Fallbrook is in Sunset Magazine's Zone 23, the "Thermal Belts of Southern California's Coastal Climate". Their description is:
"One of the most favored climates in North America for the growing of subtropical plants. This zone could be called the avocado belt, for it has always been Southern California's best strip for growing that crop. Frosts don't amount to much in these air-drained thermal belts, and most of the time (approximately 85%) they are under the influence of Pacific Ocean weather; only 15% of the time is the determining influence from the interior."
It's no accident that so many nurseries and tropical plant growers are found here!
For a summary of average maximum and minimum temperatures, rainfall, heating and cooling degree-days for nearby areas, see Worldclimate's Climate Data for 33°N 117°W, as well as the National Weather Service's California Climate Data.
The above temperatures are the median values over the month derived from correcting my temperatures for their biases. Thus the average has been forced to match the official Fallbrook recorded temperatures. A median is the value in the middle of a sorted list, so on average, half of all temperatures during a month will exceed the quoted median, and half will be below that value.
The average peak summer temperature occurs on 28 August, plus or minus a week.
There is a slow rise toward the peak average summer temperatures, both for lows and highs, but a sharp fall toward the winter temperatures.
The lowest average temperatures (lows below 50° and highs below 75°) occur from the middle of November to the middle of April.
There is a huge variability in the high temperatures. A high of 90° can occur on any day of the year. A high of 100° can occur on any day from May through October.
Low temperatures are much less variable, with the highest variability in the winter associated with rainstorms.
Fallbrook is a remarkably sunny place, with median percentages of possible sunshine ranging from 75-95% for all months except January and February, which have median values of 50%. 28% of all days in Fallbrook are completely sunny sans any clouds, and only 5% of all days in Fallbrook are cloudy all day.
July, August and September practically come with a guarantee that the sun will shine most of the day. The highest average percentage of possible sunshine, 85-95% occurs from early July to early September. Those months have no recorded days with sunshine percentages under 40%. June is not far behind in my data set for the last 3 years.
"June Gloom" is not something that can be picked out of the Fallbrook sunshine plots. June is, if anything, a sunnier month than the prior 3 months. Perhaps it is just the disappointed expectation of summer starting in June that caused June to be labeled gloomy.
The lowest percentage, 50%, occurs in January and February.
The average official Fallbrook rainfall, measured from July 1 to June 30, is 17.96". Over 30" of rain has fallen 5 times in the past 100 years. In 1960-61, the rainfall was only 5.54".
Source: VN 7/2/98, 13, by Jim Bramlett.
Worldclimate gives the average rainfall for Fallbrook as 9.1", but this was derived from an average of only 3 complete years from 1948 to 1951, and hence their average number is very poorly determined.
The median peak wind speed is 8-11 mph on every day of the year, as measured at G. Moxon's house on Via Alegre. Wind speeds measured at other locations may differ since wind depends strongly on elevation and shielding by local topography.
Individual days with high winds occur most often in the winter. Days with peak wind speeds of 15 mph or greater essentially only occur from November through April, although they do occur more rarely outside that interval.
The median peak humidity is 90-95% every day of the year except in November and December, when it goes as low as 60%. Such a high peak humidity is practically the definition of an ocean-dominated climate.
The median low humidity is ~40% every day of the year except in November and December, when it goes as low as 20%.
Low daily humidities (peak daily humidities below 50%) essentially only occur in October through March, but are infrequent enough to be almost entirely absent from the median humidity plots except at their peak occurrence rate in the last 1.5 months of the year.
Low humidities usually coincide with a "Santa Ana" condition, when the prevailing wind in Fallbrook shifts from westerly to another direction. Westerly winds of course come from the ocean and bring the usual high peak humidity condition of Fallbrook.
Wintertime has the most extreme range of humidities, ranging from very low Santa Ana values to very high on days with rain.
The variability of the minimum daily humidity is quite small from May through September, reflecting the evenness of our climate during those months.
Copyright © 1997-1999 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Last update: 2 July 1999.