winds.
KEY POINTS
Minor tidal overflow flooding is likely for the south WA and north/central OR coast around high tides today due to the Perigean spring tides. Minor flooding will be possible in low lying areas near bays, sloughs, portions of highway 101 and the lower reaches of the coastal rivers. The greatest impacts are expected to occur around hightide this afternoon with up to one foot of water.
Heavy snow returns to the Cascades, including the passes, and the Coast Range this afternoon through Monday (11/17-11/18). There are high probabilities over the Cascades for 24-hr snow amounts of 12 inches or greater for elevations above 2000-3000 feet (see graphics).
Also, snow amounts of 3-12 inches are forecast for the Coast Range above 2000 feet, heaviest above 2500-3000 feet. Expect difficult travel conditions over the passes with a60-80% chance for major travel impacts.
For the lowlands, periods of heavy rain will occur with minor urban flooding possible in low-lying areas with poor drainage.
Breezy south winds continue over the area today. Forecast wind speeds are generally not strong enough for impacts beyond minor tree damage and isolated power outages, especially for inland locations. However, there is a small chance for wind gusts over 40 mph for inland areas, which would result in greater impacts (see graphics).
Chances have continued increasing for a prolonged atmospheric river/river flooding/urban flooding event Tuesday – late week (11/19-11/22). There will also be a threat for landslides in areas of steep terrain, as well as debris flows over/near recently burned areas if the worst-case scenario verifies. See graphics for best casescenario, most likely scenario, and worst case scenario for rain amounts. Best case scenario would suggest little tono river flooding at all, while the worst case scenario would suggest widespread river flooding with majorflooding for rivers draining the coastal mountains, as well as significant urban flooding and a high threat forlandslides and debris flows. Breezy east to southeast winds Monday night into Wednesday (11/18-11/20) which could cause tree damage and isolated power outages, especially for inland locations.
Coastal Waters: Hazardous seas expected today – Thursday (11/17-11/21) with Gale to Storm Force winds and seas most likely ranging between 14-19 feet, except 20-24 ft Tuesday night into Wednesday (11/19-11/20). Very steep and hazardous seas could capsize or cause damage to vessels.
CHANGES FROM PREVIOUS BRIEFING
• Added Major Snow risk for the Cascades above 2000 feet and Moderate Snow risk for the Coast Range above 2000 feet for tonight through Monday
• Added Minor Wind risk to the Cascades Tuesday – Wednesday (11/19-11/20) and for all other areas for Wednesday (11/20)
