Cold and snowy will become wet and slushy well into next week as forecast heavy rains prompted a flood watch.
An inch of rain or more could fall in Spokane by Monday, with more precipitation in North Idaho.
Heavy snow is expected in the mountains.
This sudden reversal in the weather should boost meager snowpacks and replenish water supplies.
The change began on Monday with a quick-hitting warm front that dropped 3 inches of snow in downtown Spokane.
A weaker storm Monday night will be followed by additional storms tonight and Wednesday, Thursday night and Friday, and Saturday afternoon and Sunday.
National Weather Service forecasters said an “atmospheric river” is pointed at the Inland Northwest carrying large amounts of moisture.
Today’s forecasted high of 34 in Spokane will mark the first time the thermometer has been above freezing in 25 days. That is the eighth-longest spell of freezing weather since record keeping began in 1881. Highs may reach the lower 40s by Wednesday.
On Monday, the city of Spokane declared a stage 1 snow event to plow all arterial streets, emergency routes, hospital districts, bus routes and hilly residential streets.
Spokane Valley arterials and hilly areas were also being plowed.
Law enforcement agencies were receiving reports of collisions caused by icy conditions, but light traffic moved smoothly on major routes Monday.
A winter storm watch for heavy snow takes effect this evening for the mountains of North Idaho, northeastern Washington and the central Panhandle through Wednesday evening.
The weather service said the transition to rain today in the Spokane and Coeur d’Alene areas should start off with snow in the morning and then rain possibly mixed with snow in the afternoon. That transition will be slower in areas to the north.
Rainfall could reach nearly half an inch by Wednesday in Spokane, with yet more storms on the way with an inch likely through the weekend. North Idaho may see 2 to 4 inches of precipitation through the weekend.
Forecasters on Monday issued a flood watch for Spokane, Lincoln, Whitman, Asotin and Garfield counties in Washington and Kootenai, Benewah, Latah, Nez Perce and Lewis counties in Idaho.
The watch is in effect this evening through Friday evening.
Forecasters said they expect water to pool up in low-lying areas and along urban streets. Frozen ground will prevent water from soaking into the soil, causing it instead to drain away. Ice jams may form in smaller rivers and streams, triggering some streamside flooding.
The mountains could see up to 4 inches of precipitation by the end of the weekend, with snow levels at about 4,000 feet.