And last week, as high clouds streamed in overhead, a good example of this feature was captured by weather videographer extraordinaire Greg Johnson of Skunk Bay Weather.
During a sundog event, areas of light are seen on both sides of the sun (see example below). These are the "dogs." Sundogs are also called "mock suns"
The ancients thought that sundogs were ominous signs, foretelling events such as the death of kings. Today we know that sundogs generally occur when the sky is filled with a thin veil of ice crystal clouds, generally cirrostratus.
Now let me show you a video captured by Greg Johnson from his location in northern Kitsap County around 6:30 AM last Wednesday. From his camera, you only see one of the dogs.
The sky at the time of sun dogs was full of high ice crystal clouds, called cirrostratus. You can see the extensive veil of such clouds from the visible satellite picture taken about this time (see below):
Why sun dogs?
They occur when ice crystals in the clouds--shaped in six-sided plates--are oriented roughly horizontally. With that orientation, they preferentially bend the light by 22 degrees, creating two areas of light (22 degrees on both sides of sun), as illustrated by the figure below.
Ice crystals that are smaller and tumbling about create circular halos.
As shown in the picture above, many sundogs have rainbow colors as well, something also illustrated in the picture below.
These colors are produced by dispersion, the breaking up of visible light into its component wavelengths, as it passes through the ice crystals, not unlike what happens in a prism (see below).
Cirrostratus and associate halos and mock suns are often a sign of an approach weather system, such as a front or cyclone. Thus, although it may not foretell the death of kings, it can suggest the end of nice weather.
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 ...
This has been a very benign wildfire season so far this year, with far fewer than normal wildfires over the western U.S., with considerably less than normal area burnt (see figures below). Number of wildfires by year: WA DNR area The area burned by year: WA DNR Area The area burned by year, California. But we can not become complacent! Historically, the most threatening wildfire season in the Northwest is the end of August and early September as the atmosphere starts to cool. But why? What is so threatening about the cool late summer/early autumn periods? All is revealed in the podcast. And I also provide the forecast for the next week. Very pleasant in the west, but a bit toasty in the east. To listen to my podcast, use the link below or access it through your favorite podcast service. Some major podcast servers: Like the podcast? Support on Patreon
My podcast today will both provide the weekend weather forecast and talk about the history of wildfires in the Pacific Northwest. Wildfires and associated smoke are a major concern in the region, and some media, politicians, and others have suggested that wildfires and wildfire smoke are not normal and are a potent sign of a changing climate. They are not correct. Wildfires and their smoke are a natural part of the Northwest ecosystem. What was not normal was the period of suppressed fire during the later portion of the 20th century. A good illustration is the visit of Mark Twain in August 1895, a summer in which the U.S. Weather Bureau noted "the sun was almost entirely obscured by excessive smoke from wildfires." Twain was invited to speak in Olympia, where the chairman of the reception committee apologized for "smoke so dense that you cannot see our mountains and our forests, which are now on fire". Twain retorted “As for the smoke, I do not so much mind, I...
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