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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December Summary; Seasonal Precipitation Snapshot; La Niña; AMS in Seattle

December Summary; Seasonal Precipitation Snapshot; La Niña; AMS in Seattle


December rainfall in California was pretty much upside down compared to recent months, with near normal rainfall in the north and above normal in the south. San Diego totaled 4.22 inches (276% of their December normal) while Los Angeles had 4.55" (195%). The northern third of the state was close to normal with just rain-shadowed San Jose lagging behind at 58%. [http://ggweather.com/calif/dec2016.htm]

Despite a couple colder than normal periods, only Eureka and Sacramento had monthly average minima of more than 2 degrees below normal. At the same time, LA and San Diego average monthly minima were more than 2 degrees above normal.
[http://ggweather.com/calif/dec2016.htm]

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A snapshot of the first six months of the rainfall season (July 1 to June 30) shows totals well above normal at most locations, with the biggest gains against normal in the south, where Los Angeles and San Diego pushed to 138% and 158% of normal respectively. http://ggweather.com/water/

See also http://ggweather.com/seasonal_rain.htm which is updated daily, in the early evening.

With the potential for extensive rains in the next 10 days, I have updated the Rainfall, River and QPF Page .

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La Niña's cooling in the tropical eastern Pacific may have bottomed and the weekly Sea Surface Temperature Anomalies (SSTAs) for the past month have averaged just -0.4.

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Finally, I am headed for the 97th AMS Annual Meeting in Seattle later this month to present a paper of Heatstroke Deaths of Children in Vehicles. If you are also going to be in attendance, drop me an email and we can try to connect.
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Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather

 

 


 

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California Rainfall at the Beginning of Winter

Today, December 1st, begins meteorological winter; the three coldest months in the Northern Hemisphere. And for most locations in California it corresponds to the three wettest months.

After a much wetter than normal October (http://ggweather.com/calif/oct2016.htm) for Northern and Central California the November totals (http://ggweather.com/calif/nov2016.htm) were more of mixed bag, but still concentrated in the north.  Consequently the totals for the first five months of the rainfall season (July 1 to November 30) have the northern half of California above normal (http://ggweather.com/seasonal_rain.htm).  

Given the rainfall bias in the north the Drought Monitor is showing relief there but still 43% of Calif in Extreme or Exceptional Drought.



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

 

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A Different Flavor of La Niña?

Unlike those picture puzzles where you are asked to find subtle differences between images, a look at the NASA sea surface height anomaly images for the past three weak La Niñas (1995, 2000, 2011) plus this year (2016), leaves little doubt that what's going on in the eastern Pacific is not subtle at all.  The most striking difference is the anomalous warm water from the equator north to about 25 degrees north. This area warmed in conjunction with last year's very strong El Niño and may have contributed to the atypical winter along the west Coast of North America (see "Differences Between 2015-16 El Niño and Previous Strong and Very Strong Events").




With the current Oceanic Niño Index (ONI) already at weak La Niña levels, tomorrow's updated CPC ENSO Advisory is likely to up the odds for a La Niña this fall and winter. But can we still use the standard "La Niña playbook" of looking at past events as an indicator of broad-scale for West Coast precipitation patterns for this winter?  Last winter the conventional wisdom for the impacts of a very strong El Niño did not work out per previous events. Consequently, it looks like extreme caution should be exercised in looking for patterns based upon the climatological past related to the prospects for current La Niña. 

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


Miscellaneous La Niña Resources (use with caution):
La Niña Winter Precipitation & Temperature Climatology  
California Climatology of La Niña Events and Precipitation  
California Precipitation Climatology for Cool Neutral and Weak La Niña Events  

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October Rain Only "A Good Start"

 

October 2016 was a wet month in the northern two-thirds of the state but the south continued to be pretty dry.  (See: summary)  Monthly rainfall ranged from over 450% of normal at Eureka and Sacramento, while Los Angeles and San Diego only had 79% and 12% of their normal October rain respectively. But these numbers need to be put into context as October normals are relatively small and there is not a statistically significant relationship between October rainfall and how the rest of the rainfall season (July 1 to June 30) ultimately ends up.

San Francisco’s 2.43 inches for the month is 217% of normal (1.12”), but this ranks as only the 23rd wettest October going back to 1849. The wettest was 7.28” in 1889 (below).  One factor affecting the perception of it being a very rainy month were the number of days of rain. This year there were 12 days of measurable rain in San Francisco, the second highest number on record.  The most was 13 days in that very wet October of 1889.

Looking at the 25 wettest Octobers (below) there is not a correlation to how the seasons ultimately ended up; other than being a “good start” by saturating the soil to enhance future runoff and significantly reducing the fire danger. Eleven of those 25 wettest Octobers actually ended up below the 168-year average of 21.57”. This including the 2nd driest season on record; 1975-1976 when the season ended with a paltry 8.05”.



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


 
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When is the Hottest Day of the Year?

 

As we head toward the Autumnal Equinox (Sept. 22 @ 7:21 am pdt) most cities around California and the nation are well past their normal hottest day of the year, which typically occurs about a month after the Summer Solstice. But a few locations, especially along the West Coast, wait until August and even September to peak. And San Francisco is certainly the latest of any major United States city by not reaching its normal highest maximum temperature of 70.4 until September 24th.

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




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