09/16/2021
The first major rain event of the fall is coming in on Friday, September 17th. Be prepared for rain and cool weather if you are going out to enjoy the outdoors. Remember to layer up!
Significant Rainfall Event Friday through Sunday
National Weather Service - Portland, OR Issued: 6 AM Monday, September 13, 2021
Next Update: 4 PM Wednesday, September 15, 2021
Point of Contact: NWS Operations (24/7/365) (503) 326-2340
● The first significant, widespread rain event of the season is expected Friday through Sunday.
● Early estimates suggest over an inch of rain is possible for the Willamette Valley.
● Early estimates suggest 1 to 3 inches of rain is possible for the coast, Coast Range, and Cascades.
● Gusty south to southwest winds are possible Friday and/or Saturday.
● Unknown at this point whether rainfall would cause debris flow issues in recently burned areas.
CONFIDENCE AND DETAILS
Southwest Washington and Northwest Oregon
HIGH Confidence
The first autumn-like cold front of the season will bring widespread rain to the region Friday through Sunday.
Daytime temperatures will be 10 to 20 degrees below normal behind the front this weekend.
MODERATE Confidence
Wetting rains of greater than 0.25” for the entire area.
River flooding is not expected, but sharp rises are possible on
flashier streams.
Heaviest rain will be Friday night.
LOW Confidence
Exact rainfall totals.
Peak rainfall rates and impacts to recently burned areas.
Strength of southwesterly winds Friday through Saturday.
Details: Forecast models have been very consistent in showing a strong, autumn-like Pacific frontal system moving through the Pacific Northwest Friday through early Saturday. This system is expected to latch on to deep atmospheric river of moisture while approaching, increasing the likelihood of locally heavy rain as the front moves through. Rivers remain near seasonal baseflows, so river flooding is not expected. However, sharp rises may occur on “flashier” streams and smaller rivers such as the Grays River in Wahkiakum County, WA. Rainfall rates may be high enough to cause brief urban flooding issues in areas of poor drainage, especially if storm drains are clogged. It remains somewhat of an unknown as to whether or not rainfall rates will be sufficient to cause issues with debris flow for recently burned areas.
FORECAST GRAPHIC
Friday through Sunday (September 17-19) Official Forecast
For the latest forecast updates, visit www.weather.gov/portland
If you have questions or would like to submit weather reports, please call NWS Portland at (503) 326- 2340.
