January 13, 2024

Dry "Storm" Hits Washington State, Snow/Freezing Rain over Northwest Oregon

Today is a day of amazing weather contrast across the region, with unusual extremes around every corner.  

On one hand, the low-level air over Washington State is extraordinarily dry, because frigid Arctic air has very little moisture content.

Consider dew point, an absolute measure of the water vapor content of the air.

Dew point temperature, the temperature to which air must be cooled to get saturation (100% relative humidity), is in the single digits to below zero F over much of the state (see plot below for 2 PM values).

In western Washington, wintertime dew point temperature is typically in the 30s or low 40s.  To illustrate how unusual things are, below is a plot of the dew point temperature at the UW for the last twelve weeks.

The bottom has plummeted during the last few days, with a dew point near zero. Very dry air.  In contrast, dew point is 36F right now at Khartoum, in the Sahara Desert.


Or perhaps you prefer relative humidity (RH), which tells you how close to saturation the air is  (saturation is 100% RH).   Below is the RH forecast for 4 PM today for the surface air.    Quite low, with values in much of the state below 40%.

In contrast, relative humidity is far higher over Oregon, due to a moist weather system moving to our south (see the 2 PM visible satellite image below)


So the outside air over much of Washington is very dry.  

But now the shocker....it is even DRIER inside our heated buildings.

Below is the indoor relative humidity around Seattle.

OMG.  Many values are below 25% and some are in the teens.   No wonder your mouth is dry and your skin is cracking!


Why such low relative humidities inside?    

Relative humidity is 100 times the ratio of the amount of water vapor in air divided by the maximum amount it can hold.  

Outside air is constantly invading our homes and buildings so the moisture content is pretty much the same inside and out.   But the amount of water vapor air can hold depends on temperature and it is much warmer inside.  Thus, relative humidity is much lower inside during the winter.

Blizzard over the Western Gorge

Finally, while a dry storm is hitting much of Washington State, strong easterly winds are found in the Columbia Gorge, hitting places such as Troutdale and Portland.  At Crown Point, a scenic location in the western Gorge, winds are now gusting above 80 mph.  These winds are being driven by a historic difference between eastern Washington (high pressure) and the coastal areas (with low pressure approaching from offshore).

Snow has now spread across northern Oregon, with areas of localized freezing rain.    This was the wintry weather that was forecast to move into our region by the errant American weather model, the GFS.

Portland at 4 PM has a cover of snow






6 comments:

  1. I live on my boat in Eagle Harbor on Bainbridge. RH outside our boat this morning at 6:30am was 11.40%! I can't recall the last time it was this low.

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  2. The Climate Prediction Center missed this Arctic outbreak.

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  3. Wow, what a fascinating insight into the weather extremes across the region! The sharp contrast between the frigid Arctic air in Washington State and the comparatively milder conditions in the Sahara Desert is truly remarkable. It's intriguing to see the dew point and relative humidity variations, both outdoors and indoors, and how they contribute to the dryness experienced inside heated buildings.

    The mention of the strong easterly winds in the Columbia Gorge, reaching gusts above 80 mph at Crown Point, adds another layer to the dynamic weather patterns. The explanation of the atmospheric pressure differences between eastern Washington and the coastal areas driving these winds provides a clear picture of the complex interactions at play.

    On a side note, I recently came across an informative article about climate change mitigation and adaptation strategies that might be of interest to those reading this weather update. It delves into important aspects of addressing climate challenges. You can check it out here.

    Thanks for sharing this enlightening weather analysis!

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  4. Barely maintaining 30% RH in my house with humidifier and wood heat.

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  5. Meanwhile, in quiet and modest little Prineville, Oregon, where it seems that most interesting weather events pass us by, Saturday morning started out with tiny dry snowflakes at about 3F. Snow continued, "desert" heavy at times, throughout the day, while the temperature dropped to -1 and below. We wound up with 5-1/2 inches or thereabouts, which I think is pretty good. Got up to all of 10F or so today, well below NOAA's predicted high.

    And here I thought El NiƱo was gonna bring us milder and drier winter weather!

    Cliff, might you sometimes expand your Eastern Washington coverage to its cousins below the Columbia Gorge? We'd be mighty interested, and pleased! Thanks!

    ReplyDelete
  6. Over on WUWT, I've posted this essay which chronicles the disappearance of the wild ranier, a regionally-important beerological species, from its native habitat in the US Northwest.

    Extinction of the Legendary Wild Ranier

    ABSTRACT: Large herds of wild raniers had been present in the US Northwest until the early 1990’s. But by the end of the 1990’s, the species had all but vanished. It is now thought that climate change may have played a role in the disappearance of the wild ranier.

    ReplyDelete

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