California Rainfall and Reservoir Updates

 

Despite recent moderate precipitation amounts across the state (https://ggweather.com/seasonal_rain.htm), the rainfall and reservoir deficits continue to grow; well beyond the capability to make up the amounts in a single season. Even after the 1.79 inches that San Francisco has received to date, the total 4-season deficit is currently over 29 inches and will be over 50 inches by the end of the season, if no rain were to fall. (San Francisco normal 22.89", SF record 49.27 in 1861-1862.)

Likewise, the critical 8-Station Northern Sierra Precipitation Index (8SI) currently has a deficit of more than an entire season. 

And these large rainfall deficits are evident in the current levels of the state's reservoirs which have steadily declined over the past 3= seasons and are at just 61% of their average mid-November storage.

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

 

 

Posted

Mini Review of Last year's CPC Winder (DJF) Outlook

ABSTRACT
Comparison of last year's NOAA Climate Prediction Center (CPC) 90-day precipitation and temperature forecasts for the winter period of December-February (DJF) 2021-2022 with the actual observed conditions.

DATA SOURCES
The 90-day (DJF) outlooks were retrieved from the NOAA Climate Prediction Center (CPC) archives and the corresponding observed temperature and precipitation data were downloaded from NOAA ESRL Climate Division Data.

ANALYSIS
The CPC Winter Outlook DJF 2021-2022 did better than in several of the recent winters, partly because the overall pattern ended up close to a "typical" La Niña.  However, it must be noted that the CPC outlooks are probabilistic versus deterministic, which makes them harder to judge as right or wrong.

Here is t subjective graphical grading used below. Overall if a forecast was in the right category (i.e., above normal was forecast and above normal was observed) it was graded as "good" and marked with a "+". Conversely, if it was the wrong category (i.e., above normal was forecast and below normal was observed then it was graded as "not good" with a "-". And if the forecast was off by a single category (i.e, above normal was predicted and it was normal) or there was a mixture of above and below in close proximity to one another then graded it as "mixed" and marked with a "0".  

SUMMARY
Of the 41 precipitation regions compared, 14 (34%) regions rated as "good", 10 (24%) as "not good" and 17 (41%) as "mixed".
Of the 39 temperature regions compared, 20 (51%) regions were rated as "good", only 1 (3%) as "not good" and 18 (46%) as "mixed".

However, it is left to the individual reader to do their own comparisons and evaluate the relative usefulness of the forecasts to their particular activity.



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

Posted

A Mini-Analysis of Last year's Old Farmer's Almanac Winter Forecast

See https://ggweather.com/farmers/2022/index.html

ABSTRACT
This review subjectively compares last year's 2022 Old Farmer's Almanac seasonal precipitation and temperature forecasts for the winter period of November-March (NDJFM) 2021-2022 with the observed temperature and precipitation anomalies for the same period.


DATA SOURCES
The Winter forecasts are reproduced from the 2022 Old Farmer's Almanac (Yankee Publishing, Dublin, NH) website and the corresponding observed temperature and precipitation data were downloaded from the Climate Diagnostics Center (CDC).

ANALYSIS
The subjective graphical grading is below.  Overall if a forecast was in the right category (i.e., above normal was forecast and above normal was observed) it was graded as "good". Conversely, if it was the wrong category (i.e., above normal was forecast and below normal was observed then it was graded as "not good". And if the forecast was off by a single category (i.e, above normal was predicted and it was normal) or there was a mixture of above and below in close proximity to one another then I graded it as "mixed".  

Of the 40 precipitation regions compared, 16 (40%) regions were rated as "good", 16 (40%) as "not good" and 8 (20%) as "mixed". Of the 33 temperature regions compared, only 2 (6%) regions rated as "good", 19 (58%) as "not good" and 12 (36%) as "mixed".

However, it is left to the individual reader to do their own comparisons and evaluate the relative usefulness of the forecasts to their particular activity.


See the past reviews at https://ggweather.com/links.html#ofa


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

 

 

Posted

La Niña and California Rainfall


Most of the computer models are pointing toward the present moderate La Niña conditions persisting through the upcoming winter; for the third consecutive year. And given the past three years have seen below-normal rainfall across most of California, the immediate knee-jerk reaction has been that this will automatically be a fourth dry year, based on the misconception that La Niña always equals Dry for California. But a close inspection of past La Niñas since 1950, shows that this is not always the case.  An updated detailed analysis can be found at https://www.ggweather.com/ca_enso2021/ca_lanina.html. (See the bottom of this email for other related links)

From that analysis:




To me, the important takeaways are to be wary of "average" or "typical" La Niña conditions and to look at the range of data from which those averages are derived. And most importantly, climatology is NOT a forecasting tool, but it does give context to any categorical proclamation about the prospects for the upcoming season.

El Niño - La Niña Resource page: https://ggweather.com/enso.htm
Current Oceanic Niño Index (ONI): https://ggweather.com/enso/oni.htm
La Niña and California Rainfall: https://www.ggweather.com/ca_enso2021/ca_lanina.html
El Niño and California Rainfall: https://www.ggweather.com/ca_enso2021/ca_elnino.html
ENSO-Related US Winter Precipitation: https://ggweather.com/enso2021/

As always, comments and suggestions are welcomed.

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



 

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Posted

The Hottest Week of the Year ... or Not



For many locales across the United States, the last week of July is the hottest time of the year (i.e., the highest normal maximum temperature). And given the prolonged heat over much of the country this summer, just the idea that there is cooler weather ahead may be a reason to rejoice.

But a few locations, especially along the immediate West Coast, have a delayed peak. For example, while on average, Sacramento has its warmest day of the year on July 20th, San Jose waits until August 29th and it's not until September 24th that San Francisco reaches its maximum. The largest moderating factor is the adjacent cool water of the eastern Pacific along with the weakening and southward shifting of the Pacific High.

Full-size versions of the California and United States maps (below) can be downloaded from https://ggweather.com/warmest_cal.jpg and https://ggweather.com/warmest_us.jpg. Tabular US Daily Normals are available at: https://ggweather.com/normals/daily91.htm.






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


Posted

Visualizing the California 3-year Rainfall Deficit


The following two graphs are an effort to visualize the rainfall deficits in California over the past three rainfall seasons. Even with abundant rain last October and December, this season will end up at about 80% of normal. And following the previous two dismally dry seasons, the total 3-season totals are only between 60% and 65% of normal at many locations; meaning we are over an entire year's rainfall behind normal.






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

 

Posted

La Niña ... Not Fading Away

The current La NIña in the eastern tropical Pacific remains stubbornly in place, with ONI essentially flat-lined on the border between "weak" and "moderate" categories. (https://ggweather.com/enso/oni.htm)



Since at least the first of the year, forecast models have shown warming into "neutral" territory, but to date, reality has not cooperated. (https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table)



And significant upwelling of cool water in the ONI 3.4 region, points toward little change in the short term. (http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/wkxzteq.shtml)


One of the impacts of the ONI remaining in negative territory will be the potential for a more active than average hurricane season in the Atlantic Basin. This is reflected in the Seasonal Hurricane Forecast issued by Colorado State University earlier this morning. (https://tropical.colostate.edu/forecasting.html)

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

 

 

Posted

3-Season California Rainfall


This is a summary of rainfall across California for the past three seasons (July 1, 2019 through March 31, 2022) and overall the amounts paint a picture of significant deficits statewide. In general, the northern half of the state has only received between about half and two-thirds of its normal rainfall, while the south half is close to three-quarters.




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


 

Posted

2021-2022 Rainfall Season Updates


The 2021-2022 California rainfall roller coaster of alternating wet and dry months continued through January, but unfortunately, the trend for February thus looks to break the pattern. Below are a number of metrics to give it all some context.

San Francisco's January rainfall was the 10th driest in its 173 year period of record. Note that there were three drier Janaurys within the last decade.

San Francisco's season to date rainfall of 16.89" ranks as the 38th driest. Looking at similar (16.89" +/- 1") past amounts, eight of them ended above normal (i.e, 22.89" and six below.  


July 2021 through December 2021 rainfall percent of normal. 

July 2021 through January  2022 rainfall percent of normal. 

T
abular Summary of December and January percent of normal.




Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (650) 712-1876
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather

 























Single Station rainfall versus normal for recent years.






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