Lake-Aggregate Mesoscale Disturbances. Part V: Impacts on Lake-Effect Precipitation

Peter J. Sousounis Atmospheric, Oceanic and Space Sciences Department, University of Michigan, Ann Arbor, Michigan

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Greg E. Mann Atmospheric, Oceanic and Space Sciences Department, University of Michigan, Ann Arbor, Michigan

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Abstract

It is known that lake-effect snowstorms in the Great Lakes region depend on the synoptic-scale flow conditions. These conditions are determined in part by the synoptic-scale features that traverse the area. Forecasting the development of these storms has improved dramatically in the last decade. A remaining complicating aspect, however, is that the heating and moistening from all the Great Lakes (e.g., the aggregate) affects the large-scale winds, temperature, moisture, and stability near the individual lakes, which in turn affect the characteristics of the lake-effect storms that develop.

The effects of the Great Lakes aggregate on lake-effect precipitation is examined for a particular case in November 1982 that was characterized by a cold air outbreak followed by the approach of a weak trough into the region. Existing model output from numerical simulations that 1) included all of the lakes and that 2) excluded all of the lakes is used in conjunction with output from two additional numerical simulations that were performed and that include 3) only Lake Michigan and 4) only Lakes Erie and Ontario.

The intercomparison of output from these simulations indicates that the lake aggregate enhanced lake-effect precipitation in northern lower Michigan and in southern Ontario but diminished lake-effect precipitation in regions south and east of Lakes Erie and Ontario. The effects were the result of combined changes in wind, temperature, moisture, and stability, which likely altered the morphology, intensity, locations, and orientations of the convective bands.

These results indicate that understanding more completely how and when lake aggregate-scale circulations develop can enhance 1–2-day lake-effect and regional-scale precipitation forecasts. More importantly, these results suggest that aggregate-scale circulations that develop from clusters of heat sources or sinks can impact significantly the local precipitation distribution adjacent to a particular heat source or sink.

* Current affiliation: NOAA/National Weather Service, Pontiac, Michigan.

Corresponding author address: Dr. Peter J. Sousounis, University of Michigan, 1541D Space Research Bldg., 2455 Hayward, Ann Arbor, MI 48109.

Email: sousou@umich.edu

Abstract

It is known that lake-effect snowstorms in the Great Lakes region depend on the synoptic-scale flow conditions. These conditions are determined in part by the synoptic-scale features that traverse the area. Forecasting the development of these storms has improved dramatically in the last decade. A remaining complicating aspect, however, is that the heating and moistening from all the Great Lakes (e.g., the aggregate) affects the large-scale winds, temperature, moisture, and stability near the individual lakes, which in turn affect the characteristics of the lake-effect storms that develop.

The effects of the Great Lakes aggregate on lake-effect precipitation is examined for a particular case in November 1982 that was characterized by a cold air outbreak followed by the approach of a weak trough into the region. Existing model output from numerical simulations that 1) included all of the lakes and that 2) excluded all of the lakes is used in conjunction with output from two additional numerical simulations that were performed and that include 3) only Lake Michigan and 4) only Lakes Erie and Ontario.

The intercomparison of output from these simulations indicates that the lake aggregate enhanced lake-effect precipitation in northern lower Michigan and in southern Ontario but diminished lake-effect precipitation in regions south and east of Lakes Erie and Ontario. The effects were the result of combined changes in wind, temperature, moisture, and stability, which likely altered the morphology, intensity, locations, and orientations of the convective bands.

These results indicate that understanding more completely how and when lake aggregate-scale circulations develop can enhance 1–2-day lake-effect and regional-scale precipitation forecasts. More importantly, these results suggest that aggregate-scale circulations that develop from clusters of heat sources or sinks can impact significantly the local precipitation distribution adjacent to a particular heat source or sink.

* Current affiliation: NOAA/National Weather Service, Pontiac, Michigan.

Corresponding author address: Dr. Peter J. Sousounis, University of Michigan, 1541D Space Research Bldg., 2455 Hayward, Ann Arbor, MI 48109.

Email: sousou@umich.edu

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