Parts of NE Portland and Clark County have seen a few inches of snowfall so far tonight, but most of the Portland metro area below 500-1000 feet has been stuck with plain ol’ boring rain. However, downtown Portland and even the SW metro area will see a trace to two inches of snow by tomorrow afternoon as a cold easterly wind from the Columbia River Gorge strengthens early this morning and finally brings temperatures down close to freezing for much of the metro area. Our neighbors to the north in Western Washington saw a couple inches of wet snow earlier today, but snow has picked up once again there and will persist into Saturday afternoon.
Let’s start by looking at a map of the watches, advisories, and warnings over the Western US. When’s the last time you saw this? Every single acre of Oregon has a Winter Storm Warning or Winter Weather Advisory. Nearly all of Washington is under a Warning or Advisory, along with much of California, Nevada, Idaho, and Montana. Folks, this is the stuff dreams are made of.
Let’s start by looking at the current sea-level-pressure, 10-meter winds, and radar from the Storm Prediction Center. This low appears to be tracking just a little bit further north than forecast, and this is keeping much of Multnomah County south slightly warmer than expected.
However, when we’re talking snow in the Pacific Northwest, a few degrees makes all the difference in the world. Take a look at the current (9:40 pm) temperatures across the Portland metro area. If that’s not frustrating for folks in close-in NE and south, I don’t know what is.
But thankfully, all hope is not lost for those currently seeing rain. Our mild southerly wind will weaken through midnight and switch to easterly early Saturday morning, bring cooler and drier air into the region and turning this rain to snow.
This begs the question of how much moisture we’ll have early this morning. If we take a look at the UW radar, we can see some bands of precipitation approaching the Portland metro. Western Washington is seeing intensifying snow due to frontogenesis and uplift over the I-5 corridor.
And if we take a look at the “High Resolution Rapid Refresh” (HRRR) model from 11 pm tonight (07Z) to 3 pm tomorrow (23Z), we can see that the heaviest precipitation is expected to persist over the Portland metro area through around 4 am (12Z) before tapering off a bit. I believe most of the precipitation from 2-3 am onward will be snow for downtown north. And if you believe this model, Puget Sound will see moderate snow through tomorrow afternoon.
To summarize
The cold air has not made it to downtown Portland yet, but it will early Saturday morning, and precipitation should transition to snow after 2 am for most folks in downtown, with a later transition (perhaps 4-6 am) in the SW metro. Expect a trace-2 inches total accumulation between now and Saturday afternoon for areas south of NE Portland, 1-4 inches in NE Portland and east of I-205 (with the higher amounts generally further to the East), and 2-5 inches total in Clark County and East of I-205.
That’s all I have for now, it’s been a busy week and I’m ready to hit the hay!
Thanks for reading,
Charlie
