BASIC PATTERN:
Large Scale Pattern -
- A trough is weak off the central and N California coast. Dry conditions develop from Sep 20th onward into early Oct.
- Tropical cyclones will be less active in Sep for bringing tropical moisture into California. Tropical cyclones may remain active in southern Mexico and S Baja as is normal for Sept.
- Thunderstorms continue an issue at times in Sep for the Sierras although we expect mostly drier than normal conditions after 20 Sep.
- The sea surface temperature anomaly maps have continued to show a robust El Nino pattern along the Peru-Ecuador coast and along the equator westward to 160W. The warm SSTA pattern normally associated with El Nino is expected to continue through Oct.
- Precipitation in the longer range, late Sept...near normal rain amounts. Oct... warm and dry through California and our state's mountain areas.
- In the fall, we transition from a mostly dry and unusually warm autumn (October 2023) to a wetter trend from mid to late Nov in NORCAL through Central California. This appears to be followed by a typically wet El Nino pattern for Dec 2023. The predicted pattern by NMME supports Atmospheric River events in Dec for Northcentral California to VenturaCo. The extended monthly guidance from NMME and CFSv2 are not consistent Regarding the start of rains in Nov.
FORECASTS FOR CALIFORNIA
Forecast for Northern California:
NORCAL Precipitation Trend: Sep 1-2, 5-6 and 17-20.
NORCAL WARM/HOT SPELLS: Sep 9-15 and 23-30.
NORCAL COOL SPELLS: Sep 1-7 and 17-21.
Forecast for Central California:
Central Calif Precipitation: Sep 1-2, 6 and 17.
Central Calif WARM/HOT SPELLS: Sep 8-16 and 20-30.
Central Calif COOL SPELLS: Se[ 1-6 and 17-18.
Forecast for S California:
SOCAL RAINS: Sep 1, 11-12 and 20-21.
SOCAL WARM TO HOT SPELLS: Sep 4-10, 14-18 and 23-30.
SOCAL COOL SPELLS: Sep 2, 11-13 and 20-21.
Central Sierra Nevada Precipitation for 1-30 Sep 2023:
Main dates of TSTMS are...Sep 1-2, 5-6 and 19-21.
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The listings of dates normally included for hot and cold spells, and precipitation are approximate. They are based on our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (FoxCFSDailyAI) to 5km. Our system gives some consideration to terrain and coastal influence. We consider the CFSv2 one of the better ways to represent basic weather down in the sub-monthly time scale beyond the 15ñday GFS or monthly maps from CFSv2 or NMME.
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Southern California Deserts Outlook:
Highlights: Near normal precipitation is expected middle and late Sep,but some areas of SE California could be above normal in the mountains and deserts.
Looking Ahead — Longer Range Outlook 1-31 Oct 2023
N through Central California and Sierras: Much warmer than normal with well below normal precipitation is expected through October and likely the 1st half of November. Turning wetter later in November as El Nino starts to set up its wet pattern for California.
S California: Much above normal temperatures through October and the start of Novemberwith much below normal precipitation. Some cooling later in November with an increase in rain as El Nino develops.
(Terms and Definitions Used In This Weather Outlook)
Figures: Alan Fox
Text: Zane Stephens, Fox Weather, LLC,
Copyright © 2023 Fox Weather, LLC