Cold and Some Lowland Snow Arriving This Weekend

We have roughly another month remaining of meteorological winter, and mother nature will not be letting us transition to spring without another taste of cold and snow. 

The cold is for sure, including a hard freeze over the region.

The snow forecast is less confident--but it does look like either the Washington or Oregon western lowlands will see the flakes--the question is which one.

The movement of cold air into the Northwest has another implication:  substantial additional precipitation for a sodden California.

The Cold

For Wednesday and Thursday, a high-pressure ridge will dominate the region, producing cool, cloudy, but generally dry conditions (see upper level--500 hPa pressure level--map for Wednesday morning below).  

A benefit of the high pressure will be a suppression of the astronomical King Tides, minimizing flooding and tidal overflows.

But on Friday and Saturday, an upper-level trough will move south down the eastern flanks of the big ridge, pulling cold air from northern Canada into the interior of British Columbia and then into the Pacific Northwest. 

Here is the upper-level map for 7 PM Saturday.  You can see the offshore ridge of high pressure, but a significant rough is moving over our region.    

I have studied these snow situations for decades. This is not quite the right structure/position for major snow over the Washington lowlands, but close enough to worry.

Now let's look at the surface pressure chart for 7 PM Saturday, with colors showing the temperature just above the surface. Wow....I am going to get my gloves and wool hat ready! Purple and blue indicate cold air....cold enough to snow.

You will note a low center off the northern Oregon coast. Kind of weak, but with enough "juice" to bring snow to nearby locations. Too far south and weak to whiten Seattle....but a small error could change things.

By Sunday at 4 PM, uber-cold air will spread over the Northwest.  It will be important to get the homeless off the streets for Monday and Thursday morning.  Temperatures will drop well down into the 20s.  A hard freeze.

OK, you want to know about snow.  Below is the cumulative snowfall through Sunday night.

 

The Cascades get some and there will be lowland snow south of Tacoma and over SW Washington.

A small error in the forecast could greatly change the snow prediction....so keep tuned.