Darkest Days Occur Around Thanksgiving In The Northwest

Nov 24, 2017

Have the wet weather and dark days got you down? You’re not alone. Seasonal Affective Disorder, or SAD, is extremely common in the Pacific Northwest. Recent rains and abundant cloudy skies seem to have exacerbated some people’s experience of the lack of light this time of year, says KNKX weather expert Cliff Mass.

“I’ve had so many complaints and emails and text messages from people that are complaining about the darkness and how it’s affecting them. And some people are wondering whether this is unusually dark,” Mass said.  “People are certainly noticing the loss of light.”

The Darkest Time Of Year

So how dark is it really? Is it darker than normal?  Mass says it’s dark, but not exceptional.

“We can get objective evidence from devices at many weather stations that measure how much light is coming in,” he said.

For example, he says a look at the data from the weather station in North Seattle over the last six months is revealing.

“It is amazing how little light we’re getting right now, compared to mid summer,” Mass said.

He says during mid-summer, the average is about 30 Megajoules per square meter per day.

“And this week, we’ve been getting like three or four. So we’re talking about roughly one ninth to one tenth the amount of light from the sun now compared to the mid-summer. So it’s hugely down,” he said.

This could explain people’s need for light therapy or an extra big dose of vitamin D3. Mass says right now might feel more extreme than in years prior because of all the stormy weather we’ve had lately. But the low light is actually quite typical. And there are several reasons why.

Factors Reducing The Light

“Here in Seattle and in the Northwest, we get a double whammy of darkness,” Mass says. First, there’s the astronomical side of the equation.

“We’re at 47 degrees North and by the time you get into September and October, we’re rapidly losing sun. The nights are getting longer quickly, the days are getting very, very short. The sun’s angle is getting very low in the sky. So the astronomical part is very profound,” he said.

And in the months of September and October, the resulting change in light levels is very rapid. People feel it.   

Then there’s the meteorological side: the weather typically shifts very rapidly at this time of year, from quite nice in September or even way into October.

“We can have plenty of sun and pretty decent conditions, but then in late October into November, we go through this transition. The jet stream comes over us, the clouds stream in, the rain comes in. So it’s this rapid turn on of clouds and precipitation,” Mass said. “And that cuts the light, which is declining anyway.”

On top of those two factors, Mass says, when people turn their clocks back to standard time in early November, they get less daylight in the afternoons.

“And all of a sudden, it’s dark at five o clock and that really makes people kind of sad,” Mass said.

The Worst Is Almost Over

But Mass says hang in there if you’re struggling with the lack of light.

“We are right now in the worst week of the year in terms of clouds,” Mass said. “The cloudiest, stormiest, windiest, worst weather generally occurs during the third week of November, around the time of Thanksgiving. So, this is as bad as it’s going to get. And this year is not disappointing.”

Mass says hang in there till early December and it will get a little less stormy and wet, making it feel a bit brighter, perhaps.

“So it’s a long, long, slow climb out of it, but this is probably the worst week, when it comes to the cloud part,” he said.

Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX environment reporter Bellamy Pailthorp. Cliff Mass is a University of Washington professor of atmospheric sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to podcasts of Weather with Cliff Mass shows, via iTunes or Google Play.