San Diego Weather - Rainfall Data


Environment - San Diego Rainfall Data
John S. Stokes III
john.stokes cox.net

San Diego Rain History

As a San Diego resident I've found it hard to find a convenient place to find annual rainfall data for San Diego in a useful format. Most records are kept by calendar year, but San Diego's weather is highly seasonal with most of the rain falling in the November-March time period. I have developed a file of monthly San Diego rainfall data which presents the data by both calendar year AND by season (running from July to June).

For commentary on recent rain events or ongoing rain activity see Weather Notes.

The Data File

The file is comma delimited, in the format of:

Year, Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec, YearTotal, NextJan, NextFeb, NextMar, NextApr, NextMay, NextJun, SeasonTotal

DOWNLOAD: File is here (sandiegorain.txt). The data will come up as a separate page. It is easy to bring the data into a spreadsheet. Save the text page. Then open a spreadsheet program and import the data from the saved text file. I try to keep the file "reasonably current". Scroll down for notes about recent rain activity and file updating.

The data was derived from NWS records going back to 1850, the link I use to have here no longer works. Some of the totals in the early years may result from incomplete data. Also the rain gage wasn't always at the same exact location, there's a story about this somewhere on the web. I recall it being in something like nine different locations since 1850. The current official NWS records go back to 1875 perhaps for this reason.

If you are looking for official NWS statistics for recent days and months, go to NWS San Diego Forecast Office (climate data).

San Diego Rainfall by Calendar Year in Inches
1850 through 2016
2016 shown in red

The record calendar year was 1884 with 27.59 inches.


San Diego Rainfall by Season in inches (July 1 through June 30)
1850-1851 through 2016-2017
2016-2017 season shown in red
2016-2017


Analysis

Is there major climate change going on here in San Diego as far as rain is concerned?

The long term pattern suggests there is not. According to the following chart I prepared from the data file, grouping average rainfall by decade, rainfall has been remarkably steady.

However: Even if rainfall remains fairly constant on a per decade basis, there are three factors which are contributing to increased water shortages:
1) Increased demand
2) As my San Diego Temperature page does show a clear increase in temperature over the long term, this means that the rate evaporation is increasing, which in turn increases the demand for irrigation (note: more research here is needed)
3) Warmer temperatures causes more participation to fall as rain instead of snow over the mountains, and with a reduced snow pack there are reduced snow melts available to feed some reservoirs during the dry season.

SD_rain_by_decade
San Diego average annual rainfall by decade in inches.


Current California Reservoir levels updated at CA Department of Water Resources California Data Exchange Center

U.S. Drought Monitor at http://droughtmonitor.unl.edu/


John's Recent San Diego Rain File Updates and Rain notes
See See Weather Notes for more discussion
Rain totals are for San Diego International Airport (Also known as Lindbergh Field)

June 30, 2017 10:51 AM - Rain file updated, .02" for June thanks to a deep drizzly marine layer on June 11, the same amount for the month I recorded. The seasonal chart for 2016-2017h as been updated, the season came in at 12.97", almost 3 inches above normal and the third year of increase in a row.

June 9, 2017 10:36 PM - Rain file updated. .92" for May, nicely above normal and much needed after a couple dry months. Great shape for the summer. Note: I was away in the U.K., sorry for the late update!

May 1, 2017 2:20 PM - Rain file updated. Just .01" for April at the airport. Nothing in my gauge. So after three great months of rain, we've had almost nothing for two months. Makes for an "ideal" allergy season, I'm sure feeling it!

Reinhard Flick a coastal oceanographer at Scripps Oceanography kindly shared a cool graph he derived from the rain file data using October through September as the yearly interval. The graph brings out long term wetter normal and dryer than normal spells in visual from.

He wrote: "The red bars are the average annual (oct-sep) averages, and the black line is the cumulative residual. This is calculated by first subtracting the long-term average (now 9.88 in from 1850 to 2016 [...]) from each annual total to first get the residual, which of course can be positive or negative depending if rainfall was higher or lower than average that year. Second, the residuals are accumulated, that is the second year is the sum of the first two, the third the sum of the first three and so on."

April 1, 2017 10:48 AM - Rain file updated. Just .08" for March, about 5% of normal. The drought code for San Diego did drop in March to just "abnormally dry" the lowest of the codes. The top inch to inch and a half of the soil is now hard and dry, while deeper down there is plenty of moisture, a reversal of recent years. Still hoping for one more good rain before the dry season intensifies, but nothing is in the forecast.

March 1, 2017 7:48 AM - Rain file updated. The historic rain of February 27 with 2.34" at the airport brought the total for February to 3.71". The last three months have seen 4.22", 3.01" and 3.71" for a total of 10.94" more than a year's worth! During this time the drought code for San Diego has dropped two notches from Exceptional to Moderate, and I hope at least another notch reduction tomorrow.

February 2, 2017 10:58 AM - Rain file updated. The wonderful river of water went dry on January 24, with 3.01" for the month at that time. Been bone dry since, 3.01" was the final total, well above the average of 1.89".

January 18, 2017 3:43 PM - Rain file updated. The correct total for 2016 was 10.23" not 10.44". Thank you Jay Hansen for alerting about the error. The graphic for 2016 will be updated later today.

January 1, 2017 5:29 PM - Rain file updated. December 4.22", more than twice the normal amount! Most of this in the second half of the month. Should be very helpful for the drought as the year came in at 10.44", the second year in a row at or slightly above normal. First year since 2010 San Diego broke 10". The U.S. Drought Monitor still has San Diego as being in "Extreme" drought. Perhaps we can finally back off to being "just" Severe? Or maybe even "just" Moderate?

November 29, 2016 4:13 PM - Rain file updated. November .61", about 1/3" below normal. Some parts of the county had rain well above normal. I can confidently say there will be no rain tomorrow, this month is done.

November 2, 2016 11:32 AM - Rain file updated. October just .07" well below normal, with temperature well above normal. No rain in sight for the first week or so of November.

October 8, 2016 6:50 PM - Rain file updated. August was zero, September .32" thanks to the remnants of a tropical disturbance.

August 1, 2016 1:36 PM - Rain text file updated, July a trace, making two trace months in a row. About 1 out of 3 years will see a June-July with 0" of rain, so this is not unusual. However, my yard sure needs rain!

July 5, 2016 9:10 AM - Rain text file updated, June a trace, pretty typical for this time of the year. The 2015-2016 season came in at 11.03", about an inch above normal and the highest in five years.

June 1, 2016 7:37 PM - Rain text file updated, May .44" inches of rain, .32" inch above normal.

May 2, 2016 11:35 AM - Rain text file updated, April .55" inches of rain, .23" inch below normal.

April 1, 2016 1:45 PM - Rain text file updated, March .76" inches of rain, about an inch below normal.

March 1, 2016 10:35 AM - Rain text file updated, February just 0.05" inches of rain.

February 1, 2016 12:53 PM - Rain text file updated, January 3.21" well above normal! Meanwhile northern CA has continued to received substantial rains and there has been very significant increases in reservoir levels in the northern part of the state this past month.

December 31, 2015 8:47 PM - File updated, December 0.88"', about half of normal. The year came in at 9.89" almost the exactly the same as the normal amount of 9.85". There has been a slight increase in the reservoir levels in northern CA this past month, but continue well below normal throughout the state and much lower than they were at the start of the year.

December 1, 2015 4:30 PM - File updated, November 1.54", about 50% above normal. YTD is 9.01" already the wettest year in four years and about 3/4" above normal YTD. The reservoir levels throughout the state remain well below normal.

November 2, 2015 6:44 PM - File updated, October .43", just about normal. The year at 7.47" (corrected December 1 from 7.44") is still running about 1/4" above normal.

October 1, 2015 12:21 PM - File updated, September 1.24", obviously well above the the normal of 0.05". I have the first nine months at 7.04" about 1/4" ABOVE normal for the year! I have the last five months at 5.39" an all time record for San Diego in the normally dry period, trouncing the previous record of 3.95" set in 1977 (September of that year had no measurable rain).

September 1, 2015 10:07 PM - File updated, August 0.01", pretty usual for a typically dry August. Inland monsoonal rains I think were a bit below normal.

August 3, 2015 3:31 PM - File updated, July 1.71", historical by all measures!

July 19, 2015 7:07 PM - We've had extraordinary rains in the last couple days.

July 2, 2015 12:10 PM - File updated, June .04". The 2014-2015 season came in at 9.01", about an inch below normal, but the highest amount in four years.

May 31, 2015 8:50 PM - File updated, May 2.39", smashing the normal figure of 0.25". San Diego had the second wettest May on record, going back to 1852! The July 2014 - June 2015 seasonal total is now at 8.99", the wettest in four years and only an inch below normal

May 5, 2015 12:38 PM - File updated, April .02", obviously well below the normal of .7". Since 1852 only three years have had drier first four months than this year's 1.65". 2002 saw 1.58", 1984 saw 1.21" and 1972 an ultra dry 0.19". The average is 6.09".

March 31, 2015 8:07 PM - File updated, March .93". All of it fell in the first two days of the month, then nothing. So with the first three months well below normal, unfortunately the drought is going into the fourth year, consequences could be considerable. March also came in as the warmest March in San Diego history, beating last year's record by more than 2 degrees. Evidence from many sources indicate we are in a world wide warming trend.

March 2, 2015 7:30 PM - Yesterday came in at .68", shortchanged! Today has brought in .23" so far. Again inland and northern areas in San Diego county received more: there, the vegetation must be quite happy with all this rain!


Big cumulus over San Diego - Sunday February 8, 2009