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Research

The Lake Michigan Effect: Possible Relationship Between Lake Michigan Ice Cover and Stronger Storms in the Spring

Trevor Bengtsson and Eddie Snyder, Meteorology 4922 (Senior Seminar II) Dr. Jeff Kimpel, former director of NSSL

Virgina Silvas, Geography Graduate Student

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from the web.To restate the our research goal, we were looking to find a possible relationship between ice coverage on Lake Michigan in the winter months, and the frequency and timing of severe storms the following spring. The winter data was analyzed, for both the high ice coverage years and the low ice coverage years, and we found supporting evidence to what we had expected. The years with higher ice coverage had colder average lake surface temperatures and the vice versa.So seeing similar trend in the high ice coverage years, and also in the low ice coverage years, we grouped the similar years together for storm data analysis. Therefore the 1996 and 2014 years are considered the cold years, and 1998 and 2002 are now considered the warm years.

Results

To start, our data was selected under the criteria that it had to be from 1995 or later as we used NEXRAD radar data to filter the raw storm reports, and NEXRAD radar data was not available before 1995. The years of interest that we selected were based on an anomalously high or anomalously low amount of ice coverage on Lake Michigan. We selected four years based off the figure above, which were 1996 and 2014 as high ice coverage years, and and 1998 and 2002 as low ice coverage years.

We then gathered information from the Great Lake Environmental Research Laboratory (GLERL) on the average lake surface temperature for all of the years in question and plotted them against an average lake surface temperature averaged from 1992 to 2014.

Once the temps were plotted, we then analyzed the spring months which followed each winter by analyzing the amount of storm reports and the timing of the storm reports. First the reports were filters to prevent multiple reports from the same storms, such as multiple hail reports from one cell. This filtering was done using the following method:

1. If a thunderstorm cell continually appears in the radar imagery then it would require one TWH report (if applicable).

2. If a thunderstorm cell disappears from the radar imagery and reappears as a new storm, then it would be considered two independent thunderstorm cells, which means it can have up to two TWH reports (if applicable).

3. Once two or more thunderstorms merged into a mesoscale convective system, then it would be considered two or more thunderstorms. This means that there can be two or more TWH reports (if applicable) for this convective event.

4. Tornado storm reports were not filtered out because they occur at a shorter time scale.

These storm reports for the cold category and the warm category were then sorted by month of occurrence and then plotted in a bar graph. The results can be seen in the figure labeled Storm Reports by Month to the right. This plot showed that for the cold winter cases, storm reports begin earlier in the year than in the more mild winter cases. Also the Cold winter cases also end earlier in the year than do the more mild winter cases. So based on these, there seems to be a shift in the timing of the severe weather occurrence depending on the amount of ice coverage for the preceding winter.To address the other part of our research goal,

References

We looked at the raw totals of the storm reports, separated into Hail, wind, tornadoes, and totals. We took the averages of these reports and the standard deviation based on the averages from the winter data (1992-2014) and compared to the individual years in question, and found that none of the years showed a consistent trend and all of the data was witin one standard deviation of the mean.

In conclusion, we found that in our limited research, there is no impact on the number of occurrences of severe weather following an extrema in ice coverage. These occurrences seem to be driven by other factors, which due to time constraints and limited resources, we did not have the time to look into, but could provide more insight in future research. However, our major finding seems to be a shift in timing of the first and last occurrences of severe weather. Following these extrema years with an anomalously high ice coverage, the severe storm occurrence starts earlier in the year but also ends earlier. This could have major impacts on the forecasting for those areas surrounding Lake Michigan and allow the public to be better prepared for the risk of severe weather.