Weekend weather: Freeze warning issued by National Weather Service

A polar air mass descending across the Continental Divide this week is bringing a dramatic cooling of temperatures and the threat of freezing weather before dawn today and Friday morning.

The National Weather Service issued a freeze warning for tonight across portions of North Idaho, the northeast mountains of Washington and the Okanogan highlands.

Temperatures could range from the upper 20s to lower 30s an hour before dawn on Friday.

Warnings are issued when frost and freezes are expected during the normal growing season for a given area, the weather service said.

Tender plants such as tomatoes should be protected.

The warning extends as far south as northern Spokane and Kootenai counties.

Spokane and Coeur d’Alene should escape frost with lows forecast at 37 to 38 degrees tonight. Sandpoint has a forecasted low of 31 tonight.

Dry polar air has an upside. It is relatively free of pollutants and it allows skies to clear for abundant sunshine. Its low humidity levels allow for fast cooling after dark.

Highs will start out in the middle 60s today in Spokane, about 10 degrees below normal, and then gradually warm into the 70s by tomorrow, reaching 79 in Spokane on Sunday. The normal high today is 75.

Coeur d’Alene temperatures should be about the same as Spokane.

At higher elevations, the cool-down will be more noticeable for a drop in daytime temperatures. The mountains near Sandpoint may see daytime temperatures in the upper 40s to lower 50s.

The Lake Roosevelt recreation area should see somewhat warmer temperatures with lows dipping to about 37 tonight and highs increasing from 69 today to the 70s tomorrow and Saturday, then to 82 on Sunday.

The Columbia Basin to the west should be a few degrees warmer.

Temperatures in the Palouse should remain well above freezing tonight with lows in Pullman expected to reach 37. Highs will go from 68 today to the 70s through Sunday.