Large Scale Summary
- Hot periods could still briefly occur in Sep and Oct for a day or two, but occur outside of the rain events and between trough occurrences. Hot weather is related to dry downslope and offshore winds.
- 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 and Nov, but rain volume should be minimal until the westerlies become consistent for a time in mid Oct, and again in mid Nov. 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. - CENCAL and NORCAL rain dates: NORCAL 16,18, CENCAL/NORCAL 26,31
- However, in Dec and Jan, the general guidance currently available suggests more consistent rains through mid to late Dec, Jan, and Feb. Typically, tropical cyclones in Oct affecting Baja and SOCAL focus hot dry SantañAna-type wind conditions into California for Oct. It may become difficult to transition into wetter conditons until Oct 19-26, and mid Nov, when the tropical cyclone season finally ends.
- In the fall, including mid fall, certainly lightning and wind are important influencers of the 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, including mergers with other other nearby rain-bands, and create their own problems regarding fire development.
- PRECIPITATION: Oct 5 to 18: Don't count on rain to mitigate ignition risk in the forests of Sierra Nevada or central coastal mountains. We need to wait untiil the rains really start to happen!
- SOUTHERN CALIFORNIA into Oct 2026. PRECIPITATION DATES: SOUTHERN CALIFORNIA SAN BDNO/LA CO MTNS/ Oct 13,14,15,16, and then NORCAL/CENCAL/Sierras on Oct 26,27,28,31
- SOUTHERN CALIFORNIA DESERTS: Oct 11-15. Central Sierra Nevada: TSTMS will occur as moisture occasionally comes north into SE California/San Bernardino
Co, and into the Central Sierras, and eastern and southern deserts of SOCAL.
Outlook October
- Good indicators for breaks in precipitation for Oct are not being consistently shown. The main break in rains per the NOAA outlook maps appears to be in early Nov before the mid Nov rains begin around 10th Nov. November. Currently the rains in Nov appear to be from cutoff lows. Beginning in December, the heavier rains will begin, and focus throughout the state. Focus of heaviest rains continues from mid Dec into January 2027.
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 be taken seriously. Our estimates during the week are published in the qpfmtnrt2 extended reports.T here are plenty of good physical reasons to support heavy rains, and possible flash flooding 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 OHI. 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
modelís estimate. It is recommended to compare the model trends with the observed moisture trends (from our IVTinit field) whether rains are occurring or not. - Watch the moisture trends in Oct-Nov-Dec from our IVTinit maps, issued daily. We will not be not publish our technical
discussions on IVTInit trends in this Outlook, but reserve them for the qpfmtnrt2 reports. - As we transition to mid-fall (late Oct-Nov), there may be a few more interactions between tropical moisture and energetic troughs/cutoff lows in the westerlies and subropical regions.
- El Nino is present in the equatorial region (Nino 3.4 from about 130W to Hawaii at 160W).
Figures and Text: Alan Fox, Fox Weather, LLC
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