The first question that comes to mind is, how old is your son? because, to a certain extent his interpretation of average temps has to do with when he experienced them—when he grew up. Many people remember weather as being different now from their childhood—and many are correct. But the buzz we hear is that it tends to be warmer …
Averages, or normals, as we explain in the 2018 print Almanac on page 217, are based on 30-year periods. Currently that is 1981 to 2010. The period advances every 10 years. Virtually all meteorological services/orgs in the world subscribe to this calculation. Here is a page where you can look up a few California cities: https://www.currentresults.com/Weather/California/average-annual-city-te...
Here’s one from NOAA with records through the end of last year: https://www.ncdc.noaa.gov/sotc/national/201712
Here’s another page, perhaps more current (you do not say where in NorCal, so not sure if this covers you): https://gacc.nifc.gov/oscc/predictive/outlooks/myfiles/assessment.pdf
Records suggest that the planet has had some of its warmest years in the past 20 years (or less); we seem to see a headline to this effect almost every year! Of course, not every place is warmer, but in terms of averages, California has been in that number.
The Old Farmer’s Almanac Long Range Weather Forecasts show deviations from normal temperatures and precipitation amounts, based on 30-year rolling averages gathered by government meteorological agencies, specifically NOAA and Environment Canada. The averages from 1981 to 2010 are the latest available data; these numbers are updated every 10 years.
Our Long Range Weather Forecasts are based on three scientific disciplines:
- solar science (the study of sunspots and other solar activity)
- climatology (the study of prevailing weather patterns)
- meteorology (the study of the atmosphere)
We predict future weather trends and events by comparing solar patterns and historical weather conditions with current solar activity. Learn more about How We Predict the Weather.
How to Read Long Range Weather Forecasts
If our forecast says that temperatures will be “mild” during a certain period of time, this means that we predict milder-than-average temperatures for those dates. In other words, this does not mean that temperatures will feel mild, but rather that temperatures will not be as cold as average (based on the 1981 to 2010 averages). Likewise, “snowy” means only more snow than the 1981–2010 average.
How Accurate Are the Almanac’s Long Range Weather Forecasts?
The Almanac’s weather predictions are made up to 18 months in advance, but are traditionally 80 percent accurate nevertheless. (Not bad for more than 225 years of predicting, we think!) To get the most from long term forecasts, it’s important to look at patterns and trends and not necessarily day-by-day predictions. Weather tends to evolve in patterns that last 5 to 7 days.
As you get closer to the date of your plans, check out our 7-Day Forecasts.