30-Day Weather Outlook for April 21, 2024 to May 21, 2024

Apr 15, 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 N and North-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 have weakened. As the westerlies weaken, there continues some risk of troughs with scattered showers developing in the northern Rockies, as well as N California, Northern and Central Nevada. Troughing in Baja California related to sea surface temperature influence (IVTinit) has decreased.
Rain Dates for most of California including Central and Northcentral: April 24-25, 26-30, May 1,5-6,8-9. While rains are mostly in the central and N Sierra, and northcentral California, some reach south into Southern California at times 15-18.
Note that temperature during mid April-mid May may drop below normal for Central and S California as well as Nevada. This still supports a few frost events in April for sensitive agricultural areas in central coastal valleys,as well as Napa, Sonoma, and Mendocino Coís viticulture areas.
For forestry and upcoming Fire Season 2024 in NORCAL and SierrasÖ support continues for occasional precipitation in NORCAL with higher elevation snow in the Sierras in late Apr to first part of May.. Showers and rains occur at normal frequency and amount in the Sierras during May as late season cold showers. 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 continue drier than normal at least into July. Only precipitation dates are included in the outlook this week. Dates for the warm and cool/cold spells will return next week. For general guidance, cold periods and remaining frost risk in April to early May are most likely one to two days after periods of rain.

FORECASTS FOR CALIFORNIA

Forecast for Northern California:

NORCAL Precipitation: Apr 25-26, 28-May 1,5-6,8-10,14-18 .
NORCAL Warm-Dry Periods: Apr 17-24, May 3-4,12-13.
NORCAL Cold or Frost Periods: Apr 25-May 1, 5-10,16-18.
North Sierra Precipitation: Apr 24-25, 28-May 1, 3, 5-7,8-10,14-18.

Forecast for S California:

SOCAL RAINS: Apr 27-29, May 9 and 15-18
SOCAL Hot Dry Periods: Apr 17-25, May 2-7,11-13.
SOCAL Cool or Cold Periods: Apr 27-28, May 9-10 and 15-18

Central Sierra Nevada Precipitation:

Forecast for Central California Apr 17-May 17
Central Calif Precipitation: Apr 25-26, 29-30,May 6-7,9-10
Central Calif Warm Dry Periods: Apr 16-24,28,May 2-4,12-14
Central Calif Cold or Frost Periods: Apr 25-26,29-May 1,6-10,15-17

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The listings of dates normally included for hot and cold spells, and precipitation are approximate. They are based on 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 Apr 14-May 14. Troughing Dates: Apr 16-25, May 2-7 and 11-13. Some dates may contain a shower as well as gusty winds.

N and Central California and Sierras May 15 - June 15:

Frequency of frost will be less in May, but the overall tendency for cool conditions with near normal rains has greatest confidence in the northern mountains (Siskiyouís) and Lake Tahoe to Yosemite NP in the Sierras. For S California May 15-June 2024: Near normal temperature and precipitation for May and June.

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 now for the June - August period.

(Terms and Definitions Used In This Weather Outlook)