441 Comes Full Circle: Revisiting the March 2017 Duluth Lake-Effect Snow Event (Benji Johnson)

I am revisiting the first case I ever analyzed in ATM OCN 441—the March 17, 2017, lake-effect snow event in Duluth, Minnesota. This case was interesting because it was extremely localized. Even within the city of Duluth, some locations saw over a foot of snow, while other places received next to nothing. As a result, it will be interesting to see how this mesoscale weather event looked from the perspective of a satellite outside the earth's atmosphere. 

(All figures courtesy of Terra / MODIS Corrected Reflectance True Color Imagery)

Figure 1. Animated loop of the days surrounding the March 17, 2017 snow event in Duluth.

Figure 2. Imagery from March 11, 2017. Duluth denoted with a star. Lake Superior lake-effect bands circled in red.

Figure 3. Imagery from March 13, 2017. Duluth denoted with a star. Lake Superior lake-effect bands circled in red.

Figure 4. Imagery from March 15, 2017. Duluth denoted with a star. Lake Superior and Lake Michigan lake-effect bands circled in red.

Figure 5. Imagery from March 17, 2017. Duluth denoted with a star. 

Figures 1 through 5 display days surrounding the March 17th Duluth snow event, and highlight the conditions which generated plentiful lake-effect clouds— horizontal convective rolls and cells. The presence of these lake-effect clouds is a prerequisite for the production of lake-effect snow. The relatively ice-free Great Lakes present in these images also makes prime conditions for lake-effect snow. Open water is necessary for creating a sufficient vertical temperature differential; open water allows for upward heat and moisture fluxes which can result in precipitation. The shifting orientation of the lake-effect clouds around Lake Superior in the days prior to March 17th show the effect of shifting winds. On March 17th, a synoptic system moved into the Great Lakes region which obscured the view of any potential low lake-effect clouds. Consequently, the March 17th, Duluth, MN lake-effect snow event is not visible in the Terra MODIS Corrected Reflectance True Color imagery. This is not even counting the fact that the bulk of snow in this event came in the nighttime and early morning hours. The satellite feature used in this analysis does not have the temporal resolution needed to dive into that aspect of the snow event. In the end, even though we cannot see the mesoscale disturbance that caused the March 17th Duluth snow, we can see that conditions were favorable for lake-effect snow in the Great Lakes region in the days leading up to the event. 

Figure 6. Cloud top heights in meters.

The look at cloud top heights in Figure 6 allows us to see that the clouds in the Duluth area were relatively low, on March 17th, 2017. If we could see the individual lake-effect bands responsible for the snow in Duluth, these low clouds would be sensible since lake-effect clouds are generally capped by the boundary layer. This adds to the congruency in the case analysis so far.