An early season snowstorm, replete with blizzard conditions, buried parts of the western High Plains and northern Rockies with several feet of snow during the period Oct. 4 – Oct. 5, 2013. Four feet of the white stuff was measured at Deadwood, SD, while 43 inches of snow was reported at Lead, SD, both near Rapid City. One to two feet of snow was reported at many locations across western South Dakota and eastern Wyoming.
For Rapid City, this storm provided the greatest snowfall for any single October day within a more than 100-year period of record. The 19.0 inches easily eclipsed the second place snowfall record of 9.9 inches set back on Oct. 19, 1919. It was also the third greatest single day snowfall event across all months.
Casper (in eastern Wyoming) established numerous records or near records due its 16.2-inch storm total. These included:
• Biggest snowstorm so early in the season (previously was 18.7 inches for Oct. 16 – 17, 1998)
• Third greatest October snowstorm and tenth greatest snowfall of any month (based on records beginning in 1937)
• Record daily snowfall of 12.4 inches on Fri., Oct. 4 broke the previous record of 3.2 inches in 2005
The snow:liquid water content of the snow was roughly 10:1, a large value for this normally moisture-starved region.
Winds during the main storm event gusted to 71 miles per hour at Ellsworth Air Force Base and 70 miles per hour near Bison and Usta, both in western South Dakota.
Unseasonably cold temperatures and biting wind chills made the snowstorm event even more noteworthy.
Although the snowstorm/blizzard was spectacular and record-breaking (hence newsworthy), it is important to place it in seasonal perspective. To do this, I examined contiguous U.S. snow cover for the morning of Oct. 6 for the period 2003 – 2013 (11 years) using data from NOAA’s National Operational Hydrologic Remote Sensing Center (NOHRSC). NOHRSC is the keeper of snow records and provides a daily snow coverage map using satellite imagery, surface snow reports and aerial transits across selected locations. I did not look at snow depth or water equivalent maps at this time. Figure 1 shows the snow coverage for Oct. 6 for these 11 years.
During the 11-year period (that is all the data that was available), average contiguous U.S. snow coverage on Oct. 6 was 3.46%. For the early morning of Oct. 6, 2013, coverage was at 7.3%. The greatest coverage for the 11-year period was 9.6% in 2009; 2005 saw the second greatest coverage at 8.3%. Four years out of the 11 saw at least 7% coverage; five of the 11 years saw 0.4% or less. Most of the years with extensive snow cover for the date had snow coverage in roughly the same area (South Dakota and Wyoming) as the snow event of 2013.
It is clear that while snow events at this early date are not unusual, especially for the South Dakota and Wyoming area that was affected, the magnitude of the event was definitely extreme.
Given the drought that has affected the region, one can only view this event in a positive light. Computer models and associated weather forecasts for the rest of the upcoming seven days bring two storm systems out into the western High Plains. These systems are expected to be wet ones, too, with one to two inches of liquid / melted precipitation anticipated for South Dakota, North Dakota and Wyoming during the seven-day period. If this is the case, October could be moving toward a record-breaking rainfall month across the western High Plains and northern Rockies.
© 2013 H. Michael Mogil