NOAA's National Centers for Environmental Information
February began with approximatly 43 percent of the contiguous U.S. (CONUS) covered by snow according to NOAA's National Snow Analysis. Snow covered many of the western mountain locations including the Rockies, Cascades and Sierra Nevada ranges. Snow also blanketed much of the northern and central Plains, Great Lakes, southern Appalachians and the Northeast. Some snow melt occurred during the first week of February, but snow cover across the CONUS remained fairly stable until mid-month. A significant cold-air outbreak occurred across the central U.S. bringing the coldest temperatures seen across the country in more than 30 years. From February 13-16, snowfall accumulated from the central and southern Rockies into the central and southern Plains and into the Great Lakes. The largest accumulations occurred across portions of central and northeastern Texas as well as across the Midwest and Ohio Valley. According to the Regional Snowfall Index (RSI), the South region experienced a Category 3 event. An analysis created by NOAA's Weather Prediction Center illustrated that temperatures from Nebraska to the Gulf Coast were more than 40°F below average on February 15. Accompanying these bitter cold temperatures was widespread accumulations of snow, which by February 16, blanketed 73.2 percent of the conus — the highest daily value in the historical record (since October 2003). The previous daily record was 70.9 percent on January 12, 2011. Coverage on February 16 extended from the western mountains to the Great Lakes and Northeast and down to the Rio Grande River and Gulf of Mexico. Another snow event occurred from February 16-20 and extended from Texas into the Ohio Valley and Northeast. According to the RSI, the South region, again, experienced a Category 3 event as the bulk of the heaviest snowfall occurred across Arkansas with six to twelve inches of new snow. After two weeks of extremely cold conditions, temperatures rebounded and the CONUS snow cover retreated significantly throughout the remainder of the month. On February 28, approximately 23 percent of the CONUS was covered by snow — the minimum extent observed for the month of February. A blanket of snow spanned from the western mountains to the Great Lakes and across the Northeast.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the February snow cover extent for the CONUS was approximately 1.6 million square miles, 425,868 square miles above the 1981-2010 average. This was the 5th largest value in the 55-year satellite record. Above-average snow cover was observed across parts of the northern Rockies and much of the Plains, Great Lakes, Northeast and Deep South. Below-average snow cover was observed across the Coastal Ranges, Sierra Nevada, southern Rockies and a portion of the northern Plains. For the winter, snow cover extent was 83 thousand square miles above the 1981-2010 average. This was the 18th largest value in 55 years.
Melting of winter and spring mountain snowpack provides a crucial summer water source across much of the western United States. The total annual water budget for agriculture and human use in the mountainous West is highly dependent on the amount of snow melt that will occur in spring and is proportional to the amount of snow on the ground, which can be approximated by a measure of the snow water equivalent (SWE). On January 31, SWE values were near- to above-normal across parts of the Cascades as well as portions of the northern and central Front Range. Below-average SWE values blanketed most of the West from the Coastal Ranges to the Sierra Nevada Range and across much of the Rocky Mountains and the Great Basin. By the end of February, SWE values were above the median value across much of the northern Rockies and northern Cascades. Basins-wide statistics across the Sierra Nevada, the Great Basin and the central and southern Rockies had SWE values from 50 to 75 percent of the median value and as low as 25 percent across the southern Rockies.
Great Lakes surface ice cover during January was well-below average and expected to remain below average throughout the remainder of the cold season. During the cold-air outbreak in the middle half of February, ice coverage increased rapidly across the Great Lakes and peaked at 42.9 percent coverage on February 21. On February 19, NOAA visible satellite captured lake surface ice drift across the southern tip of Lake Michigan. A view from the John Hancock Tower in Chicago offers another perspective of the ice cracking and drifting to the east across the lake. It is likely that the peak surface ice coverage for the 2020-21 season across the Great Lakes occurred during February. Despite the rapid increase of ice coverage in February, the peak of 42.9 percent on February 21 remains below the long-term average of approximately 53 percent. By February 28, lake surface ice cover across the Great Lakes waned to approximately 16 percent.
