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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Posted

Drought Update - Still a Long Way to Go!

The latest Drought Monitor dropped this morning, and it shows a significant improvement over the past month. The area in the Exceptional Drought has fallen from 28% of the state to less than 1%, and the area in Extreme Drought is now at 16% compared to 52%. But over two-thirds of the state is still in at least Severe Drought or greater and the remaining areas of the state are still Abnormally Dry.
 
While, acknowledging that drought is much more than just precipitation (See “Defining Drought..It’s Not Just Rainfall), the following data will give some context to the extreme rainfall deficits over the past two-and-a-half rainfall seasons. In general, across the state, at least a full season’s normal rainfall would be needed, in the next six months, to balance the rainfall deficit that has accumulated.

The charts that follow are for the state as a whole, California’s 10 Hydrologic Regions, eight major cities, and the three Sierra Precipitation Indices.
 
Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather




 























 

Posted

California Precipitation Snapshot

With a couple of days' break in the rain, here is an update of the current rainfall versus normal. While some of the numbers look downright gaudy, the storm door needs to remain open for several more months to overcome the rainfall deficits of the past two winters. Individual images are  available at: https://ggweather.com/water/



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

 

Posted

3rd Strongest Storm since 1950

Today's storm across the SF Bay Area, is tied as the 3rd strongest storm since 1950 on the Bay Area Storm Index (BASI), and the strongest in 26 years. BASI is based on the 24-hour rainfall at the official NWS site in Downtown San Francisco, the maximum sustained wind at San Francisco Internation Airport, and the highest wind gust at elevations below 1500 feet in the nine Bay Area Counties.

As of 2 pm, Downtown SF had 2.50" (for the maximum BASI value of 4), SFO had a sustained wind to 41 mph (for the max BASI value of 3), and the highest gust has been 86 mph at Wolf Back Ridge in the Marin headlands at 1120' for 2.7 points.. 

For info on BASI and past storms see https://ggweather.com/basi.htm 

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




Posted

Increased Debris Flow Risks - Resources


With the strong likelihood of significant high-intensity rainfall over parts of North and Central California on Sunday and Monday comes the increased risk of debris flows (and flash flooding) in recently burned areas.

In the aftermath of a wildfire, there is a huge load of material deposited on the ground. Burned vegetation also changes the water balance of the denuded hillsides from wildfires by increasing the soil's water repellency. All of these factors combine for increased runoff of debris downslope.




There are lots of variables, like vegetation type, slope, and rain intensity that ultimately determine the likelihood and impact of debris flows in each individual burn scar.  The USGS produces very comprehensive analyses of these post-fire risks at https://landslides.usgs.gov/hazards/postfire_debrisflow/. However, the basic rules of thumb, mostly used operationally look at rainfall intensity and amount.


Other resources:
https://www.wrh.noaa.gov/lox/hydrology/files/DebrisFlowSurvivalGuide.pdf
https://www.weather.gov/riw/burn_scar_flooding

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

 

Posted

Updated Climate Normals Page (1991-2020)

Updated Climate Normals Page (1991-2020)

I have updated the US Climate Normals pages at Golden Gate Weather Services with the new 1991-2020 normals. These pages are designed to give quick, user-friendly access to both the monthly and daily normals for thousands of United States locations. (The normals for the previous periods of 1981-2010 and 1971-2000 are also available)


Please let me know of any comments or corrections.



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

 

Posted