30-Day Weather Outlook for December 1, 2024 to December 31, 2024

Dec 02, 2024

BASIC PATTERN:

Large Scale Pattern

Rain Dates: December 1, 5-7, 12. The next rains, per CFSDaily are January 1-4 2025. Mountain snows appear most likely December 7, 12-13 then 19-20.
Support for troughing continues in the eastern N Pacific from the Oregon/Washington coast at 125W to about 145W, and Central Pacific from 150W to the Dateline. Still some troughing in California is possible due to downstream forcing from the persistent troughing near the Dateline to 160W.
In November - early December warm conditions are frequently interrupted by cold NNW-N wind events and some rains. If warmer than average temperatures occasionally occur, they will be related to troughs and lows arriving from the west in the fairly weak subtropical storm track.
Seasonably cool and wet conditions occur in mid Dec and in Jan 2025. After a mid-January mild and dry break, late January and February appear to return to near then above average precipitation.
In February and March 2025, watch for a possibly robust return of cold and snowy conditions focusing in NW California and the ORWA coast (Oregon and Washington).
For forestry. we expect a reduction in the fire season conditions as moisture continues to increase at vegetation levels near the surface. Bottom line is: still some very near term warm and breezy periods with rapid shifts to cold and showery (rainy in NORCAL), with snow in mountains.
For season 2024-25 we could actually see three wetter than average months: periods of heavy rains focusing in parts of December and the January - February period. January has the possibility for wetter than average conditions in central and N California.

Forecast for Northern California

NORCAL Precipitation: Dec 1, 7, 15, 19-21.
NORCAL Mild/Dry Periods: Dec 3-5. Dec 17-18.
NORCAL Cold or Frost Periods: Dec 1-3 and 18-19, 25-30.

North Sierra Precipitation: Dec 1, 6-8, 15, 19-22.
Central Sierra Precipitation: Dec 1, 7-8, 15, 19-22.

Forecast for Central California

CENTRAL CALIFORNIA Precipitation: Dec 8-9 and 14-15, 20-22.
CENTRAL CALIFORNIA MILD DRY PERIODS: Dec 4-6, 8-12,and 20-23.
Central California Cold Periods,Frost: Dec 3-6 and 17-18, 24-29.

Forecast for Southern California

SOCAL PRECIPITATION: Dec 8-10 and 13-15, 21-22.
SOCAL MILD PERIODS: , Dec 1-7, 16-18.
SOCAL COLD/FROST PERIODS: Dec 3-4,8-9, 18-20.

Note that the dates for these rains are to be considered very approximate!

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The listings of dates normally included for hot and cold spells, and precipitation are approximate. They are based on GFS and our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (FoxCFSDailyAI) to 5km. Our AI system gives some consideration to terrain and coastal influence. Although we consider the CFSv2 one of the better ways to represent basic weather in the sub-monthly time scale, performance of the CFSDaily. CFSv2 daily products during storm seasons has been especially inconsistent and difficult to apply to the useful criterion needed by cropland agriculture, and viticulture beyond the 15ñday GFS.

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Southern California Deserts Outlook

SOCAL deserts: near average temperatures, and about average rainfall for the period. However, it appears that there are some cold and showery/rainy events in S California deserts Dec 8-10, 14-15, 21-22.

Looking Further Ahead — January 1 – January 31, 2025
Precipitation appears to turn above average for end of Dec through mid Jan. January 2025 has above normal rainfall with mountain snows. Heavy rains at ORWA coast and coastal mountains with possibly
some higher than average snow levels occur ORWA region (Oregon, Washington) due to subtropical influence. In midwinter, heaviest rains occur mainly coast/Cascades, due to Atmospheric Rivers in Jan-Feb. Some of these rains from ORWA reach into NORCAL and N Sierras. Bottom line: while ORWA receives heavy rains in Dec, NORCAL and Central California mostly receive near average amounts overall wetter than average with plenty of mountain snows in the Sierras during the late Dec and most of Jan 2025. Dry and warmer weather returns to Sierras and Central-S California finally in Feb. Freezes continue possible in SOCAL valleys Riverside-San Diego Coís at times in Jan and Feb following cold fronts, mainly when dry airmasses occasionally pass through.

(Terms and Definitions Used In This Weather Outlook)