Satellite really shows us "in the squeeze" tonight as a fresh batch of cold/dry air is surging west across the Rockies into Eastern WA and moisture approaches from the SW. We are in the middle, which is a classic ice or snow storm setup! 00z models have really come into agreement for no precip from system #1 Saturday night, but all have precip in here after sunset Sunday. Not a lot, but that all day ice storm last January? It only produced .17" of "rain" at PDX! Doesn’t take much to make a mess when it’s freezing rain.
We will probably not get above freezing Monday. It’s a common error to bring the temp in Portland above freezing in the first 24 hours of an ice storm. Very unlikely with air this dry. As moisture falls into it heat in the atmosphere is used for evaporating the moisture. For example, if it’s 32 with a dewpoint of 16 when the precip starts Sunday evening, the temperature will probably drop to 27 and the dewpoint comes up close to 27 as the air saturates. Then it takes a long time to raise the temperature 5 degrees as cold air continues to pour out of the Gorge. It happens every time.
As mentioned last night, short term issue is cold and especially wind. Speaking of "the squeeze". PDX-DLS gradient is over 10 millibars this evening, and I would expect a 13-14 mb gradient Saturday night and again Sunday night. This pattern in the past has produced 80+ mph winds at the west end of the Gorge, while it’s almost calm across 2/3 of the metro area.
And just for you Longview folks: Probably freezing rain or maybe briefly snow Sunday evening, then a change to rain by Monday midday. High Monday near 34.