MSGID: 1:317/3 644c09da   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
   April 28, 2023 - Heavy Snowpack in California   
      
      [image04282023_main.jpg] [image04282023_rollover.jpg]   
      
      April 26, 2023 April 24, 2022   
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      A boom year for Sierra Nevada snow is expected to create a massive   
      spring “Big Melt”, with potential for widespread flooding.   
      
      The Moderate Resolution Imaging Spectroradiometer (MODIS) on board   
      NASA's Terra satellite acquired a true-color image of snow atop the   
      Sierra Nevada on April 26, 2023. A second true-color Terra MODIS image,   
      acquired on April 24, 2022, can be seen by clicking on the date below   
      the images. When toggling between the two images, it's easy to see that   
      this year's snowpack is massively larger than a similar date in 2022.   
      
      Many parts of central California received 200 percent or more of   
      expected precipitation this water year, which started on October 1.   
      Eleven moderate-strength atmospheric rivers hit the southern Sierra   
      Nevada this year, which is twice the average number. Precipitation from   
      these storms contributed to a breach of the Los Angeles Aqueduct, the   
      re-emergence of Tulare Lake in the San Joaquin River Valley, and heaps   
      of snow on the range.   
      
      But it wasn’t only a wet year, it was also an unusually cold year.   
      According to the National Weather Service, parts of the central coast   
      experienced the coldest winter since 1978-1979. The combination of cold   
      and wet added up to an anomalously high snowpack in both the southern   
      Sierra Nevada Mountains and at lower elevations along the range.   
      
      As of April 1—which is typically the date of peak snowpack—the   
      Institute of Arctic and Alpine Research (NSTAAR) estimates showed the   
      greatest amount of snow water equivalent since records began. On that   
      date, snow water equivalent (SWE)—a measurement of how much water you   
      would get if all of the snow in a given area melted at once—was   
      measured at four times (439 percent) the average for April 1. Mountains   
      in the central part of the range were at 284 percent of normal, and   
      slopes to the north were 271 percent of normal.   
      
      Snow that falls in the Sierra Nevada each winter is a natural reservoir   
      that typically slowly melts and flows down into the river valleys in   
      spring and summer. In a typical year, this snowpack accounts for about   
      30 percent of California’s water supply.   
      
      This year, thanks to rapidly rising temperatures, water is already   
      melting rapidly, raising concerns about flooding from a “big melt”. On   
      April 25, the National Weather Service, San Diego warned of a big   
      warmup over the next several days. Temperatures were expected to reach   
      90s in some locations, and as high as 105˚F in some desert locations,   
      such as the Coachella Valley in Riverside County.   
      
      To prepare for expected flooding, the National Park Service warned   
      that, with the Merced River expected to rise to 2 to 3 feet above flood   
      stage, several locations in Yosemite National Park will likely be   
      closed within the next few days. The Merced is likely to reach flood   
      stage on and off from late April until July.   
      
      Both the Tulare Lake Basin and the San Joaquin River Basin are already   
      flooded from heavy winter rains, and are expected to receive a   
      tremendous amount of additional water from snowmelt, which may send a   
      “cascade of water” into the San Joaquin Valley. Based on the heavy   
      snowpack, speculation suggests that increased flows into this region   
      may persist until fall.   
      
      Image Facts   
      Satellite:  Terra   
      Date Acquired: 4/26/2023   
      Resolutions:  1km (142.2 KB),  500m (509.8 KB),  250m (1.6 MB)   
      Bands Used: 1,4,3   
      Image Credit: MODIS Land Rapid Response Team, NASA GSFC   
      
      
      
   https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2023-04-28   
       
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