Mountain Weather Forecast

Weather Synopsis

A stable and unusually warm pattern will persist through much of next week as a strong ridge of high pressure remains parked just offshore. This ridge blocks the storm track in the eastern Pacific, maintaining dry conditions with mostly clear skies across the region. Little change in the large-scale pattern is expected through the weekend, but locally, the diurnal cycle and easterly pressure gradients will have an outsized impact.

We're in an extended peak of the June-uary warmth. Freezing levels remain exceptionally high for late winter, generally between 10,000 and 13,000 feet with only minor fluctuations. Near-freezing temperatures persist within an increasingly shallow cold pool at lower elevations near and east of the Cascades, although most locations will rise above freezing during the mid-day hours as the cold pool continues to erode from the top down through Sunday.

Despite generally light winds aloft, surface pressure gradients will continue to force easterly flow through mountain gaps as cold air east of the Cascades pushes westward. Localized moderate easterly winds peak Friday evening as pressure gradients across the Cascades approach the "strong" range (-9 mb). These gap winds favor the lower mountain passes, including Snoqualmie Pass and portions of the southern Washington Cascades near the Cascade Crest. These winds will pull low clouds through the Snoqualmie Pass corridor overnight before retreating eastward during the day. The cold pool is sufficiently shallow that the higher passes should maintain cloud-free skies. 

With the cold air pool mostly confined to lower elevations, expect temperatures at 5000 ft to rise into the upper 40s to mid-50s both Saturday and Sunday. Washington Pass will be an exception where the cold pool remains deep enough to maintain temperatures in the 20s and 30s at pass elevation. A similar setup exists below 3500 to 4000 ft in other east-side and pass-area locations. Temperatures are likely to rise quickly above the trailheads and low cloud layer.