30-Day Weather Outlook for May 1, 2024 to May 31, 2024

Apr 30, 2024

BASIC PATTERN

Large Scale Pattern

The focus of lingering upper lows continues west of the Pacific Northwest, and also at 138-145W to the west of Northern and Central California.
Our IVTinitô analysis shows the calculated estimate of one day (Day0 Total Integrated Vapor Transport (TIVT24), based on the sea surface temperature anomaly pattern from the coast out to 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.
As we approach the end of the rainy season, the westerlies continue to weaken. As this occurs, there continues some risk of troughs with scattered showers occasionally developing in N California, the Sierras.
Troughing in Baja California related to sea surface temperature influence (IVTinit) had decreased a bit in the Baja region but may continue to assist upper low development for SOCAL and N Baja to Arizona with a few showers.
Rain features are spotty in early May. Rain dates: May 5-7, and 11-12. Some end of month rains in May are suggested by CFSv2 for 25-31 and possibly June 1, mainly occurring central to N Sierra, NORCAL.
For forestry and upcoming Fire Season 2024 in NORCAL and SierrasÖ support continues for occasional showers in NORCAL and in the Sierras in end of May and early June.
Monsoonal TSTMS and rainfall are currently expected below normal for W and NW Mexico. Therefore, the moisture source for monsoonal conditions in California and Arizona appears to be drier than normal during the transition to early summer.

FORECASTS FOR CALIFORNIA

Forecast for Northern California:
NORCAL Precipitation: May 5-7, 11=12,25=31
NORCAL Warm-Dry Periods: May 1-3,9-10,14-22
NORCAL Cool and Breezy Periods: May 5-7, 11-12,25-31
North Sierra Precipitation: May 5-7, 11-12,25-31
Central Sierra Precipitation: May 5-7, 11-12,25-31

Forecast for Central California
Central Calif Precipitation: May 5-7, 11-12,25-31
Central Calif Warm Dry Periods: May 1-3,9-10,14-22
Central Calif Cool Periods: May 5=7, 11-12,25-31

Forecast for S California
SOCAL RAINS: May 5, 14-16, 29-30
SOCAL Warm Dry Periods: May 2-4,10-13
SOCAL Cool or Cold Periods: May 6-7, 12, 28-30

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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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Looking Ahead — Longer Range Outlook April 14 - May 14, 2024

Southern California Deserts Outlook

Troughing Dates: May 5, 12, and again around end of May. Some dates may contain a shower as well as gusty winds.

For June 2024
N and Central California and Sierras

Overall tendency for cool conditions with near to above normal rains has greatest confidence in the northern mountains (Siskiyouís) and Lake Tahoe to Yosemite NP in the Sierras. The cool showery conditions may linger into mid June. For S California June 2024: Late May is cooler than normal for the most part. Early to mid June also appears cooler than normal due to deep coastal marine layer and residual troughing through mid June. Troughing through mid June would favor breezy and dry conditions for the S and E Deserts of Southern California.

Outlook for July Monsoonal Conditions
W Mexico is shown by CFSv2 monthly outlook maps to have below normal precipitation and above normal temperature. The same basic pattern continues for August 2024. Bottom line for California monsoonal rain conditions and thunderstorms below normal rainfall and below normal lightning, for the June - August period.

(Terms and Definitions Used In This Weather Outlook)