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Is Wildfire Smoke Making Our Fog More Persistent?

Is Wildfire Smoke Making Our Fog More Persistent?

Satellite image for western Washington round 1 PM Saturday

 The National Weather Service’s forecast for Saturday had an issue.  For central Puget Sound it was predicting clouds within the morning after which turning into largely sunny (see under)

1605327949 7 Is Wildfire Smoke Making Our Fog More Persistent

But as an alternative fog held in ALL day, one thing proven by the Space Needle PanoCam at 3:10 PM Saturday.  You do not see circumstances like that holding in all day very a lot.
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And the UW excessive decision forecasts of fog/log clouds for five PM Saturday began with fog within the morning and quickly burned it again (see forecast at the moment).
Is Wildfire Smoke Making Our Fog More Persistent
An error that the NOAA/NWS HRRR mannequin additionally made (forecast for five PM Saturday additionally proven):
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In truth, this error–the unrealistic burn off of low-level cloud–has occurred a number of instances through the previous few week, with fog and low stratus displaying uncommon persistence.
Local meteorologists and a number of the NOAA modelers have been musing that maybe, simply maybe, there’s a motive for this uber-persistent low clouds and our mannequin’ incapacity to get it proper:  wildfire smoke.
And there are good bodily the explanation why smoke is perhaps the reason.
For instance, smoke scatters a number of the photo voltaic radiation again to area, lessening the photo voltaic heating accessible to burn off the fog.
In earlier blogs I confirmed the impact clearly by presenting the photo voltaic radiation on the roof of my constructing earlier than and after the smoke moved in on Sept 11th (see under).
1605327951 300 Is Wildfire Smoke Making Our Fog More PersistentSmoke at any stage, lowering photo voltaic radiation reaching the floor, might assist the fog persist.   Many operational climate forecast fashions don’t have have this impact.  However, the NOAA HRRRsmoke mannequin AND the UW  mannequin do attempt to simulate the photo voltaic dimming from smoke.  Thus, we have to discover one other clarification.
And there’s one. 
Cloud droplets typically type on small particles within the ambiance referred to as Cloud Condensation Nuclei (CCN).  Smoke particles can act cloud condensation nuclei.  So including smoke can result in MORE cloud condensation nuclei and MORE cloud droplets (see left facet under).  If the quantity of water accessible does not change (which is generally the case) then having extra nuclei results in extra, however smaller cloud droplets .  And it seems the having extra particles results in the cloud being extra reflective, which REDUCES the photo voltaic radiation accessible to burn off the cloud.
1605327952 123 Is Wildfire Smoke Making Our Fog More PersistentMore particles from smoke or air pollution could make a cloud extra reflective, one thing we see within the Pacific as marine visitors provides particles to low clouds, producing a function referred to as ship tracks (see under).
Is Wildfire Smoke Making Our Fog More Persistent
And there’s extra!   Having quite a lot of small particles works towards producing drizzle, which takes moisture out of the fog/stratus.  Bigger droplets turn out to be heavier and fall out extra rapidly, gathering different droplet as they fall.  Thus. having the moisture in smaller droplets helps preserve the fog!
Now right here is the important thing challenge.   Most fashions, together with the UW WRF and the NOAA HRRR mannequin don’t correctly simulate these cloud results and thus fail to forecast the power of smoke to maintain the clouds round.

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The above is a bodily believable clarification, and definitely there have been enhanced values of small particles within the decrease ambiance over Puget Sound  on Saturday (see the small particles focus at Seattle’s Beacon Hill under).
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Some of my colleagues on the NOAA Lab in Boulder, CO consider the above is an actual chance, and through the subsequent month UW graduate pupil Robert Conrick can be exploring this mechanism with subtle modeling experiments.  Will let you realize what we discover out. 
Such conditions are why science is a lot enjoyable, with fascinating theories to check and actual sensible worth once we remedy the thriller.
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