State University of New York at Oswego

Oswego, New York

Sarah A. Rogowski

NOAA/National Weather Service Baltimore/Washington Weather Forecast Office

Sterling, Virginia

Lake-effect snow (LES) events are well-documented in lake-effect prone areas such as downwind of the U.S. Great Lakes. LES events generally take the form of narrow, often elongated bands of moderate to heavy snow, and are influenced by topography in their creation and maintenance. In contrast, terrain plays a key role in so-called lake-enhanced upslope snow (LEUS) events and in more general synoptic-scale upslope snow events. These terrain-forced events are high impact, localized, and long-lasting (often multi-day) meteorological phenomena. Wintertime LEUS events along with prolonged upslope flow snow events occur frequently in less-populated and more mountainous regions of the Appalachians, however their effect on those impacted is usually major. In a typical winter season, there are about 10 LEUS and upslope events, with as few as 5 or as many as 20 possible. In particular, the Allegheny Front Range region, spanning an area extending from south-central Pennsylvania through western Maryland across eastern West Virginia and extreme western Virginia, is prone to significant LEUS and upslope snow events that can produce over a half foot of snow in some cases.

This study focused on developing a climatology of lake-enhanced upslope and upslope snow events along and near the Allegheny Front Range region for an area including western Maryland, eastern West Virginia and far western Virginia for the purposes of improving forecasting of these events. This project analyzed all known lake-enhanced upslope and upslope events that occurred during the winters from December 2004 through March 2008 along the western slopes of the Allegheny Front.

For purposes of this study, an event was defined when storm spotters and/or other cooperative observers recorded at least 1.5 inches (38 mm) of snow. LEUS was defined when the mean steering wind direction over the Allegheny Front was between 270º and 340º, there was less than 45º of directional wind shear, and cold air advection was occurring. Meteorological data analyzed were obtained from nearby surface observations in the mountains and upper air data from two sites: Washington-Dulles, VA (KIAD) and Pittsburgh, PA (KPIT). Data were analyzed for surface through 500 hPa wind direction, wind speed, and moisture. Model forecast soundings were reviewed from NCEP's RUC model for Elkins, WV. Maps will be created for climatologically-favored wind speed, wind direction and moisture content for areas prone to frequent LEUS and upslope snow showers.