30-Day Weather Outlook for October 1, 2024, to November 1, 2024

Oct 01, 2024

BASIC PATTERN:

Large Scale Pattern

The focus of lingering upper troughs continues west of the Pacific Northwest, and troughing at 135-145W off NORCAL.
Our IVTinitô analysis shows the calculated estimate of one day (Day 0) Total Integrated Vapor Transport (TIVT24), based on the sea surface temperature anomaly pattern from the coast out the Dateline-180W. This is calculated by Fox Weather LLCís CyclogenIVT AI application each day. It shows for us the potential areas for development of troughs and rains upstream from California and the West Coast. Physical units of TIVT are the same as for 24 hour TIVT from the Center for Western Weather and Water Extremes (CW3E).
For forestry and the early to mid-Fall Fire Season 2024 in NORCAL and Sierras with the bottom line: recurring hot periods and below average precipitation we continue to see quite a bit of support for dry hot east winds in northcentral and N California from the 26th Sep to about mid Oct. Some of these appear to be associated with cutoff upper low (typical for late Sep and Oct). After a dry thunderstorm event, the dry east winds develop, including in overnight periods,therefore, overnight dry east winds are to be monitored.
The main effect from tropical cyclones, even in a meager monsoonal season such as this one, is dry hot east winds with high temperatures 100+ in coastal foothills, foothills in Riverside/ San Bernardino Coís, and foothills near both the coastal mountains away from the marine layer in NORCAL, and in the Sierras.
California appears to have below average rainfall in October. Rains of significance would more likely be showery, inconsistent, and would contain lightning (TSTMS), even during mid Oct, when rains appear most likely. Widespread areal coverage by light to moderate rain would be nice, but donít expect it. The next opportunity for a good rain into California (SOCAL, Central California, and NORCAL, appears to be mid November.
Other than some near normal rainfall for SOCAL in mid to late Nov, the rain amounts predicted for California and SOCAL appear below average.

Forecast for Northern California
NORCAL Precipitation: Oct 4-5 north coast, showers psbl 16-18 and 21-22 North Coast and Sierras.
NORCAL HOT PERIODS Highs of (98-103 possible),early in first week of Oct, and after dry cold frontal passages during periods of 8-13 Oct and again in the 90s inland valleys late Oct during dry eastwind periods.
North Sierra Precipitation: Oct 16-18, 22-23
Central Sierra Precipitation: Oct 16-18. 22-24

Forecast for Central California
CENTRAL CALIFORNIA Precipitation: Oct Shallow marine layer at coast. Shower possible Oct 15-16, 22-23.
CENTRAL CALIFORNIA HOT PERIODS: remaining warmer than average. Hot spell first few days of OctÖhighs 100-105 on hotter days foothills and central valley and Salinas/San Benito Valleys, again hottest in foothills and south Salinas Valley away from marine influence.

Forecast for Southern California
SOCAL RAINS: Oct 21-23 Oct briefly, but with intermittent hot spells before and afterward.
SOCAL HOT PERIODS: Temecula-Riverside-Escondido foothills 100. Hottest in inland areas), 7-11, 17-18. Temperatures remain above average.
SOCAL MILD PERIODS: Oct 3-5, Oct 16, Oct 20-23.

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The listings of dates normally included for hot and cold spells, and precipitation are approximate. They are based on GFS and our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (FoxCFSDailyAI) to 5km. Our AI system gives some consideration to terrain and coastal influence. Although we consider the CFSv2 one of the better ways to represent basic weather in the sub-monthly time scale, performance of the CFSDaily. CFSv2 daily products during storm seasons has been especially inconsistent and difficult to apply to the useful criterion needed by cropland agriculture, and viticulture beyond the 15ñday GFS.

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Southern California Deserts Outlook

SOCAL deserts: above average temperatures, and below average rainfall for the period. However, it appears that there are some showers/thunderstorms in N and Central California mountains/Sierras. Above average temperature overall, with recurrent hot spells during Sep in Owens Valley to the SOCAL deserts area. Rainfall remains below average in NORCAL and Sierras. Mild conditions alternate with hot in coastal valleys of Central and N California, for the most part. Unstable airmasses break the marine inversion at times in N California, with some days of above average temperatures. However, recurrent troughing deepens the marine layer and onshore flow. For Southern California, away from the coastal influence area, we look for above average temperature overall.

Rainfall will remain below average with the a few mountain/desert TSTMS. In Oct we currently appear to have above average temperature but tending towards near average precipitation in the Sierras, and in mountains of Central to Southern California, but below average rainfall in NORCAL.

Looking Farther Ahead
California temperatures appear to return to above average in N California during October. Precipitation is below average for that month. It turns cooler after mid Oct, with rains starting to develop North Coast from
Humboldt Co northward about end of Oct. Mid Nov turns briefly above average for precipitation in NORCAL and north-central Sierras for a few days. Dec returns to average or subnormal rainfall in NORCAL from Bay Area north, and seasonably wet in the ORWA region (Oregon, Washington), mainly coast and Cascades due to atmospheric Rivers.

(Terms and Definitions Used In This Weather Outlook)