La Nina Snows Over the Pacific Northwest Followed by Very Cold Air

The atmosphere over the eastern Pacific is thoroughly locked into a La Nina-type pattern, with the snowpack being refreshed for NW skiers and those concerned about the water supply next summer.

The snow water equivalent (the amount of water in the snowpack if melted) is in decent shape (see below), being above normal for the northern and far eastern portions of Washington State, but slipping to about 3/4 normal for the southwestern Cascades.

There was some improvement last night, when 8 inches to a foot of new snow  over the Cascades due to an upper level trough moving southward along the eastern flank of a big ridge over the northeastern Pacific (see below).

As I have noted in earlier blogs, a ridge in the eastern with cool northerly/northwesterly flow moving over the Northwest is typical of mature La Nina events. That sets up the cool temperatures, while the upper level trough moving southward provides the precipitation.

But to get lowland snow one needs to get an upper trough of just the right amplitude and position, which doesn't happen often.  Too far inland, and the cool air and precipitation are too far east.  Too far offshore, we are cold and dry.

Another, more vigorous, trough will approach on Saturday (see below), resulting in another snowy period in the mountains.

The 48h total snowfall ending 4 PM Saturday is enough to make a skier smile, with over two feet at high elevations in the Cascades and a relatively low snow level on Saturday (Snoqualmie Pass the eastern Cascade slopes will get plenty).

Another trough comes through on Sunday morning (see below), with most of the action slipping southward into Oregon, which really needs the snow.

The 48h snowfall total ending

But what really got my attempt was the very cold air predicted to move into our region early next week.  The coldest air in a very long time.  Here is the UW WRF model surface (2-m) air temperature forecasts for 4 AM Monday and Tuesday.

WOW.   East of the Cascades many locations will get below 0F, some locations will be way below.  Twenties near the water and teens elsewhere in western WA.

You might think about protecting your exposed water pipes.

from Cliff Mass Weather and Climate Blog http://ift.tt/2BZ2Sc2