I recently wrote a series of posts about the atmospheric river events that occurred in California in late December 2022 into early January 2023 (see my posts starting with December 30th and ending with January 13th). A couple of days ago, I knew that I wanted to find some summary precipitation totals covering all the atmospheric river events starting from December 26, 2022. I was not surprised that I was having difficulty finding such maps and data. I know that National Weather Service River Forecast Centers might have access to or help me find the maps and data that I was looking for. I called the NWS California-Nevada River Forecast Center (CNRFC). I talked to Brett Whitin, P.E., a Service Hydrologist with the California-Nevada River Forecast Center. Brett was very helpful and we have been in touch over e-mail as I worked on this article. The graphics he obtained for me and his assistance over e-mail helped to make this post possible. Thank-you Brett!
I told Brett what that I was looking for something similar to the Total Precipitation Map for December 24th to January 10th for California done by The Weather Prediction Center using data from the AHPS Precipitation Analysis. Brett took the time to spend a few minutes with me on the telephone, saying that he would send me some graphics over e-mail.
The first graphic that Brett sent me is prepared by the Center for Western Weather and Water Extremes. This graphic is one of my favorites. The graphic refers to the water year 2023. I know that the USGS uses a water year from October 1 through September 30. The current water year is from October 1, 2022 through September 30, 2023. I asked Brett about the Water Year he said “We (at the CNRFC) go by water year instead of calendar year because our dry season is really summer through early fall. So to capture a wet season, we go by Oct 1 through Sep 30 of the following year as our water year.”
A couple of things leaped out at me when I look at the graphic shown above. That is, the 24 atmospheric rivers are broken down by strength and by region. The map shows the strength scale and more importantly for our purposes where “each atmospheric river was strongest over the coast.” While I have been focusing in my blog on the atmospheric rivers that impacted California, I was aware that the atmospheric rivers may have impacted Oregon and Washington, with both states seeing rain and/or snow from these events.However, my focus here is on California.
Moving on to total precipitation, when I went to The Weather Prediction Center’s twitter page on January 19th, I noticed that they updated the Total Precipitation Map to reflect the period from December 26th through January 17th, I took a screen shot of their tweet which I share below along with a direct link to the tweet. Note the listing of selected precipitation totals especially the top four, an incredible amount of rain. Of interest are the sites that had a record for the 23 day period: Oakland, San Francisco International Airport, and Stockton.
I don’t want to leave out the snowfall from these atmospheric rivers. See the following map for snowfall totals which include snow fall totals for selected sites, note the area on pink that received over 15 feet of snow.
Brett and I spent a little time talking about the importance of showing rainfall departures from normal precipitation. He assisted me by sending me the two graphics that I will share below. The first map shows the percent of normal annual precipitation for the period from December 26 to January 11th. While this map ends at January 11, 2023 and does not go through January 17th, it does depict the impacts of the heavy rainfall over the 16 day period in California, especially in southern California. If I am able to obtain a similar map for the period from December 26th to January 17th I will share it in a later post.
The final map Brett sent me shows the 90-day percent precipitation, created on January 18th. Brett clarified that this map depicts the 90-day percent of normal precipitation for the 90 day period. I am drawn to the areas in Central and southern California in blues and purples showing at least 200 percent of normal precipitation fell during the 90-day period.
I hope that the graphics that I have shared here, with the help of Brett Whitin, have given you an overview of the extraordinary amounts of rain and snow that fell over parts of California during the atmospheric rivers that occurred from December 26 through January 17. If I get updated versions of any of these graphics, I will share them in a later post.
In closing, I want to mention two sites that Brett told me about that I think some of you might be interested in exploring. I mentioned the Center for Western Weather and Water Extremes earlier. I was interested in their work on atmospheric rivers including but not limited to their scale characterizing the strength of atmospheric rivers, atmospheric river forecasts, interactive maps, and atmospheric river aerial reconnaissance. The second site he pointed me to is the California Data Exchange Center, the CDEC is under the umbrella of the California Department of Water Resources. The CDEC has a wealth of information that some of you might be interested in including but not limited to data for river basins and individual rivers, current and monthly precipitation data for river basins, climate and hydrology, water quality, water supply and burn areas. For example, if I wanted to find information about a particular river in California, I would explore the CDEC site in addition to the
