BASIC PATTERN:
Large Scale Pattern –
- Overall, the longwave pattern continues mostly dry and hot. Some showers and TSTMS are indicated during August.
- The number of days over 100 degrees in Fallbrook, Escondido, and interior San Diego County will tend to go above normal in Aug and late July due to strong and persistent upper high pressure.
- Precipitation Trend Jul 21-Aug 21. Precipitation Dates for N and Central California: Isolated dry thunderstorm (TSTM) about 4-5 Aug,then 11-17 Aug dry TSTM Sierras. 18 Aug in the North coastal mountains, Siskiyou’s and NE Plateau. The sea surface temperature anomaly maps to about July 15 have been showing a robust El Nino pattern along the Peru-Ecuador coast and along the equator westward to 160W. The very warm SSTA pattern associated with El Nino (greater than 2.5 C) on July 14 extended to 135W. The warm SSTA pattern normally associated with El Nino is expected to continue expanding west toward the Dateline during Aug.
- Precipitation trends in S and W Mexico thru mid July: Tropical cyclone-type rains: 21-23 Jul. Hot and scattered TSTMS during late Jul in NW Mexico.
- In California, hot spells occur thru Jul as strong upper high pressure develops. Some cooler influence with deeper marine layer into N and Central California occurs 18-19th. A few light showers/TSTM occur during 26-29 July and also 11-17 Aug in central and N Sierras.
- In California, the Sierras have near normal rainfall from Tahoe south through the central Sierras in Aug per latest CFSv2 guidance. However, Sept and Oct appear to be very dry through California and our state's mountain areas.
- In the fall, we transition from a mostly dry autumn (October 2023) to a wetter trend in late Nov for NORCAL and N-central California, followed by a wet, typical El Nino type of Dec 2023. This is in response to an increasing El Nino pattern, this late Nov and Dec.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
Norcal PRECIPITATION Trend: Aug 4 and 11-17.
Norcal WARM/HOT SPELLS: Jul 21-Aug 2, 7-12 and 21-23.
Norcal COOL SPELLS: Aug 4-6 and 13-17.
Central Calif PRECIPITATION: Dry with rain unlikely (few light shwrs E 11-16).
Central Calif WARM/HOT SPELLS: Jul 21-3, 7-13 and 20-23.
Central Calif COOL SPELLS: Aug 4-6 and 14-17.
Forecast for Southern California:
SOCAL RAINS: Aug 5-6 (E deserts) and 13-15 (E deserts).
SOCAL WARM/HOT SPELLS: Jul 21-Aug 3, 8-13 and 16-23.
SOCAL COOL SPELLS: Aug 5-6 and 15.
Forecast for Central Sierra Nevada:
Central Sierra Nevada Precipitation - Main dates of TSTMS are... Aug 4-5 and 11-17.
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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 system gives some consideration to terrain and coastal influence. We consider the CFSv2 one of the better ways to represent basic weather down in the sub-monthly time scale beyond the 15–day GFS or monthly maps from CFSv2 or NMME.
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Southern California Deserts Outlook for July 21 - August 21, 2023
Highlights: Below normal rainfall from monsoonal influences in most areas but near normal rainfall (showers) through the Sierras. Tropical cyclone influences remain well to the south in Baja up to mid Aug.
Looking Ahead – Long Range Outlook - August 22 - September 22, 2023
Western Mexico… including all of Baja California: above normal rainfall for the period approximately mid to late Aug. However, the wet trend does not extend into California for September.
S California Coast through mountains: Seasonably hot with near normal rainfall consisting of mountain thunderstorms (TSTMS).
S California Deserts through central and east San Bernardino Co: Seasonably hot with near normal rainfall consisting of desert TSTMS.
N and Central California: It is from Aug 15 – about Sep 1. High pressure and hot weather will tend to alternate with troughing, minimally showery conditions in the Sierras in Sep and cooler, dry and breezy conditions. A good descriptive expression to aid fire readiness over late Aug, and Sep 1-30: “hot-dry-breezy” with some hot NE-E wind events.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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