Defining Drought ... It's Not Just Rainfall


Defining Drought … It’s Not Just the Rainfall

With the fading odds of having even a normal rainfall season across most of California (http://ggweather.posthaven.com/poor-odds-of-reaching-normal-after-dry-first-7-months-of-the-rainfall-season) the “D” word is being once more making its way into many conversations. But, what exactly is constitutes a “drought”. There is no simple answer and it certainly depends on who ask and where they live.

The American Meteorological Society defines drought as “A period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance”. The important takeaway from this broad brush definition is the use of term “hydrological imbalance” and not rainfall deficit. This is especially true in California where the State’s diverse infrastructure means water falling in the northern half of the state strongly impacts hydrologic imbalances many hundreds of miles away in the south.

Broadly, drought can be subdivided into four categories: meteorological drought, hydrological drought, agricultural drought, and socioeconomic drought.

Meteorological drought is a measure of the “degree of dryness” resulting from rainfall and snowfall deficits. There is additionally a very important temporal aspect which impacts the other types of drought by its dependence on not only the degree of deficit but also its longevity. These deficits can be measured as the number of days without rain or the percent of an average amounts of precipitation over days, months, years of even decades.

Hydrological drought is a measure of water supply available from rivers, reservoirs and groundwaters; and the infrastructure to distribute that water. The temporal aspect is even more important with hydrological drought as there can be significant time lags between when precipitation occurs and it impacts surface or subsurface supplies. [This is one of the reasons that meteorologists in California and the West use July 1 to June 30 rainfall season as opposed to the hydrologist’s October 1 to September 30 water year (http://ggweather.posthaven.com/rainfall-season-vs-water-year)]  

Agricultural droughts operate on a short time scale as a precipitation deficit during even a short growing season can have significant impacts. These impacts are exacerbated (or mitigated) by crop type, the availability of stored water (i.e., hydrologic drought) plus soil type and moisture.

Socioeconomic drought is the impact on human activities and the related economies and is a function of all the previous three types of drought as well as metrics like population change and water usage patterns.

A variety of indices and other metrics have been developed to attempt to quantify drought, though one that is good for agricultural drought may not be as adept at capturing socioeconomic impacts.

The bottom line is that drought has many intersecting layers and the effects of any or all of these drought types is dependent upon the user and his location. Drought is complicated!

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/


Additional Resources:
American Meteorological Society (AMS) https://www.ametsoc.org/ams/index.cfm/about-ams/ams-statements/archive-statements-of-the-ams/meteorological-drought/
National Drought Mitigation Center (NDMC)
http://drought.unl.edu/DroughtBasics/TypesofDrought.aspx
National Center for Environmental Information (NCEI)
https://www.ncdc.noaa.gov/monitoring-references/dyk/drought-definition
Western Region Climate Center (WRCC)
https://wrcc.dri.edu/Water/drought.php

 

Posted

Groundhog Day: More than a Furry Forecast and a Movie

This morning it has been reported that Punxsutawney Phil did see his shadow and thus forecast six more weeks of winter for 2018.

Groundhog Day has its roots in an ancient Celtic celebration called Imbolog. This date is the midpoint between the winter solstice and the spring equinox. In an agrarian society that was very dependent on the weather, this was a time to celebrate having made it halfway through winter. The superstition arose that if the weather was fair on Imbolog, the second half of the winter would be cold and stormy, but if the weather was cold and overcast or stormy, the second half of the winter would be mild.

In Christian times, February 2nd was celebrated as Candlemas, but the earlier Imbolog superstition continued. In Scotland they said, ``If Candlemas be bright and clear, there'll be two winters in the year'' and in England, they said, ``If Candlemas be sunny and warm, ye may mend your mittens and look for a storm.''

The Romans learned of this tradition from the Celts, and eventually brought them to the area that would become Germany. Eventually German immigrants brought these beliefs to Pennsylvania. Their tradition of predicting the weather became centered on the woodchuck, or groundhog, and if he could see his shadow, there would be six more weeks of winter.

A newspaper in Punxsutawney, PA helped keep the tradition alive and in 1887 declared Phil as America’s official forecasting groundhog. As the story became embellished each year the other newspapers picked it up and the rest as they say is history. Regionally there have been a number of other furry rodent contenders such as General Beauregard Lee of Atlanta, Sir Walter Wally in Raleigh, NC and Jimmy of Sun Prairie, WI.  And in 1993 the motion picture "Groundhog Day" popularized the event even further.

For NOAA's National Climatic Data Center's look at this tradition and its associated climatology see https://www.ncdc.noaa.gov/customer-support/education-resources/groundhog-day.
Other resources can be found at http://www.groundhog.org/.

But, most importantly:


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

Poor Odds of reaching Normal after dry first 7 months of the Rainfall Season 


Statewide rainfall percentages of normal through the first seven months of the rainfall season range from dry in the normal to very dry in the south. See http://ggweather.com/seasonal_rain.htm. And an analysis of previous seasons for key locations around the state with low totals for the first seven months does NOT bode well for the likelihood of at least normal rainfall for the 2017-2018 season.

Summarizing the tables below:

San Francisco: This is the 47th driest season through January. Only 2 seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
San Jose: This is the 32nd driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
Santa Rosa: This is the 37th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
San Jose: This is the 32nd driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
Eureka: This is the 50th driest season through January. Only 3 seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
Redding: This is the 16th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
8 Station Northern Sierra Index: This is the 29th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
Sacramento: This is the 47th driest season through January. Only 1 season that has been this dry or drier have ended the full season with at least normal rainfall. 
Fresno: This is the 8th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
5 Station Central Sierra Index: This is the 4th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
6 Station Southern Central Sierra Index: This is the 4tht driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
Los Angeles: This is the 11th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 
San Diego: This is the 16th driest season through January. No seasons that have been this dry or drier have ended the full season with at least normal rainfall. 

BIG CAVEAT: Please keep in mind that a below normal rainfall season does NOT necessarily equal drought. In addition to the rainfall, drought in a particular region of the state is also a function of stored surface and ground water, as well as the infrastructure to import water from other parts of the state. It can also vary by usage as the needs of a rancher needing water to grow grass to feed his cattle is very different than a water manager in an urban area.



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/

 

Golden Gate Weather Services 20th Anniversary




January 2, 2017

Today marks the 20th anniversary of the founding Golden Gate Weather Services. After almost 24 good years with the National Weather Service I ventured out on my own for what has been 20 great years. Here are some of the things I have been privileged to do in that time:

     1998Golden Gate Weather Services founded by Jan Null, CCM 
     200+ - Television interviews
     1000+ - Radio and newspaper interviews
     146 - “Weather Corner” columns in the San Jose Mercury News
     150 - Golden Gate Weather Blog posts
     500+ - Cases retained in as a forensic meteorologist
     35+ - Trials testified in as a forensic meteorologist
     100+ - Depositions testified in as a forensic meteorologist
     742+ - Pediatric Vehicular Heatstroke Deaths tracked on NoHeatstroke.org 
     18 - Presentations to national groups about Pediatric Vehicular Heatstroke
     2 - National Public Service Awards re: heatstroke from NHTSA & NWA
     1 - Presentation to US House Science Committee about El Niño
     30 - Years as Adjunct Professor/Lecturer at SFSU and SJSU
     800+ - Intro and Severe Weather classes taught at SFSU and SJSU
     14 - Articles written for Weatherwise magazine
     6 - Years as part-time contract meteorologist at PG&E
     2 - Years as Director of Meteorology at PlanetWeather.com

Thanks for all of your support and friendship over the years.

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

What Do Meteorologists mean by “Normal”?

Is it:
a.  conforming to a standard; usual, typical, or expected?.
b.  a line, ray, or other linear feature intersecting a surface at right angles?
c.  a town in Illinois?
d.  none of the above?

Meteorologically it is indeed “none of the above”. Recently, I have been asked several times about what meteorologists and climatologists mean by “normal”.  (I optimistically hope that the questions are in the context of the weather, and not whether meteorologists themselves are “normal”!)

Most users get that “normal” is some kind of average, but climatologically it is a very specific average. “Normal” is defined by the World Meteorological Organization (WMO) and its member nations, including the United States, as a 30-year average of a weather element (i.e., temperature, rainfall, wind, etc.) that is recalculated every decade (http://www.wmo.int/pages/prog/wcp/wcdmp/GCDS_1.php). The current “normal period” is the 30-year period from 1981 through 2010 and next one won’t be until data is in for the 1991-2020 period. A 30-year period was chosen as long enough to dampen out extreme short-term variations, but also not so long as to disguise changes over time.

The use of a standardized climatological normal gives a common benchmark against which conditions can be compared. This is not only in the context of whether a given day or event is “normal” but also whether there are shifts in conditions from one climate normal period to another.
Certainly, other metrics like the average over a locations entire period of record (POR) or the average of the most recent 20 years can and are used. But the standardized “normal” period give a common point of reference.  And it does make a difference!

For example, looking at the historical rainfall record for San Francisco, it can indeed be seen that there have been some decided differences in our point of reference.  The current normal (1981-2010) annual rainfall in San Francisco is 23.65 inches.  Even compared to the previous normal period (1971-2000) there was a significant difference; with a 6% increase from previous normal of 22.28”.

The table below shows the variation in San Francisco’s 30-year averages, with the normal years highlighted in red. The highest 30-year average was 24.81” for the 1860-1889 period, and the lowest was 19.51” in the 1942-1971 period.
 
A snapshot of California key city precipitation and temperature normals can be found at http://ggweather.com/normal/ with data for over 9800 United States locations at http://ggweather.com/normals/. For more complete normals see https://www.ncdc.noaa.gov/cdo-web/datatools/normals.
 
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

Dismal Beginning to SF Rainfall Season

 

Despite a rather dismal amount of rainfall in San Francisco thus far in December (0.15") this is only the 32nd driest beginning to the rainfall season (Jul 1 to June 30) going back to 1849-1850.  There has been 3.40" to date; thanks mostly to a nearly normal November. 

However, looking at similar years with between 2.90" and 3.90" (i.e., +/- 0.50" from the current 3.40") only 4 of those 22 years (18%) have finished above normal (23.65").
 

Dec 21st Rank

Season

thru Dec 21

Season Total

1

1958

-

1959

0.81

10.46

2

1917

-

1918

0.88

11.48

3

1936

-

1937

1.10

22.39

4

1862

-

1863

1.35

13.74

5

1939

-

1940

1.67

27.17

6

1956

-

1957

1.89

15.04

7

1868

-

1869

2.01

21.35

8

2013

-

2014

2.08

12.54

9

1959

-

1960

2.12

15.47

10

1911

-

1912

2.15

14.06

11

1850

-

1851

2.30

7.42

12

1890

-

1891

2.36

17.58

13

1980

-

1981

2.49

14.63

14

1905

-

1906

2.50

20.42

15

1878

-

1879

2.63

24.44

16

1930

-

1931

2.64

13.54

17

1887

-

1888

2.65

16.74

18

1943

-

1944

2.69

17.86

19

1978

-

1979

2.77

18.70

20

1990

-

1991

2.82

14.08

21

1976

-

1977

2.86

11.08

22

1986

-

1987

2.88

13.86

23

1910

-

1911

2.91

25.49

24

1872

-

1873

2.97

15.66

25

1923

-

1924

3.03

11.62

26

1854

-

1855

3.05

23.83

27

1929

-

1930

3.10

16.28

28

1953

-

1954

3.10

14.27

29

1974

-

1975

3.15

18.33

30

1932

-

1933

3.25

14.93

31

2011

-

2012

3.35

15.64

32

2017

-

2018

3.40

 

33

1991

-

1992

3.52

19.20

34

1989

-

1990

3.54

14.32

35

1975

-

1976

3.56

8.05

36

1933

-

1934

3.64

12.91

37

1863

-

1864

3.77

10.08

38

1967

-

1968

3.79

14.46

39

1908

-

1909

3.81

25.57

40

1883

-

1884

3.83

32.32

41

1907

-

1908

3.83

17.35

42

1870

-

1871

3.84

14.11

43

1938

-

1939

3.85

12.53

44

1891

-

1892

3.89

18.53

45

1935

-

1936

3.90

24.96

46

1948

-

1949

3.95

18.28

47

1921

-

1922

3.96

19.91

48

1898

-

1899

3.99

16.87

49

1876

-

1877

4.00

11.04

50

1877

-

1878

4.05

35.18

51

1897

-

1898

4.07

9.38

52

1895

-

1896

4.10

21.25

53

1949

-

1950

4.13

16.78

54

1925

-

1926

4.15

20.69

55

1919

-

1920

4.27

10.46

56

1999

-

2000

4.28

24.89

57

1886

-

1887

4.29

19.04

58

1869

-

1870

4.38

19.31

59

2000

-

2001

4.38

19.47

60

1860

-

1861

4.42

19.72

61

1971

-

1972

4.46

11.06

62

1856

-

1857

4.49

19.91

63

1855

-

1856

4.53

21.66

64

1946

-

1947

4.65

14.89

65

1993

-

1994

4.71

15.22

66

2008

-

2009

4.74

18.11

67

1865

-

1866

4.81

22.93

68

1912

-

1913

4.85

11.97

69

1853

-

1854

5.07

23.87

70

1851

-

1852

5.09

18.55

71

1902

-

1903

5.13

18.28

72

1977

-

1978

5.26

27.86

73

1947

-

1948

5.32

15.59

74

1968

-

1969

5.35

25.09

75

1881

-

1882

5.70

16.14

76

1916

-

1917

5.73

15.78

77

1963

-

1964

5.79

12.32

78

2007

-

2008

5.79

17.35

79

1901

-

1902

5.80

18.98

80

1965

-

1966

5.84

16.33

81

1992

-

1993

5.91

26.66

82

1893

-

1894

6.00

18.47

83

1903

-

1904

6.02

20.59

84

2009

-

2010

6.07

24.09

85

1960

-

1961

6.14

13.87

86

1988

-

1989

6.19

17.43

87

1942

-

1943

6.23

21.88

88

1914

-

1915

6.24

27.41

89

1931

-

1932

6.26

21.09

90

2015

-

2016

6.30

23.26

91

1979

-

1980

6.31

24.57

92

1937

-

1938

6.36

25.48

93

1934

-

1935

6.41

23.22

94

1998

-

1999

6.44

23.49

95

1906

-

1907

6.50

26.17

96

1940

-

1941

6.61

35.05

97

1941

-

1942

6.72

26.66

98

1928

-

1929

6.77

15.21

99

1927

-

1928

6.79

19.64

100

1961

-

1962

6.90

17.65

101

1900

-

1901

6.92

21.17

102

1884

-

1885

6.98

18.10

103

1995

-

1996

6.98

24.89

104

2003

-

2004

7.06

20.54

105

1857

-

1858

7.15

21.81

106

1858

-

1859

7.16

22.22

107

1915

-

1916

7.31

27.12

108

2004

-

2005

7.33

31.87

109

1861

-

1862

7.39

49.27

110

1859

-

1860

7.42

22.27

111

1964

-

1965

7.46

22.29

112

1985

-

1986

7.67

28.68

113

1892

-

1893

7.94

21.75

114

1954

-

1955

7.96

15.74

115

1987

-

1988

7.98

17.74

116

1882

-

1883

8.04

20.12

117

2016

-

2017

8.20

32.34

118

2005

-

2006

8.35

34.42

119

1913

-

1914

8.43

29.60

120

1909

-

1910

8.44

19.52

121

1969

-

1970

8.45

20.80

122

2006

-

2007

8.49

16.89

123

1873

-

1874

8.63

24.73

124

1896

-

1897

8.78

23.43

125

1955

-

1956

8.78

27.17

126

1867

-

1868

8.79

38.84

127

1879

-

1880

8.87

26.66

128

1904

-

1905

8.94

23.45

129

1966

-

1967

8.94

29.41

130

1888

-

1889

8.96

23.86

131

1880

-

1881

9.00

29.86

132

1875

-

1876

9.01

31.19

133

1944

-

1945

9.06

21.82

134

1962

-

1963

9.21

22.15

135

2010

-

2011

9.22

28.87

136

1951

-

1952

9.41

32.56

137

1874

-

1875

9.44

20.56

138

1945

-

1946

9.45

21.64

139

1899

-

1900

9.47

18.47

140

1920

-

1921

9.52

23.16

141

1957

-

1958

9.58

36.48

142

2012

-

2013

9.66

16.61

143

1952

-

1953

9.86

21.10

144

1926

-

1927

10.00

25.43

145

1981

-

1982

10.28

36.63

146

1871

-

1872

10.41

30.78

147

1982

-

1983

10.41

38.17

148

1924

-

1925

10.87

30.81

149

1918

-

1919

10.92

25.64

150

1894

-

1895

11.06

25.70

151

1997

-

1998

11.51

47.22

152

1996

-

1997

11.65

22.63

153

2002

-

2003

11.88

23.87

154

1922

-

1923

11.91

22.17

155

2001

-

2002

11.99

25.03

156

1970

-

1971

12.16

18.79

157

1983

-

1984

12.25

22.47

158

1973

-

1974

12.31

27.96

159

1984

-

1985

12.60

20.01

160

1994

-

1995

12.86

34.02

161

1852

-

1853

13.00

35.26

162

1864

-

1865

13.40

24.73

163

1950

-

1951

13.66

24.00

164

2014

-

2015

15.02

18.19

165

1866

-

1867

15.21

34.92

166

1972

-

1973

15.71

34.36

167

1885

-

1886

15.78

33.05

168

1849

-

1850

17.27

33.10

169

1889

-

1890

20.67

45.85


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

Burn Area Flooding Ecology


INCREASED FLOODING POTENTIAL IN BURN SCAR AREAS

The changed ecology of burned areas significantly increases the risk of flooding and flash flooding.


- Burned vegetation changes the water balance on denuded hillsides

- Burned organic matter on the soil increases water repellency

- Runoff is increased, carrying debris rapidly downslope



Additionally, runoff flows and debris combine with autumn leaves to clog drains for localized ponding and flooding on and around roadways.

See also https://www.weather.gov/riw/burn_scar_flooding

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/

 

The Bigger Picture: October ENSO Pacific Climatology vs. Seasonal Precipitation

This Early October Comparative El Niño and La Niña Climatology is designed as a quick reference to allow users to see patterns, or non-patterns, between "similar" ENSO (El Niño Southern Oscillation) warm and cool Sea Surface Temperature (SST) events using the NASA JPL Sea Height Anomaly products. My initial takeaway is that by looking at the bigger picture and not just the equatorial Oceanic Niño Index (ONI) data, may give a better idea of the potential impacts from one season over another in terms of winter precipitation.

See http://ggweather.com/enso/october/



Comments, observations or suggestions gratefully welcomed.

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
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Updated El Niño and La Niña Resourcces

With the recent trend of cooling in the tropical eastern Pacific and the increasing probabilities of at least a weak La Niña this coming Fall/Winter, I have updated many of the resources on EL NIÑO / LA NIÑA RESOURCE PAGE.  Some these are:

California La Niña Precipitation Climatology 
California El Niño Precipitation Climatology
US Winter Precipitation & Temperature Climatologies:  El Niño | La Niña
Oceanic Nino Index (ONI) (updated monthly)
Worldwide SST Historic Anomalies

Mega-Caveat: Please use these climatologies with great caution, primarily as a way of "book-ending" the range of possibilities, NOT as a forecasting tool. The two most recent events (i.e., Very Strong El Niño in 2015-16 and the Weak La Niña in 2016-17) were poster children for "All ENSO" events do not behave the same" and that there are lots of other global factors to consider.


 

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/

 

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What is a 500-year storm?

The ongoing catastrophic rainfall and flooding in Texas as the result of Hurricane Harvey have pushed often misunderstood and misused terms like “500-year storm” into the headlines. Probably the most important thing to keep in mind is that the time period (i.e., 100-year, 500-year, 1000-year) has nothing to do with the amount of time between events!

Instead, the terminology is the result of statistical calculations called “return period”, “return frequency” or “extreme period” analysis. These calculations estimate the probability of an event happening in any given year; and not the interval between similar events. For example, a 100-year storm has 1 chance in 100 of occurring, or one percent probability of happening in any given year.


It should also be noted that a 100-year rain event does not necessarily equate to a 100-year flood. Due to changes in a watershed, like the of filling in of channels or the paving over of permeable areas, the extent of flooding may change for the same amount of rainfall.


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/

 

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