California, 2021

Dense Fog in California, January 8 to 9, 2021

January 8 to 9, 2021 · NWS HNX · 4 events in 4 counties and zones

High pressure strengthened over California on January 8 resulting in another night of clear skies, light winds and inversion conditions in the San Joaquin Valley. As a result, areas of dense fog reformed during the evening of January 8 and the early morning hours of January 9.

The toll

Deaths
0
Injuries
0
Property damage
None recorded
Crop damage
None recorded
Events
4

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS HNX wrote it up.

High pressure strengthened over California on January 8 resulting in another night of clear skies, light winds and inversion conditions in the San Joaquin Valley. As a result, areas of dense fog reformed during the evening of January 8 and the early morning hours of January 9. The fog lifted into a low cloud deck during the late morning which hung around until late afternoon.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Hanford, CA wrote its last area forecast discussion before the first event at Jan 8, 4:55 PM PST, 4 hours 55 minutes earlier.

Area forecast discussion, Jan 8, 4:55 PM PST, 4 hours 55 minutes before
Area Forecast Discussion...UPDATED
National Weather Service Hanford CA
455 PM PST Fri Jan 8 2021

.UPDATE...
Updated AIR QUALITY ISSUES section.

&&

.SYNOPSIS...
A weak weather disturbance will clip our area today, bringing
little more than a slight increase in winds and periods of cloudy
skies. Otherwise, high pressure will provide slightly above
normal temperatures, along with late night and morning fog in the
San Joaquin Valley through the weekend and into next week.

&&

.DISCUSSION...
AM fog continues to lift out into a broad area of stratus north of
Kern County. Otherwise, only a few high/mid clouds seen across the
region as a weak shortwave edges through today. This will open the
door for the upper level ridge to build overhead.

The ridge will be the dominate feature throughout the forecast
period, with only a few minor drops in heights as storms move
through the Pacific Northwest over the next week days. This will
keep the forecast quite benign outside of Tule Fog.

Tule Fog is expected to develop daily with this stable air mass
in place, though where stratus lingers throughout the previous day
there could be a lower threat of fog development the following
day.

&&

.AVIATION...
LIFR with local VLIFR visibility due to fog in the San Joaquin
Valley developing again after 06Z Saturday. Otherwise, MVFR with
local IFR conditions will prevail over the central California
interior during the next 24 hours.

&&

.AIR QUALITY ISSUES...
On Saturday January 9 2021...Unhealthy for sensitive groups in
Fresno...Kern and Tulare Counties. Fireplace/Wood Stove Burning
Status is: No Burning Unless Registered in Kings...Madera...Merced
and Tulare Counties. No Burning For All in Fresno and Kern Counties.
Further information is available at Valleyair.org

&&

.CERTAINTY...

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

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

&&

.HNX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory from 10 PM this evening to noon PST Saturday
for CAZ180>188.

&&

Meadows

weather.gov/hanford

Event by event

4 dense fog. Local standard time, as filed.

Dense Fog, Fresno

When
January 8, 9:50 PM PST to January 9, 2:10 AM PST
Where
Fresno forecast zone
Reported by
ASOS

Fresno reported visibility below a quarter mile.

Dense Fog, Foggy Bottom

When
January 8, 11:15 PM PST to January 9, 10:55 AM PST
Where
Foggy Bottom forecast zone
Reported by
ASOS

Hanford reported visibility below a quarter mile. NWS employees reported visibility between 500 and 1000 feet with drizzle from 0620 PST to 0700 PST between Hanford and Visalia and between Hanford and Kingsburg.

Dense Fog, Tulare County

When
January 8, 11:15 PM PST to January 9, 8:30 AM PST
Where
Tulare County forecast zone
Reported by
AWOS

Visalia and Porterville reported visibility below a quarter mile.

Dense Fog, Merced and Madera

When
January 9, 2:50 AM PST to 4:40 AM PST
Where
Merced and Madera forecast zone
Reported by
ASOS

Merced reported visibility below a quarter mile.

What these are

Dense Fog
Fog reducing visibility to a quarter mile or less, filed where it caused accidents or disruption.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, January 2021

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 928485, 928484, 928486, 928483.