Golden Gate Weather Services

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

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

The latest IRI/CPC "plume" forecast is still indicating a minimal La Niña event at best. To that end I have put together a climatology of California precipitation for cool neutral (ONI -0.2 to -0.4) and Weak La Niña (ONI -0.5 to -0.7) events. See http://ggweather.com/enso/ca_lanada.htm and summarized in the graphic below.

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

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

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

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

The following pages have been updated.  As always, let me know of any changes, corrections or additions.

2016 Thunderstorm & Tornado Resources

2016 Hurricane Resources 

2016 Fire Weather Forecasts and Links 

El Niño/La Niña Resources

Heatstroke Deaths of Children in Vehicles

All of the above, and much more, can be accessed from the Meteorologist's Links page. 

Blog: Most of these emails and other material get archived in the Golden Gate Weather Services Blog.

Twitter:  Short updates and links send more frequently via @ggweather 

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

In looking at past La Niña events, the one thing that is clear is that almost anything can happen when it comes to winter precipitation across the Golden State.  The images below show the "average" precipitation for the 20 previous La Niña events going back to 1950 but more importantly the wide range from the driest to the wettest California winters (Nov. - Mar.) for each of the categories (Weak, Moderate and Strong).  [Additional images and data can be found at US Winter Precipitation & Temperature Climatology: La Niña and California Climatology of La Niña Events and Precipitation]






 


The bottom line is that it is too early to tell the strength of forecast La Niña and more importantly even within a specific strength category the range of solutions leaves no clear signal based on the past climatology.

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

The 8-Station northern Sierra Nevada (see map) precipitation Index (8SI) has reached a milestone. Rain and snow over the weekend pushed its total since July 1st to 55.71". This is over an inch above normal for the entire seasonal (July 1 to Jun 30) total of 54.52”.  Normal 8SI for the remainder of April plus May and June is approximately an additional 4 inches.



The 5-station San Joaquin Basin Index is now at 39.71" compared to their seasonal total of 42.57" and the 6-station Tulare Basin Index is at 26.00" compared to their full season normal of 30.50".



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


Note: There will be a minor discrepancies between these figures and those published by Calif. DWR which uses the Oct. 1 Water Year instead of the historical rainfall season of July 1 to June 30.  And inexplicably DWR also does not use the standard 30-year climatological normal (1981-2010) but rather non-standard average period of 1922-1998 for the 8-Station Index (50.00") and 1961-2010 for the 5 and 6-Station Indices.