No Rain in October Climatology

With the progs continuing to show a dry pattern through the end of the month there have been a number of comments and inquiries about how common it is to get zero or very little rain in October.
Here are some factoids in regards to the past 164 years of San Francisco October rainfall dating back to 1849.

- There have been 13 previous years (8% of the time) when there have been no measurable (i.e.,≥ 0.01") in October.
- There have been a total of 32 years (19%) with a tenth of an inch or less for the month.
- Ironically both the wettest (49.27" in 1861-62) and driest (7.42" in 1850-51) rainfall seasons (i.e., July 1 - June 30)  in SF history have occurred in years when there was no rain in October.
- The average rainfall for the season after an October with less than a tenth of an inch of rain is 21.04". 

- Normal (1981-2010) San Francisco rainfall in October in 1.12 inches and there are normally  4 days with measurable rainfall. 


Jan Null, CCM
Golden Gate Weather Services



Sept. California Climate

Climatologically California temperatures were all over the map for September 2013 with huge variations.  Average monthly maxima ranged from 3.5 degrees above normal at Eureka to -3.8 below at Redding, only 100 miles apart.  In between san Francisco was "normal" with a 0.0 degree anomaly.

Rainfall likewise saw huge anomaly differences with positive anomalies in the north half of the state and below normal in the south.  Eureka had over 5 times their normal rainfall (517%) with a monthly total of 3.05" and San Jose's 0.66' was 367% of normal. 




Equinox; Typhoon; Colorado Floods

The Autumnal Equinox is this Sunday, September 22 at 1:44 pm pdt (2044 UTC).  See

Typhoon Usagi in the western Pacific is currently entering the Luzon Strait between Taiwan and the Philippines and on a direct track toward Hong Kong.  See:

Bob Henson of UCAR has put together an excellent analysis of recent flooding in Colorado titled "Inside the Deluge".  See