Research Topics and Results

MCS Initiation and Development near the Great Lakes
This research examines the effect of a large body of cold water (like the Great Lakes) on the formation and development of large convective systems. In the warm season, these large lakes tend to be much cooler than the surrounding land, which creates a natural temperature gradient near the shore of the lakes, especially in quiescent conditions. However, the duration, magnitude, and depth of the "cold dome" over the lake have yet to be thoroughly examined. With the advent of high-resolution observations, reanalysis datasets, and mesoscale models, we now have the opportunity to more thoroughly study the land/lake boundary conditions and the impact of those boundaries on MCS development and formation.

The cases in this section were selected either from the climatology of large MCS events created earlier, or are cases from external time periods which show key features for convective and MCS initiation and upscale growth. The number of cases has been trimmed from 11 to 7 to 4 currently. Two cases in this study (LS1 and LM1) are analyzed in much greater detail because they are used in model simulations and show the effects of the nearby cold lake without too much contamination from precursor convection.

Cases proximate to Lake Superior:
Case LS1: 0700 30 July 2006
This is one of the primary motivating cases of the entire study. Early cloud cover and a precursor MCS moved through the area along the southern shore of Lake Superior, lowering the temperature locally in the area. The air over the lake remained quite cool throughout the day on 29 July, while the air over the land quickly warmed back close to its previous temperature. This set up a sharp thermal gradient along the southern shore of Lake Superior, which was likely deeper than normal because the air over the lake had been cooled through a deeper layer because of the convection that morning. Once the LLJ kicked in during the overnight period on 30 July and very warm, moist air arrived from the Great Plains, convection formed and grew upscale along the land/lake boundary.

Case LS2: 0500 24 July 2005
A similar case to the previous event, but this one is included to show that not every case which looks like it has an impact from the lake is actually lake-driven. Because the cold dome over the lake can be (and usually is) very shallow, a larger-scale synoptic front can mask and basically invalidate the shallower temperature gradient induced by differential land/lake heating.

Cases proximate to Lake Michigan:
Case LM1: 1800 08 June 2003
This case was chosen for further study because it highlights one way Lake Michigan can affect convective development. A large frontal system passed across Lake Michigan about 6 h before the event studied here. In the clear air behind the passing cold front, south-southwesterly flow meant that some of the air streaming toward the center of the surface cyclone was heated over land the entire time, while just a few kilometers further west, the air took a trajectory over Lake Michigan. This difference and warming in the clear air occurred between 1200 and 1800 UTC, so differential surface heating was certainly a possibility. A second convective line developed along the shore of Lake Michigan and moved eastward, trailing the primary convective line by ~200 km. Modeling results show that the removal of Lake Michigan causes much more widespread convection (since all of the insolation is now affecting land), and creates an arc of convection at the leading edge of the warming. Thus, the lake signficantly impacted the shape of convective development.

Case LM2: 1600 18 July 2005
A key case to determine the effect of differential heating along a front and frontal acceleration over a lake. A cold front was passing through Minnesota and then Wisconsin overnight on 18 July. The convection dissipated over Wisconsin and Lake Michigan soon after daybreak. However, another small line of convection fired downstream of Lake Michigan, near Traverse City, MI, and quickly redeveloped into a line in Michigan. While useful as a case study -- especially for showing another way that Lake Michigan may affect MCS development -- it event did not simulate very well, given the small scale nature of the initial convective burst and the importance of observations over Lake Michigan.