Wednesday, September 30, 2020

Smoke and the Reddened Sun is Back

Last night, as the sun was setting on the Olympics, the approaching California smoke was apparent.

And this morning, the sun, obscured behind the spreading smoke veil, reddened the sky while fog threatened to engulf the city.  Beautiful, really.

The visible satellite image at 9:46 AM clearly showed the smoke over western Washington and the conduit of smoke stretching back to northern CA.


Fortunately for those of us who enjoy breathing, the bulk of the smoke stayed aloft, something often true of smoke imported from afar.   Air quality sensors at the ground show degradation along the Oregon coast and, to a lesser degree, in western Washington where some air quality sites have declines to "moderate" levels of small smoke particles.


For example, in Seattle (below), small particle concentrations have increased from typical background levels (around 5 micrograms per cubic meter for PM2.5 particles) to around 25.  Most people will not notice this level of smoke.


The biggest protection we have from the overlaying smoke is the inversion layer near the surface, where temperature is increasing with height.  Inversions suppress vertical motion of air.

The vertical sounding at the WA coast this morning, produced by weather instruments lofted by a weather balloon, showed the inversion clearly (see below).  Temperature values are noted on the x axis, height (in pressure) on the y-axis.  850 is about 5000 ft.  Temperature (the right solid line) increases with height to about 950 hPa...about 2000 ft above sea level.


Air does not like to mix through inversions, but as temperature at the surface increases, the inversion will weakening. Model forecasts suggest that enough of the inversion will remain to prevent large amounts of smoke from reaching the surface.  Just a gradual, modest degradation over the day.

The general weather pattern is not shifting much during the next day, so light smoke should remain for awhile.

I should note that the smoke can be traced to northern California where a Diablo wind event occurred over the weekend.  In such events, strong/dry northeasterly winds develop over the region that can start and spread fires, with Diablo winds driven by high pressure east of the Sierra Nevada.  Fortunately, the Diablo winds have declined, and northern CA smoke production has lessened (see satellite picture this AM below).


On Sunday, winds will switch to northerly over our Northwest and remove the smoke.

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Tuesday, September 29, 2020

Smoke is Approaching and Will Settle In Tomorrow over Washington State

 An unwanted California import is now approaching and on satellite photos its ominous tendrils are reminiscent of dementors and deadly hallows of Harry Potter fame.

A recent (11 AM)  visible satellite image is worrisome (see below), with northward-bound smoke from California now extending over most of the Oregon coast and starting to extend above the southern Willamette Valley.


The latest available NOAA HRRRsmoke forecast show the smoke rapidly moving north and west.    Starting with the total smoke aloft, by 11 PM tonight smoke--some dense--will be over western Washington (purple and red signify the greatest concentrations)


And by 11 AM Wednesday will be across all of Washington State.


And at 11 PM Wednesday, a fresh batch of smoke will be moving northward out of California.

The greatest concentrations of smoke will remain aloft over western WA, but some will reach the surface here in Puget Sound.  To illustrate, let me show you the predicted smoke in an east-west vertical cross section across Puget Sound (the valley between the two mountain ranges in the cross section).

At 10 PM tonight, smoke, some of it dense, will be above Puget Sound at elevations of roughly 10,000 to 20,000 ft.  The moon will be obscured a bit.


11 AM Wednesday morning will see the smoke layer lowered  with modest concentrations of smoke reaching the surface.   Probably not enough to be hazardous, but some sensitive folks might notice it.


And smoke sticks around at low levels through 11 PM tomorrow (Wednesday), with modest concentrations at the surface.  This is nothing like our last smoky period, but skies will be hazy.


Unfortunately, the atmospheric pattern, bringing smoke up from California, will continue through Thursday.

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My 101 Class

As I have mentioned before, I am teaching Atmospheric Sciences 101, an introduction to weather and climate, this fall.  Not surprisingly, it will have to be online (Zoom).    But perhaps this is a rare opportunity as well.

As you know from this blog, I am really into outreach to the community through my blog and podcast (and previously my radio segment on KNKX).   I would like to try doing outreach this quarter with the online 101.

If you are over 60, you can sign up for the wonderful UW Access program, where for only a few dollars (I believe 5), you can audit UW classes.   So I encourage all of those interested in taking the class to do so.  Access students can't register until the third day of class, but I can give them the zoom address.

The class meets M-TH at 9:30 AM starting this Wednesday (Sept. 30th).  The class outline is here.
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My latest podcast:




If you would like to support the creation of the podcast, please visit my Patreon site
KNKX and Cancel Culture is found here.