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.




Comments

Post a Comment

Popular posts from this blog

Why so little lightning in the Pacific Northwest? And a very nice weekend ahead.

Image
During the past 24-hours, there have been a few lightning strokes over the region (see below) but nothing to write home about (see below). It turns out that the Pacific Northwest and the remainder of the West Coast have some of the lowest frequencies of thunderstorms in the entire country (see below). But why?    My podcast provides the answer. And I also give the weekend forecast....and I think most will like what I have to say. 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 
Read more

The Time of Year You Can See the Air Move

Image
  Most of the time, you can not see the air move.   You can feel it, but the complex, turbulent motions are invisible to you, except when it interacts with leaves and branches on trees and plants. But for a few weeks of the year, the sky is full of small, cotton-like tuffs that like a natural MRI machine reveals the complex three-dimensional motions of the atmosphere.   Cottonwood season.  And we right in the middle of it.   Being cottonwood aware is of particular value this year.  It reveals the active dispersion and movement of air that makes the outdoors essentially COVID safe, and thus should be of some comfort for those nervous about transmission outside. Cottonwood seeds are embedded in small cotton-like fibers.   A million seeds weigh about 3 pounds.  Yes, each seed and tuff weights about .000003 pounds.   And that fact, plus the cottonwood tuff, means that these seeds fall VERY, VERY, VERY slowly.   So slowly that they are excellent markers for the three-dimensional flow of the
Read more

A Much Colder Than Normal April: But How Unusual?

Image
  April was a chilly month over the Northwest, but how chilly?     It turns out the answer depends on where you are located. The difference between this April's temperatures from normal across Washington State (below) shows that the entire state was well below normal.  The eastern side of the state was particularly frigid:  some areas were more than 6 degrees below normal.   Considering the west side of the state, the April mean temperatures at SeaTac Airport are plotted below.   This April was the coolest since 2011. April 2020 was in 15th place for the coolest April since the mid-1940s and was a bit more than 4F below normal.  So if you felt that you were cheated out of normal spring warmth...you are right. But if you really wanted to experience extraordinary April cold you had to be east of the Cascade crest. Consider Yakima.  Wow.  It had the third coldest April temperature since the mid-1940s.   And the all-time record in 1955 was only slightly colder. If you want a longer-te
Read more