BASIC PATTERN:
Large Scale Pattern –
- In the near term, we continue under the influence of troughing in the north-central and east-central North Pacific, related to both the midlatitude sea surface temperature anomaly forcing (SSTAs), indicated by our IVTinit™ system. The Madden Julian Oscillation (MJO) also currently adds a weak influence, in the form of a stronger belt of westerlies across the mid latitudes (41-55N) of the North Pacific. Both the MJO and IVTinit influence the longwave circulation out 15-30 days, and affect the pattern and timing of day-to-day weather here in California and the west coast.
- In September, we continue a chance for showers coming into SOCAL and to W Arizona, with some rains into SE California as well, with focus on San Bernardino Co deserts east and south. At times, TSTMS develop over the Peninsular Range (Mt San Gorgonio south to Northern Baja California.
- During late Sep, we begin to see upper lows forming off the coast of northcentral and central California. Fronts come into the Pacific Northwest, weaken, split from the westerlies, and move SSW then SW off central and southcentral California. Tropical easterlies and SE flow remain active into most of Sep through Baja California, bringing moisture into SOCAL and Arizona. The outlook map for September precipitation suggests above normal rainfall from tropical systems, mainly thunderstorms (TSTMS)in Arizona and possibly SOCAL, and possibly one or two tropical cyclone remnants.
- For Oct 2022-Jan 2023, CFSv2 and NMME short term climate model maps are posted at the end of this report. For late Sep and early Oct, the CFSv2 model predicts warmer than normal conditions for California. Modestly above normal rainfall is suggested for SOCAL and the Sierras from Lake Tahoe south, but warmer than normal for N California. We appear to transition to mild or warm but dry conditions in January 2023.
- Precipitation Trend—through October 19....Most TSTMS will be focusing into S Nevada and Arizona. The next period of TSTMS would be about Aug 30-Sep 5. Thereafter, next period of rains is suggested by CFSDaily about Sept 19-22. There is a small hint of come possibly significant rains into N and Northcentral California mountain areas during the first part of Oct, but nothing more can be said about it at this time.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: Sep 18-19, 21-23, Oct 2-3,Oct 9-10 and Oct 16-20.
CENTRAL CALIF Rains: Sep 18-19, 21-23, Oct 3, 10 and 17-19.
WARM SPELLS: Sep 25-27, Oct 6-8 and 13-15.
COOL SPELLS: Sep 19, 21-23, Oct 1-3, 9-11 and 19.
Forecast for Southern California:
SOCAL RAINS: Sep 18-19, 21-25, Oct 4, 10-11 and 18-19
SOCAL WARM AND HOT SPELLS: Sep 21-30, Oct 8-9 and 14-18.
SOCAL COOL OR COLD SPELLS: Oct 3-4, 10-11 and 19.
Forecast for Central Sierra Nevada:
Dates of mountain showers-TSTMS (Central & S Sierra): Sep 21-23, Oct 2, 9-10 and 16-19.
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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 September 15 – October 15, 2022
Highlights: Hot weather alternates with usual late season TSTM conditions during Sept. Watch for a possible tropical cyclone-associated heavy rain event that covers the southern and eastern deserts on Sep 17-19 and 21-24 from a tropical cyclone again. Perhaps another similar event to Sep 10-12 may occur again Sep 23-24. Some of rains may drift north into southern and central California mountains, San Bernardino Co deserts, and Sierra east slopes.
Looking Ahead – Long Range Outlook
October 15 – December 30... NORCAL and Central California coastal valleys, and Central Valley: bove normal temperatures will continue late Sep 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 very dry in Oct. This is followed by a burst of above normal rainfall from the Bay Area North into Oregon, as well as 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 these early season rains in Nov. This appears to be followed by wet conditions during Dec 1-20 or so in N California, and near normal in the central and south.
For SOCAL mountains westward to coast: After a wet September from Tropical Cyclone Kay, it turns drier than normal again in Oct through first half of Nov. A burst of possibly significant rains occurs in N California from the Bay Area north into Oregon in mid Nov through the first part of Dec.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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