A very wet frontal system arrives over the Pacific Northwest tomorrow morning, with the heaviest rain moving through tomorrow night and very early Thursday morning. For most of us it’ll be just rain west of the Cascades. But once again cold air is getting dragged back into the central/eastern Gorge (the part of it east of the Cascade Crest) due to an approaching storm out in the Pacific. In other places this is called “cold-air damming” and that’s what is really going on; cold air is dammed up east of the Cascades. This time the airmass isn’t as cold as previous events, so even in the western Gorge (west of Bonneville Dam) the airmass will be marginally cold for freezing rain. Regardless, an Ice Storm Warning is up for very heavy 30-32 degree rain Wednesday AM through Thursday morning. A lot of ice can form on objects even at just 30-31 degrees, especially when the sun goes down. Believe it or not, this is the 5th ice storm we have seen in the western Gorge! Wow, typically I’ve only seen 1/2″ or more every other year on average. It’s not too unusual to have freezing rain 5 times in one winter, but not actual ice storms with the heavy accumulation. Total ice thickness could exceed 1″ this time again.
Once you get into the Central & Eastern Gorge (Cascade Locks to The Dalles) the cold air is deeper to start with so precip type will be snow…maybe 3-6″, then as the cold air thins tomorrow evening it should go to freezing rain out there too.
There won’t be any real warming west wind on Thursday to get the cold air out of the Gorge, but the gradually warming airmass should go above freezing that day.
Will there be freezing rain in the metro area?
I don’t think so…it probably won’t get cold enough even at Troutdale. Just expect a very wet day tomorrow.
There IS a flood watch out for all areas west of the Cascades due to about 2″ rain expected tomorrow morning through Thursday afternoon. Expect more isolated areas of flooding tomorrow night and early Thursday. Plus a few larger rivers may reach flood stage again.
These first 7 days of February have been the 3rd wettest start in Portland’s weather history. The number will sure climb with another 2″ on the way!
Chief Meteorologist Mark Nelsen