Tuesday, January 8, 2013

The Winter Murk of Eastern Washington

Some folks think of eastern Washington as a dry desert with lots of sun.  For the warm portion of the year that is generally true, but during midwinter (roughly November to February), much of eastern Washington is cloudy and cool, with the region from Yakima though the Tri-Cities to Spokane stuck in a persistent murk of low clouds and near-freezing temperatures.
In fact, much of eastern Washington was stuck in this unpleasant situation for much of the last two weeks, with a welcome break occurring last night.    To illustrate, here are the temperatures at Pasco and Yakima for the past 2 weeks.   Murkville.  Very little daily temperature variation --temperatures were stuck around 30F forever.

You can look at the observations at Pasco for the 24-h ending last night to see how this episode ended. For much of yesterday the surface temperatures were near freezing and fog, freezing rain, rain and ice pellets were observed.   Warming was occurring aloft but it wasn't until late in the day that strong southerly flow mixed down to the surface and temperatures soared in the 50s.


So what is going on?   Much of eastern WA is a topographic bowl, with higher terrain (Cascades, Okanagan highlands, Rockies, Blue Mts, plateau of eastern WA surrounding it.  During the winter, cool air tends to settle into this bowl, producing what is known as a cold pool.   This cold pool can be quite shallow....a few hundred meters to a kilometer in depth--- with an inversion capping it.  Inversions are very stable and it is hard for air to mix down.  The cool air becomes saturated and thus fog and low clouds are often present.


Let me show you how shallow the cold air can get by presenting the temperature data from a 400 ft high meteorological tower at Hanford, WA around 9 AM last night.  22F warmer at 400 ft than near the surface!


Here is a satellite picture from January 3--you can see the low clouds, which were banking up on the eastern side of the Cascades. This often happens when there is lower pressure over western WA compared to the east.



What causes the strong winds that helps mix out the cool pool?  Generally, this is associated with passage of a vigorous front or low pressure center after a period dominated by high pressure. 

8 comments:

Rod said...

Cliff,

We regular readers knew that. No need to apologize.

But yes, good ol' Yakima. Grew up there from three years old to thirteen years old. The weather was generally cold and innocuous in the winter, but they did have their moments. Good gawd, it is lucky I made it out of there.

The orchardists used to light those "smudge pots" in the 50s and early 60s. Woah Nellie. People today would not believe the crap that was pulled back then...

Bonnie said...

You're right about the murkiness, Cliff! I live in Ellensburg and it had been 2 weeks of cold, fog and drearyness until yesterday (Monday). Sometime around mid-afternoon, the temperature started climbing quickly (from somewhere in the 20's to almost 50) in the span of an hour or two. And the wind came howling out of the NW ... we were *averaging* 27 knots on our backyard weather station and our highest gust was 45 knots. The snow was melting so fast that the water poured off our roof was like it was raining. It was pretty amazing! The warm temps and the high wind lasted for about 8 hours.

smokejumper said...

Yeah that inversion went out with a bang. The wind sounded like a freight train. So I have 12in sprinkler risers in my orchard, and at 2pm they were covered with our snowpack and by 8pm green grass was already appearing

But this has been one of our warmest winters in recent memory. I know those temperature graphs dont show it but we have had zero intrusions of artic air. Any cold has been 100% radiational cooling due to long nights.

A good archive is soil temperature and typically we can have 1 to 2 feet of frozen ground, but the 8in soil temperature right now is 36 degrees. Which was fine because that flash melt got absorbed into the ground like a sponge but its muddy. Nasty out there.

Ron said...

While sunshine may have benefits for people's emotions, it's overrated as a source of warmth at this latitude at this time of year. Case in point was last week. On Wed (2 Jan) Spokane was overcast with a high of 26F. The clouds dissipated and the temperature plummeted that night to 6F. Thursday (3 Jan) we were sunny all day with a high of only 24F. After dropping to 10F that evening, the clouds moved in and we warmed overnight and had a high of 27F on Friday. All of the warming/cooling was solely due to radiation. So the coldest of the 3 days was the sunny day. With our low sun angle and snow cover, solar radiation does much less to warm us than terrestrial long-wave radiation. So I'd rather have my cloud blanket at this time of year, and save the sunshine for the warm season.

Bill Lenihan said...

Cliff, I am curious as to the extent, if any, the dam pools on the Columbia and Snake Rivers influence winter weather on the East Side.

Hindu said...

I actually like a few weeks of the low cloud inversions here in Tri-Cities. Nice break from the unrelenting sun of summer. When the air quality degrades and it gets to be a stinky freezing fog, then I've had enough

Thompsonized said...

Cliff, the murkiness in Ellensburg combining the snow and freezing fog prevented us from seeing one telephone pole to the next. In this picture, you should see out truck with the whole city of Ellensburg beyond it https://twitter.com/thompsonized/status/289068299554271232/photo/1

We couldn't even see the mountains from our property in the mountains...

snowave merced said...

My first winter in Plain.. I'm moving later this year. I can handle the snow and cold, but 3 months of constant low clouds where you can't even see the mountains in your back yard is clausterphobic. I might as well be in Kansas.