Most folks are not thinking about substantial snow in the mountains during late April and early May, but such snow will be a reality this year.
During the next 48-h, 3-8 inches will fall on the Cascade passes and more is predicted during the next week or so.
The key source of the upcoming cold, snowy weather are two upper-level lows that will move in tonight and Monday night (see upper-level maps at 2 AM Monday morning below). This kind of pattern has been rare this El Nino winter.
So how much snow could we expect on Monday and early Tuesday?
Below is the 5 AM Sunday accumulated snowfall forecast through 5 AM Tuesday of the high-resolution NOAA/NWS HRRR model.
Impressive. Over a foot at higher elevations. 4-8 inches in the passes. Large values in the mountains of southern British Columbia as well.
The UW high-resolution modeling system has a similar solution, but we have even more to offer: we run an ensemble of many forecasts to understand the uncertainty of the forecasts. Using this system, the snow accumulation at Stevens Pass (around 4000 ft in the central WA Cascades) is shown below.
Some uncertainty, but the average is about 6 inches for this event.
How unusual is a half foot or more of Cascade Mountain snow this time of the year?
To gain some insights into this interesting question, below is the daily average and daily extreme snowfall at Stampede Pass from 1944 to 2016.
On average, this site receives about an inch around May 1. But extreme days this time of year have received 10-15 inches. So getting some snow at this point in spring is no big deal.
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Announcement: There will be no Northwest Weather Workshop this year.
Why? Because we lost two important partners. The Seattle National Weather Service Forecast Office has told me they are no longer interested in hosting and participating in this regional weather gathering. And the other partner, the Puget Sound Chapter of the American Meteorological Society, has died. I am looking for new partners for next year. Keep tuned.