Fallbrook, CA High and Low Temperatures, and Percentage of Possible Sunshine For Last Year

The plot above shows, from top to bottom:

• The high temperature (blue crosses) recorded under my porte cochere, which is probably biased high by 2-4°.
• The median high temperature (upper dark-colored continuous line) since 1994. Specifically, it is a 29-day running average of the high temperature, 14 days before a given date and 14 days after a given date, using data from all recorded years.
• The low temperature (green crosses) recorded several feet away from my house, which is probably biased high by 2°.
• The median low temperature (middle black continuous line) since 1994. Again, it is a 29-day running average.
• The amount of possible sunshine (red crosses), as estimated by me. The percentage has been divided by 10 to fit on that plot, so a 10 means 100% of possible sunshine.
• The median amount of possible sunshine (bottom dark blue continuous line) since 1994. Again, it is a 29-day running average.

Caveats

There are several caveats to be noted about the data, which are explored further in Analysis of Biases in T. Chester's Fallbrook Temperatures:

1. My high temperatures are about 4° higher than the official Fallbrook temperature for official temperatures less than 90° and about 2° higher than the official Fallbrook temperature for official temperatures over 90°. My "high temperature thermometer" is located underneath my porte cochere, and the concrete underneath it traps solar heat and may keep the temperature there a bit warmer. However, there is no noticeable effect versus the amount of sunshine, which leads me to question whether there is any significant bias due to this cause. Thus this bias may simply be due to a bias in my thermometer.

2. My low temperatures are about 2° higher than the official Fallbrook temperature for official temperatures over 40°. Below that temperature, my low temperatures can range to over 10° warmer than the official temperature, which is probably caused by my location in the Winterwarm area compared to the location of the official Fallbrook temperature near downtown. My "low temperature thermometer" is located in a natural area fairly close to my house and close to a large Canary Island Pine, which may produce a slight high bias for the low temperatures. I don't believe the magnitude of this effect is large, but I'll place another high-low thermometer in a more open area sometime to check it.

3. I am absent from Fallbrook about 9 days per month, usually for 3 days per week for 3 weeks, and hence the high and low recorded temperature for that period of 3 days will be recorded accurately, but two days of "lower highs" and "higher lows" were not recorded. This biases the mean high and low temperature record slightly high and low, respectively. My analysis shows that this causes a bias of much under 1°, probably due to the high correlation of temperatures from day to day.

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Copyright © 1997 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/current_temps.html
Comments and feedback: Tom Chester
Last update: 2 January 1998.
The plot may have been updated later - see the date at the top of the plot.