January 24, 2022

Air Quality Declines As Inversion Slowly Weakens Overhead

 Inversions, in which temperatures INCREASE with elevation,  suppress vertical mixing, which in turn allows pollutant concentrations to increase near the surface.

And with a strong inversion over western Washington and Oregon the last few days, air quality has degraded to moderate levels at several locations.  

To illustrate, below is a map  (at 7 PM today) showing the concentrations of small particles (less than 2.5 millionths of a meter) that are capable of passing deep into your lungs. Nasty stuff.

 Low concentrations are green, with moderate values in yellow and orange, and red being even higher.  The Puget Sound region has degraded air quality and it is even worse around Portland.  Generally good in the mountains.


Graphic provided by PurpleAir

You can see the declining trend of air quality in Seattle with a plot of the small particle concentration during the past few days (below).  A progressive upward trend in small particles.


The sources of the particles include combustion from heating, burning of gas and diesel fuels in cars, and from burning wood in fireplaces and wood stoves.

During most winter days, these emissions are little problem around here, with stormy, wind conditions and an atmosphere that facilitates vigorous vertical mixing of air in the lower atmosphere.

But during the last three days, high pressure aloft has produced a well-defined inversion, as noted in the vertical sounding at Quillayute this morning at 4 AM. (Quillayute is on the northern WA coast)--see below.  Red is temperature, the x-axis indicates temperature (°C) and the y axis is height in pressure (700 is about 10,000 ft) 

You can think of an inversion as a meteorological barrier to air motion.  Here is a beautiful example of what happens when smoke hits a low-level inversion (see below).... it is like hitting an invisible barrier.

Image by S/V Moonrise

The particle concentrations we experienced the last few days are NOTHING compared to what we breathed during wildfire events, something shown by the plot of small particle concentrations from summer 2017 to now (see below).   September 2020 was the big "winner" with values about ten times higher than what we experienced today.


The good news is that our winter concentrations are getting lower and lower, as fewer homes burn wood (very dirty), cars and trucks get cleaner, electric cars become more numerous, and with effective burn bans and other restrictions by air quality groups like the Puget Sound Clean Air Agency.

And some other good news...the inversion is weakening and will probably break later today--maybe even with a glimpse of the sun.  And stormier conditions will return on Friday.

Prepare to take a deep, healthful breath!



January 23, 2022

The Southern Oregon Coast Hits 79F as a Super-Inversion Develops over the Northwest

Update at the end!

High pressure and a super-inversion have developed over the Northwest, and jaw-dropping weather contrasts have developed--both in the horizontal and the vertical.

For example, yesterday (Saturday) temperatures zoomed up to near 80F on the southern Oregon coast, with 79F at Brookings, Oregon (see yesterday's max temps, below, click on the image to expand).  The forecasts were right.


At the same time, temperatures were in the 40s in eastern Oregon and BELOW FREEZING in large sections of the Columbia Basin of Washington (see Saturday's high temps below). 

If you were in frigid, sub-freezing Wenatchee yesterday and wanted to warm up by 20F you could do it--by going up into the mountains.  


This morning, the Puget Sound lowlands are enshrouded in fog, but clear skies are only about 1000 feet above.  

Want proof?  Here is a picture from around 1200 ft in Bellevue, looking west, provided by Dr. Peter Benda.  Fog covers the lowlands, but blue skies are aloft.


Or this picture from the top of West Tiger 3 (2500 ft) by 
Dr. Steve Cobert.  Cougar Mountain is an island in a sea of fog and low clouds.


The pattern is confirmed by the visible satellite image at 8:16 AM this morning (below), with the western lowlands enshrouded by fog, as is the Columbia Basin.  But the coast is clear.


The origin of these sharp contrasts is strong high pressure, which has produced a super-inversion over the region.

The upper level (500 hPa, about 18,000 ft) for yesterday at 4 PM (shown below) clearly indicates a strong ridge of high pressure just offshore.   And just east of such ridges, very strong sinking occurs.


Such sinking produces what is known as a subsidence inversion.   An inversion is when temperatures INCREASE with height over some layer of the atmosphere, which is the inversion (opposite) of what normally occurs:  temperature decreasing with height.  

Why do high-pressure areas create inversions you ask?  

 Because sinking air is compressed and warmed.  The sinking is larger aloft but weakens towards the surface (because the ground is in the way!).    Also the clear skies aloft air enable radiational cooling from the surface before any fog forms.

Let me show you how impressive the inversion was this morning.  The radiosonde-based vertical sounding at Quilayute shows warming of about 18C (roughly 32F) in the lower few thousand feet (see below).  WOW.

And aircraft coming into and out of SeaTac airport measure temperatures, and this morning at 8 AM temperatures increases from the lower 30s near the surface to the 50s above 2000 ft.  Double wow.

Image from Seattle SnowWatch, funded by the City of Seattle

Hike to the top of Tiger Mountain today (at about 2500 ft) and you can have your lunch in bright sun and perhaps 60F, with your hike starting near freezing.  My kind of hike.

High pressure will be hanging around through Thursday, after which precipitation will return to the Northwest.  It has been a nice break from the rain, providing a chance for things to dry out a bit and lessening the chances for landslides and slope failures after a very wet period.
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Important Update at 3:43 PM

With a strong inversion, there was a huge difference between the temperatures at Tiger Mountain Family Nudist Park --37F-- (elevation 646 ft) and Poo-Poo Point (about 1550 ft) -55F (see map below).   In fact, Poo Poo Point, which is known for hang gliding,  peaked at 57F.

So roughly 20F higher about 900 ft up.  A very strong inversion.

I suspect the Nudist colony folks may be moving up the hill to Poo Poo Point today for obvious reasons.  Stay tuned, this could get interesting!  







Air Quality Declines As Inversion Slowly Weakens Overhead

 Inversions, in which temperatures INCREASE with elevation,  suppress vertical mixing, which in turn allows pollutant concentrations to incr...