Dense Fog in California, February 4, 2021

Name: Dense Fog in California, February 4, 2021
Start: 2021-02-04T06:10
End: 2021-02-04T08:50
Location: California

February 4, 2021 · NWS HNX · 2 events in 2 counties and zones

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 2

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.

The cold front which pushed through the area on February 3 moved out of the area during the mroning of February 4 reuslting in clearing skies and diminsihed winds across the area. High pressure strengthened offshore during the morning of February 4 producing a dry northwest flow over the area. However, residual low level moisture left over from the strong storm in late January resulted in low clouds and patchy dense fog to form by sunrise in portions of the eastern San Joaquin Valley with visibility below a quarter mile being observed in Reedley and Visalia. The fog lifted into a low cloud deck by late morning which dissipated by 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 Feb 4, 3:34 AM PST, 2 hours 36 minutes earlier.

Area forecast discussion, Feb 4, 3:34 AM PST, 2 hours 36 minutes before

Area Forecast Discussion
National Weather Service Hanford CA
334 AM PST Thu Feb 4 2021

.SYNOPSIS...
Northwest flow will keep the region dry and seasonal today.
A gradual warming trend is expected through the weekend and
temperatures are forecast to remain nearly steady through next
week.

&&

.DISCUSSION...
A strong dry trough pushed through the region yesterday with
strong gusty winds across the Tulare county portion of the Sierra
and across the Tehachapi mountains. Upslope flow kept the low
clouds in across the north facing slopes in the Kern county.

The trough has exited to the east but the upslope clouds remain
along the north facing slopes of the Kern county mountains. The
winds have died down as well. A thin strip of low clouds have
formed in the SJV. If we weren't so mixed, we would be fogging up.
the models are clearing things out after sunrise today. Low clouds
are starting to clear out along the foothills in Tulare county. We
will see some clouds today as a strong NW flow will keep us more
seasonal today with some clouds developing this afternoon, still
should be nice day.

A Rex block pattern has developed in the Eastern Pacific and wont
be breaking down until Saturday. The ridge still remains just
offshore as we are on the east side of the ridge in a NW flow. The
pattern is stagnant into next Monday. A weak short wave will
skirt tour north but will push the ridge south and a more zonal
flow sets up across the region for next week. Steady temperatures
just above normal are expected with dry conditions. Tule fog
might be an issue in the SJV next week, but confidence remains low
to put it in the forecast.

&&

.AVIATION... Mountain obscuration in fog and stratus in north and
west slopes of the Tehachapi Mountains through at least 06z Friday.
Strong, gusty winds in excess of 55 mph are likely trough and below
the Kern County mountain passes and into the immediate desert
locations through at least 06Z Friday. Otherwise,VFR conditions
will prevail across the central CA interior for the next 24 hours.

&&

.AIR QUALITY ISSUES...
On Thursday February 4 2021... Fireplace/Wood Stove Burning Status
is: No Burning Unless Registered 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 high.

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...
None.

&&

public/aviation/fw....JDB
pio/idss..............Bollenbacher

weather.gov/hanford

Event by event

2 dense fog. Local standard time, as filed.

Dense Fog, Fresno

When: February 4, 6:10 AM PST to 8:50 AM PST
Where: Fresno forecast zone
Reported by: AWOS

Reedley reported visibility below a quarter mile.

Dense Fog, Tulare County

When: February 4, 6:50 AM PST to 7:55 AM PST
Where: Tulare County forecast zone
Reported by: AWOS

Visalia 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

Every storm in California in 2021 Every state in 2021 This day in weather history Warnings in California, February 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: 931768, 931767.