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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Mixed 2016 California Summer Temperatures

Overall the summer of 2016 was a real mixed bag in regards to California temperatures.  The average maximum temperatures anomalies for meteorological summer (i.e., Jun-Jul-Aug) ranged from below normal near the coast from about San Francisco north to above normal over most of the remainder of the state. (http://ggweather.com/calif/summer2016.htm). It should be noted that in San Jose the average summer temperature was right on "normal" with an anomaly of zero!  
 
The average summer maxima for the past seven years has likewise been mixed, with no year showing the same (i.e., positive or negative)  anomaly for all 8 cities. And only Fresno had the same, in this case positive, for all seven years. (Below)




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

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One of the mildest San Francisco Augusts in 143 years

Temperature records in San Francisco began in 1874 and this August will tie as only the 4th time that there was not a daily maximum temperature all month that did not exceed 70 degrees. In 1942 the highest reading for the month was only 67 degrees, while in 1917 and 1882 the highest was 69. On August 8, 2016 the maximum was just 70 degrees, tying it with 1881.

So far in August 2016 the average maximum temperature has been 64.6, and given forecast maxima of around 64 degrees for the remainder of the month this will change little. The normal August high temperature in San Francisco is 68.1. But even with prolonged coolness, the average for the month will only rank as about the 35th coolest on record.

The major player in the mild weather has been a persistent weak trough of low pressure over the West Coast for most of the month and a likewise persistent marine layer.  It should be noted that the sea surface temperatures along the coast west of San Francisco remained above normal for the entire month.


The story is different farther inland and away from the cool coastal air with August monthly maximums generally above normal.


Finally I would be remiss if I did not point out that Mark Twain NEVER SAID "the coldest winter I ever spent was summer in San Francicsco". (per http://www.marktwainproject.org/).  But if he had, it would likely have been a year like 2016.

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

 

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Confusing 5-minute Weather Observations


Caveat Emptor.

Some NOAA websites are beginning to display ASOS (i.e., airport weather) observations every 5-minutes.  An example is http://www.wrh.noaa.gov/mtr/sfcobs2.php.  While at first blush this seems like an awesome way to see more timely data, it can cause confusion when comparing it to daily maximum and minimum readings.

Example of 5-minute readings:


The 5-minute readings are actually an "instantaneous" 1-minute observation at the particular time noted. The problem arises in that the maxima and minima are a "5-minute average" of five adjacent individual 1-minute readings.  Consequently, that average could be less than one of the 5-minute readings.

For example, at the hottest time of the day you have an instantaneous 5-minute reading of 85 degrees at 14:30.  However, if the readings at 14:27, 14:28, 14:29 and 14:31 were all 84 degrees, then the maximum reading would be 84.2, which would be rounded to 84.

Correction: In rereading the ASOS criteria I think I misinterpreted how’s it’s calculated (i.e., the 5-min values are the average of the previous five 1-min values) and that rounding due to C to F conversions may be more of a factor.  But overall I am right for the wrong reasons and for the real world the confusion remains with seeing different 5-min values than the climatological max/min temps.



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

 

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End of the 2015-16 Rainfall Season


Today is the last day of 2015-16 California rainfall season and it certainly has been an interesting one.  Going into the season with El Niño developing in the Pacific, I don't know anyone who envisioned that Northern California would have seen a significantly greater percent of normal amounts than Southern California; once again highlighting that 2015-16 was the Poster Child for "All El Niños Are Not the Same".

The map and table below an also be found at http://ggweather.com/ca2015rain.htm.





The following map was generated from the Western Region Climate Center


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

 

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Is a "Different" La Niña Brewing?

Are the impacts, from the La Niña that is forecast to develop later this year, going to be "typical" or will they be more of an outlier solution like that of the fading El Niño? (Differences Between 2015-16 El Niño and Previous Strong and Very Strong  Events)  

A comparison of the current NASA Sea Surface Height anomalies and those in May 1998 show some reason to keep an open mind. Note the large positive anomaly north of the equator; which is the same mass that was at least partially responsible for the 2015-16 El Niño being atypical.

And this area is literally outside of the Niño 3.4 box where SST anomalies are measured and used to gauge the presence and strength of ENSO events. Consequently, while the Oceanic Niño Index (ONI) may be showing cooling, this area will need to be watched as well.

In that context, even La Niña - Anything Goes for California Precipitation may not give enough clues for this coming winter. As always, it will be interesting and challenging. Stay tuned.


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




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