Large Scale Summary
- Rain Dates Octobr 8-11th in NW California and Siskiyouís.
- September is turning dry as tropical cyclones remain distant from our California region.
- Hot periods occur between the infrequent rain events and between trough occurrences, especially where dry downslope NE flow is indicated.
- Regarding the transition to autumn, we remain close to guidance from NOAA/NCEP/ CPC/NWS. An increase in thunderstorm (TSTM) activity is reasonable in September, and as well as the emerging overall pattern. We do expect some early season showers in Sep, but with minimal rain volume. Depending on how much rain occurs, the risk for wildland fires could be diminished at times, but donít count on it! Typically, tropical cyclones affecting SOCAL focus the hot dry SantañAna-like wind
conditions, and may never transition to wetter conditions. Certainly lightning and wind are important influencers of the autumn fire weather season. 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, merging other nearby rain-bands, and create their own problems regarding fire development.
CENTRAL CALIFORNIA
- PRECIPITATION_DATES: Sept 25-28, , Oct 8-11 in NW California. Systems are convective, with small areal coverage. Despite any heavy showers that may occur, there is very limited moisture available at this point in the season, so donít count on rain to mitigate ignition risk in the forests.
SOUTHERN CALIFORNIA
- PRECIPITATION DATES: SOUTHERN CALIFORNIA SAN BDNO/LA CO MTNS/ Oct 12-15.
- SOUTHERN CALIFORNIA DESERTS: Oct 10-15 rains possibly moving west from Arizona, 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.
Extended Outlook
- The main break in rains per the NOAA outlook maps appears to be in 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 - 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 taken seriously.are published in the qpfmtnrt2 extended reports. There 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. Developments in the extended
pattern can be followed by the moisture trends in the IVTinit maps. It is recommended to compare the model trends with the observed moisture trends (from the IVTinit field) whether rains are occurring or not in the IVTinit pattern - As we transition to mid-fall (late Oct-Nov), there May be afew more interactionss 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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