30-Day Weather Outlook for December 1, 2021, to December 31, 2021

  • Dec 01, 2021

BASIC PATTERN:

Large Scale Pattern –

  1. A moderate to strong sea surface temperature anomaly gradient, will bring a shift to cold, showery, blustery cold frontal passages, with periods of moderate rains, and local moderate to seasonably heavy snow in Sierra Nevada.
  2. December: It turns wet with northern and Central California…near or a little wetter than normal as troughing increases into California. Southern California has a chance for near or above normal rainfall in this pattern. The good news is low snow levels in the Sierras…mostly 2500-4000 ft…some snow levels to 1500-2000 ft in the NW California coastal mountains at times. A break in the rains around the holidays is possible.
  3. January: Colder than normal. Turning drier than normal along the California coast, but normal precipitation in the mountains, Sierras, and plenty of snowfall.
  4. February: Very dry in all of California, including SOCAL, but near normal rainfall in far N California and Siskiyou Mountains, and the north coast Humboldt Co north.
  5. March: Continued very dry in most of California, but with above normal precipitation in N California Mendocino Co north, and in the mountains (northern Sierras, and Siskiyou’s). Recurrent NW flow from an area of colder than normal sea surface will tend to shift California into a colder than normal pattern. This suggests more frequent frost/freeze events than usual for Jan and Feb, including SOCAL citrus and avocado regions.

FORECASTS FOR CALIFORNIA

  1. We shift from a drier and warmer than normal period during the last week of Nov to a predominantly wet period for most of Dec.
  2. Precipitation Trend: The main dates of precipitation with this latest forecast are: Dec 6-7, 9-12, 13-15, 18-19, 22-25  per GFS model.  CFSDaily is showing, beyond 25: Dec 26, Jan 1-7, Jan 10.
  3. Precipitation Trend: The main dates of precipitation with this latest forecast are: Dec 6-7, 9-12, 13-15, 18-19, 22-25 per GFS model. CFSDaily is showing, beyond 25: Dec 26, Jan 1-7, Jan 10.

N and Central California- Dec 4 2021-Jan 4 2022:

NORCAL Rains: Dec 6-7, 9-12, 13, 15, 18-19, 23-25, Jan 3.

CENTRAL CALIF Rains: 7, 9-10, 13-14, 18-19, 23-24, Jan 3 (north areas).

WARM SPELLS: 5, 12, 17, 22, Dec 31-Jan 2.

COLD SPELLS: 7-8, 10-11, 18-20, 24-27, Jan 5-6.

FROST AND FREEZE: 8, 14, 16-17, 20-22, 26-28, Jan 4-5.

Forecast for S California – Dec 4 2021-Jan 4 2022:

SOCAL RAINS: Dec 7 (north areas), 13-14, 19, 24-25, 27.

SOCAL WARM SPELLS: Dec 5-6, 11-12, 17-18, 22-23, Jan 1-4.

SOCAL COOL OR COLD SPELLS: Dec 13-15, 19-20, 24-26, 27-28.

FRONTS WITH RAINS: Dec 13, 19, 24, 27.

Frosts may follow on: 15-16, 20-21, 26, 28-30.

 Sierra Nevada: Dec 4-Jan 4 2022:

Dates of mountain rains and snows: Dec 7, 9, 11-12, 13-14, 18-19, 24-25, Jan 4.

----------

The listing of dates normally included for hot and cold spells, and precipitation are based on our CFSDaily and CFSDailyAI forecast products, and present generally expected trends in precipitation (both products) and temperature (CFSDailyAI) to 4km. Our system gives some consideration of terrain and coastal influence. We consider the CFSv2 as one of the better ways to represent basic weather down in the sub-monthly time scale beyond the 15 day GFS or monthly maps from CFSv2 or NMME.

----------

Southern California Deserts Outlook for Dec 4 2021-Jan 4 2022:

Highlights: A turn to wetter but colder than normal for the deserts is suggested for Dec. Temperatures will drift to normal in a progressive trend through Dec, with increased frequency of frosts towards the   holidays to end of Dec, mainly on the dates in which rain is not occurring.

Looking Ahead – Long Range Outlook

N and Central California Jan 5 – Feb 25 2022:

Summary: Colder than normal is expected across northern and central California Jan 7 onward through Feb. Near normal precipitation is suggested for NORCAL north portions in January, but below normal rain for the Delta and Bay Area counties in Jan.  Near normal precipitation (rain and snow) is suggested in the northern and central Sierras. Cooler and drier than normal for southcentral California and Salinas Valley and central coast are expected. 

For SOCAL Jan 5 – Feb 25 2022:

Jan 7th onward will have near or below normal temperatures for S California, and continued cool in Feb. Watch for an increase in frost/freeze frequency in Jan and Feb from dry cold fronts. The best chances for frost/freeze will follow these fronts as winds subside and inversions develop through valleys. Below normal precipitation is expected in S California for 8 Jan onward, and Feb with dry to very dry conditions both months. Occasional Santa Ana winds develop. These bring warming to the coast, but areas of freeze or wetbulb freeze in coastal valleys overnights,when winds subside, colder air plus valley inversions  will produce frost and freeze to many SOCAL coastal and inland valleys.

CFSv2 monthly guidance suggests some troughs coming south into SOCAL and Arizona at times during Jan and Feb. There is not much rain in such a pattern, but plenty of wind and opportunity for frost and freeze in the prime winter food-crop areas of the southern deserts and SW Arizona. Again, the best chance of frost/freeze will be following dry cold frontal passages and after offshore winds subside. Cold inversions develop when winds are light and the air mass is dry. Many times these come with light offshore flow or weak onshore flow that have little inland penetration of moisture from ocean or beach.  

Looking Ahead – March 2022:

The overall trend for late February (26-28), and month of March… recurrently colder than normal, with near normal precipitation.  This suggests some improvement in the snow cover for mountain areas (Sierra Nevada), even though above normal precipitation is not currently indicated. However, this scenario also indicates possibly aggressive frost and freeze periods occurring in the early spring budding period in central and northern California.

(Terms and Definitions Used In This Weather Outlook)

Alan Fox & Zane Stephens...Fox Weather, LLC
Copyright © 2021, Fox Weather, LLC, Used by permission.

Share This Post: