Large Scale Summary
- Support for troughing focuses near 130-145W. The main governing agent is the MJO with a maximum along about 170W-180. There is also an IVTinit feature
located 126-135W. The main issues for California are rain systems with their small band sizes but containing moderate to locally heavy rain rates. - Tropical cyclone events are an increasingly minor factor after mid Oct. Precipitation Amounts and Fire Risk: There has been a decrease in fire risk for the Sierras of northcentral to N California due to increased moisture with the rains.
- Near average, with spotty above average precipitation is suggested for SOCAL in mid to late Oct. Above average precipitation for NORCAL— from the Bay Area northward, and above average precipitation for the North Coast: Mendocino Co north to southwest Oregon.
- The combination of above average NW flow along the NORCAL and North Central California coast will tend to favor more of the dry windy events typical of fall, some of which are Santa Anas which produce upwelling near the California coast, even if the current pool of unusually warm sea surface west (upstream) of 127W continues. This combination is not as robust for above normal rainfall into Central California, so we should see more prolonged dry spells develop at times in Nov despite some good rain events in mid to late Nov.
- Rain Dates: Oct 19-21, 25-26,29-31, Nov 5,24-25
Near Term Forecast Oct 18 — Nov 29 2025
- NORCAL PRECIPITATION DATES: Oct 19-21, 25-26, 31. NOV 5, 24-25
- COLD/FREEZES/WINDS: 22, 27-29, NOV 1-2, 8-10, 22-23, 27-29.
- WARM/DRY PERIODS: 23-24, NOV 12-22.
- MOUNTAIN SNOWS: 19-20-21, 25-26, 31. NOV 5, 24-2
- CENTRAL CALIFORNIA PRECIPITATION DATES: 19-20, 25-26, 31. NOV 5, 24-25
- COLD/FREEZES/WINDS: 22, 27-29, NOV 1-2, 8-10, 22-23, 27-29
- WARM/DRY PERIODS: 23-24, NOV 12-22.
- MOUNTAIN SNOWS: 20, 25-26. NOV 5, 24-25
- SOUTHERN CALIFORNIA PRECIPITATION DATES: 19-20, 25-26, 30-31. NOV 5, 25
- COLD/SANTA ANA WINDS: 22, 27-29, NOV 1-3, 8-10, 22-23, 27-29
- WARM/DRY PERIODS: 23-24, NOV 12-22.
- MOUNTAIN SNOWS: 20, 25-26. NOV 25
- SOUTHERN CALIFORNIA DESERTS PRECIPITATION DATES: 20,25. NOV ,25
- COLD/N-NE WINDS: 20-21, 26-27, 30-31. NOV 1, 4-6, 9, 19-21, 22, 24-26
- WARM/DRY PERIODS: 23-24, NOV 12-22.
- MOUNTAIN SNOWS: 20, 25-26. NOV 25
Medium Term Outlook: Nov 1 — Nov 30
- The IVTinit pattern along with the Madden Julian Oscillation (MJO) both are showing a tendency for troughing in the subtropical mid N Pacific near
the Central California and NORCAL coast, and also near Santa Barbara Co (S California). - Northern California rain dates estimate: Dec 8-10, 10-18,20-23,27-30.
- Southern half of California rain dates estimate: Dec 8-10,11-18,20-24,27-30.
DISCUSSION OF NOAA/NCEP/CPC MAPS FOR DEC 2025 — JAN 2026
- In Dec it turns wet with significant rains possible 8-10, 10-18,20-23, 27-30 with above average snow levels in the NORCAL mountains, to Central Sierras. Above average snow levels also are indicated for SOCAL mountains. That is consistent with potential for Atmospheric River (AR) systems in Dec.
- Eventually, the belt of westerlies in the mid to eastern N Pacific has support to meander far enough south to tap more subtropical moisture for storms coming into California, beginning in December 2025. The latest CFSv2 information for Jan 2026 shows a possible pause in the rains, with below average rain amounts in late Jan for the central and south portions of California, but near average for NORCAL.
Figures and Text: Alan Fox, Fox Weather, LLC
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