Large Scale Summary
- Regarding the transition to mid autumn, we remain close to guidance from NOAA/NCEP/ CPC/NWS for Central California and SOCAL. We do expect some early season showers in Oct due to rains associated with tropical moisture coming into frontal zones from the south. Rain dates from our CFSv2 extended daily maps: 26-30 Oct, 1 Nov, However, rain volume from upper lows and troughs in Nov, is still expected to be above average according to the NOAA CPC guidance.
- Rain volume will be heaviest as the westerlies start to develop into the coast in late Oct, 1-2 Nov and in mid Oct, and again 1-2,5 and 11-17 Nov, both in NORCAL and in the Sierras. Depending on how much rain occurs, the risk for wildland fires could be diminished at times, mainly in late Oct and mid to late Nov.
- In Dec and Jan, the general guidance currently available suggests more consistent rains through mid to late Dec, throughout the state in Jan, and in NORCAL
coast to Siskiyous in Feb. It may become difficult to transition into wetter conditons until mid to late Oct and Nov, when the tropical cyclone season finally comes to an end. - In the fall, including mid fall, certainly lightning and wind are important influencers of autumn fire weather. So, even if some wet periods occur, presence of lightning/
TSTMS and gusty/fickle winds are certainly risk factors to consider, even in a wet fall. - Bands of showers associated with upper lows and rains, can easily develop severe weather situations. This includes mergers with other other nearby rain-bands, and create their own problems regarding fire development.
- PRECIPITATION: Oct 15-Nov 15: Our CFSv2 daily outlook maps show most widespread rains for the dates mentioned in a) and b) above. Don't count on rain to mitigate ignition risk in the forests of Sierra Nevada or central coastal mountains in Nov.
- SOUTHERN CALIFORNIA PRECIPITATION DATES: SOUTHERN CALIFORNIA SAN BDNO/LA CO MTNS/ Oct 13,14, and then NORCAL/Central California Sierras on Oct 28,29.
- Central Sierra Nevada: TSTMS are possible as moisture occasionally comes northwestward into SE California/San Bernardino Co, and to the Central Sierras.
SOUTHERN CALIFORNIA and west Arizona Deserts: Oct 26-28.
Outlook for October
- Good indicators for precipitation in Oct are not being consistently shown in Arizona or SOCAL deserts. Rains in Nov per the NOAA outlook maps appear to be in early Nov before the mid Nov rains begin around 10th and onward in Nov. Currently the rains in Nov appear to be from landfalling lows and cold fronts. Beginning in late Nov, and Dec, the heavier rains appear to begin, and focus through in a few incidents thru most of California. Focus of heaviest rains continues from mid Dec into January 2027. Mid Dec 2026 ñ most of Jan 2027 appear to be the wettest periods.
Extended Forecast
- December 2026 rainfall well above average for N, Central, and above average for S California. Possibility exists for only
short breaks between significant rains. - The Jan 2027 Outlook maps for rain in Jan and Feb from NOAA should still be taken seriously. Our estimates during the week are published in the qpfmtnrt2 extended
reports. - The most reliable physical reasons to support heavy rains, are in mid Dec thru Jan. There still appears enough support for possible flash flood in mid Dec through Jan 2027.
- Warm oceanic mesoscale eddy patterns, plus unusually warm SSTAs (Synoptic Anomalous Warm Ocean Surface SAWOS and Oceanic Heat Index (SAWOS/OHI) are good physical indicators for rain probability and amount. Developments in the extended pattern can be followed by the moisture trends in the IVTinit maps. These
are observed moisture fields, not just a numerical model's estimate. It is recommended to comparethe model trends with the observed moisture trends (from our IVTinit field) whether rains are occurring or not. - As we transition to mid-fall (late Oct-Nov), there may be a few more interactions between tropical moisture and energetic troughs/upper lows in the westerlies and subropical regions.
- El Nino is present in the equatorial region (Nino 3.4 region) 130W ñ 165W. about 130W to Hawaii at 160W to at least 170W).
Figures and Text: Alan Fox, Fox Weather, LLC
Copyright © 2026 Fox Weather, LLC.