December 07, 2023

The Darkness

 It has been often said that it is darkest before the dawn.

Well folks, we have been very dark and dawn is a long way off.

The image from the Seattle SpaceNeedle at noon Wednesday, was dismal at best (see below)

So what do the numbers say?  How dark have we really been?

Below is a plot of incoming solar radiation from the WSU AgWeather network site in Seattle (near the UW) over the past year.  

The last two days have been abysmal, with 0.57 and 0.87 MJ (megajoules) per square meter.  During the midsummer we often get above 30.

To put it another way, during mid-summer we can get around 50 times more warming rays from the sun than during the past few days.  

What about Pasco in the Columbia Basin?  Surely that location would be brighter! (see below).  

Nope, the same story.

The trouble is that we start with a relatively northerly latitude with short days.... so there is meager solar radiation to start with.

Then we add very thick, deep clouds from a strong atmospheric river. Plus lots of precipitation.  The visible satellite imagery at noon for December 5 and 6 are shown below.  The atmospheric river/frontal clouds are clearly visible and had spread over both sides of the Cascades.

The combination of weak sun, short days, and plentiful clouds makes solar energy problematic in our region during the winter.    Take a look at the average solar resource (the fancy name is irradiance) for December.  Not much in the Northwest.  A different (and better) story over the desert U.S. southwest.

Weather forecasting models predict solar radiation reaching the ground, something I have never shown in the blog until today.  But now I will give you a peek!

The forecast for 1 PM today shows dark colors (less sun) over the region with the murk being particularly bad over the western slopes of the Cascades.

Saturday looks better in northern CA, but far worse in western Oregon and Washington.  Why?  Because ANOTHER atmospheric river is coming in.

Want solar relief? It will be much brighter on Tuesday (see below) as a ridge of high pressure builds (temporarily) over the eastern Pacific.  

Get your sunglasses ready.😊

December 05, 2023

Subtropical Warmth, Heavy Rain, and Filling Reservoirs

You did not have to travel to Hawaii this morning to experience subtropical warmth or tropical-intensity showers.  It was here in the Pacific Northwest.

As a substantial atmospheric river interacts with our terrain, large amounts of precipitation have fallen during the last 36 h, with extreme contrasts over a few miles.

Before are the 36-h totals.  Some locations over NW Oregon and SW Washington got to around 8 inches...and more is coming.  6-7 inches in the Cascades.

But as impressive as the large totals are (breaking daily records at some locations), the LACK of rain in some amazing rainshadows is also notable.  

Consider the rain shadow northeast of the Olympics.  Over the higher terrain, there were over 6 inches in 36h. In contrast, a station west of Port Townsend only had 0.12 inches, and portions of Whidbey Island were only about a quarter of an inch (see below).

To put it another way, there was about a fifty-fold difference between the rain at higher elevations and downstream in the rainshadow.   Amazing.

The air over us has felt subtropical.  The temperatures this morning have gotten into low-60s  (see proof below).  The dewpoints (a measure of water vapor content) rose into the mid-50s.   

The freezing level (the level of the atmosphere where temperature declines to 32 F) was as high as 11,000 ft this morning based on the Salem, OR radiosonde (see below).   All rain in the mountains!

All this warm rain is rapidly filling our reservoirs, which is a good thing.  The water level in the big Chester Morse Lake that supplies a large proportion of Seattle's water is going up fast (see plot below).

Finally, let's get back to the subtropical origins of the air over us.  Below are 72h trajectories.....3D paths over time... of the air that was over Seattle this morning ( I used the wonderful NOAA Hysplit website to create these).

Our air started around 30N//.the latitude of northern Baja California!  The air did not come from Hawaii, so let's not call it a Pineapple Express. 😀

Things will dry out a bit for the remainder of this week before ANOTHER atmospheric river reaches our shores on Saturday (see below)--so keep your umbrellas and rain jackets handy!

The Darkness

 It has been often said that it is darkest before the dawn. Well folks, we have been very dark and dawn is a long way off. The image from th...