Mega powder. The other ski areas received far less (like 6-8 inches at Snoqualmie and Stevens). Why so much at Mission Ridge? And how well did the models forecast it?
The key to the big snow is Mission Ridge's location on the eastern slopes of the Cascades and a relatively unusual circulation with moist easterly flow rising up along those slopes. As shown by the map below, Mission Ridge is on a ridge extending east-southeast from the central Cascades. The ski area is relatively high (5000-7000 ft).
Yesterday, a low center passed over and south of Washington State. To illustrate, here are the wind (barbs), temperatures, and heights (like pressure) at 850 hPa pressure (about 5000 ft above the surface). With a low centered on the Oregon/WA border, strong easterly/northeasterly flow was pushed right into Mission Ridge, with cold temperatures (blue color). That produced large upslope flow on the terrain of Mission Ridge, with lots of precipitation (which results from the powerful upwards motions).
The UW high-resolution model forecast initialized Sunday at 4 AM, did suggest heavy snowfall along the eastern slopes of the Cascades (see forecast of 24h snowfall ending 4 AM Monday), but it underplayed the amount (forecast only 8-12 inches).
Unfortunately, there is virtually no weather radar coverage over the eastern slopes of the central and northern Cascades, but the Pendleton, Oregon radar did show substantial enhancement over the eastern slopes of the southern WA Cascades (showing about 1 inches of water...about 10-15 inches of snow).
For the rest of us, we can look forward to considerable sunshine this week, as cold, arctic high pressure and easterly offshore flow spreads over our region. Sun is a great gift this time of the year and will gladden the hearts of all those tending towards seasonal affective disorder.
The latest European Center simulation suggests that Seattle will experience highs around freezing and lows in the mid to low 20s. Upper teens in colder spots of western WA.
I should note that the QUALITY of the Cascade snow this year has been excellent because of the virtual absence of warm/wet periods when we get rain on snow...and the resulting change of powder to Cascade concrete.
Ironically, our cold and sun will be accompanied by very heavy rain in California as the jet stream gets displaced southwards into Lotus Land. Here are the 72h precipitation totals ending 4 AM Thursday and 4 AM next Monday. Huge totals in the Sierra (5-20 inches). Great news for California water resources. Drought is rapidly ending there.