Percentage of Possible Sunshine For Fallbrook, CA

Plots Of Percentage of Possible Sunshine, All Measurements And Median Averages
Table Of Median Monthly Temperatures And Percentage Of Possible Sunshine
Histograms Of The Distribution Of All Measured Sunshine Percentages For All Years and Each Month
Summary of Fallbrook's Sunshine Variation

Plots Of Percentage of Possible Sunshine, All Measurements And Median Averages

Each day that I am in Fallbrook all day, I record my estimate of the percentage of possible sunshine, defined as the total number of hours of actual sunshine divided by the number of daylight hours. I estimate it only to the nearest 10%, and could often be in error by 10% since I make my estimate at the end of each day from memory.

Because I'm away from Fallbrook about 10 days a month, my data sample two-thirds of all days, which is enough to show the trends well.

The following plots use the sunshine data I have been collecting since 25 September 1994 (more info).

All individual sunshine measurements are shown in the plots on the left. To show all individual points in that plot, I have offset each year by subtracting (year - 1994) from all non-zero measurements, and adding (year - 1994) to days with 0 sunshine.

A 31-day running median average is shown in the plots on the right. (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.)

Most of the bumps and wiggles on the median average plots probably result from averaging only 3 years of data. All plots span 1.5 years to easily see the seasonal variation.


(Click on graph for bigger and better image.)
Color Code

(Click on graph for bigger and better image.)

The color code for individual years is as follows:

YearColor
1994Blue
1995Green
1996Red
1997Gray

Table Of Median Monthly Temperatures And Percentage Of Possible Sunshine

The following table gives the median monthly values of the temperatures, which are the values given in the median plots above for the middle of each month. In addition, the median value of the percentage of possible sunshine is given.

Median Monthly Values
MonthHighLowSunshine (%)
Jan64 46 50
Feb69 46 50
Mar71 48 80
Apr74 49 80
May78 55 75
Jun80 57 80
Jul85 59 95
Aug89 61 90
Sep89 61 80
Oct80 54 75
Nov73 48 85
Dec69 44 85

Histograms Of The Distribution Of All Measured Sunshine Percentages For All Years and Each Month

The plot below gives the distribution of all measured sunshine percentages. The histograms are in units of fraction of all measurements. Hence from the plot you can deduce that:

I suspect that the peak at 50% isn't real, but is just an artifact of my non-rigorous method of estimation. You can mentally smooth those values over the neighboring bins of 40 and 60% to get a probably-more accurate histogram.


(Click on graph for bigger and better image.)

The plots below give similar histograms for each month. Each plot combines four months, with each month color-coded. The first color on the left corresponds to the first month listed in the title. As an example of reading one of the plots, here are some conclusions from the plot for May and June. May is the 3rd month from the left of the "May, April, May, June" plot below, graphed in red, and June is the 4th month from the left, graphed in yellow:

Perhaps it ought to be called the "March-April-May-June Gloom", since those months are pretty indistinguishable for sunshine percentages....

Each plot combines four months, with each month color-coded. The first color on the left corresponds to the first month listed in the title.

MonthSunshine Percentages
November, December, January, Februaryplot
March, April, May, Juneplot
July, August, September, Octoberplot

Summary of Fallbrook's Sunshine Variation

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.


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Copyright © 1998 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:
http://sd.znet.com/~schester/fallbrook/weather/tjc/sunshine.html
Comments and feedback: Tom Chester
Last update: 2 January 1998.