Interaction between high pressure centered over the Great Basin and a low pressure center off the northern Baja coast produced an offshore easterly flow over central CA maintaining a dry airmass with unseasonably warm temperatures for early December. Mainly clear skies, light winds and inversion conditions allowed for fog to form towards daybreak on December 2 from Merced County northward.
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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.
The episode as NWS HNX wrote it up.
Interaction between high pressure centered over the Great Basin and a low pressure center off the northern Baja coast produced an offshore easterly flow over central CA maintaining a dry airmass with unseasonably warm temperatures for early December. Mainly clear skies, light winds and inversion conditions allowed for fog to form towards daybreak on December 2 from Merced County northward. The fog in Merced County dissipated one to two hours after developing.
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 2, 2:00 AM PST, 5 hours earlier.
Area Forecast Discussion National Weather Service Hanford CA 200 AM PST Thu Dec 2 2021 .SYNOPSIS... Patchy fog is possible in the nights and mornings until at least Friday as high pressure aloft continues. Afternoon high temperatures will be around 10 degrees above average until the end of the week. Expect a cooling trend beginning this weekend, then a slight chance of light precip by early next week. && .DISCUSSION...Another warm day occurred throughout much of the area, as highs reached into the 70s for much of the lower elevations yesterday. Even some Sierra Nevada foothill locations, such as Mariposa and Oakhurst, reported daytime highs into the lower 80s. This is due to a strong ridge of high pressure that remains in control and will likely persist until Friday. Some moderation in temperatures is expected in the meantime; however, daytime highs will remain well above average for early December. Near record highs are possible once again today, or within a couple of degrees in some locations, such as Hanford and Merced. The probability of reaching today's record highs at these locations are around 30 percent (72 degrees at Hanford and 71 degrees at Merced). Patchy fog will continue to develop during tonight into the daylight hours of this morning and may become locally dense in the San Joaquin Valley by sunrise or shortly before. Valley fog will also be possible again by early Friday morning. A dry upper-level low is forecast to move into southern California on Friday, while another low pressure system remains offshore and moves south toward Baja California over the weekend. These upper-level lows will provide little effect on our weather, although the upper-level ridge of high pressure will retrograde off the West Coast and moderate temperatures. Afterward, an inside-slider trough is projected to move over the Great Basin by Monday night and will at least provide a little more cooling. A change in the pattern is in store for next week as the latest ensemble and deterministic guidance remain in agreement, although the low pressure system that moves over the Great Basin may provide little if any precipitation over our portion of Central California, including the Sierra Nevada from Yosemite to Sequoia NP, where the best chances remain. There is a slight chance for precipitation in northern valley portions of our forecast area, or towards Merced and Madera. However, any precipitation in the San Joaquin Valley may be very light showers or sprinkles. Precipitation amounts of up to 0.10 inch, including a dusting to around an inch of snow, are expected in the Sierra Nevada, mainly during Monday night. Otherwise, temperatures will lower closer to seasonal averages for Monday and remain steady until the middle of next week. There is some potential for increased winds in the typical prone areas by late Monday into Tuesday, but will continue to monitor. && .AVIATION...In the San Joaquin Valley, areas of MVFR conditions with isolated IFR visibility due to haze/mist through 18Z Thursday and again after 09Z Friday. Otherwise, VFR conditions prevailing elsewhere across the Central CA Interior for the next 24 hours. && .AIR QUALITY ISSUES... On Thursday December 2 2021... Unhealthy for sensitive groups in Fresno... Kern... Kings 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... None. && public...BSO aviation....DCH weather.gov/hanford
The national radar mosaic for the moment the first event began.
1 dense fog. Local standard time, as filed.
Visibility below a quarter mile was reported in Merced.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, December 2021
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: 988013.