Temperatures will drop into the 20s early Tuesday morning, but it will feel much colder.
The wind chill temperature at 5 a.m. Tuesday is forecast at 16 degrees in the Tri-Cities by the National Weather Service.
In the Blue Mountains, the wind chill could be below zero.
A powerful cold front is expected to move south over the Tri-Cities late Monday afternoon through the night.
It will bring colder temperatures and gusty winds, says the weather service.
Winds of 18 to 23 mph are forecast for Monday evening, gusting as high as 38 mph in the Tri-Cities.
The overnight low is forecast at 20 degrees.
Tuesday winds will be calmer but the low Wednesday night will be colder at a predicted 9 degrees in the Tri-Cities.
Highs will fall into the 40s from Tuesday through Halloween in the Tri-Cities, with lows in the teens and 20s from Wednesday night through Saturday night, according to the weather service.
Children will need to bundle up on Halloween. The high Thursday should be about 48, with a low of 23 degrees that night.