Ice Storm and High Wind in California, December 31, 2020

Name: Ice Storm and High Wind in California, December 31, 2020
Start: 2020-12-31T03:27
End: 2020-12-31T23:15
Location: California

December 31, 2020 · NWS HNX · 3 events in 1 county or zone

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 3

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.

A low pressure system dropped southward just east of the Sierra Nevada during the morning of December 31. This system pushed a cold front through the area during the morning during the morning of December 31 which brought some gusty winds to the Kern County Mountains and Deserts with several stations measuring gusts exceeding 40 mph. This system also produced a period of post frontal rain showers in which the rain froze as it came into contact with the surface over the elevated valleys. Freezing rain was reported in the Tehachapi area which resulted in California Highway Patrol pacing traffic along State Route 58 for a short period of time. In addition, light snow was reported along Interstate 5 over the Tejon Pass. Most of the area measured a tenth of an inch or less of precipitation from this system. However, some persistent upslope clouds banked up along the Tehachapi Mountain range during the evening resulting in freezing fog and black ice along State Route 58. Skies cleared out though as 2021 arrived.

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 Dec 30, 5:23 PM PST, 10 hours 4 minutes earlier.

Area forecast discussion, Dec 30, 5:23 PM PST, 10 hours 4 minutes before

Area Forecast Discussion
National Weather Service Hanford CA
523 PM PST Wed Dec 30 2020

.UPDATE...To include updated air quality information.

&&

.SYNOPSIS...A cold frontal passage tonight into Thursday morning
will bring some light showers to mainly the Sierra from Yosemite to
Kings Canyon. Otherwise dry weather will prevail over much of the
district Thursday through Saturday. Little diurnal change in
temperature and humidities can be expected through Saturday. A
change to a more active and wet pattern is possible next week.

&&

.DISCUSSION...Short wave ridge overhead today with seasonable
temperatures across the district. Satellite imagery shows bands
of high clouds passing over central California this afternoon
ahead of an approaching trough over the Pacific Northwest. This
trough will dive SSE tonight over California and bring some
light precipitation from around midnight tonight through Thursday
morning. Most of the precip will occur over the Sierra Nevada
around Yosemite where one to two tenths of an inch of rainfall is
possible. 1 to 2 inches of snow could fall down to 4000 feet as
well. A trace to a few hundredths of an inch of rain could fall in
the San Joaquin Valley around Merced County. It's also possible
for a few light showers/snow flurries to occur in the Mountains
around Frazier Park, possibly along the Grapevine. Some patchy fog
and frost is still possible in the southern SJV tonight. The
trough quickly exits on Thursday night as another short wave ridge
slides in behind it. This could set the stage for more widespread
fog on New Year's Eve night.

Models are continuing to show a transition to a more active zonal
flow pattern aloft next week. While there is good model agreement
in this pattern change, the timing and placement of disturbances
within the flow is still very uncertain. Models are focusing them
a little farther north over the last couple of runs, though there
is still an impressive system depicted next Wednesday (Jan 6).

&&

.AVIATION...
Areas of IFR with local LIFR in fog can be expected in the San
Joaquin Valley from 08z to 18z Thursday. Local IFR ceilings in
showers over the Sierra Nevada from 06z to 18z Thursday. VFR
conditions can be expected elsewhere over the central California
interior for the next 24 hours.

&&

.AIR QUALITY ISSUES...
On Wednesday December 30 2020...Fireplace/Wood Stove Burning
Status is: No Burning Unless Registered in Fresno...Kern...Kings...
Madera and Tulare Counties. Further information is available at
Valleyair.org

CERTAINTY...

The level of certainty for days 1 and 2 is medium.
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...
None.
&&

public...DCH
aviation....DCH

weather.gov/hanford

Event by event

1 high wind, 1 ice storm, 1 freezing fog. Local standard time, as filed.

High Wind, Tehachapi Area

When: December 31, 3:27 AM PST
Where: Tehachapi Area forecast zone
Measured: 56 kt (64 mph) measured gust
Reported by: RAWS

The Bird Springs Pass RAWS measured a peak wind gust of 65 mph.

Ice Storm, Tehachapi Area

When: December 31, 5:30 AM PST to 11:00 AM PST
Where: Tehachapi Area forecast zone
Reported by: AWOS

Freezing rain was reported in Tehachapi during the morning of December 31 resulting in traffic being paced along SR 58.

Freezing Fog, Tehachapi Area

When: December 31, 8:15 PM PST to 11:15 PM PST
Where: Tehachapi Area forecast zone
Reported by: AWOS

Freezing fog was reported in Tehachapi with visibility reduced to below a quarter mile at times with temperatures in the upper 20s.

What these are

High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.
Ice Storm: Freezing rain accumulating a quarter inch or more of ice, or less where it caused significant damage.
Freezing Fog: Fog that froze on contact with roads, vehicles or structures.

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

The same day elsewhere

Every storm in California in 2020 Every state in 2020 This day in weather history Warnings in California, December 2020

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: 927119, 927121, 927120.