Golden Gate Weather Services

In the past week there has been extensive media coverage and headlines about "the worst California drought in 1200 years". This was based on a paper to be published in Geophysical Research Letters by the AGU. However a thorough reading of that paper,"How unusual is the 2012-2014 California drought?", indicates that this "worst" declaration should have at least a few asterisks. The article is not inaccurate but it takes only a limited view at looking at the current California drought.

- The study defines drought using the Palmer Drought Severity Index (PDSI). This is an agricultural index, based on soil-moisture as a function of both temperatue and precipitation. While, agriculture is incredibly important in California, it is not necessarily the best metric for the state's overall water deficit and its impacts.

- The paper also does not look at all of California. Instead it only examines the PDSI for central and southern California (i.e. NCDC California Climate Divisions 4, 5, 6, 7). This methodolgy gives a skewed prespective since much of the water used throughout the entire state originates in northern California (i.e., Climate Divisions 1,2,3) and the 3-year deficit has been less there than in the sampled southern two-thirds of the state. [For additional context see the just released NOAA California Drought Assessment.]

The bottom line is that the paper really only speaks to agricultural drought in central and southern California while both the Ranked 3-year Precipitation and PDSI show that currently the drought in northern California is only on the order of the 4th or 5th driest in the past 120 years; certainly not the driest in the past 1200 years statewide.

Jan Null, CCM
Golden Gate Weather Services

Links referenced above:
http://www.whoi.edu/page.do?pid=50242&tid=3622&cid=207049 
http://www.drought.gov/drought/content/products-current-drought-and-monitoring-drought-indicators/palmer-drought-severity-index 

Compilation of 5-day rainfall statewide totals and current percent of normal.

Jan Null, CCM
Golden Gate Weather Services

Great soaking rain across much of California and we will see many rainfall season-to-date percent of normal rainfall jump significantly.  Some to above normal. (see http://www.cnrfc.noaa.gov/awipsProducts/RNOWRKCLI.php  which is reissued daily at 6 PM).  This is all good and every inch of rain helps ease the drought.

But, looking at the broader picture of the deficits from the last 3 seasons (2011-12, 2012-13, 2013-14) shows what a long uphill battle it will be.  For example, the 3-season deficit for San Francisco at the beginning of the rainfall season was 26.07 inches. If you add that to the 23.65 inches needed for this season to ultimately reach normal we would need 49.73 inches to be at "normal".  The all-time rainiest season in SF history was 1861-62 when there was 49.27".  Or for every 1 inch of rain in San Francisco we will only erase about 3% of this long term deficit!

Below is a table of the rainfall to date (through 6 pm last night) for the combined last 3 seasons plus this season-to-date, thge deficit and the percent of normal.

Jan Null, CCM
Golden Gate Weather Services

Through 8 am this morning downtown San Francisco had received 1.13 inches of rain.  Below are the 25 rainiest days (midnight to midnight) in downtown SF since July 1, 2009.  The current total would make it the only the wettest day since last February, BUT with rain continuing to fall today's total should climb rapidly up the list.

Jan Null, CCM
Golden Gate Weather Services

Despite the recent rain, California ended up with below normal rainfall in November 2014. Precipitation ranged from 82% of normal at Redding to 48% at Sacramento in northern California, 93% at San Jose to 37% in Fresno in central California and from 46% in Los Angeles to 37% in San Diego.

In terms of the droughtit is important to note, that even reaching "normal to date" rainfall for this season does not address the carry-over deficits from the past two seasons.

Temperatures were universally above normal, ranging from 1.8 above normal at Redding to 5.3 above normal at San Diego.

See http://ggweather.com/calif/nov2014.htm 

 Jan Null, CCM
Golden Gate Weather Services

Given the headlines and breathless commentators in the Spring and early Summer of 2014 there seemed to have been wide expectations of a strong El Niño beginning about now.  But was a strong El Nino really ever forecast for this winter?

A look at the monthly IRI mid-month forecasts beginning in February would argue, with the exception of a blip in April into the low-moderate category, that the 25 models represented in the IRI "plume" have consistently been portraying a weak event.  [That blip and some of the April hypebole may have been the result of the extensive sub-surface pool of anomalously warm water being transported eastward by a large Kelvin wave at the time.] 

The values portrayed in the graph below are the averages for the forecast members from the dynamic and statistical model categories and then the overall average.  But even looking at individual members, there was no month with mone than one member into the strong category, and most had none.

Jan Null, CCM
Golden Gate Weather Services
http://ggweather.com

 If you have trouble viewing the image below, it can also be found at:  http://ggweather.com/enso/fcsts.jpg 

With the  possibility of some scattered showers lingering into gametime (5 pm pdt) of the 4th game of the World Series on Saturday, here are some links looking back to a much more dramatic event.  In 1962, the 6th game of the World Series between the Giants and Yankees was washed out by the infamous "Columbus Day Storm".

Historic Newsreel Footage of 1962 Storm
http://ggweather.com/1962storm.MP4 

Summary of 1962 Storm from Mark McLaughlin
http://thestormking.com/tahoe_nuggets/Nugget_151/nugget_151.html 

Summary of Columbus Day Storm Review
http://oregonstate.edu/ua/ncs/archives/2012/oct/fifty-years-later-legacy-columbus-day-storm-still-stands 

Bay Area Storm Index - 2nd Strongest Bay Area Storm
http://ggweather.com/basi.htm

Jan Null, CCM