30-Day Weather Outlook for November 25, 2021, to December 25, 2021

Nov 25, 2021

BASIC PATTERN:

Large Scale Pattern –

A moderate to strong sea surface temperature anomaly gradient, coinciding with frontal passages into the Pacific Northwest will focus the rains mostly north of California, and into the Pacific Northwest for the last week of Nov.
December: Wet, and in northern and Central California…wetter than normal as the storm track repositions itself over California, and delivers heavy rains to N and Central California, and Oregon. Weather in early Dec is warmer than normal in the near term (first week or two). There is a turn to heavy rains early in the month, then during the holiday period, i.e. possibly 5-13, then 18-24, and 25-31 Dec. Cold and snowy weather in the mountains develops around the holidays.
January: Colder than normal. Turning drier than normal along the California coast, but normal precipitation in the mountains, Sierras, with plenty of snowfall.
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.
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

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.
Precipitation Trend Nov 29 2021-Jan 1 2022: Dates of rain are: Dec 5-13, then more consistent rains Dec 18-24 and Dec 25-31. Heaviest rains occur about Dec 19, 22-24, then Dec 27-30.

N and Central California- Nov 25-Jan 1:

NORCAL Rains: Dec 1-2 (light rain north areas), 5-13, 15-24, 25-30.

CENTRAL CALIF Rains: Dec 5-13, 18-24, 25-26.

WARM SPELLS: Nov 25-26, Dec 1-2, 28-29 (mild and rainy).

COLD SPELLS: Dec 8-26 (turning cooler than normal 14th onward)

FROST AND FREEZE: Nov 25, Dec 14-15, 27-28.

Forecast for S California – Nov 25-Jan 1:

SOCAL RAINS: Dec 7-8, 10-12, 16-18, 20, 23-24, 26.

SOCAL WARM SPELLS: Nov 25-29,Dec 1-2, 28-29.

SOCAL COOL OR COLD SPELLS: Dec 6-12, 16-20, 23-24, 26-27.

FRONTS WITH RAINS: Dec 7, 10, 17, 20, 23, 26.

Frosts may follow on: Dec. Dec 9, 13-15, 19, 21-22, 30.

Sierra Nevada: Nov 25-Jan 1:

Dates of mountain rains and snows: Dec 7-13, 15, 18-30.

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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.

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Southern California Deserts Outlook for Nov 29 – Jan 1:

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, on those dates when rain is not occurring.

Looking Ahead – Long Range Outlook

For N and Central California Jan 1 – Feb 15 2022:

Summary: Colder than normal is expected across northern and central California Jan 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 1 – Feb 15 2022:

Summary: January 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 through Jan 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 of the 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.

(Terms and Definitions Used In This Weather Outlook)