Cold Weather and a CHANCE of Light Snow on Sunday Night

Saturday evening update: not much precipitation with the system tomorrow evening, so even the chances of some flurries is getting small near sea level.  So just cold air.  But a heads up...the latest runs have some snow on Saturday...but lets wait on getting too excited about that!
 
This week was a good one for snow in the Cascades and colder air will soon be visiting the Northwest.  And perhaps some of us in the lowlands may get a dusting of the white stuff Sunday night, before a week of cold and sun arrives.

First, the mountains snows this week.   We FINALLY enjoyed a weakening of the extraordinarily persistent ridge of high pressure along the west coast, with cool flow from the southwest providing 10-20 inches at many locations above 3000 ft in the Cascades (see 500 hPa weather map for 10 AM on Wednesday, the solid lines are the heights of that pressure surface, with winds parallel to the height lines).  Very different from the uber-ridge pattern of the past few weeks.

The impacts on snow at major Cascade ski areas were substantial.  Here are the snow depths at Snoqualmie Pass, Stevens Pass, and Mt. Hood.

Snoqualmie Pass

Stevens Pass

 Mt. Hood

Snoqualme Pass was a big winner, gaining 20 inches. Stevens got about 10 inches, Mt. Hood a bit less.

 Let's check on how well the overall snow pack is doing compared to normal (see figure below of the % of normal snow water equivalent).  Washington is below normal, but not dangerously so...roughly 70% in the North Cascades to about 50% near the southern border.   Oregon is not so lucky, running from about 40% in the north to 20% in the south.  Skiing has not started a Mt. Ashland and many other Oregon ski resorts.  California is a disaster area.   They have a big problem.

What about the future for us?  Think cold and dry.

Our old friend, the east Pacific ridge of high pressure will be coming back, but this time it will shift slightly west, allowing strong northerly flow and cooler air to invade the Northwest (see map)

Our temperatures will drop to below normal, with highs only in the lower 40s.  But this is generally a  dry pattern for us and one that should bring considerable sun during the week.

But we do have one shot of some very, very light snow in the lowlands.  Sunday evening a week upper level trough will move though and than might do two things:  bring in colder air and produce a few light showers...perhaps snow showers.  Don't worry...we aren't going to end up like Atlanta (where the National Weather Service DID forecast snow and poor human response caused unnecessary havoc).

To illustrate the change in conditions, here is the surface chart for 10 PM tonight (Friday).  The colors are temperatures at 925 hPa...about 2500 ft above the surface).  Yellows are the warmest, purples are very cold.

 Here is Tuesday at 1 PM.  See the difference?  Really cold air in southern BC, with eastern WA getting a piece of it.  Cooling west of the Cascades.  But if you look closely you will see that the winds are from the east...and that means dry conditions for us west of the Cascade crest.

Total snow fall during the next 72 h?  Pathetic totals, with perhaps 1-2 inches in the Cascades.  Better in the Rockies.  Little further relief for Washington and Oregon ski areas.

The West Coast ridge appears to be immortal this year...if only we had a meteorological silver stake to put it out of its misery.