30-Day Weather Outlook for June 15, 2024 to July 15, 2024

Jun 17, 2024

BASIC PATTERN

Large Scale Pattern

The focus of lingering upper lows continues west of the Pacific Northwest, and troughing at 140-150W.
Our IVTinitô analysis shows the calculated estimate of one day (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. Physical units of TIVT are comparable to CW3Eís 24 hour TIVT.
With early summer, the upper westerlies continue to decrease speed. Surface onshore flow remains robust due to airflow from a cold ocean to the hot inland valleys and deserts.
There continues support for mostly dry troughs with, and followed by gusty downslope winds in central California, and dry/occasionally windy conditions in SOCAL mountain and desert areas in mid June. These decrease late in the month, but with onset of occasional hot conditions.
For forestry and upcoming Fire Season 2024 in NORCAL and Sierras there is support for rains on 17 June in NORCAL (mostly mountains).
Monsoonal TSTMS and rainfall are currently expected to remain well below normal for W and NW Mexico for the entire tropical summer rainy season (through September). A tendency for weak troughing from southcentral Baja California and westward tends to induce weak lows or cyclonic flow. This maintains the lack of support for tropical cyclones and dry W flow in central Baja. Therefore, the moisture source for tropical monsoon conditions in California and Arizona appears to be drier than average during most of the summer and into September.

FORECASTS FOR CALIFORNIA

Forecast for Northern California

NORCAL Precipitation: JUN 18. 22-23
NORCAL Warm-Dry Periods: JUN 14-15, 19-20, 24-30, July 3-8 and 11-14
NORCAL Cool and Breezy Periods: JUN 17-18, 21-23, Jul 1-2, 10 and 16-17
North Sierra Precipitation: JUN 17, 22-23 and Jul 16.
Central Sierra Precipitation: JUN 17, 23 and Jul 16

Forecast for Central California

Central Calif Precipitation: No precipitation other than coastal drizzle.
Central Calif Warm/Hot Periods: JUN 14-16, 18-21, 24-Jul 1, 3-9 and 11-14.
Central Calif Cool Periods: JUN 17, 23, Jul 2 and 10

Forecast for Southern California

SOCAL RAINS: No precipitation other than coastal drizzle
SOCAL Warm or hot-dry Periods: JUN 13-21, 24-Jul 2, 4-9 and 11-14
SOCAL Cool Periods: JUN 23, Jul 3 and 10

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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 17-18 breezy but no precip) and 25 (no precip). About normal temperatures. Recurrent upper low or trough activity is suggested for N Baja- SOCAL in June, leading to more persistent drizzle out at the coast, but minimal if any precipitation for the deserts.

For July 15 - August 15
N and Central California and Sierras

Above average temperature overall, with a transition to recurrent heat waves during July and August. Rainfall will recover to near or slightly below average. For Southern CaliforniaÖ Above average temperature overall, with a transition to recurrent heat waves during July and August. Rainfall will recover to near or slightly below average.

Monsoonal Conditions
Mexico is shown by CFSv2 monthly outlook maps to have below average precipitation and above average temperature in the NW Mexico region that normally feeds tropical moisture into California for summertime thunderstorms. The abnormally dry conditions appear to persist through August and into September. This is consistent with the IVTinit tendency for weak troughing near central Baja and westward. This pattern generally discourages tropical cyclone formation. Along with the persistently dry conditions this pattern will tend to encourage unusually hot conditions in the sunny areas of NW Mexico as well as the southern and eastern deserts of California.

(Terms and Definitions Used In This Weather Outlook)