Sunday, February 23, 2020

Strong Winds and Heavy Mountain Snows Today

A lot of weather action today.  A strong front has just moved through Puget Sound and is now pummeling the mountains and Portland (see image below for 8:11 AM).   Behind the front is cold, unstable air that is producing convection (including some thunderstorms).  This unstable air will be moving in this afternoon---so expect showers and sunbreaks over western Washington today.


The front was vigorous enough that is brought fairly strong winds, gusting to 40-50 mph in exposed locations, and was even stronger in the eastern Strait of Juan de Fuca (see below).


The winds with the front have produced substantial numbers of power outages, particularly over the south sound-- including 25000 household serviced by Puget Sound Energy (see below) and 466 customers served by Seattle City Light (mainly south of the ship canal.


But the even more strong winds are yet to come.   The front is connected to a low pressure center that is now approaching northern Vancouver Island (see larger scale infrared satellite image below).


As shown by the latest UW WRF model forecasts, that low center will move westward, and as it does so, a large north-south pressure difference will develop over western Washington--which should cause a substantial acceleration of winds.  Expect gusts of 30-40 mph over much of western Washington.

Sea level pressure map at 7 AM.

Sea Level Pressure Map at 4 PM

The latest forecast of the National Weather Service HRRR (High Resolution Rapid Refresh) model for 3 PM today shows strong gusts (to 50-60 mph) along the coat and into the Strait of Juan de Fuca.   Not a good day for a ferry ride to the San Juan Islands.  And 40-50 mph gusts over southern Puget Sound
But as in late night commercials...there is more!    The cold, unstable air, driven by strong flow to the west, will be forced to rise by the Cascades and Olympics producing bountiful snow above 3000 ft---as much as 1-2 feet in places (see map of 24-h snowfall ending 4 AM Monday)


The Cascade snow could use a bit of freshening.

And then on Monday we will have clearing skies and some sun, with dry conditions in the lowlands through Friday.

Saturday, February 22, 2020

Stunning Lenticular Clouds Downstream of Mount Rainier

Native Americans, who were astute observers of the natural environment, had a saying:  "when Tahoma (Mount Rainier) has a hat, rain will soon follow."

Today it developed a hat of great beauty.

Looking out the window of my colleague, Qiang Fu, this afternoon, I saw it.  A series of stacked lenticular (lens-shaped) clouds downstream (west) of Mount Rainier (see below).  Stunning.


A bit closer view by Nicole Geer (below) shows the structure a bit better.


But why not go far closer....say from the nearby peak of Crystal Mountain, the home of a wonderful 360° high resolution live cam?

The view around 4 PM was extraordinary, with the "stacked plates" of several lenticular/mountain wave clouds clearly evident.


Pull back and you can get some perspective.  Stunning


And as the sun set and dusk settled in, the lenticular clouds remained, even as the general sky cleared a bit.  

As discussed before in this blog, lenticular clouds form as air is forced to rise by a mountain barrier, and then, like a swing, oscillates back and forth in the vertical (see figure below from my weather book).  As the air rises, it cools, and if moist enough, a lens-shaped cloud forms--with the potential to get several stacked clouds depending on the moisture structure in the vertical.  The clouds evaporate as the oscillating air sinks.

Having air close to saturation is good for the development of lenticular clouds, as is increasing wind approaching the mountain.  Both occur as weather systems approach the area--thus, there is good physical reasons for the Native American observation about a "hat" forming on the big mountain before rain falls.  In fact, the 1:30 PM infrared satellite image Friday (see below) DOES shows a weather system offshore--one that is heading towards our region.

Bottom line:  If you don't have a weather satellite handy, you can learn a great deal about future weather by being a perceptive observer.