A Look Back at the CPC 2016-17 Winter Outlooks


It's time to take a quick look back at the good, the bad and the ugly of the CPC Winter Precipitation and Temperature Outlooks from this past winter. Because of the probabilistic nature of this outlooks this review, like previous reviews, is very subjective. But at least in the West, when their sub-headline for the just finished winter was "Drought expected to persist in California" followed the previous winter's busted above normal El Niño forecast, the efficacy of the product certainly needed scrutiny. See or details CPC Winter 2016-17 Seasonal and Monthly Precipitation and Temperature Outlooks in Review:




Jan Null, CCM
Golden Gate Weather Services
jnull@ggweather.com

  

 

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California 2nd Rainiest Jul-Feb

 

Statewide, the first eight months of the current rainfall season were the 2nd wettest on record in California going back to 1895-96. This season's 28.03" statewide was just short of the 1968-69 record of 28.30". Looking at the individual climate divisions, the Sacramento drainage (Clim Div 2) and the Northeast Interior (Clim Div 3) had their wettest ever, while the San Joaquin drainage (Clim Div 5) had their 3rd wettest. Neither of the Southern California climate divisions (i.e., Clim Div 6 and 7) were in the top 10.    



Jan Null, CCM
Golden Gate Weather Services
jnull@ggweather.com

 

 

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California Rainfall Data Archive


In response to many many requests for how this rainfall season compares to previous wet years I have put together an archive of monthly rainfall for data for about 50 California locations. The data is cobbled together from a variety of NOAA and NWS sources. The data is for each location's entire period of record, but beware some locales have missing data. My plan is to update this at the end of the rainfall season (i.e., June 30). Please let me know of any comments, errate of suggestions. See http://ggweather.com/monthly/ . Enjoy.



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

 

 

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Rainfall Season vs. Water Year

 

Unlike most parts of the United States, California’s Mediterranean climate is defined by its “summer drought” given that there is a natural break between one rainy season and the next.  This was recognized by settlers as far back as the Gold Rush and since that time the most common metric to quantify California (and other western states’) rainfall has been a July 1 to June 30 “rainfall season”. Consequently, thousands of reports, studies and analyses related to California rainfall have been based on the rainfall season, including the following from is some of the earliest chronicling of California weather.
 

Conversely, because there is lag of several months to when streamflows in the state’s rivers are at their lowest, hydrologists have historically (and logically for their purposes) used a Water Year (WY) metric from October 1 to September.

However, about two years ago, for reasons that have never been adequately explained, the National Weather Service (NWS) Western Region decided, without the opportunity for comment from the rest of the meteorological community or the public, to start calculating their rainfall products (i.e., Climate Station Precipitation Summary , and others) in regards to the hydrologist’s Water Year. (The remainder of the NWS, by the way uses the calendar year for summarizing rain data, as they do not have a natural summer break in rainfall.)  While this might be nice for consistency with the hydrologic community it puts them out of step with the vast wealth of historic data and others in the rest of the meteorological community.  This was even highlighted by a recent article in the LA Times, “Ideologies clash as weather service realigns rainfall calendar

The numerical differences between rainfall season and water year are slight (i.e., typically only about 3% of the annual amount) given the small amount of rain that typically falls in the months of July, August and September. And that rain is not lost, it is either counted at the end of one methodology’s season or the beginning of the other’s.

As stated about, the problem comes about when trying to compare data published by the NWS in terms of the hydrologist’s WY, with data from past events which have been characterized by meteorologists’ rainfall season.  [To their credit, NWS San Francisco Bay Area automatically generates a table which has both the rainfall season and water year, and it is my understanding the software used was made available, but unfortunately not adopted, by other NWS offices.]

An effort has been made, outside the NWS, to make available to the public and meteorological community data showing rainfall in terms of the July 1 to June 30 rainfall season with products like California Rainfall Season Totals. But this does not address the amount of unnecessary effort expended by everyone, but a very small group, to keep the data consistent and meteorologically logical.
 
Jan Null, CCM
Golden Gate Weather Services
http://ggweather.com
jnull@ggweather.com

 


 

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Not the Wettest January or Season to Date


Yes, January and the Rainfall Season to date (July 1 to January 31) have been wetter than normal, but they are far from "the wettest" or record-setting. Only the 5-station Central Sierra Index had their wettest January on record, but that period of record goes back to only 1913, more than 60 years shorter than most of the other records. Of the individual stations with long periods of record extending back to the mid-19th century, San Francisco's 9.42" was only the 16th rainiest and Redding's 11.45" was their 23rd wettest.

Likewise, the season-to-date number have been impressive, but most have not even been in the top 10 wettest. 


The following are the Top 10 Wettest Januarys.


The following are the Top 10 Wettest July through January.


Jan Null, CCM
Golden Gate Weather Services
jnull@ggweather.com

 

 

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California Precipitation Snapshot; Bay Area Storm Index

The California precipitation picture got a lot prettier over the weekend; especially in Sierra Nevada which saw huge gains. For example the the southern Sierra Nevada (i.e., Tulare Basin) jumped from 103% of normal on January 1 to 165% through yesterday (January 8), while the northern and central Sierra increased to 173% and 172% respectively. See  http://ggweather.com/water/



In the San Francisco Bay Area the Sunday storm ranked as an 8.5 on the Bay Area Storm Index (BASI).  This was based on a 24-hour downtown San Francisco rainfall total of 1.62", a maximum sustained wind at SFO of 44 mph and a peak (below 1500' elevation) wind gust of 75 mph at Spring Valley in San Mateo County above Crystal Springs. This is the highest ranked storm since October 2009 (see archive).  

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather

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