So far, it's been a mild, snowless winter for much of the U.S. and many ski resorts, from California to Maine are desperate for a return to more typical conditions. But while the economic hardship imposed on these communities is of concern, a lack of sufficient snowpack to feed metropolitan reservoirs poses a more significant threat. This is especially true across the American West, where mountain snowfall is the primary source of water for public consumption, industry and agriculture; the dearth of snow in the Sierra Nevada is of particular concern in light of the massive population that resides across the semiarid landscape of Southern California.
The primary culprit for this snow drought appears to be the La Nina weather pattern, characterized by high pressure over the eastern Pacific. In such years, Pacific storms are shunted to the north and onshore moisture flow is shut off along the California coast; some of these storms end up dropping southward through the Rockies (as is occurring today) providing some relief to that region. Indeed, so far this winter, the few significant cold fronts that have invaded the U.S. have plunged from Canada into the Heartland, unaccompanied by Pacific moisture. Some of these atmospheric troughs have ignited snowstorms across the Southwest and Southern Plains as moisture streamed in from the Baja and Gulf of Mexico but the Northern Plains have remained high and dry.
Some climatologists also point to lower atmospheric pressures over the North Atlantic, favoring a mild, southwesterly flow across the Lower 48. Whatever the cause for our warm and snowless winter, it is not likely related to global climate change; one need only recall the severe cold and heavy snows of last winter to realize that our current dilemma does not necessarily represent a developing trend. In fact, current seasonal forecasts, to the extent that they are accurate, predict a return to more typical winter conditions for the remainder of the season. As always, time will tell.