Cold, dry air from Canada is replacing the moist Pacific flow of the past several days, bringing sunshine and temperatures below normal until Saturday.
Highs today should reach the upper 20s to near 30 in Spokane and Coeur d’Alene, but lows may drop into the middle teens.
The main body of arctic air is moving east of the Rockies into the Plains states and central U.S. this morning, but the Inland Northwest is receiving what forecasters described as a glancing shot.
The wind chill effect, or the combined feel of wind and cold on the skin, was 16 degrees in Spokane at 11 a.m. under a temperature of 27 and a northeast wind of 13 mph.
The colder weather remains in the region until Friday night when a weak Pacific storm system moves ashore to moderate temperatures and bring a 40 percent chance of snow through Saturday and a 20 percent chance of snow Saturday night.
Highs move back above freezing on Saturday and Sunday. Mostly cloudy conditions are expected on Sunday.
Fog and stratus clouds that had formed in the Pullman and Lewiston areas are expected to clear out this morning with the drier air from the north.
At 7 a.m., it was 24 at Spokane International Airport, 28 in downtown Spokane, 21 in Coeur d’Alene, 22 in Deer Park and 25 in Pullman.
While precipitation is running above normal since Oct. 1, snowfall in Spokane is about half of normal for the season.
The Spokane airport has received 6.27 inches of precipitation since Oct. 1, including 0.77 inches so far in January.
By comparison, snowfall so far this season totals 11.5 inches compared with a normal of 23.5 inches through Jan. 5.
El Nino warming of the tropical Pacific, a condition that began late last year, typically leads to reduced snowfall amounts in the lower elevations of the Inland Northwest and lower precipitation totals.
So far, this season’s El Nino is shaping up to be a wetter version with precipitation just above normal, which is good for building mountain snow packs and creating a reservoir of water for spring and summer stream flows.
In addition to changing precipitation patters, El Nino often causes warmer than normal temperatures in the region, but the National Weather Service shows the fall and winter seasons so far have been very close to normal for temperature based on a calculation called “heating degree days.”
The weather service reported 3,049 heating degree days since July 1 compared with a normal of 3,096 through Jan. 5.
Heating degree days are a running total of the number of degrees colder than 65 that were reported through the period based on a mean temperature for each day.
A coastal Pacific high pressure ridge that can create a split in jet stream winds aloft during El Nino has formed repeatedly just off shore in the past two months, causing cold air to spill southward into the region periodically.
An element of the pattern is a persistent cyclonic circulation over the interior of northern Canada that has also sent cold air into the central U.S. and eastern seaboard.