Search Results
Abstract
Large spatial and temporal variations were observed in the location of the upwind cloud edge over Lake Michigan during five westerly wind lake-effect events in November 1995 through January 1996. This study examines the impacts of variations of Lake Michigan surface water temperatures (and corresponding surface fluxes) and upwind static stability on the location of the upwind edge of lake-effect clouds, which develop as cold air crosses the lake during the winter. Data used in this study were collected during the 1995/96 National Weather Service Lake-Effect Snow study. Spatial variations in the location of the upwind lake-effect cloud edge are shown to be related to spatial variations in surface heat and moisture fluxes between the lake surface and overlying air. Surface fluxes are influenced by both the distribution of lake surface water temperatures and variations of surface wind speed, air temperature, and relative humidity. Temporal variations of heat and moisture fluxes from the lake surface and low-level static stability upwind of the lake correlate well with changes in locations of the upwind lake-effect cloud edge. In general, increases in total flux over a particular period tended to correspond with westward change in the position of the upwind cloud edge, whereas decreases in total flux corresponded to eastward shifts of the upwind cloud edge. Atmospheric static stability below the upwind inversion was found to be more important than the inversion height in controlling the location of the upwind cloud edge over the lake, with increases in stability corresponding to eastward shifts in its location.
Abstract
Large spatial and temporal variations were observed in the location of the upwind cloud edge over Lake Michigan during five westerly wind lake-effect events in November 1995 through January 1996. This study examines the impacts of variations of Lake Michigan surface water temperatures (and corresponding surface fluxes) and upwind static stability on the location of the upwind edge of lake-effect clouds, which develop as cold air crosses the lake during the winter. Data used in this study were collected during the 1995/96 National Weather Service Lake-Effect Snow study. Spatial variations in the location of the upwind lake-effect cloud edge are shown to be related to spatial variations in surface heat and moisture fluxes between the lake surface and overlying air. Surface fluxes are influenced by both the distribution of lake surface water temperatures and variations of surface wind speed, air temperature, and relative humidity. Temporal variations of heat and moisture fluxes from the lake surface and low-level static stability upwind of the lake correlate well with changes in locations of the upwind lake-effect cloud edge. In general, increases in total flux over a particular period tended to correspond with westward change in the position of the upwind cloud edge, whereas decreases in total flux corresponded to eastward shifts of the upwind cloud edge. Atmospheric static stability below the upwind inversion was found to be more important than the inversion height in controlling the location of the upwind cloud edge over the lake, with increases in stability corresponding to eastward shifts in its location.
Abstract
The influence that the overlake boundary layer has on storm intensity and structure is not well understood. To improve scientists’ understanding of the evolution of storms crossing Lake Erie, 111 events during 2001–09 were examined using observations from Weather Surveillance Radar-1988 Doppler (WSR-88D), surface, buoy, and rawinsonde sites. It was found that on average, all storm modes tended to weaken over the lake; however, considerable variability in changes of storm intensity existed, with some storms exhibiting steady-state or increasing intensity in specific environments. Noteworthy changes in the storm maximum reflectivity generally occurred within 60 min after storms crossed the upwind shoreline. Isolated and cluster storm modes exhibited much greater weakening than those storms organized into lines or convective complexes. The atmospheric parameters having the greatest influence on storm intensity over Lake Erie varied by mode. Isolated and cluster storms generally weakened more rapidly with increasingly cold overlake surface air temperatures. Linear and complex systems, on the other hand, tended to exhibit constant or increasing maximum reflectivity with cooler overlake surface air temperatures. It is suggested that strongly stable conditions near the lake surface limit the amount of boundary layer air ingested into storms in these cases.
Abstract
The influence that the overlake boundary layer has on storm intensity and structure is not well understood. To improve scientists’ understanding of the evolution of storms crossing Lake Erie, 111 events during 2001–09 were examined using observations from Weather Surveillance Radar-1988 Doppler (WSR-88D), surface, buoy, and rawinsonde sites. It was found that on average, all storm modes tended to weaken over the lake; however, considerable variability in changes of storm intensity existed, with some storms exhibiting steady-state or increasing intensity in specific environments. Noteworthy changes in the storm maximum reflectivity generally occurred within 60 min after storms crossed the upwind shoreline. Isolated and cluster storm modes exhibited much greater weakening than those storms organized into lines or convective complexes. The atmospheric parameters having the greatest influence on storm intensity over Lake Erie varied by mode. Isolated and cluster storms generally weakened more rapidly with increasingly cold overlake surface air temperatures. Linear and complex systems, on the other hand, tended to exhibit constant or increasing maximum reflectivity with cooler overlake surface air temperatures. It is suggested that strongly stable conditions near the lake surface limit the amount of boundary layer air ingested into storms in these cases.
