Apr 29, 2009

Trends in twentieth-century U.S. extreme snowfall seasons

by
Kenneth E. Kunkel, Michael A. Palecki, Leslie Ensor, David Easterling, Kenneth G. Hubbard, David Robinson, Kelly Redmond
,
American Meteorological Society
  • Examines temporal variability in the occurrence of the most extreme snowfall years, both those with abundant snowfall amounts and those lacking snowfall using a set of 440 quality-controlled, homogenous U.S. snowfall records
  • Calculates the frequencies with which winter-centered annual snowfall totals exceeded the 90th and 10th percentile thresholds at individual stations
  • Finds the area-weighted conterminous U.S. results do not show a statistically significant trend in the occurrence of either high or low snowfall years for the 107-yr period, but there are regional trends
  • Finds large decreases in the frequency of low-extreme snowfall years in the west north-central and east north-central United States are balanced by large increases in the frequency of low-extreme snowfall years in the Northeast, Southeast, and Northwest
  • Finds during the latter portion of the period, from 1950–51 to 2006–07, trends are much more consistent, with the United States as a whole and the central and northwest U.S. regions in particular showing significant declines in high-extreme snowfall years, and four regions showing significant increases in the frequency of low-extreme snowfall years (i.e., Northeast, Southeast, south, and Northwest)
  • Finds in almost all regions of the United States, temperature during November–March is more highly correlated than precipitation to the occurrence of extreme snowfall years
  • Finds El Niño events are strongly associated with an increase in low-extreme snowfall years over the United States as a whole, and in the northwest, northeast, and central regions
  • Finds the impacts of La Niña events are strongest in the south and Southeast, favoring fewer high-extreme snowfall years, and, in the case of the south, more low-extreme snowfall years occur
  • Finds the Northwest also has a significant reduction in the chance of a low-extreme snowfall year during La Niña
  • Finds a combination of trends in temperature in the United States and changes in the frequency of ENSO modes influences the frequency of extreme snowfall years in the United States