BASIC PATTERN:
Large Scale Pattern -
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The IVTinit pattern (sea surface temperature anomaly forcing) favors troughing in the N and NE Pacific at 150-160W and some downstream troughing in N California region at 112-118W (Nevada, Sierras, E California). These troughs will tend to extend into Northern and Central California, around Oct 15-22. Rains are indicated for NORCAL and Central California and Sierras, and a few light showers may reach into SOCAL eastern mountains.
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Tropical cyclones will continue in southern and SW Mexico in Oct, but are unlikely to affect California except possibly 14-15 Oct in SOCAL/Central California.
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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 classic El Nino pattern continues to develop with colder than normal sea surface developing in Indonesia from Sumatra east to New Guinea and the Australia north coast, per the typical pattern.
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Precipitation trends in longer range, up to 15 Nov: Precipitation Dates: Oct 10 (weak), 14-15 partly cloudy/showery. Upper low appears to cause rains SE SOCAL-Arizona Oct 18. Other rains occur Oct 22-23, 25-26, 31-Nov 1, Nov 7-9, Nov 13-15 per CFSv2. In general NMME is mostly drier than normal until it finally turns wet in early Jan 2024.
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In Nov, we transition from mostly dry and warm periods in early Nov to a brief wet period in mid Nov. From the Thanksgiving holiday weekend on through mid Dec it appears to be intermittently wet-typical for El Nino. As mentioned last week, we are selecting the period mid Dec through Jan 2024 and Feb 2024 to have mostly above normal rainfall throughout California, due to the expected El Nino pattern. Bottom line: we still expect a robust El Nino rain season for Dec - Feb, but the timing is a bit uncertain this far in advance. The pattern of rains appears typical for El Nino, with highest rain anomalies focusing in Central and S California, and more typical winter rain amounts for N California.
FORECASTS FOR CALIFORNIA
Forecast for Northern California:
NORCAL Precipitation: Oct 22-23, 25-26, 31-Nov 1, Nov 7-9
NORCAL WARM/HOT SPELLS: Oct 28-29 (warm), Nov 3-6 and 12-13
NORCAL COOL SPELLS: Oct 22-27, 31-Nov 2 and 7-10
Forecast for Central California:
Central Calif Precipitation: Oct 22-23, 25-26, 31-Nov 1, Nov 7-9
Central Calif WARM/HOT SPELLS: Oct 28-29 (warm), Nov 3-6 and 11-13.
Central Calif COOL SPELLS: Oct 22-26, 31-Nov 1 and 7-10
Forecast for S California:
SOCAL RAINS: Oct 18, Nov 7-9.
SOCAL WARM TO HOT SPELLS: Oct 22-31 (warm), Nov 1-6 and 11-13
Central Sierra Nevada Precipitation for Oxctober 8 - Novemver 9:
Main dates of rains or showers and/or snow... Oct 22-23, 25-26, Nov 7-9
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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 Oct.
Looking Ahead — Longer Range Outlook 1-31 Oct 2023
For Nov 1-30, 2023 N and Central California and Sierras:
Periods of warmer than normal with near to below normal precipitation are still possible in Nov. It turns briefly wet about Nov 11-18 and again during the Thanksgiving holiday period. There will be a couple of halting attempts at an Atmospheric River, but for the most part, forecast guidance suggests a basically normal rainfall pattern for NORCAL. That said, one AR can kick monthly rainfall for NORCAL above normal. A more consistent El Nino pattern sets up near and west of the coast in Dec.
S California:
Above normal temperatures recur for most of Nov. Cool periods coincide with the rains during Nov 14-21, and the Thanksgiving holiday period. Wet conditions develop in mainly late Nov, and in Dec 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