Snow is really coming down over the Cascades right now! Snoqualmie Pass is currently “chains required on all vehicles except all-wheel-drive,” and Stevens is only slightly better with chains required on trucks and traction tires required for all vehicles. And the top of Alpental looks downright stormy.
As the radar below shows, a cold front is currently bringing rain from Olympia to Eugene with heavy snow in the mountains, but the Central Cascades are still getting hammered.
This is because we have very strong westerly flow at the mid and upper levels of the atmosphere (see the current winds at 300 mb/~30,000 feet, the jet stream is right over us), with moderate WNW flow hitting the Olympics on the coast. This air is cool, moist, and unstable, and is headed directly into the Cascades, forcing it to rise and creating prodigious amounts of snow in the process. The snow decreases in intensity rapidly after you cross the Cascade crest as air sinks.
Areas like Cle Elum at milepost 85 some 30 miles east of the crest are still getting moderate snow, but based on what I can make out of the webcams and radar imagery it appears as though the snow stops near Thorpe, which is near MP 101 on I-90.
Additionally, we have a strong Puget Sound Convergence Zone that is helping keep precipitation going between Lynnwood and Seattle and is further enhancing snow in the Central Cascades. This will be the storm that gives Summit West at Snoqualmie enough to open.
Remember to check my I90 and Snoqualmie Pass webcams page for the latest conditions over the pass. During events like these, it provides a fascinating view of how drastically our weather can change over such short distances.
That’s all for now… woke up and couldn’t fall back asleep! See you later today with a Monday update.
Charlie
