30-Day Weather Outlook for May 17, 2024 to June 16, 2024

May 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 Northern and Central California.
Our IVTinitô analysis shows the calculated estimate of one day (Day0 TotalIntegrated Vapor Transport (TIVT24), based on the sea surface temperature anomaly pattern from the coast out to 180W. This is calculated by Fox Weather LLC's 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 upper westerlies continue to weaken while the surface onshore flow strengthens as the deserts heat up while the coast remains cool.
Rain Dates from our CFSDailyAI system: minimal north coast May 17-18,19-21, and 22-23 May from GFS. From CFSDailyAI beyond May 23: May 20-21, 26-27,30-31 Yosemite/Sierras crest to Fresno Co. May 20-21,16-27, 30-31-June 1 coastal clouds/drizzle in San Luis Obispo Co to Ventura Co, May 20-21. 29-31, and June 1-4 Central Sierras. Showers possible Tuolumne-Mariposa Coís. Cold showers/rains Siskiyou mountains NE Plateau and into mountains of Lassen Co on 2-5-6 June. Cold, mostly cloudy and showery Humboldt/Trinity/W Siskiyou Coís Jun 2-5, 7-11.
There continues an increase in support for dry troughs with and followed by gusty downslope winds in central California, and dry/occasionally windy conditions in the SOCAL deserts areas.
For forestry and upcoming Fire Season 2024 in NORCAL and Sierras support will be decreasing for showers in NORCAL and in the Sierras in end of May and in first 10 days or so of June. The daily CFSv2 can continue to be inconsistent regarding timings and locations of measurable rainfall.
Monsoonal TSTMS and rainfall are currently expected below normal for W and NW Mexico. Therefore, the moisture source for tropical monsoon 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 19-21 (N areas), 27-28, 30-Jun 2, 5-8 and 10-14
NORCAL Warm-Dry Periods: May 24-25, Jun 4 and 15-18.
NORCAL Cool and Breezy Periods: May 19-21, 27-Jun 3 and 5-14.
North Sierra Precipitation: May 19-22, 29-31, Jun 5-8, 11 and 14.
Central Sierra Precipitation: May 20-21, 30-31, Jun 6-8, 11 and 14.

Forecast for Central California
Central Calif Precipitation: May 21 (N areas) and Jun 5-7
Central Calif Warm Dry Periods: May 23-27, Jun 3-4, 8-9 and 13-18.
Central Calif Cool Periods: May 21-22 and Jun 5-7.

Forecast for S California
SOCAL RAINS: Jun 6.
SOCAL Warm Dry Periods: May 17-19, 22-30, Jun 3-5, 10-12 and 14-18.
SOCAL Cool Periods: May 21, Jun 1-2 and 7.

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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 for June

Southern California Deserts Outlook
Troughing Dates: Jun 6-7.

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.Some hot weather spikes may occur after 15 June in NORCAL and the N Sierra foothills (west slope), similar to the hot spell on 8-9 May. 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 (see (e) above).

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 September period, but dry and hot conditions.

(Terms and Definitions Used In This Weather Outlook)