Salina, Utah to Arington, Washington

WSDOT has a lot of information and cameras. Check them for pass conditions and traffic.

If pass conditions allow, I82/90 is the most direct way over the Cascades. And if you get over by early afternoon, I405/I5 will take you north to Arlington without too much hassle. The usual commuter rush hour patterns apply, but up to the moment details are available. Google Maps seems to have good traffic data and time estimates.

I've done the Fall City etc route, but even in a car it's more of slow country drive. WA9 north of US2 will have the same north bound rush hour problems as I5 (the commuters are just as good at seeking alternatives).

That's assuming you are traveling now, as opposed to your usual summer invasion time. Then US2 or even WA20 is an option.

Currently its rainy and warm in Seattle, with the mountains keeping the Canadian cold well to the east.

X2 per Y-Guy. Midday traffic in Seattle area is the best transient time. If you take I90 you could jump off at Fall City, Monroe to Everett, slower 2 lane drive.

Pretty simple route through Utah & Idaho, once you hit Hermiston you need to consider two things; the winds from Hermiston to Ellensburg can be treacherous and look at the pass conditions on I-90's Snoqualmie Pass Road & Weather Conditions if you're not dealing with a winter snow storm then take I-82 to I-90. If things are bad then you can take I-84 to I-5 but traffic between Olympia & Everett can be as bad as LA.

You could take I-82 and then jump off at Hwy 97 to Hwy 2 but I wouldn't do this when snow is a consideration. Also, no matter which way you go you need to have chains, even along the Columbia River on I-84 you will find there is a section that technically requires them.

How about the shortest interstate route?