Mountain Weather Forecast

Weather Synopsis

An unusually strong ridge of high pressure parked just offshore maintains a beautiful weekend of weather across the Pacific Northwest through early next week. It's hard not to sound like a broken record when the weather pattern remains stubbornly static. The ridge is bringing some of the warmest January temperatures we can remember to the highest elevations of the Pacific Northwest. The mercury rose to 44F at Camp Muir Saturday afternoon, confirming freezing levels well above 10,000 ft. Overnight low temperatures only dropped to 36F and we suspect that much of the daytime rise in temperature readings may be due to solar radiation and reflection. Still, these numbers are impressive for this station. 

Saturday is a strong candidate for the peak warming of this extended warm period as the high-pressure center drifts slightly northward through the weekend, then begins to weaken. Freezing levels in the 11,000 to 12,500 ft range Saturday night should drop by around 500 ft each 24 hours...aka, you probably won't notice.

With light N winds aloft not reaching the ridgelines, the 3D structure of the shallow pool of cold air east of the Cascade Crest will be more noticeable in most mountain areas. Stronger E winds on Friday sloshed this cold air up against the east slopes of the Cascades Friday night. The resulting deeper cold pool has been slower to warm at lower elevations on Saturday. Although these winds gradually decrease over time, we expect a similar diurnal pattern to play out Saturday night into Sunday, with a secondary low-elevation freezing level redeveloping over the passes and east slopes of the Cascades. By Monday, the ridgeline winds shift westward, begin eroding, and moderate the cold pool east of the Cascades.

A January drought has been a relatively common occurrence for our region in recent years. The current iteration takes that pattern into hyperdrive, with an unusually powerful ridge of high pressure parked off our coastline through the weekend into the first half of next week. 

With 10,000 to 12,500 ft freezing levels and light winds aloft through the weekend, the drivers of local weather are focused on subtle shifts in cold air pooled east of the Cascades. Easterly pressure gradients peaked Friday night and remain stronger than originally forecast into early Saturday. This has driven the shallow pool of cold air to slosh up against the east slopes of the Cascades, thickening it over the mountain slopes (and thinning it farther east, such as at Mission Ridge). The result is that the cold air pool is slightly stronger and slightly deeper than this time Friday morning. A secondary freezing level can generally be found below 4500 ft (5500-6000 ft at Washington Pass). The layer of cold air will be accompanied by a shallow layer of low clouds that get ushered into Snoqualmie, but not the higher passes, during the overnight and morning hours.

As easterly winds gradually ease Saturday through Sunday, expect the cold air pool thin and warm air to expand further into the middle elevations east of the Cascade Crest. Plan for a range of temperatures over short distances. Cold air should generally remain limited to lower elevations near and east of the Cascade Crest and passes. Once you ascend in elevation, expect warm, dry, cloud-free conditions.