Atmospheric River To Bring Friday Rain & Wind
By Rod Hill on 2022-11-03
An Atmospheric River is taking aim at the Northwest with hours of mostly steady rain expected Thursday night, Friday and Friday night. Atmospheric Rivers are elongated plumes of precipitable moisture in the Pacific that channel into a location from as little as 12 hours to at times 3 days. These events have the potential to deliver flooding rainfall depending on the duration of the episode.
This time around, a leading warm front will bring to our region Thursday night, hours of steady rain Friday daytime and hours of heavy rain rates Friday evening. The relatively short duration of heaviest rain between Friday 3:00 pm and the midnight hour should prevent river flooding except for spotty locations.
Weather models show event totals nearing 4.00" along the coast, reaching 2.00" in the I-5 corridor and 4-6" in the mountains. The totals may cause minor flooding of smaller and waterways Friday overnight into Saturday morning. The main widespread impact will likely be ponding of water of roadways and typical low spots or locations with pour drainage.
Weather models show in bright colors the heaviest rain falling Friday evening. Weather models suggest extreme rain rates between 4:00 and 10:00 pm. Localized areas could see an inch of rain in an hour, leading to rapid high water issues. A blend of weather models suggest Portland and Salem could see as much as 2-3" of total rainfall if extreme rain rates develop over a period of several hours.
In addition to heavy rain, gusty southwest winds will blow. The National Weather Service has issued a Wind Advisory for much of the I-5 corridor in effect Friday, ending 1:00 a.m. Saturday. Gusty winds between 35-50 mph are expected. The strong wind gusts of 40 mph or higher often bring down tree limbs leading to power outage.
Snow levels will rise Thursday overnight to 6,000 feet and will jump to 8,000 feet Friday, bringing inches of heavy rain to Mt. Hood and the Cascades.
A trailing cold front will clear the Willamette Valley early Saturday morning, ending the high wind threat west of the Cascades and breaking rainfall into scattered showers. Travelers should be prepared for heavy snow over the Cascades Saturday overnight and Sunday with snow levels lowering to near 2,000 feet.
Meteorologist Rod Hill
Winter Outlook 2022-2023