Regional Snowfall Distributions Associated with ENSO

Regional changes in winter total snowfall distributions and snowfall frequency are identified over the continental United States in association with warm and cold phases of the El Niño/Southern Oscillation (ENSO). The analysis is motivated by numerous requests for seasonal snowfall forecasts during the 1997 ENSO warm phase and a desire to improve winter season climate forecasts. Geographic regions with spatially coherent ENSO warm, cold, and neutral phase snowfall distributions are identified using a composite technique. This analysis reveals three early winter, five mid-winter, and three late winter regions with significant shifts in snowfall. Principle discoveries include (1) increased (decreased) snowfall during an ENSO cold (warm) phase relative to neutral phases in the northern Great Lakes during late winter, (2) less (more) snowfall during a cold (warm) phase relative to neutral years the Northeast, (3) less snowfall (relative to neutral winters) in both warm and cold phases in the Ohio Valley (early winter) and Midwest (mid-winter), (4) more (less) snowfall in the Pacific Northwest during ENSO cold (warm) phases, and (5) more snowfall in western Texas during ENSO warm phases. Additional results examine the variation in the frequency of light, moderate, and heavy snowfall events during ENSO warm and cold phase winters. Combining the identified snowfall regions and snowfall frequency analysis with an ever improving ability to forecast ENSO warm and cold phases will improve seasonal snowfall forecasts. Mitigation strategies and potential benefits for agencies impacted by ENSO induced snowfall anomalies will be discussed.