: Cliff Mass Weather Blog This blog provides updated forecasts and comments on current weather or other topics Wednesday , November 20, 2013 A Hard Freeze and Modified Arctic Air Hits the Northwest The air felt very different today . nbsp Colder , drier and without a cloud in the sky . nbsp And it was different , as we switched the air mass over us from maritime polar to modified continental . polar The result will be the first hard freeze over the region , with 20s being common west of the Cascade crest and teens in colder , valley locations . nbsp Even colder in valley's east of the Cascade . crest I am teaching atmospheric sciences 101 right now and the funny thing was that today my lecture was on air masses--large , relatively uniform blobs of air , thousands of km in . dimension One