30-Day Weather Outlook for October 1, 2022 to October 31, 2022

Oct 03, 2022

BASIC PATTERN:

Large Scale Pattern –

In the near term, we continue the influence of troughing in the north-central and northeastern North Pacific, related to the midlatitude sea surface temperature anomaly forcing (SSTA) patterns, indicated by our IVTinit™ system. The Madden Julian Oscillation (MJO) also currently adds a contribution, in the form of a stronger belt of westerlies across the mid latitudes of the North Pacific (45-55N). Both the MJO and IVTinit influence the longwave circulation out 15-30 days, and affect the pattern and timing of day-to-day weather in California and the Pacific Northwest.
In early to mid October we continue a chance for showers from tropical cyclone remnant moisture arriving into Arizona and southern Rockies to Texas.
During Oct, upper troughs from the west Pacific re-intensify as they move into a more favorable cyclogenetic environment at 175-160W. The troughs progress eastward, then dive SE as they approach 145-140W, then tend to turn ENE with rains into the Pacific Northwest and N California. As the storm track (jet stream) seasonally migrates farther south in Oct – Nov, the probability of rains into Central California will tend to increase, with rains reaching into Southern California at times during about 15-22 Nov per the usual pattern.
Both the CFSv2 and NMME (North American Multi-Model Ensemble) are currently in agreement for a wetter than normal November for the northern half of California. This is not supported by current trends in sea surface temperature anomaly pattern in the eastern midlatitude N Pacific.
For Oct 2022-Jan 2023, CFSv2 short term climate model maps are posted at the end of the graphical version of this Outlook report. For the first half of Oct, the CFSv2 model predicts warmer and mostly drier than normal conditions for California. Modestly above normal rainfall is suggested for the Sierras from Lake Tahoe to Yosemite during the second half of Oct. Interestingly, the CFSv2 model hints at a wet December for California. This is certainly a welcome trend, but is not currently supported by the North American Multi-Model Ensemble (NMME). The trends in rainfall that we see after mid Dec 2022, and in Jan 2023 will depend on how much support develops for cyclogenesis near the California coast during late Oct – Nov.
Precipitation Trend—through November 30...Next rains occur Oct 11-14, Oct 26-29, Nov 6-11 per the CFSv2 short term climate model, and about Nov 15-22 per the usual climatological trend.

FORECASTS FOR CALIFORNIA

Forecast for Northern and Central California:

NORCAL Rains: Oct 11-14, Oct 24-29, Nov 6-11, Nov 15-22.

CENTRAL CALIF Rains: Oct 5, 12-14, 25-28,Nov 6-10.

WARM SPELLS: Sep 30-Oct 4 and 19-21.

COOL SPELLS: Oct 5-6, 10-14, 25-29 and Nov 6-12.

Forecast for Southern California:

SOCAL RAINS: Oct 12-14, Oct 27-30, Nov 7-11, Nov 16-22.

SOCAL WARM AND HOT SPELLS: Sep 30-Oct 5, Oct 7-8, 17-23.

SOCAL COOL OR COLD SPELLS: Oct 12-16 and 28-31-Nov 8-12.

Forecast for Central Sierra Nevada:

Dates of mountain rains (Central & S Sierra): Oct 11-14, Oct 27-30, Nov 7-11, and Nov 15-22.

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The listings of dates normally included for hot and cold spells, and precipitation are very approximate. They are based on our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (CFSDailyAI) to 4km. Our system gives some consideration to 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 October 15 – October 31, 2022

Highlights: Risk of tropical cyclones continues along the coast of Baja California and the Gulf of California in Oct. For the southern deserts, the season for tropical cyclone moisture is drawing to a close. We are already seeing the seasonal recurvature of cyclones into the western Mexico coast as of 28 September, and the seasonal trend is close to the long term mean schedule. Tropical cyclones will continue turning inland primarily over southern Baja, crossing the Gulf to landfall along the coasts of Sinaloa, and Nayarit. There still is a chance for tropical cyclone moisture to head NNE from Sonora into Arizona to produce heavy rains. Tropical cyclones in Nov focus into mainly Sinaloa and Nayarit south, including the areas of Manzanillo and state of Michoacan.

Looking Ahead – Long Range Outlook

November 1 – December 31... NORCAL and Central California coastal valleys, and Central Valley: Above normal temperatures will continue late Oct thru Nov across most of California. Seasonable to warmer than normal conditions continue across N and Central California in Nov. It looks predominantly warm and dry in Oct. This is followed in Nov by a burst of above normal rainfall from the Bay Area north to Oregon, as well as interior N California, with near normal rainfall for central California. Recent short term climate model solutions have been suggesting an up-tick in rainfall about Nov 15-30, possibly continuing into the first part of Dec. Interestingly, for N California, the periods of above normal precipitation are also warmer than normal. This combination suggests a persistently high or higher than normal snow level during the early season rains in Nov. This appears to be followed by wet conditions during Dec 1-19 or so in N California, and near normal in the central and south. These argue for higher than normal snow levels in the Sierras and NORCAL mountains during the Nov-Dec rain periods.

For SOCAL mountains westward to coast: Our latest CFSDailyAI/FoxDaily forecast out for the period Oct 12-13 suggest a good rain for SOCAL ...Santa Barbara and San Luis Obispo Co’s on the 12th, and Santa Barbara-Ventura-Los Angeles Co’s north through Kern and Tulare Co’s and into the southern Sierras on 13th as well. There is a possibility of a few more mountain showers in SOCAL from Ventura Comountains east through Los Angeles Co (San Gabriel Mountains), and into the San Bernardino Mountains on 20-21 Oct. Another (presumably cutoff low) rain or showery episode occurs in SOCAL mountains and the mountains of central and northern Arizona somewhere around Oct 28. These are in addition to the possible events we mentioned for mid to late Nov.

(Terms and Definitions Used In This Weather Outlook)