Happy New Year!
Today, a modest low center will cross the Olympic Peninsula as it moves eastward across the area (see plot of 6 hr pressure and temp forecast). No windstorm for us. Modest winds (15-30 mph sustained) will be experienced to our south where the large pressure differences are found. South of the low we will first experience a warm front passage this morning, followed by a cold front this afternoon.
Astoria has already experienced the warm front...take a look at the attached plots to see what happens. With the warm front temps increased rapidly (into the 50s!), and the dewpoint (a measure of humidity) jumped as well. Winds shifted from SE to SW and increased in speed.
As discussed yesterday, substantial snow has fallen in the mountains, greatly increasing the threats of avalanches, particularly since the underlying layers are weak. WSDOT has closed I90 for the time being and I imagine they will be completing serious avalanche control before letting people through (it is interesting how Snoqualmie closes so much more than SR-2, I assume because of the close-in steep slopes to I90).
The heaviest precipitation from today's system will be from the central Cascades southward (see the 24h precip plot) and I think the Olympics will be spared the worst. We are talking serious precipitation down there--5 to 10 inches in the mountains--and flooding is a possibility. Regarding lowland snow later tonight and tomorrow morning, the biggest threat is over SW Washington and northern Oregon--but it will be close for us (see latest prediction by the weather model--the WRF-GFS) The temperatures over central PS will be marginal for snow and with the heaviest precipitation to the south, the cooling effects of melting precip from aloft will be correspondingly strongest southward where the intensities will be there. So the salt probably won't be needed tonight in Seattle. But don't be surprised to see some wet snow mixed in...and if you are at higher elevations...there may be a white coating.
PS: Comment on the mayor's new salt plan. This is a positive step to be sure...but the city must not constrain the use of salt to only such large (4 inch) snowfalls. There has been very disruptive events with lesser amounts..where salt could have help tremendously. One is noted in my NW weather book...on Nov 27, 2006 (Pg 72). I remember that event well.. I walked home that night due to all the ice..and only about twoto three inches fell. And we need more snowplows with metal edges. I just got an email from Sea Tac Airport...they have 27 pieces of snow removal equipment..as much as the entire city!