A blast of wintry air is descending on Seattle this week, bringing with it the coldest temperatures so far this year and the prospect of the season’s first substantial snowfall.

Snow could come as early as Sunday night but mostly to the Cascades and areas of higher elevation, as winds converge around the Olympics and bring showers stretching from Snohomish to Pierce counties. Any snowflakes drifting along the Interstate 5 corridor aren’t likely to stick, according to the National Weather Service.

But that is set to change as a mass of cold air sweeps in from Canada, sending temperatures dipping into the teens and not breaking above 40 degrees Fahrenheit for several days, according to Jeff Michalski, a meteorologist with NWS in Seattle. 

“We’re cold, and it’s just a matter of if we get any moisture over us, and where,” Michalski said.

Some snow is likely in the Seattle area beginning Tuesday evening, he added, with accumulations of an inch or less by Wednesday. The forecast remains uncertain and NWS is advising residents to be prepared for wintry conditions, with the possibility for additional snow later in the week and into next weekend as temperatures remain frigid.

Seattle officials have said they are prepared to activate hundreds of emergency shelter beds across the city for people who are homeless in response to a snowstorm or cold weather event — defined as snowfall more than an inch deep or forecast temperatures of 25 degrees or below for multiple days. The NWS forecast for the Seattle area calls for a low in the mid-20s on Wednesday night, with temperatures in the 20s continuing for the next three days.

Seattle emergency-management officials are “monitoring the weather forecast and conditions, and assessing that against our existing emergency plans,” including options for emergency sheltering, said Kate Hutton, a spokesperson for the city’s Office of Emergency Management.