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
While the Northwest has been drier than normal, it has been drenching wet a few hundred miles to the north. An unusually strong atmospheric river ....a long current of moisture stretching southward to the subtropics...has been in place for days, bringing large amounts of water vapor to Alaska. And the atmospheric river will be in place for several more days, slowly moving southward. To illustrate, the scale and beauty of the atmospheric river, here is a water vapor satellite image for 11 AM today. The lighter areas have more water vapor. You can see the current of moisture extending from near Hawaii into central BC. This current is the result of low pressure over the Gulf of Alaska and high pressure offshore of California. A forecast of total water vapor content in the atmosphere for 11 PM tonight shows a healthy atmospheric river (white and blue colors indicate the higher amounts of moisture). As this atmospheric river slams into the mountainous West Coast, the air is forced to ...
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