Avalanche and High Wind in California, December 27, 2018

Name: Avalanche and High Wind in California, December 27, 2018
Start: 2018-12-27T02:35
End: 2018-12-27T13:15
Location: California

December 27, 2018 · NWS HNX · 4 events in 3 counties and zones

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.

Areas of dense fog formed during the morning of December 27 as clear skies and light winds prevailed over the San Joaquin Valley. The fog resulted in some minor vehicle accidents in the Fresno area as the fog reduced visibility to a few hundred feet. However, the fog dissipated in the San Joaquin Valley by late morning as a cold front pushed southward through central California. Areas of dense fog persisted through the early afternoon along the valley facing slopes of the Tehachapi Mountains as a result of strong upslope flow that accompanied the front. The cold front also produced a period of gusty winds along the west side of the San Joaquin Valley as well as along and below the passes in Kern County where several stations measured gusts above 35 mph.

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 26, 3:32 PM PST, 11 hours 3 minutes earlier.

Area forecast discussion, Dec 26, 3:32 PM PST, 11 hours 3 minutes before

Area Forecast Discussion...UPDATED
National Weather Service San Joaquin Valley - Hanford CA
332 PM PST Wed Dec 26 2018

...UPDATED AIR QUALITY SECTION...

.SYNOPSIS...A cold front will push through the area on Thursday
bringing a period of increased winds as well as a few showers to
the mountains. Dry weather will prevail for Friday through early
next week with below normal temperatures.

&&

.DISCUSSION...Cool northwest flow prevailing over our area today
with a dry airmass in place. Other than a narrow strip of fog
between Madera and Wasco that was present earlier this morning,
visibility in the valley was excellent. The fog has since lifted
and dissipated. A mid level cloud deck associated with a weak
deformation band is currently dropping southward through our area
today and visible imagery is showing some upslope strato-cumulus
over the southern Sierra foothills and along the valley facing
slopes of the Tehachapi Mountains. Otherwise this has been a
partly to mostly sunny day across our area with temperatures
running 2-4 DEG F below yday at this time with generally light
winds prevailing.

WRF indicating a moisture deficient cold front pushing southward
through our area on Thursday. Any precipitation from this system
will likely be confined to a few sprinkles or flurries over upslope
favored areas, and will likely be very light since this system
lacks significant moisture. The main impact from this system for
our area; however, will be a period of increased winds along and
below the passes in Kern County on Thursday afternoon and evening.
A period of downslope northeast winds is also anticiapted over the
higher elevations of the Southern Sierra Nevada Thursday night
and Friday morning. At this time, forecasted winds look marginal
for any sort of highlights.

High pressure is progged to build inland into Norcal on Friday as
a trough deepens over the desert southwest. This will keep and
cold and dry northerly flow over our area and allow for
temperatures to drop to their lowest levels observed since last
winter. Winds are expected to diminish across the area on Friday
afternoon and evening and with clear skies, light winds and a dry
airmass over San Joaquin Valley, temperatures across much of the
valley will likely plummet below the freezing mark on Saturday
morning. Since this is progged to be the first freeze of the
season a Hard Freeze Watch has been pasted for the San Joaquin
Valley for late Friday night and Satruday morning.

The medium range models and their ensemble means are in fairly
good agreement with a strong upper ridge remaining situated off
the CA coast from Sunday through the middle of next week which
will maintain a cool and dry northerly flow over our area. This
will keep dry weather across our area through the period and with
a dry airmass in place fog coverage over the valley will be
minimal each morning. A slight recovery in temperatures is
anticipated on Sunday then temperatures will remain fairly steady
at slightly below normal levels through the period.

&&

.AVIATION...Across the San Joaquin Valley, areas of MVFR with
local IFR conditions in low clouds and fog (especially along the
east side). Local clouds will also bank-up along the Sierra
foothills and north facing slopes of Tehachapi Mountains. Surface
wind gusts of 35 knots or greater will occur through and below the
eastern slopes of the Kern County Mountain passes after 09Z
Thursday. Otherwise, VFR conditions will prevail over the Central
CA Interior during the next 24 hours.

&&

.AIR QUALITY ISSUES...On Thursday December 27 2018...
Fireplace/Wood Stove Burning Status is: No Burning Unless
Registered in Fresno and Kings 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...
Hard Freeze Watch from late Friday night through Saturday
morning CAZ089>092.

&&

public...DS
avn/fw...Molina
synopsis...DS

weather.gov/hanford

Event by event

2 dense fog, 1 high wind, 1 avalanche. Local standard time, as filed.

Dense Fog, E Central S.J. Valley

When: December 27, 2:35 AM PST to 9:35 AM PST
Where: E Central S.J. Valley forecast zone
Reported by: ASOS

Visibility below a quarter mile was reported in Fresno, Madera and Atwater.

High Wind, Kern Cty Mtns

When: December 27, 3:14 AM PST
Where: Kern Cty Mtns forecast zone
Measured: 52 kt (60 mph) measured gust
Reported by: RAWS

The Jawbone Canyon RAWS reported a peak wind gust of 60 mph.

Dense Fog, Sw S.J. Valley

When: December 27, 8:53 AM PST to 9:25 AM PST
Where: Sw S.J. Valley forecast zone
Reported by: ASOS

Visibility below a quarter mile was reported in Hanford.

Avalanche, Kern Cty Mtns

When: December 27, 9:35 AM PST to 1:15 PM PST
Where: Kern Cty Mtns forecast zone
Reported by: AWOS

Visibility below a quarter mile was reported in Tehachapi.

What these are

Dense Fog: Fog reducing visibility to a quarter mile or less, filed where it caused accidents or disruption.
High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.
Avalanche: A mass of snow sliding down a mountainside that caused a death, an injury or damage.

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

The same day elsewhere

Every storm in California in 2018 Every state in 2018 This day in weather history Warnings in California, December 2018

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: 791001, 791015, 791002, 791007.