30-Day Weather Outlook for January 17 to February 10, 2025

Jan 16, 2025

BASIC PATTERN:

Large Scale Pattern

Precipitation Dates for January 17 – February 10: Rains January 29 and 31. Rains in February: 3-9, mainly in NW or N California. Another wet period occurs 12-16 February per CFSv2.
Support for troughing continues in the central N Pacific from about 130-145W (mainly NE to N of Hawaii), and at 160W to near the Dateline is N to NNW of Hawaii. A third (weaker) area of troughing extends from about Hawaii to near Central California.
For forestry. After a wet start in early January, we expect drier than average winter fire season conditions in NORCAL and Central California. Moisture in dry brush has increased, but will decrease again due to Santa Ana type winds developing in the central to north Sierra west slope areas. The recent dry patterns here in NORCAL, the Sierras, and in SOCAL are stark reminders of the changeability of wet and dry periods, during the middle of the wet season, and as we look onward to climate change.
The bottom line is: Continued drier than average, overall, but briefly interrupted with the rain or showers, mostly with higher snow levels. Trends in snow level have been irregular in the medium range model guidance, but are trending to higher levels again at this time. It should be remembered that a drier climate scenario does not necessarily mean smaller rains, but more infrequent though heavy rains, and a shorter wet season. This is something to remember in preparation for fire season readiness.

Forecast for Northern California
NORCAL Precipitation: January 17- February 10. Rains: January 29, 31. February 1-10.
NORCAL Mild/Dry Periods: January 21-28. Mid February mild period.
NORCAL Cool Periods & Frost: Cool days, some showers as shown above, but with below normal frost occurrence.
North Sierra Precipitation: January 27-31, Feb 1-10.
Central Sierra Precipitation: January 27-31, Feb 1-10.

Forecast for Central California
CENTRAL CALIFORNIA Precipitation: January 27-31, February 1-10.
CENTRAL CALIFORNIA MILD DRY PERIODS: January 18-19, 29-31 includes showers..
Central California Cold Periods, Frost: January 19-21, but with rains/showers 29-31.

Forecast for Southern California
SOCAL PRECIPITATION: Precipitation is not shown in SOCAL through January 30, possibly January 31, February 1-10 as mostly light showers.
SOCAL MILD PERIODS: January 22-28, 29-30. Cooler 31st.
SOCAL COLD/FROST PERIODS: January18, 28-31.
Note that we can receive both mild daytime conditions, and frosty early mornings during the same dates.

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 15thday GFS.

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Southern California Deserts Outlook
SOCAL deserts: Colder than average during rainy periods.
Rainfall amounts below average.
Rain dates in SOCAL Deserts: January 31 possibly. February 1-10 rainfall below average.

(Terms and Definitions Used In This Weather Outlook)