April 13, 2020

A New Discovery? The Chehalis River Fog Jet

The high-resolution satellite imagery yesterday morning revealed a transient, but fascinating feature:  a narrow current of fog emanating out of the western portion of the Chehalis River valley.   This fog current then passed over Aberdeen and Hoquiam before pushing out into the Pacific Ocean.

Here is the NOAA/NWS GOES satellite image around 8 AM Sunday that shows this amazing feature.  You can see the fog collecting in the Chehalis River valley and then jetting out to the west.  Just amazing how this current was able to maintain integrity for tens of miles.  About roughly ten miles offshore it lost its structure, with the cool, moist air producing a blob of low clouds.


If you look closely, a weaker fog jet was produced at the exit of the Columbia River.    

Just as a reminder, here is the Google terrain map for the region.  The Chehalis River Valley is well defined with relatively steep side slopes.  Cool air can drain from side valleys into the main Chehalis channel, resulting in cool air in the valley.   And if the air is moist enough, the air is cooled to the dew point, producing fog.


Surface observations Sunday morning at the same time as the satellite image shows easterly (from the east) flow at Hoquiam and temperature of 36F...and even cooler down in the valley towards Montesano.   Cool, dense air escaping the valley was aided by a regional pressure gradient with higher pressure inland and lower pressure towards the coast.



The observations at Hoquiam Airport illustrate the weather conditions during the passage of the "fog jet".  The time is in UTC (same as Greenwich Mean Time) with 1405 being 7:05 PDT.  The fog was only over them for about an hour, with easterly winds of 7-8 knots and temperatures in the mid-30s.


High resolution weather prediction models got a piece of this feature.  Here is the predicted wind fields for 7AM from the UW 4/3 km runs (the grid points are 4/3 km apart).  You can see the easterly flow and a relatively narrow jet of strong winds.


And the forecast for 9 AM, showing surface winds and temperature (shading), indicates cold air in the Chehalis River Valley and the plume of cool air moving out into the Pacific.


The much coarser NOAA/NWS HRRR model (3-km grid) had a difference solution.  Here is the forecast visibility for the same time.   A very weak plume of low visibility is coming out of the Chehalis River valley, but there is a distinct plume and an offshore fog area associated with the Columbia River valley.  The NOAA model doesn't have the resolution to properly simulate the narrow Chehalis River valley.


Anyway, this feature is perhaps a one on the meteorological Richter scale, but fascinating nevertheless, and a good test of my profession's high resolution models.




14 comments:

  1. Ever since GOES17 came along, watching the movement of minute eddies and micro-currents in the atmosphere has been fascinating and most enjoyable. Makes one appreciate the beauty of the atmosphere and how it is constantly moving and changing over ours heads all the more.

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  2. Cliff
    I noticed that the fog formed to a lesser extent in the Willapa river valley to the south of Aberdeen. The terrain is different than that of the Chehalis river valley and it is a much shorter river.

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  3. like a bizarre sea creature with a long snaky tongue

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  4. Chehalis gap in reverse. If you had strong easterlies coming out of the straits and everything was just right, maybe you could get a convergence zone on the west side of the Olympics

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  5. That's a very captivating phenomenon. I'm envious of those who may have witnessed it from a viewpoint high enough to allow appreciating that it was occurring. We've not had fog just NE of UW in Seattle, but I've noticed that we've had thin ice on our bird baths the last several mornings and frost on our lawn in places and on local roofs. I'm guessing that with this crystal clear night sky, higher pressure and still air, the air temperature may not be 32, and but this ice owes to local evaporative cooling as heat radiates out of the ground, water and other objects, and voila!, surface temps fall below 32 and ice forms, which is also interesting.

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  6. Amazingly dry air in NW Bellingham yesterday. I measured a minimum dew point temperature of 10F - off the charts compared with previous Aprils in my period of record and a value below which I've hitherto recorded only in strong Fraser outflow events during winter - and a minimum relative humidity of 14% - a new all-time record for my location since I've been measuring. The next lowest RH value in my period of record is 20%. I also measured 0.16" of evapotranspiration yesterday - a value more typical for mid-summer. In fact, evapotranspiration at my location exceeds precipitation for the month thus far by nearly an order of magnitude - very unusual for this time of year. However, soil moisture, is still quite high despite all of the dry air and paltry precipitation though soil temperatures have been marginal for grass growth. I have, in fact, only mowed my lawn twice this season primarily due to the unusually cool weather we've had with clear nights, dry air and little wind allowing for efficient radiational cooling. There have been no days so far this month at my location with daily minimum temperatures at or above average and several nights at or below freezing. This is the first April in my period of record during which I've measured a temperature of 32F or below. The warmest temperature I've measured this month is 62F. I have not measured a temperature of 65F since late September and have not measured a temperature of 70F since mid-September. This is by far the longest streak of days with maximum temperatures below 65F and below 70F in my record. Striking contrast compared with April 2016 during which Bellingham recorded its all-time monthly record high temperature of 83F!

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  7. I watch the GOES 16 stuff all day for things like this, but Sunday morning is not my power web time. Last week there was the reverse of the fog jet on the morning of Tuesday April 7. Easterlies coming through the Snoqualmie pass drainage cut a clear channel through Puget Sound's morning cloud cover for quite a ways, it was pretty cool to watch.

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  8. That is a double wow! First the image of the fog jet but second that the models showed the air movement. Amazing,

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  9. Cliff,

    I'm finding the atmosphere increasingly interesting. Perhaps some day I will amass enough knowledge to find a little discovery like this on my own. If so, I'll share it with you.

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  10. We have Snohomish river fog jets which leave the delta and crown over Hat island all the time in fall.

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  11. And for more information on the movement of fog and how it relates to cats, may I suggest Carl Sandburg's poem "Fog.":)

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  12. Reminds me of the fog feature called the Majollica Snake featured in the movie The Clouds of Sils Maria.

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  13. I have been drawing the fog in the Chehalis Basin for the last few years, this perspective is really exciting to see! thank you!

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  14. This is happening again right now. I can see it from my house in Grays Harbor City, 3 miles west of Hoquiam.

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