Record Dry Year Continues in California
California is enduring its driest calendar year on record as October draws to a close with no significant precipitation on the horizon for the rest of the month. San Francisco (airport location) has picked up just 2.12” of rainfall since January 1st, almost as dry as Death Valley where 1.71” has been measured so far this year. The last significant rainstorm to hit San Francisco was on December 25-26, 2012 when 1.10" was measured at the airport.NOAA’s precipitation ranking by state (top) and by division (bottom) for January-September 2013. Since there has been virtually no rainfall in California so far this October, the California situation is not likely to look much different when the January-October versions are released in mid-November.
The downtown San Francisco site (where precipitation records began in 1850) has picked up only 3.94” of precipitation since January 1st, by far its driest such period on record, the previous such being 5.72” in 1976. Normal precipitation for the January 1-October 31 period is 15.93”, so they are running at just 25% of normal. The driest full calendar year on record was 9.00” in 1917.
Although the San Francisco Bay area has been the most anomalously dry region in California (so far this year), all of the state has been exceptionally dry. Assuming no additional rainfall occurs over the next week (as currently forecast) here is a table of where some key sites sit precipitation-wise:January through October precipitation totals so far this year compared to normal for the period. Death Valley received .75" in July, tying its wettest July on record with 1954 (records began in 1911). This is in sync with what was a very wet summer monsoon for the desert Southwest region.Why not to worry (yet)
With the rainy season approaching heavy precipitation would be normal for November and December so it is much too early to speculate if 2013 will go down as the driest calendar year on record for the state or any individual locations. Also, it should be emphasized that California does not actually consider calendar year precipitation as that significant. It is seasonal (or water year) precipitation, which runs from July 1-June 30, that matters. For the past water season of 2012-2013 conditions were not so dire since heavy, above normal precipitation occurred in November and December of 2012.Map a tables of California precipitation for the water year of 2012-2013 (July 1, 2012-June 30, 2013) and also or 2011-2012. Heavy rains and snow in November and December 2012 prevented the season from approaching near-record dry levels and the state’s reservoirs are filled to near normal capacity for this time of the year.
Map and tables from Jan Null, Golden Gate Weather Services, San Francisco.KUDOS:
Jan Null of Golden Gate Weather Services for much of the above information.
Christopher C. Burt