Posted by: Richard | December 7, 2014

San Francisco Bay Area Short and Long Term Forecast- 11/18/2017 7AM PST

San Francisco Bay Area Weather Forecast (Including Santa Cruz County) – (1 to 2 days)   Mostly sunny today.  Mostly clear tonight becoming mostly cloudy in the north bay and partly cloudy in the south bay on Sunday.  Light winds.  High temperatures in the low 60’s.  Low temperature mostly in the low 40’s.  

Extended Forecast for Central California (Including Napa County south to Monterey County and east into the Sierras –  (3 to 7 days – (11/20/17-11/24/17) – Mostly cloudy with an increasing chance of rain in the north Sunday night.  Mostly cloudy with rain likely in the north and a chance of rain further south on Monday. Mostly cloudy with a chance of showers north of the Golden gate Monday night with a slight chance of rain further south, otherwise partly cloudy in the south.  Mostly cloudy on Tuesday with a decreasing chance of showers in the north, otherwise partly cloudy in the south. Mostly cloudy with a slight chance of rain in the north otherwise partly cloudy in the south Tuesday night and Wednesday.  Partly cloudy Wednesday night through Friday.  High temperatures in the high 50’s to low 60’s.   Low temperatures mostly in the low 40’s. 

Long Range Weather Outlook Northern and Central California 8 to 15 days (11/25/17 – 12/01/17)  Partly cloudy at the beginninog of the period then a chance of rain developing over much of the area later in the period.   Temperatures near normal.

Extremely Long Range Weather Outlook Northern and Central California 16 to 20 days (12/02/07 – 12/06/17)  Rain at times in the north and a chance of rain in the south at times.  Normal temperatures.



  1. Do you see the possibility of the westerlies breaking thru underneath the projected building ridge(the 4th week of Dec) sometime in Jan?

    • Sure, but who is to say that far out in time whether the pattern change will be a breaking underneath or the jet going over the ridge and coming into California from the north or northwest. Since we are entering a weak El Nino year, the potential for a west to east jet is a stronger possibility. Either way, that far out in time, it is way too uncertain to answer your question. Recent computer models are suggesting a more chaotic pattern for the end of the year with each model run showing something different, so stay tuned.

  2. I’d love an quick and dirty explanation to why this persistent overcast weather in the Bay Area – it beats heat this early in the year, but it’s getting old.

    • The reason is fairly simple…we have had a stagnant trough along the coast which means cooler air aloft that also creates a strong onshore flow off the ocean which is cool. This is often the weather near the coast in May and June but the flow has reached very far inland so all of us feel that very cool weather that people who live in San Francisco experience every summer. Even snow showers have been experienced at the higher elevations as a result of the low pressure trough.


  3. Happy New Year, Richard,
    And YES, I have been one of your fans, in weather.

    • Thanks Ann,

      Why are you interested in the weather and my blog specifically?


      • Well, anything will give me a clue as to the possibilities in terms of rain predictions which it’s something so crucial to our environment as well as to Northern California small farmers.

        But it’s so delighted to know that RAINS will be upon us, finally.


  4. Precipitation amounts for next week should be between 2 to 5 inches in coastal and valley locations by the end of next week with higher amounts in the mountains and upslope hills around the Bay Area. By the end of the week, all locations should be above normal for the year.

  5. WooHoo~ Finally, real rains are in the forecast.

  6. I remember the simmering cloud banks that roll over the Skyline to sink into South San Francisco. Thick with moisture. As the train rolled out of the city, I would look up out the window and imagine those big trees up there enjoying that wonderful wet shower of fog. The coastal mountains in most cases don’t have enough elevation to create orographic cloud formation capable of creating rain in the absence of some low pressure trough. There are exceptions with good height; Diablo, Hamilton, and Tamilpias? And these peaks can create enough cloud lifting for rainfall. The marine layer that is sucked into the California Valley through Martinez Straight and creates the famous San Francisco fogs is rich with water but unfortunately very thin. When this wet air encounters the cooler air of the mountain slope, cumulus clouds can develop but are stunted because the thin layer limits moisture. If microwave heating was employed to inhibit cloud formation on the mountain flanks, that water vapor then becomes added to the mountain peak rain shower. These rainfall amounts on the mountain’s top would be small- in the order .01-.05. But the marine layer can sometimes penetrate the Bay Area for many days of the year and the annual accumulation could be significant and would be added to stream flow.

    • Tom your comments about microwave heating is very interesting for research, but I am uncertain about the methodology.

  7. Hi Richard-
    What are your early prospects for this upcoming Ca rainy/snow season for 2016-17? We are having a lot of troughiness this summer, more than I have seen compared to the last several. The SSTs are much cooler finally and we are heading into another solar sunspot min, plus a possible neutral-a weak La Niña.

    • We can only go by history of La Nina events, and they are generally lesser rainfall for Southern California and higher for the Pacific Northwest which leaves us in the middle area where we could experience either so we should probably have average rainfall for the year with colder type storms from the Gulf of Alaska.

  8. Thanks Richard for letting me post here. You’re right. Microwave heating is an area for research. Not many have any interest. Especially scientists with money to spend. The country will spend billions on research to find if Mars has a viable water source but not much to find water for California. The Governor’s big ditch to the Southland will only dig the water woes a deeper hole. A brick in the toilet and watering on odd Tuesdays is not going to work.
    Some of the brightest minds reside in California. Let’s hope they wake up from the big sleep and help the water situation.

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