Mountain Waves / Standing Waves
The Ridge along the north shore of Lake Superior, including Duluth, sometimes induces waves in the atmosphere similar to those produced by mountain ranges. Satellite and personal observations have identified a variety of wavelike features. These features include lenticular clouds sitting stationary above the ridgeline and wavelike patterns in stratocumulus clouds extending well downstream of the ridge. Sometimes higher altostratus or cirrostratus cloud form, similar to mountain generated cirrus associated with the Rocky Mountains. On satellite they appear as smooth or fibrous clouds extending well downstream from the north shore of Lake Superior but with a sharp back edge that aligns itself over the ridgeline. These middle and high clouds form when a wave, which propagates vertically into the middle or upper troposphere, encounters a moist layer. The rising motion in the ridge part of the wave lifts the moist air to form clouds that are then blow downstream by the wind.
References and More InformationDan Miller, Science and Operations Officer, National Weather Service, Duluth, MN
Forecasting Staff, National Weather Service, Duluth, MN
AMS Glossary definitions
“Mountain Waves and Downslope Winds” training module from the MetEd website
Additional ReadingBrady, R. H. and J. S. Waldstreicher, 2001: Observations of Mountain Wave-Induced Precipitation Shadows over Northeast Pennsylvania, Wea. Forecasting, 16, 281-300.
Smith, R. B., 1979: The influence of mountains on the atmosphere. B. Saltzman, Ed., Adv. Geophys., 21, 87-230.
[ Specifically note pages 88 and 89. ]
Kirkwood, P. D., D. M. Gaffin, and S. S. Parker, 2002: An Unexpectedly Heavy and Complex Snowfall Event across the Southern Appalachian Region. Wea. Forecasting, 18, 224-235.