Mountain Weather Forecast

Weather Synopsis

The weather pattern appears to be returning to a pattern more typical of a La Nina winter where storms approach the region from the NW. This pattern will begin tapping back into the colder air that has largely been bottled up in the high latitudes in recent weeks. However, with warm air in place on both sides of the Cascades, the first system starts warm and wet with plenty of high altitude snowfall but ends with a strong cooling trend and impressive post-frontal snowfall for most elevations.

A potent frontal system approaches our region Monday night with increasing moderate to heavy rain and snow for the western Olympics and Mt. Baker with increasing light rain/snow for other areas of Washington. A warm sector of the storm should allow snow levels to slowly rise to around 4500 ft for the Olympics, 3000 ft for the north Cascades, and 3500 ft for most other areas. Moderate to strong WSW to SSW winds will buffet the entire region.

A wave riding along the WSW-ENE oriented trailing cold frontal boundary arrives over Washington State Tuesday morning, bringing moderate to heavy rain/snow and another round of strong ridgeline winds as the cold front re-orients the front to SW-NE. The front should pass much of the Cascades during the mid-day hours with a gradual shift from SW to more W winds along with cooling late in the day. Snow levels peak around 3500-4000 ft during the mid-day and afternoon hours, then start falling late in the day for the Olympics and Mt. Baker area. Models identify a strong convergence over the mountain loop that will extend ENE to around Washington Pass from mid-afternoon through the early evening hours.

The upper trough transits the region Tuesday night. Expect moderate postfrontal snowfall for the west slopes of the Cascades will be locally heavy as the convergence shifts southward toward Stevens Pass Tuesday evening and snow ratios become higher. Convergence banding becomes less pronounced overnight, but light to moderate snow showers continue for the west slopes of the Cascades with light showers spilling over to the east slopes. The westerly push of winds will be strongest during the late evening hours, but expect strong winds for the major mountain gaps, Mt. Hood, and east slopes of the Cascades throughout the night.

A ridge builds offshore as light snow showers taper from south to north during the afternoon hours. Expect a chilly start to the day with snow levels rising to 2500-3000 ft during afternoon flurries.

2:38 PM update: Adjusted the speed of the wind in the above description Tuesday night.