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




 























 

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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

 

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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




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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

 

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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

 

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Shifting Climate - Warmer & Drier Later

For San Francisco, the new climate normal period of 1991-2020 is both drier and warmer than previously (1981-2010). The hottest day of the year was 70.4° on September 24th, and it is now 70.6° and a week later on October 1st.
 

And San Francisco's rainfall season is now slightly (3%) less and delayed by about a week. The new normal date for the first 2" of rain for the season is now November 14th, compared to November 8th.


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

 

20 Years of Hot Cars and Tragedies

Today, July 24th, marks the bittersweet 20th anniversary of my involvement with Pediatric Vehicular Heatstroke (PVH).  On that sunny 86° summer afternoon in 2001, I got a call from a reporter telling me about the death of a 5-month-old boy inside a hot car in San Jose and asking, “How hot could it have gotten in that car?”.  And so began my 20-year journey of measuring how hot cars get and the tracking of the tragic deaths of children in hot vehicles.

In trying to find the answer to the reporter’s query, I found only a single article and it was for a single 93-degree day in Louisiana. But my scientific curiosity was piqued and during that summer I started tracking temperatures inside vehicles. I was startled at not only how hot it could get but also how rapidly the temperature rose in the car.

The following summer, I did a controlled study where I sampled temperatures in cars over 16 days that ranged in temperature from 72° to 96°.  I was also working on another project with the Stanford University Hospital Emergency Medicine Department and became acquainted with Dr. Catherine McLaren and Dr. James Quinn. They became my co-authors for the article “Heat Stress from Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles”.  This article was published by the American Academy of Pediatrics in 2005 and became the “go-to” article on the topic and has been referenced worldwide.

The article also led to my working with numerous child car safety groups and other organizations, and ultimately to my tracking the instances and circumstances that led to the deaths of children in hot cars. A dedicated website, NoHeatstroke.org was created to give easy access to this research and timely updates when there were PVH tragedies. Through the years, I have spoken at dozens of national conferences, given countless webinars and literally hundreds of interviews to increase awareness and share ideas on
preventing deaths of children in hot cars.

This 20-year milestone is important to acknowledge the children that have died and to continue to raise awareness about children dying in hot cars. If even one child is saved from being left in a hot car, it is more than worth the years of researching these tragic and unnecessary deaths.

 

Sincerely,
Jan


Jan Null, CCM
Adjunct Professor of Meteorology
San Jose State University
Email: jan.null@sjsu.edu  
Web: https://noheatstroke.org 
Twitter: https://twitter.com/ggweather
Facebook: https://www.facebook.com/noheatstroke/

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Driest California Average Rainfall on Record

  

The just ended California rainfall season has ended with the driest average statewide rainfall in the 126 seasons on record going back to 1895. And the 2-season average is the second driest with just 60% of normal. Similarly, half of California's 10 hydrologic regions saw their driest on record for the 2020-2021 season. The two-season numbers were only slightly better, primarily in the southern half of the state. [Data Source: Western Region Climate Center (https://wrcc.dri.edu/)]





 






Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services
Phone: (650) 712-1876
Email: jnull@ggweather.com
Web: http://ggweather.com
Twitter: @ggweather
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2020-2021 Rainfall Season Recap and Historical Context


 

Wednesday will mark the end of what has been a dismally dry 2020-2021 rainfall season across California with many stations logging one of their top ten driest seasons on record. And even more significant are some of the two-season totals which are also among the driest, especially in the critical watersheds represented by the Sierra Nevada Indices. And most troubling in terms of the Sierra Nevada are extremely dry three and four-year totals.


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








 

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