BASIC PATTERN:
Large Scale Pattern –
- A moderate to strong sea surface temperature anomaly gradient, coinciding with the dashed curve off the N California and Pacific Northwest coast will be the main player for storm developments into N California in Nov and Dec. Along this persisting frontal zone, smaller troughs and lows will tend to develop.
- Soils and vegetation have moistened in N California and Sierras (North and Central)from the recent storms. This has greatly decreased the fire risk in the near term. We still need to monitor high Haines Index coupled with dry downslope NE-E wind events in the N Sierras for a little while, into Nov.
- Wetter periods now appear to a couple of storms in early, and mid Nov. Dec will have near normal rainfall most areas. The best chance for above normal rainfall would be along the central coast from Monterey Co to Sonoma Co.
- Dry conditions return for midwinter months of Jan – Feb in northcentral through S California, as the La Nina pattern re-establishes and remains dominant through the rest of the season into Mar. Apr has a better chance for near normal rainfall (for end of the usual wet season).
FORECASTS FOR CALIFORNIA
- Troughs and lows bring the possibility of rains and showers into N California, and a few showers into central California during Nov. Dec appears most prolific for rain amounts for N and Central California per model guidance from CFSv2. A stronger La Nina pattern is expected to shift the pattern to dry in most of California during late Dec 2021, and continued unusually dry in Jan-Feb 2022.
- Precipitation Trend Nov 1-30: Dates of rain are: Nov 2, 4-5, 7, 11-12, 16-25, 26-27 and a good set of storms in early to mid-Dec.
- Nov 1-30: N and Central California: Troughs and cold fronts become more active in Nov. Mid Nov is the time of the frequently occurring early period of general winter rains. NORCAL Rains: Nov 2, 4-5, 7, 11-12, 16-25, and 26-27. CENTRAL CALIF Rains: Nov 5, 12-13, 17-18, 20-21, and 23-28. WARM SPELLS: Seasonable temperatures with few warm spells across N California due to a wetter than normal series of storms N Calif warm spells: Oct 31-Nov 1 and Nov 28-30. COLD SPELLS: N Calif: 3-7, 12-13, 17-19, 22-25, and 27. 29-30. Frosts: Best chance of frost/freezes for N Calif: Nov 3, 6, 13-15, 19, 22 and 29-30.
- Forecast for S California – Nov 1-30: SOCAL Rains: Continued very dry with possible light showers Nov 8, 13, 21 and 27-28. SOCAL Warm Spells: Oct 30-Nov 1, Nov 2, 11-12, 18 and 24. SOCAL Cool or Cold Spells: Cooler Nov 8-9, 19-20 and 25-26. Fronts with rains: Nov 8, 13, 21 and 27. (small rains are expected with drier than normal conditions continuing. Frosts may follow showery fronts on Nov 9, 14, 22 and 29-30.
- Sierra Nevada: Nov 1-30… Date of Mountain Rains and Snows: Nov 5-6, 13-14, 17-18, 21-22, and 24-28.
- N and Central California Fire Risk: Fire risk is reduced due to wetter soils and seasonably cooler weather. Some brief increase in fire risk: Nov 6, 9-10, 14-15 and 28-30.
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 Nov 1-30:
Highlights: Well below normal precipitation will continue. although a couple of deeper troughs could bring a few showers and light cool rains into the desert region on Nov 8, 13, 21 and 27-28. Temperatures will be near or above normal through most of the period with high pressure aloft to the south and SW.
Forecast: Warmer than normal with below normal precipitation is expected for southern California and the desert region through Nov. A couple of deeper troughs could bring some increase in brief showers with the more likely dates of light rain and showers listed above. There is a slightly wetter trend, although overall drier than normal in early Dec.
***Looking Ahead – Long Range Outlook Dec 1 – Jan 31 2022... N and Central California:
Latest versions of CFSv2 monthly guidance suggest near normal rainfall in Dec. Above normal precipitation for N and Central California and Sierras for Dec in a few spots. Heaviest rains will be expected in Dec, followed by a midwinter dry spell, with mainly sparse rains after 1 Jan. Late Jan, Feb, and Mar 2022 appear abnormally dry for most of California.
For SOCAL Dec 1 - Jan 31 2022:
In Dec, above normal rainfall is possible early to mid-month, followed by a turn to dry and cold (frosty) for the holidays. Rainfall continues below normal in Jan, Feb, followed by a possible return to normal in early Mar 2022. Best chance for rains in SOCAL appears to be in early to mid Dec, then dry and frosty for the Dec holidays.
General Frost Risk….Dec 1 – Jan 31 2022…: It trends to colder than normal after mid Dec. We suspect that the most significant periods for frost would be end of Dec and early to mid Jan 2022, as cold lows and windy cold fronts alternate with Santa Ana wind events.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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