Active Weather Ahead: Quick Clippers, Arctic Blasts and GFS record setters

The first part of this week features strong south-westerly flow, gusty conditions with slowly rising snow levels and good uplift precipitation over the Cascades. While a Winter Storm Warning remains in effect for much of the Cascades today, some of this is likely to changeover to rain, especially over Snoqualmie Pass.  

Image from USDA.gov

As of Monday morning, NOAA didn't forecast the Snoqualmie River to quite reach minor flood stage (~20 kcfs) at the Falls, but stream flow projections were trending higher, expected to crest Tuesday morning. Should make for another great viewing from the observation decks.

New Years Day at Snoqualmie Falls (river flow crested at ~15 kcfs). 
PC: Twitter user @andrewchesnut1

Wednesday-Sunday…more interesting…

By now you’ve probably noticed that, unlike last month, the snowflakes for this week on the phone app aren’t yet disappearing.  

There is some colder air expected to dive down from British Columbia, grazing Western Washington in what the National Weather Service is describing as a “quick clipper.” This will probably lead to chilly rain showers for most of Puget Sound, but possibly periods of wet snow/wintry mix around 1,000ft. elevation in the foothills.  This would include parts of Snoqualmie Ridge and Wilderness Rim in North Bend.  Accumulations expected to be minor at this point.  Something to watch closely though.  Potentially not the main event though…

Sunday and beyond ..most interesting!

There’s a lot of buzz on social media since the turn of the year showing model runs calling for a major Arctic Blast invading the PNW around end of week.  The weather models are extremely varied at this point as it essentially boils down to two factors:

• Will a very cold Arctic Blast make its way, usually via the BC/Frazier River Valley express, to Western Washington, or will it stay bottled up north in Canada, or just move east of the Cascades.  The latter could still set some record cold temperature readings for E. Washington, and leave Puget Sound area with colder, but not record cold conditions.  There is building consensus it will be cold enough for snow, but just how cold?

• Will there be enough moisture around?  Snow is always tricky to forecast in Western Washington because cold flow from the north doesn’t often come with precipitation.  One favorable setup is a wrap-around precipitation band more from the west and/or a convergence zone setup to enhance said precipitation. We had a few of these play out during last February’s Snowmageddon, as well as in December 2008.

Snoqualmie snow, February 12, 2019

Snoqualmie December 2009 snow.

Now let’s take a look at some interesting long-range forecasts for this “Sunday and beyond” period (snapshot of model runs as of 1/6 @ 8 am).

Note the Global Forecast System (GFS) model has Snoqualmie reaching not only single digits, but below zero!?!?  Admittedly I haven’t seen this wild of a prediction in the 5 years I’ve been watching the models.  The last time Snoqualmie actually hit single digits was December 1990 and the last time for the big 0° reading was 1957. 

Only time will tell, but the GFS model is considered to be a lower resolution model.  It’s often scolded nationally for lacking the higher resolution vs. the European model when projecting hurricane paths, wind speeds and mountain snow accumulations.  

That doesn’t mean GFS is wrong ‘all’ of the time, but based on track record and just common sense of how rare such a super cold event would be, it’s difficult to give that forecast much credibility at this point.