Extended Abstract (140K)P12.7
ELBOW 2001—studying the Relationship between Lake Breezes and Severe Weather: project overview and preliminary results
David M. L. Sills, MSC, King City, ON, Canada; and P. Taylor, P. King, W. Hocking, and I. Nichols
The Meteorological Service of Canada, York University, University of Western Ontario and University of Guelph - Ridgetown College conducted a field experiment last spring / summer as part of ELBOW 2001: The Effects of Lake Breezes On Weather. The object of ELBOW 2001 is to better understand the relationship between lake breezes and severe weather, including heavy rain, hail and tornadoes, in southwestern Ontario. The anticipated benefits of the study include concepts, tools and algorithms to help severe weather forecasters assess the threat associated with lake breezes and tailor watches and warnings based on this information. This will hopefully result in more accurate watches / warnings and longer lead times.
The stable marine air delivered by lake breezes generally suppresses convective activity in areas immediately downwind of the Great Lakes. However, the leading edge of the lake breeze, called the 'lake breeze front', is a zone of enhanced moisture, lift, shear and vorticity that can act to trigger the development of thunderstorms in a convectively unstable environment. This is especially true when lake breeze fronts interact or when they collide with thunderstorm gust fronts. Southwestern Ontario, surrounded by lakes on three sides, is an ideal location to study the effects of these low-level boundaries on severe weather in the region.
MSC and York University conducted a successful pilot study in 1997 and the results indicated that lake breezes had a considerable influence on the timing, location and intensity of severe weather. The 2001 field experiment was more comprehensive and built on the experience gained in 1997. It was run between May and August, 2001, over which a number of intensive, multi-day observations were made. Experimental instrumentation included the NRC Twin Otter research aircraft, a 14 station mesonet, 4 rawinsonde systems, two wind profilers, a portable X-band Doppler radar and mobile observation equipment. These platforms were located within the effective Doppler range of the Environment Canada operational weather radar located in Exeter, Ontario, since this radar is well-suited for detecting low-level boundaries in optically-clear air. A special version of the MSC operational regional forecast model (GEM) with 2.5 km horizontal grid spacing was also run in real-time in support of the experiment.
Summer 2001 was hot and unusually dry in southwestern Ontario resulting in frequent lake breezes and less severe weather than usual. However, several events of interest were captured. The data from this study are now being analyzed and some recent results will be presented.
Poster Session 12, Tornado and Severe Storm Environments
Thursday, 15 August 2002, 3:00 PM-4:30 PM
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