BASIC PATTERN:
Large Scale Pattern –
- During August, the CFSv2 short-term climate model predicts above normal rainfall for those areas normally subject to monsoonal convective rains, including Arizona’s northern, eastern and far-southern mountain and watershed areas. In California, the area most likely to receive above normal rainfall is the central Sierras from about Alpine Co south to about Fresno and Madera Counties. There is a robust area of above normal rainfall along western Mexico extending from Sinaloa and Nayarit states in Mexico north into the Four Corners Plateau area of the Rockies, including the states of Utah, Colorado, New Mexico, and Arizona.
- In September, the pattern shifts, with above normal rainfall over the Canadian Pacific coast, and near or a little above normal rainfall in far NW Washington. Washington and Oregon have near normal rainfall for the month, while California also has near normal rain. There is a small chance for above normal rainfall in Trinity and northern Mendocino Counties in Northern California for September.
- For the fall, the best chance for above normal rainfall in California will be along the N California coast in November. October and December return to the dry and persistently warm trend. By contrast, the NMME short term climate model suggests uniformly dry and warmer than normal during Sep – Dec (except for a wet anomaly in Nov).
- Precipitation Trend - Some thunderstorms (TSTMS) with rains focusing into Arizona mainly east portions Aug 12-15th, and Cape Mendocino north into Oregon about Sep 10. Otherwise it looks dry for Arizona, west half of Nevada and central to N California.
- Continued very dry across northern and central California through the next 30 days with little monsoonal moisture reaching these areas. Some monsoonal showers are possible across southern California with a gradual increase the latter half of Aug and still wetter later in the month.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: Dry thru Aug 16. A few mountain showers/TSTMS 17-18 and Sep 3-6.
CENTRAL CALIF Rains: Isolated showers 15-18 (most light and over the mountains).
Other shwrs: Aug 28-31 and Sep 2-5.
WARM SPELLS: Much above normal thru Sep 5. Hotter Aug 13-16 and 24-27.
COOL SPELLS: Sep 8-12.
Forecast for Southern California:
SOCAL RAINS: 14-18 (isolated showers E areas/mountains), 22-27 and Sep 1-5.
SOCAL WARM AND HOT SPELLS: Aug 14-20, 24-28 and Sep 1-6.
SOCAL COOL OR COLD SPELLS: Sep 9-11.
Forecast for Central Sierra Nevada:
Dates of mountain showers-TSTMS: Aug 14-19 (sctrd Sierra crest showers), 21-26 (showers), 29-Sep 5 (occasional showers).
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The listings of dates normally included for hot and cold spells, and precipitation are very approximate. They are based on our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (CFSDailyAI) to 4km. Our system gives some consideration to terrain and coastal influence. We consider the CFSv2 as 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 August 14 – September 14, 2022
Highlights: Hot weather alternates with usual monsoonal TSTM conditions during August and early Sept. Watch for a possible tropical cyclone-associated heavy rain event that covers the southern deserts 26-30 Aug and in early Sept. The rains then drift north into southern and central Nevada, and the east slopes of the Sierras.
Looking Ahead – Long Range Outlook
September 15 – November 15... NORCAL and Central California coastal valleys, and Central Valley: Warmer than normal in Sept, with some hot conditions (highs in the mid-90s to near 100 in the September hot spells. Near normal precipitation in the Sierras and Siskiyou Mountains, and Trinity Co north along the coast range with a few showery periods. Inland valleys (Sacramento and San Joaquin Valley systems remain drier than normal through Sept. October turns wetter than normal along the NORCAL coast from Mendocino Co north, but temperatures remain above normal due to warm nights during the rainy periods, and some hot spells during the intervening dry periods. Otherwise above normal temperatures are expected to continue throughout central California due to recurrent upper high pressure with a few dry downslope wind events.
For SOCAL mountains westward to coast: Above normal temperature. There is potential to continue warm and dry through Oct and early Nov. Foothill and coastal valley highs L80s to L90s m90s (avocado areas), but intermediate valleys persistently into the m90s. Tropical cyclone-associated moisture increases around the first week of September, and again about mid-September in the mountains and deserts of SOCAL. At least a seasonably hot September is suggested by the current update of the CFSv2 model. There may be some more coastal cooling with eddy conditions becoming more dominant for a time at the SOCAL coast in mid-September. Watch for a return of hot weather in mid Oct as Santa Ana conditions develop.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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