A dry start to the SF rainfall season; What does it mean?

 

So far, the 2018-2019 rainfall season has been pretty dry, with only 0.21” having fallen in downtown San Francisco. But it is far from the driest, with 26, out of 169 previous July 1st to October 31st totals having lesser amounts.

Looking at the 47 seasons that ranged from 0.00” to 0.42” for teh first 4 months of the rainfall season:
25 (53%) ended with less than 80% of normal by June 30th,
15 (32%) ended with between 80% and 120% of normal, and
7 (15%) of the seasons finished with more than 120% of normal.

It is interesting to note that both San Francisco’s all-time driest and wettest seasons began dry. The driest was 1850-1851 with a July to October total of 0.33” and a final seasonal total of just 7.42”. Conversely, 1861-1862, after having only 0.02” through October, finished with a fantastic (except for the flooding) record season of 49.27”.

List of the 48 driest beginnings to the SF rainfall season:

 

 

 

End of Season

Rank

Season

Jul-Oct

Total

% Normal

1

1855-1856

0.00

21.66

92%

2

1905-1906

0.00

20.42

86%

3

1929-1930

0.01

16.28

69%

4

1932-1933

0.01

14.93

63%

5

1861-1862

0.02

49.27

208%

6

1915-1916

0.02

27.12

115%

7

1917-1918

0.02

11.48

49%

8

1863-1864

0.03

10.08

43%

9

1870-1871

0.03

14.11

60%

10

1880-1881

0.05

29.86

126%

11

2002-2003

0.05

23.87

101%

12

1995-1996

0.06

24.89

105%

13

1928-1929

0.07

15.21

64%

14

1955-1956

0.07

27.17

115%

15

1952-1953

0.08

21.10

89%

16

1871-1872

0.09

30.78

130%

17

1859-1860

0.10

22.27

94%

18

2003-2004

0.10

20.54

87%

19

1866-1867

0.11

34.92

148%

20

1980-1981

0.11

14.63

62%

21

1868-1869

0.15

21.35

90%

22

1872-1873

0.16

15.66

66%

23

1903-1904

0.17

20.59

87%

24

1949-1950

0.18

16.78

71%

25

1978-1979

0.19

18.70

79%

26

2015-2016

0.20

23.26

98%

27

2018-2019

0.21

??

??

28

1958-1959

0.21

10.46

44%

29

1875-1876

0.24

31.19

132%

30

1867-1868

0.24

38.84

164%

31

1946-1947

0.27

14.89

63%

32

1966-1967

0.27

29.41

124%

33

1911-1912

0.28

14.06

59%

34

1887-1888

0.30

16.74

71%

35

1914-1915

0.31

27.41

116%

36

1961-1962

0.33

17.65

75%

37

1850-1851

0.33

7.42

31%

38

1890-1891

0.33

17.58

74%

39

1948-1949

0.33

18.28

77%

40

1993-1994

0.33

15.22

64%

41

1864-1865

0.35

24.73

105%

42

1971-1972

0.35

11.06

47%

43

1990-1991

0.36

14.08

60%

44

2008-2009

0.36

18.11

77%

45

1893-1894

0.39

18.47

78%

46

1906-1907

0.40

26.17

111%

47

1953-1954

0.41

14.27

60%

48

2017-2018

0.42

17.53

74%

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

Posted

CPC Winter Outlooks and an Updated El Niño Forecast

 

 

With the latest NOAA 2018-2019 Winter Outlook just released, here's how the previous three CPC Winter Precipitation Outlooks "verified". At least here on the West Coast they seem to have pretty much missed the mark.



And the just updated IRI/CPC Oceanic Niño Index (ONI) forecast is significantly warmer than last month's; pushing the winter months into the moderate El Niño category.

However, even in the moderate El Niño category there is still a large range of solutions and little predictive value. See https://www.ggweather.com/ca_enso/ca_elnino.html for the California and https://www.ggweather.com/enso2016/us_elnino.html for the US.



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

 

Posted

New & Improved El Niño (and La Niña) California Precipitation Climatology


The Climate Prediction Center (CPC) currently has an El Niño Watch for this coming Fall and Winter, though they have been gradually decreasing its probability of occurrence in recent months.


I have put together a new & improved comprehensive California Precipitation climatology for ENSO (i.e., El Niño and La Niña) events. See 
https://www.ggweather.com/ca_enso/ca_elnino.html and https://www.ggweather.com/ca_enso/ca_lanina.html.



The climatology is based upon the 10 California Hydrologic regions (map) and generated with the updated (and excellent) Western Region Climate Center's California Climate Tracker tools.

As always, corrections, comments and corrections are greatly appreciated.

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

 

Posted

PG&E and SoCal Edison Mesonets

In recent months both Pacific Gas & Electric (PG&E) and Southern California Edison (SCE) have been installing extensive weather station networks. Primarily mounted on utility poles they gather wind, temperature and humidity data every 10 minutes. Currently PG&E has about 100 stations online and SCE about 70 stations; and it is my understanding that more are being installed. (San Diego Gas & Electric (SDG&E) has had a similar mesonet of about 150 stations for about 5 years) The data is available on MesoWest and on via NWS graphical interface. However, neither MesoWest or the NWS page let's one parse out just these mesonets, so I have put together a couple pages, both in tabular and map/graphical form.

PG&E: Table, Map 
SCE: Table , Map
SDG&E mesonet
These have both been added to the Mesonet section on my Meteorologist Links page.

Enjoy and please let me know of any comments or suggestions.

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Email: jnull@ggweather.com  
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/




 

Posted

California Summer Temps Mostly Above Average - Recap

 

Meteorological summer (i.e., June, July, August) has ended and most of the Golden State ended up with above normal temperatures. The biggest anomalies were over the southern half of the California and over the northern interior.  



Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (408) 379-7500
Email: jnull@ggweather.com  
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/

 

Posted

San Francisco still a month away from average hottest day


San Francisco is still a month away from their normal hottest day of the year! Conversely, most other cities around California and the nation are well past their normal hottest day, 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 24t.
Source: http://ggweather.com/normals/daily.htm 

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (408) 379-7500
Email: jnull@ggweather.com  
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/

 
Posted

El Niño Rainfall Climatology


With the eastern tropical Pacific warming and most forecasts leaning toward at least a weak El Niño event this coming winter I have put together a new climatology looking at early-August conditions relative to the subsequent rainfall season.  I have also updated several previous ENSO climatologies with regards to rainfall and temperatures.

 

New: Early August Comparative Weak/Moderate El Niño Seasonal Rainfall Climatology 



Updated: US Winter Precipitation & Temperature Climatologies: El Niño  |  La Niña
Updated: California El Niño Precipitation Climatology
Updated: California La Niña Precipitation Climatology 

Updated links to all of the above and more at EL NIÑO / LA NIÑA RESOURCE PAGE


Posted

Summary of California 2017-2018 Rainfall Season Ending Tomorrow

The California 2017-2018 rainfall season ends tomorrow with totals across the state below normal and on the order of half of the totals recorded in 2016-17. See http://ggweather.com/ca2017rain.htm and http://ggweather.com/ca2016rain.htm.



See also the Precipitation Snapshot at http://ggweather.com/water/



Also the Western Region Climate Center's Precipitation Anomaly maps from https://wrcc.dri.edu/anom/cal_anom.html



Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/

 
Posted

Updated Resource Pages; Tioga Pass by the Nummbers


I have updated the following Weather Resource pages for 2018. But please let me know of any errata, suggestions or additions. Enjoy.

2018 Thunderstorm and Tornado Resource Guide

2018 Hurricane Resource Guide

2018 Fire Weather Resource Guide


~~~~~~~~~~~~~~~~~~~~~~~~

With Tioga Pass due to open Monday (5/21/2018) here are some historical records going back to 1980.



Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (408) 379-7500
Email: jnull@ggweather.com  
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/


 
Posted

Beware Daily Weather Records!!

 

During big rain events, a particular rainfall amount may be touted as record rainfall for the date, just as during hot weather the temperature may be proclaimed a daily maximum record. Ideally, meteorological data should be based on where we are in our orbit around the sun and not a particular calendar day. This is because our calendar is slightly flawed when it comes to specific days as it takes 365.25 days to circle the sun giving us a leap day every four years.

Consequently, the dates in a leap year after February 29th, are all displaced by one day. That is, April 6th in 2017, 2018 and 2019 is the 96th day of the year, while April 6th in a leap year (i.e., 2016, 2020) is the 97th day. So, if a record event for a particular date happened in a leap year versus a non-leap year we are actually comparing different days based upon of position relative to the "solar year".

For example, the largest rainfall amount for San Francisco for April 21st is 1.39” in 1880, a leap year so it was the 112th day of that year. But the record for April 22nd, is 0.43” in 2007, not a leap year so it is also the 112th day of the year!
Which is correct?  The bottom line is that neither is really right all of the time!
 

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (408) 379-7500
Email: jnull@ggweather.com 
Web: http://ggweather.com
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/Golden-Gate-Weather-Services-151100414926621/

 

Posted