This is going to be a quick one; I’ve got a few personal tasks I’m trying to bust out today.  But there’s a very interesting weather event going on tomorrow Tuesday, if you’re a seasonal temperature nerd like I am.

Remember how earlier in the fall we had two brief teases of cold Canadian air, that dipped down from the north and gave much of the Pacific Northwest a few unseasonably chilly days & nights?  Well…it’s happening again.  Check out this 12z GFS map from this morning, courtesy of TropicalTidbits:

Wow…the airmass at 4,500 feet over north-central Oregon (i.e. The Dalles) will be down near -12C tomorrow morning!  That’s 10 degrees Fahrenheit, which will be the actual temperature along some of the nearby mountain slopes at the same elevation.  I don’t think I’ve ever seen an airmass this cold in October before, at least not east of the Cascade crest.  It looks nearly as cold as the November 2014 event, which gave the Gorge a historic early snowstorm followed by record cold temperatures.  Halloween 2003 apparently came pretty close though.

This is going to mean temps on the east side way below freezing at night – likely in the teens even in the lowest elevations Tuesday night, and probably struggling to make it much above 40 during the day.  The clear skies and low humidity will facilitate nighttime chills, so probably even DLS drops to the 15-20 range.

That cold air will spill into Portland via an east wind; tomorrow should see widespread gusts across the metro area from 30 to 50 mph.  Maybe a few power outages if a vulnerable tree comes down in the wrong place.  Temperatures should stay in the 40s during the daytime, but wind chills will be in the 20s.

The coldest arctic air moves out of the Columbia Basin by Wednesday afternoon.  A weaker Canadian high pressure slides down to the east Thursday and Friday.  It won’t reload the cold air to our east, but it will keep a cool offshore wind blowing across the east side of Portland for much of the upcoming week.  In short, our already chilly October is going to end cold as well.

One quick thought:  If this pattern were to repeat itself again just two weeks from now?  Then we’d potentially be talking about a “real” winter weather scenario for the Gorge and east side.  Right now the long-range maps don’t show a ridge retrogression, but they do show more arctic air in central Canada and the north-central U.S out around the 7th-8th of November.  We will have to watch closely.

Bundle up!

Karl