Dense Fog in California, January 7 to 8, 2021

Area Forecast Discussion...UPDATED
National Weather Service Hanford CA
353 PM PST Thu Jan 7 2021

.UPDATE...
Updated AIR QUALITY ISSUES section.

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.SYNOPSIS...
Calm, dry weather will continue with areas of nighttime and morning
fog possible through Saturday morning. Another weak disturbance will
track through northern California on Friday and may bring a slight
increase in winds and a slight chance of light showers to the higher
elevations especially near Yosemite National Park. Otherwise, much
of this coming week will be dry with slightly above normal temperatures.
Nighttime fog with some becoming dense will be possible each night
the next several days with high pressure building into the region.

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.DISCUSSION...
Some dense fog did again develop overnight and this morning as the
passage in a shortwave disturbance through the region last night was
quick and allowed for some clearing skies and radiational cooling.
Another tricky fog forecast for this evening as a weak trough axis
associated with a Pacific shortwave trough begins to move through
Northern California and Oregon tonight and tomorrow. The clouds
assoicated with this trough is the wild card as well as any lifting
and mixing mechanisms that will certainly accompany the trough axis
passage. Timing will be key though as we found out with last night's
disturbance. If the timing is such that there will be a slower
progression or if it happens later than it did last night then fog
will greatly be mitigated, at least the dense variety. Too much
lifting could also bring more of a stratus deck as the fog is lifted
upward. As of right now we have held off on a Dense Fog Advisory and
will take a more wait and see approach.

The passing disturbance tonight will have minimal moisture and
precipitation is not expected in the lower elevations. There is a
slight chance for light showers in the higher elevations especially
around the Yosemite area as the main disturbance moves further north
of our CWA. Winds will be generally light but as the trough axis
moves through localized winds may become breezy for a short duration.

On Saturday Pacific ridging begins moving into the region and will
by late this weekend will become highly amplified with the ridge axis
going northward well into western Canada. With this ridging in place
our precipitation chances will be nil but overnight and morning dense
valley fog will become more likely. A backdoor cold front does
encroach the southwest but looks to stay on the eastern side of the
Sierra Nevada but may increase easterly winds in the Kern Desert
areas on Monday. Unfortunately though precipitation looks non-existent
through next week with Pacific ridging firmly in place. Not good for
the rain and snow lovers out there, I include myself in that camp.
But nighttime/morning valley fog aficionados will most likely have
their fill over this next week.

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.AVIATION...
LIFR with local VLIFR visibility due to fog are possible in the San
Joaquin Valley 06Z through 19Z Friday. Otherwise, MVFR with local
IFR conditions will prevail elsewhere over the central California
interior during the next 24 hours.

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.AIR QUALITY ISSUES...
On Friday January 8 2021...Unhealthy for sensitive groups in Fresno
and Kern Counties. Fireplace/Wood Stove Burning Status is: No Burning
Unless Registered in Kings...Madera and Tulare Counties. No Burning
For All in Fresno and Kern Counties. Further information is available
at Valleyair.org

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.CERTAINTY...

The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is high.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.

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.HNX WATCHES/WARNINGS/ADVISORIES...
None.
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public...Andersen
aviation....MV

weather.gov/hanford