Substantial Late-Season Mountain Snow Ahead

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.

Stevens Pass on Sunday Afternoon

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.

In any case, expect a significant bump up in regional snowpack by midweek.

But the impressive thing is that the snow and cold are not over on Tuesday.  The latest model forecasts have several more cold lows moving through during the subsequent week.

As a result, a LOT more snow is expected to fall.  For example, below is the predicted accumulated snowfall for the next five days from the highly skillful European Center model.  ANOTHER FOOT (or more) at some mountain locations.

And the extended forests after that have even MORE snow.

Regional ski areas should think about reopening for glorious May skiing.

And no, global warming does not cause bountiful May snow. 😉

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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.

El Nino is Rapidly Collapsing

 It's finally happening.   

The pesky El Nino, with warmer than normal surface waters across the central and eastern tropic Pacific, is finally dissipating.  

And the effects of El Nino, including a wet California and warm Northwest, should be fading.

Consider the temperatures in the Nino 3.4 area of the tropical Pacific shown below (the difference from normal is illustrated).  El Nino peaked in late November at around 2.1C above normal sea surface temperatures.   Right now it is about 0.6C above normal and declining rapidly.

The latest prediction of the NOAA/NWS climate forecast model (CFSV2) is for the El Nino to be gone (0°C anomaly from normal) by the end of May (see below).  And then we move into a strong La Nina (cold tropical Pacific) by autumn.

This model predicts the extension of colder-than-normal surface water over the tropical Pacific during the next few months (see below).  Wow.  Talk about oceanographic whiplash.

With El Nino weakening, the large-scale weather patterns are unlocking and the Northwest weather situation is forecast to be very different during the next weeks compared to earlier in the winter.

During El Nino winters (and this one), southern California is very wet, with the Northwest being on the drier side.  In contrast, the latest forecast of accumulated prediction from the US GFS model through 11 May is shown below.  Virtually nothing will fall over southern California and wet conditions will prevail over the Northwest.   

Something has changed.

And a strong La Nina foretells major changes next winter, greatly increasing the chances for lots of mountain snow and colder-than-normal temperatures.  

My suggestion:  if you can make some good deals on ski equipment, do so....

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Announcement:  I will do a special online zoom session at 10 AM on Saturday for Patreon supporters, with a deep dive into the upcoming wet period and the implications for this summer.  Plus, I will answer your questions.