Large Scale Summary
Support for troughing continues in the central North Pacific from about 155-170W (mainly N to NNW of Hawaii), and at 128-140W off the California coast at 35-45N. Showery conditions in Sierras June 1-4. Look for a transition to hot conditions about mid June.
Near Term Forecast
Northern California
- Precipitation dates in N coast and N-Central Sierras are: June 1-2,3-5,8-10.
- Mild/Dry Periods: Cool to near seasonally average temperatures near the rainy periods.
Central California
- N Sierra precipitation: June 1-2, 3-5, and 8-9.
- Central Sierra precipitation: 1-2, 3-5, 8-9 June.
Southern California
- Showers are sparse and disorganized at this time. We move into more of a spring marine morning drizzle pattern in early June.
- Mid May appears to have a greater chance for deep marine layer events, so that the hot conditions are mainly intermittent and inland, while the cool periods are at the coast and coastal valley areas. Colder nights San Luis Obispo Co valleys if clearings occur for a time overnights/early mornings after the marine drizzle periods.
Southern California Deserts
- With weakening of troughs in general, return to a more normal beginning of hot weather during mid June. A little cooler than average during recurrent development of troughs and cold fronts from the Great Basin (Nevada/Utah) into Arizona (persistent northwest flow patternfor S California). It turns warmer than average for a period in mid June. Rainfall amounts mostly near average.
Medium Term Outlook — June 23 - July 23
Northern California
- Near average rainfall. Summer monsoonal showers/TSTMS will tend to be delayed until early to mid July.
- For valleys and mountains of Northern California, turning hotter and drier than average during first month of summer (10-30 June).
Southern California
- 15 June - 15 July: Near average precipitation with near average temperature. More persistent marine layer conditions during May will tend toward a shallower and more erratic marine layer influence. Therefore, watch for interspersed hot periods accompanied by shallow coastal marine layer conditions at times during mid June.
- Transition to dry hot conditions by mid June and going into late June as tropical cyclone conditions start to develop off southern Baja.
- 30 Day Precip/Temp maps for June and July suggest a return to minimal monsoonal TSTMS but continue above average temperatures. Please note that well above normal temperatures are suggested in the NCEP/CPC guidance for June — with heat wave conditions in the Sierra Nevada foothills and west slope areas from El Dorado Co south in June. Below average rainfall is expected in Sierras from monsoonal thunderstorms (TSTMS), due to a dry June for monsoonal conditions in western Mexico.
- For the valleys of Southern California: Turning warmer and drier than average at times during June. We note from the NCEP monthly guidance included next page that significant hot spells are a possibility in June for inland SOCAL citrus and avocado regions if or as tropical cyclones develop near southern tip of Baja. There is risk of highs reaching to near 105 in the Ramona-Temecula areas and 95-100 in Fallbrook during mid to late June.
- A very late onset of monsoonal TSTM conditions develops during late July or early August with below average rain amounts for Arizona, SE California, and the Sierras, and below normal monsoonal TSTM activity for Jalisco Sonora Sinaloa states, and Michoac·n on the south coast.
Figures: Alan Fox, Text: Alan Fox, Fox Weather, LLC.