tag:ggweather.posthaven.com,2013:/posts Golden Gate Weather Services 2020-03-25T14:09:34Z Jan Null tag:ggweather.posthaven.com,2013:Post/1523569 2020-03-25T14:05:59Z 2020-03-25T14:09:34Z Geographical Analysis of San Francisco Rainfall

Despite being only about 49 square miles (i.e., approximately 7 miles by 7 miles), San Francisco's rainfall is nearly as diverse as its many cultures. Strongly influenced by its topography and proximity to the Pacific Ocean, its wettest location receives 34% more rainfall than its driest. 

[This is a follow-up to a similar rainfall analysis done looking at the “rainshadow” in the Santa Clara Valley (https://ggweather.posthaven.com/the-santa-clara-valley-rainshadow).]

Normal (i.e., 30-year averages from 1981 to 2010) annual rainfall data was extracted from PRISM (Parameter-elevation Relationships on Independent Slopes Model) for 315 gridpoints spaced at 0.01 degree (~0.55 miles) intervals across approximately 60 square miles covering San Francisco, adjacent waters, and extreme northern San Mateo County. To visualize this, the data was plotted and isohyets (i.e., contours of equal rainfall) were drawn.

San Francisco's rainfall patterns are the byproduct of moist air from the Pacific being forced upward by the terrain (i.e., orographically), resulting in the windward slopes seeing enhanced precipitation amounts as the air cools and condenses. On the leeward side downward forcing causes the air to become drier with less rainfall resulting.

Over San Francisco, the moist southwesterly flow coming onshore with many storms from the Pacific Ocean, is nearly perpendicular to the north-south ridge running pretty much through the center of The City. As it ascends toward this ridgeline the rainfall amounts increase from about 22” along the Great Highway to a maximum of 28.26” annually near Laguna Honda Hospital; just southwest of Twin Peaks. [Note that there is an even higher maximum of 30.17” over the higher terrain of Mount San Bruno in San Mateo County].

The air then dries out as it descends downward into the eastern side of San Francisco with a minima of about 21” along the waterfront between the Bay Bridge and Candlestick Point.

It is important to that this analysis is based upon the 1981-2010 30-year normals, and the “new" 1991-2020 normals which  will be published next year, will be on the order of about 1 inch (~4%) lower.

Click HERE or on the map for full-size image.


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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1523315 2020-03-24T18:21:08Z 2020-03-24T18:22:11Z California Rainfall Deficit Update

With only a few exceptions, the recent rain across the state has just kept up with the previous March 1st normal-to-date figures. The picture is pretty discouraging if the amounts needed (i.e., deficits) to reach normal by the end of the rainfall season (i.e., June 30) are examined. For example, from the table below, the Northern Sierra 8-Station Index (8SI) needs another 29.25 inches to reach their end of season normal of 54.52 inches. The 8SI March 24 to June 30 normal is 9.42", so 310% of that amount would be needed.

The good news is that the state's major reservoirs are near, or in some cases above, historical averages to date. See https://cdec.water.ca.gov/reportapp/javareports?name=rescond.pdf

The other good news is that the prospect of a very early fire season has been somewhat mitigated in the short-term.

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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1513890 2020-02-26T17:11:59Z 2020-02-26T17:13:21Z Does a Dry February Mean a Wet March or April

There has been speculation in the past few days that a dry February portents a wet (i.e., "Miracle") March. However, a look at the years when San Francisco has had less than 0.50" of rain in February does not support that thesis. In fact, only 6 of those 18 years had above normal March rain totals. 

The odds are only slightly better for the combined total of March and April, with only half above normal.


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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1513006 2020-02-24T16:45:00Z 2020-02-24T16:50:15Z SF Record Dry Days and Updated California Period of Record Rainfall

There is lots of obvious interest in the lack of rain, with many California location going ZERO for February; even with an extra Leap Day.

1. It is likely that there will be no rain in SF through the end of the month; which will make a total of 32 dry days since the City's last measurable precipitation (i.e., 0.09" on 1/28). This will be tie it with 2013-2014 as the 4th longest winter dry spell. Previously:
 
For context, here are some other record San Francisco dry and wet spells from Climate of San Francisco (https://ggweather.com/sf/)

2. Also with heightened interest in the historical context of this year's rainfall I have put together Period of Record monthly rainfall for over 50 California locales; including the Sierra Nevada Indices and the seven state Climate Divisions. See https://ggweather.com/monthly/


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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1511906 2020-02-21T18:06:11Z 2020-02-21T18:07:17Z Updated California Rainfall by the Numbers

Lagging rainfall statewide totals projected through the end of February paints a dim picture climatologically for the outcome of the 2019-2020 rainfall season. Forecast models remain dry through at least February 29th, except for some possible light convective showers over southern California and the Southern Sierra Nevada, but any of the expected rainfall there will not shift totals to any appreciable degree.









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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1508881 2020-02-12T17:55:13Z 2020-02-12T17:57:33Z Defining DROUGHT ...  It's NOT Just Rainfall




Defining Drought … It’s Not Just the Rainfall


Whenever California has the potential for a below normal rainfall season, like now, the D” word starts making its way into the media and everyday conversation. But what exactly constitutes a “drought”. There is no simple answer and it certainly depends on who you 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.

And there is no single metric, be it the Drought Monitor, reservoir levels or seasonal rainfall deficits, that is the right tool for everyone. The needs of a water district manager are very different from those of a farmer, a local industry, a ski resort operator or a homeowner.

Broadly, drought is 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 function of the water supply available from rivers, reservoirs and groundwater; and very importantly 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 of 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!

Additional Resources:


Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (650) 712-1876
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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Jan Null
tag:ggweather.posthaven.com,2013:Post/1506343 2020-02-04T19:06:39Z 2020-02-04T19:10:37Z California Rainfall Season to Date by the Numbers

Except for December, the current California rainfall season has been rather disappointing across most of the state. And, climatologically the prospects of most regions in the state getting back to normal by the end of the season (i.e., June 30th) are not particularly promising. Only Eureka and Los Angeles have reached or exceeded normal more than half the time for similar years; while San Francisco and the 3 Sierra Indices have reached or exceeded normal only between 5% and 20% of the time. 

    

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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1494887 2020-01-02T18:27:40Z 2020-01-02T18:29:33Z California Mid-Winter Dry Periods


Cue "It's Not Unusual" (by Tom Jones), because an extended period of dry weather in the middle of winter isn't unusual for northern and central California. And given, the current medium range models the next chance of significant rain may be another week and a half off.

Based on San Francisco's daily rainfall, over the past 69 rainfall seasons (i.e., July 1 to June 30) there has been a "dry" period in December or January averaging 19 days. For practical purposes a "dry period" here is defined as consecutive dry days with no rain, or consecutive days broken by no more than two non-consecutive intervening days of very light (* i.e., ≤ 0.08 inches) rain].

The shortest dry spell was 8 days which occurred twice, in 1957-58 and again in 1994-95.  Both of these seasons were during El Niño events!  The longest dry spell was 56 days in 2014-2015, when there was 18.19 inches.  All of these dry periods began in December or January with the exception of the 1964-65 period which was 19 days but did not begin until February 6th.

Even the very wet El Niño seasons of 1982-83 and 1997-98 had intervening dry spells and 22 and 17 days respectively.

Data available at https://ggweather.com/enso/winter_dry_spells.htm

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

Season

Consecutive        *Dry Days

Begin Date

*Intervening Days/Amount

1950-51

13

17-Dec

 

1951-52

12

6-Dec

1/.08

1952-53

13

21-Jan

 

1953-54

13

21-Dec

1/.01

1954-55

16

14-Dec

 

1955-56

20

28-Jan

 

1956-57

33

6-Dec

2/.03

1957-58

8

6-Dec

 

1958-59

12

12-Jan

 

1959-60

13

15-Dec

 

1960-61

36

19-Dec

1/.02

1961-62

21

22-Dec

 

1962-63

42

18-Dec

 

1963-64

19

25-Dec

2/.08

1964-65

19

6-Feb

 

1965-66

21

7-Jan

1/.02

1966-67

30

11-Dec

1/.01

1967-68

23

19-Jan

 

1968-69

13

24-Dec

 

1969-70

12

26-Dec

 

1970-71

29

17-Jan

 

1971-72

21

30-Dec

 

1972-73

15

24-Dec

 

1973-74

11

20-Jan

 

1974-75

22

5-Dec

2/.04

1975-76

25

10-Jan

 

1976-77

26

13-Jan

 

1977-78

16

20-Jan

1/.02

1978-79

15

19-Dec

 

1979-80

26

18-Jan

 

1980-81

16

5-Dec

 

1981-82

12

6-Jan

 

1982-83

22

24-Dec

 

1983-84

15

31-Dec

 

1984-85

11

27-Dec

 

1985-86

21

8-Dec

 

1986-87

15

7-Jan

 

1987-88

28

30-Jan

 

1988-89

11

11-Jan

 

1989-90

36

26-Nov

 

1990-91

17

20-Dec

 

1991-92

17

8-Jan

1/.04

1992-93

14

22-Jan

 

1993-94

20

15-Dec

1/.03

1994-95

8

31-Jan

 

1995-96

15

31-Dec

1/.02

1996-97

20

27-Jan

2/.07

1997-98

17

15-Dec

2/.03

1998-99

21

21-Dec

2/.02

1999-00

27

14-Dec

1/.03

2000-01

22

16-Dec

1/.03

2001-02

18

3-Jan

1/.02

2002-03

19

24-Jan

 

2003-04

11

10-Dec

1/.04

2004-05

17

9-Dec

 

2005-06

14

3-Dec

1/.03

2006-07

12

5-Jan

 

2007-08

10

11-Jan

 

2008-09

18

3-Jan

 

2009-10

12

31-Dec

1/.05

2010-11

14

31-Dec

 

2011-12

49

1-Dec

 

2012-13

16

7-Jan

1/.01

2013-14

36

12-Dec

2/.08

2014-15

56

21-Dec

1/.07

2015-16

9

25-Dec

2/.06

2016-17

10

23-Dec

 

2017-18

13

21-Dec

 

2018-19

11

25-Dec

 

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1487530 2019-12-10T19:01:36Z 2019-12-10T19:05:16Z December 2019 California Precipitation Snapshot


Recent rains have pushed rainfall to date numbers to respectable levels across most pf the state, with the biggest numbers in the farther south. Also available https://ggweather.com/water/



 








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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1470690 2019-10-27T17:06:26Z 2019-10-27T17:52:00Z Quick Comparison of Oct. 2017 and Oct 2019 North Bay Wind Events

A quick comparison of winds from Oct. 9, 2017 and Oct. 27, 2019 showing max wind gusts at RAWS sites to be very similar.







 

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1470113 2019-10-25T18:56:50Z 2019-10-26T03:56:03Z A Diablo Winds Primer A Diablo Winds Primer

Diablo Winds are warm dry winds originating when strong high surface pressure builds over the northern Great Basin. The resulting flow from high pressure inland to lower pressure off the California coast is warmed and dried by compressional heating as the air sinks from the Great Basin, which is nominally between 4000 and 5000 feet, down to sea level. The primary impact area is over and downwind of the Coast Range and Diablo Range, from about Lake County in the north to San Benito County in the south. [This pattern also produces strong north winds down the Sacramento Valley and downslope northeast wind in the northern Sierra Nevada.] 

 

These areas of high pressure in a favorable position in the Great Basin are most common in the fall and winter months as the polar jet stream makes its seasonal progression southward.  Troughs and ridges moving along the jet stream begin affecting the northern portions of the Great Basin.   In certain configurations, the jet stream pattern encourages strong sinking motions and the development of surface high pressure areas in the northern Great Basin.  In that position, these highs can generate Diablo Winds and when they move or extend farther south Santa Ana winds can be the result.



The seasonal timing of Diablo, and Santa Ana, Winds is extremely important in regard to wildfire danger. One of the chief characteristics of California’s predominantly Mediterranean climate is its protracted dry period from about May through October. Consequently, these strong, warm and dry winds occur after months of very little, if any, precipitation and when fuels (i.e., grasses, shrubs and forests) are at their driest.

The exact trajectory and strength of Diablo Winds is due to the strength and location of the high in the Great Basin and likewise the strength and location of lower pressure to its southwest. During a Diablo Wind event this trajectory will often begin as a more northerly wind and shift to one from the northeast. This flow is significantly altered as it flows over and down first the Sierra Nevada and then the Coast Range, with the channeling of the wind over ridges and down canyons sometimes drastically increasing its velocity. The vertical temperature patterns associated with the Diablo Wind weather type often have the result of constraining the wind flow against the mountains, almost as if there were a “lid” just over the top of the coastal mountains.  Winds pushing from northeast to southwest are then squeezed through and augmented at the ridge line and on the lee, southwest, slopes in what is known to meteorologists as the “hydraulic jump” phenomenon.

One common “rule of thumb” diagnostic for Diablo Winds in general is to look at the pressure gradient (i.e., difference in pressure) between Winnemucca in northern Nevada and San Francisco; with the higher the difference meaning stronger wind speeds. This comes with the large caveat that the exact location of a Great Basin High and offshore low can dramatically alter the resultant wind speed and direction.

The current and previous 24 hours of Winnemucca (WMC) to San Francisco (SFO) pressure gradients can be found in the lower half of https://www.wrh.noaa.gov/mtr/versprod.php?pil=OSO&sid=001, under SFO-WMC. The more negative the number, generally the stronger the offshore winds. 
Historically, here are several significant SFO-WMC surface pressure gradients days:
    Oct. 20, 1991:   -13.1 mb    Tunnel Fire
    Oct. 8, 2017:     -17.8 mb    North Bay Fires
    Oct. 24, 2019:   -16.3 mb    Kincade Fire

The etymology of the term “Diablo Winds” dates to shortly after the 1991 Tunnel Fire which devastated a large area of the Oakland and Berkeley hills. Myself and another forecaster (John Quadros), working at the National Weather Service office in Redwood City at the time, found that after the 1991 fire, calling offshore wind events in the Bay Area as “the northern California version of Santa Ana winds” was awkward at best, and meteorologically fuzzy at worst. We somehow fell upon the name Diablo Winds as a double entendre because they generally blow from the direction of Mt. Diablo in the far East Bay, and "diablo" translates from Spanish as “devil”; thus, devil winds.

Special thanks to Dr. John Monteverdi for his suggestions and editing.


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

 

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1459013 2019-09-24T17:07:01Z 2019-09-24T17:09:08Z Not All "Blobs" are Necessarily Equal

 

In recent week there have been numerous articles highlighting the strong Sea Surface Temperature Anomalies (SSTA) that have developed in the Gulf of Alaska and northeast Pacific Ocean; and equating them to the "Blob" that was a dominant feature in 2014 to 2016 period.  However, it is important not to look at these particular SSTA areas in isolation without looking at SSTA patterns in other parts of the eastern Pacific.  (This is a path that has sometimes been mistakenly taken in the past in regard to El Niño, where ENSO temperatures were taken out of context relative to other parts of the Pacific. One example was the Very Strong El Niño event in the winter of 2015-16, which is looked at in the following: https://ggweather.com/enso/compare/.)

While the current (September 2019) SSTA for the northeast Pacific does show significant positive SSTA warming in the northern half of the Gulf of Alaska, it is somewhat weaker and farther north that seen in 2014 and 2016. Also of note this year is the strong positive SSTA area west of California, a feature that was weaker and farther south in 2014 and non-existent in 2016.

The bottom line, is that the strength, location and interaction of these anomalous areas, as well as others in the Pacific, and even globally, all affect the circulation patterns of the West Coast differently; thus great caution should be used in drawing any simple (i.e., 1 + 1 = 2, or "blob" = California drought) conclusions as to their impact on the upcoming winter.

This post is also available at: https://ggweather.com/blob.htm

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


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Jan Null
tag:ggweather.posthaven.com,2013:Post/1438762 2019-07-29T20:34:27Z 2019-07-29T21:06:10Z The Santa Clara Valley Rainshadow

 Often when it rains in the San Francisco Bay Area the lowest rain amounts are in San Jose and the surrounding environs of the Santa Clara Valley. To quantify this the normal (i.e., 30-year average from 1981 to 2010) rainfall over the region was analyzed. The data used was from PRISM (Parameter-elevation Relationships on Independent Slopes Model) at Oregon State University. Annual average rainfall was extracted for 600 gridpoints spaced at 0.05 degree (~0.55 miles) intervals over approximately 1300 square miles covering most of Santa Clara and the northern part of Santa Cruz Counties.

Rainshadows are the byproduct of moist air being lifted by the terrain (i.e., orographically) resulting in upward forcing on the windward slopes and thus enhanced precipitation amounts as the air cools and condenses. On the leeward side, the downward forcing causes the air to become drier with less rainfall resulting.

.


In the SF Bay Area, the moist southwesterly flow coming onshore from the Pacific Ocean is often perpendicular to the Santa Cruz Mountains, which are oriented from northwest to southeast. After ascending the mountains and producing sometimes copious amounts of rain, the air dries out as it descends downward into the Santa Clara Valley. This produces about fours time more rain near Ben Lomond (~60 inches) than near San Jose Airport (~15 inches) which is only 22 miles away. (Click here or on the map for full-size image)


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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1425463 2019-06-28T13:58:42Z 2019-06-28T15:32:25Z 2018-2019 California Rainfall Season - Good but not Great This Sunday, June 30th, marks the end of the 2018-2019 California rainfall season. Below are summaries of rainfall across the state. An important takeaway, despite "record-setting" headlines, is that for the vast majority of the state it was only a "good" above-normal year and not even in the top 20% of the wettest seasons. [Data also at https://ggweather.com/ca2018rain.htm and https://ggweather.com/water/]



San Francisco
POR begins 1849-1850
2018-19: 25.50, 109%
Rank: 40th of 170 seasons

San Jose
POR begins 1892-1893
2018-19: 16.63, 112%
Rank: 36th of 127 seasons

Eureka
POR begins 1886-1887
2018-19: 41.00, 102%
Rank: 50th of 133 seasons
 
Redding
POR begins 1892-1893
2018-19: 39.92, 115%
Rank: 38th of 127 seasons
 
Sacramento
POR begins 1940-1941
2018-19: 24.57, 133%
Rank: 12th of 70 seasons
 
Fresno
POR begins 1881-1882
2018-19: 11.44, 99%
Rank: 32nd of 138 seasons
 
Los Angeles
POR begins 1876-1887
2018-19: 18.82, 126%
Rank: 39th of 143 seasons
 
San Diego
POR begins 1850-1851
2018-19: 12.41, 120%
Rank: 36th of 169 seasons
 
8-Station Index
Northern Sierra Nevada
POR begins 1921-1922
2018-19: 68.44, 126%
Rank: 19th of 98 seasons
 
5-Station Index
Central Sierra Nevada
POR begins 1913-1914
2018-19: 49.79, 117%
Rank: 22nd of 106 seasons
 
6-Station Index
Southern Sierra Index
POR begins 1922-1923
2018-19: 37.06, 122%
Rank: 23rd of 97 seasons


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


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Jan Null
tag:ggweather.posthaven.com,2013:Post/1408925 2019-05-14T14:13:30Z 2019-05-14T17:47:11Z May Rainfall Climatology

 

With the rain looking likely over the next week or so, below is some May rainfall climatology for the Bay Area and California.






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


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Jan Null
tag:ggweather.posthaven.com,2013:Post/1406035 2019-05-06T17:43:50Z 2019-05-06T17:46:28Z El Niño keep chugging along

  

For the past 5 months, the Oceanic Niño Index (ONI) has been stuck in the middle of the Weak El Niño category (i.e., +0.50 and +1.0) and the models are keeping it in that range through the end of the year!  Going back to 1950 (https://ggweather.com/enso/oni.htm) there are only three back-to-back years with kind of similar patterns, but none close enough in my estimation to be reasonable analogs. They were 1968-69 to 1969-70, 1986-87 to 1987-88, and 2014-15 to 2015-16.  California precipitation patterns related to El Niño years can be found at https://www.ggweather.com/ca_enso/ca_elnino.html


 


Current SST Temperatures with Niño Region insets


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






 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1404077 2019-05-01T17:06:40Z 2019-05-01T17:13:07Z A Dry April, but Still Looking Good

 

After well above normal February and March rainfall, percentages in April across most of California dropped to well below normal. However, season-to-date numbers are still mostly above normal, and in many locations their seasonal (July 1 to June 30) normals have already been reached. See https://ggweather.com/seasonal_rain.htm and https://ggweather.com/water/.





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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1386098 2019-03-15T18:08:14Z 2019-03-15T19:04:15Z "Storm" - Still relevant after almost 80 years


“ STORM” by George R. Stewart, should be REQUIRED READING if you are a meteorologist, meteorology student, deal with or communicate California weather on a regular basis, or anyone whose day-to-day activities in California are impacted by the weather.  I have just finished rereading it for probably the 5th time and couldn’t put it down.

I first read “Storm” when I was an NWS meteorologist intern in 1975 and identified with one of the characters in the book, the Junior Meteorologist (JM) at the Weather Bureau in San Francisco. Over the years, I have given or loaned copies to over a dozen friends and colleagues and even though it was written in 1941, the meteorology is still sound and incredibly insightful. Likewise, the impact of a storm across California for 12 days in a winter where there had been early talk of a drought resonates strongly with this year’s headlines. Interwoven throughout the book are the interactions between the weather, the utilities, railroads, commerce, the airlines and people, which are just as relevant today as they were almost 80 years ago.



Please, do yourself a favor and track down a copy. It’s in many libraries, plus I often find copies squirreled away in used bookstores and there are numerous versions available on Amazon. (And when you finish “Storm”, read Stewart’s “Fire” which looks at another timely topic, the impact of a wildfire in the Sierra Nevada.)

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

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1384834 2019-03-12T17:22:20Z 2019-03-12T17:31:39Z Comparison of the 2018-2019 Winter Outlooks to Reality?

 

How did the 2018-2019 Winter Outlooks that were issued last fall compare with reality? This year, in addition to looking at the CPC forecasts, several outlooks from the private sector were added for comparison. In all of the outlooks I see big-time errors; begging the question is there "skill" and "value" in these products? See http://ggweather.com/cpc/2019/


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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1382709 2019-03-07T17:36:38Z 2019-03-07T17:39:37Z California Rainfall and Reservoir Update

 

2018-2019 CALIFORNIA WATER BY THE NUMBERS

It's should be no surprise that abundant rainfall this season has translated into a pretty bright picture for water supplies across the Golden State. 

The latest Drought Monitor shows California with its least amount of drought-impacted area since 2011. With only 0.60% in the Moderate Drought category (D1) and 9.56% in D0 (Abnormally Dry), California is at its most drought free since 8-30-2011. 

 The latest California Precipitation Snapshot shows rainfall already approaching or above normals for the entire is rainfall season (July 1 to June 30).

Of particular note is the 8-Station Northern Sierra Index, with state's largest reservoirs, which is now at 128% of normal and just 2.33" shy of their seasonal normal of 54.52".

  
And all of the above translates into California reservoir levels close to or exceeding historical averages for this time of year. 


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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1370421 2019-02-04T19:25:15Z 2019-02-04T19:27:05Z February 5th Bay Area Snow; But Not like 1887 or 1976


Historically, February 5th is the snowiest day of the year in San Francisco and the Bay Area. Of the 11 days when snow has been recorded near sea level in San Francisco, twice before on February 5th. In 1887 and again in 1976. (https://www.ggweather.com/sf/snow.htm)


The event on February 5, 1887, was the snowiest on record with over 3 inches in the downtown area of the City.  This is well documented in Mark McLaughlin's wonderful  "San Francisco Snowstorms" document (http://thestormking.com/Sierra_Stories/San_Francisco_Snowstorms/san_francisco_snowstorms.html)


And the last time there was an accumulation of snow near sea level in San Francisco was on February 5, 1976, with up to an inch downtown and 5" on Twin Peaks. (Spectacular photograph below: Art Frisch, SF Chronicle), 



The forecast conditions for tomorrow, February 5, 2019, do NOT look like a repeat of either one of the previous snow events. But the combination of much colder air moving into the region and continued bands of showers overnight should at least whiten the hills above 2000' and in some areas, especially inland possibly down to into the 1000' to 1500' range.

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


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Jan Null
tag:ggweather.posthaven.com,2013:Post/1364319 2019-01-17T17:47:23Z 2019-01-17T17:49:03Z Significant Rainfall Gains Statewide


The first 16 days of January have seen great rainfall recoveries across California from recent storms. Most locales have jumped by about 20% versus their Jan. 1st %-of-normal numbers. The very important 8-Station N Sierra Index (8SI) has jumped to 89% of normal while both Redding and Sacramento are now just above normal. For others see below or https://www.ggweather.com/water/.

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



 

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1357709 2018-12-27T21:21:28Z 2018-12-27T21:22:08Z California Rainfall Update and Odds

 

With no rain in the forecast through the end of the year, here are some updates on where California stands precipitation-wise. Most of the state north of the Tehachapis is about 75% of normal, while to the south it is averaging from near to slightly above normal.

Through Dec 31, San Francisco will be at 5.95 inches or 65% of normal. This is the 63rd driest out of the 170 seasons dating back to 1849. Looking at the 30 seasons that had this value plus/minus an inch, the corresponding end of the rainfall season (Jul 1 through Jun 30) totals ranged from 11.06" to 27.86". This breaks down further with 6 seasons at < 60% of normal, 11 seasons at 61-80% of normal, 8 seasons at 81-100% and 5 seasons in the 100 to 120 percent of normal. 

https://www.ggweather.com/water/
 





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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1347307 2018-11-25T21:20:44Z 2018-11-25T21:21:49Z Significant Rainfall Gains

Last week's rains made a significant dent in California rainfall deficits, pushing many northern California areas from around 10% of their normal late November rainfall to over 50% of normal. And forecast charts continue to show at least moderate rain at times this week in the Tuesday through Thursday timeframe. See https://www.ggweather.com/seasonal_rain.htm and https://www.ggweather.com/water/









 

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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Jan Null
tag:ggweather.posthaven.com,2013:Post/1339280 2018-11-02T14:09:55Z 2018-11-02T14:11:53Z 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
 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1333918 2018-10-19T17:56:56Z 2018-10-19T17:59:16Z 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
 

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1327940 2018-10-01T20:04:40Z 2018-10-01T20:05:42Z 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

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1320787 2018-09-11T19:39:31Z 2018-09-11T19:41:20Z 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: TableMap
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/




 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1318314 2018-09-04T16:15:38Z 2018-09-04T16:20:49Z 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/

 

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Jan Null
tag:ggweather.posthaven.com,2013:Post/1314773 2018-08-24T15:55:15Z 2018-08-24T15:58:08Z 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/

 
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Jan Null