how might climate change affect heavy lake-effect snowstorms kenneth kunkel, nancy westcott, and...
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![Page 1: How might climate change affect heavy lake-effect snowstorms Kenneth Kunkel, Nancy Westcott, and David Kristovich Illinois State Water Survey Champaign,](https://reader034.vdocuments.us/reader034/viewer/2022042717/56649d785503460f94a5a825/html5/thumbnails/1.jpg)
How might climate change affect heavy lake-effect
snowstorms
Kenneth Kunkel, Nancy Westcott, and David Kristovich
Illinois State Water Survey
Champaign, IL
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Great Lakes-Climate
• The Great Lakes have a number of effects on local climates, particularly on locations immediately downwind
• Such locations experience enhanced snowfall in winter, warmer winters, and cooler summers compared to locations distant from the shoreline
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Seasonal Cycle of Air Temperature and Lake Surface Temperature
From Kristovich 1998
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Lake-effect Snow
• In the late fall and early winter, cold frontal passages bring in air that is much colder than the lakes
• This cold air is warmed and moistened by the warm lake surface waters
• Snow forms in this warmer (but still cold) and moister air and is deposited on the lee shores
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Main pressure and frontal features associated with lake-effect snow
From Laird and Kristovich (2002)
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Satellite loop showing development of clouds over lake after frontal passage
QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.
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Radar image of snow bands
10 20 30 40 50 60
0700 UTC 11 Nov 1996 2000 UTC 11 Nov 1996
B2B1
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Assessment Study
• Examined the weather conditions that were conducive to heavy lake-effect snowstorms (8 inches or more occurring over a 24 hour period)
• Initial focus was on Lake Erie, but the results were extended to Lakes Superior and Michigan
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Weather Conditions Associated with Heavy Lake-effect Snow
• Surface air temperature in the range of 14-32°F (-10 to 0°C)
• Difference between lake surface temperature and air temperature greater than 13°F
• Wind speed greater than 14 mph• Wind direction allowing a long passage
over lake
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Climate Model Analysis
• Used two future climate simulations-one from the Hadley Centre (United Kingdom) climate model and the other from the Canadian climate model
• Examined differences in the frequency of heavy lake-effect snow conditions between the present and the end of the 21st Century
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Climate Models
• There are differences in the way these two models are constructed
• Climate models break the atmosphere into boxes and determine values of weather conditions for each box
• The boxes in the Hadley Centre model for the atmosphere are smaller than those in the Canadian model
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Climate Models
• However, the boxes in the Canadian model for the ocean are smaller than those in the Hadley Centre model
• The treatment of the land surface is more sophisticated in the Hadley Centre model than in the Canadian model
• Model differences lead to different projections for the future
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Results
• The Hadley Centre model projects a greater than 50% reduction in the frequency of heavy lake-effect snow by 2100 while the Canadian model projects a more than 90% reduction
• The reduction is almost entirely due to warmer winter temperatures (about 5°F for the Hadley Centre model and 10°F for the Canadian model)
• An increase in lake-effect rain is likely to accompany the decrease in lake-effect snow
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Results (continued)
• For southern Lake Michigan, the decrease is about the same as Lake Erie. However, there is a much smaller decrease for the Lake Superior snowbelt (only about 10% for the Hadley Centre model)
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Confidence in results
• Although there are model differences, these two models (and all other climate models) indicate significant warming over the Great Lakes
• Thus, the eventual decline in the frequency of heavy lake-effect snowstorms seems highly likely
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Potential Effects of Ice Cover?
• Lake-effect snow is greatly diminished once ice cover develops
• Duration of ice cover will decrease in a future warmer climate
• Longer season for lake-effect snow could compensate
• Our results for the end of the 21st Century take this into account; however, this could be an important compensation in the early portion of the 21st Century (which we did not examine)
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This study indicated that air temperature is the key
The following analysis is based on the primary importance of air
temperature
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Historical Climate Analysis
• An examination of historical climate data provides some insight into possible future outcomes
• This analysis assumes that, as temperatures rise, the day-to-day variations remain the same
• This assumption may not be valid, but the analysis of the two GCMs did not indicate significant changes in variations
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Heavy Snow
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Benton Harbor
Houghton
Traverse City
Iron Mt
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New Climate Model Results
• Recently available projections from a newer version of the Hadley Centre model and a U.S. model are consistent in indicating significant warming in the Great Lakes region
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Provided by Katharine Hayhoe and Donald Wuebbles
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Provided by Donald Wuebbles
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What About Total Snowfall?
• In our assessment, we did not study the effects of climate change on total snowfall
• An examination of past historical data may provide some guidance
• This examination shows that warmer winters are generally less snowy
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Conclusions
• Climate models suggest that during the 21st Century, heavy lake-effect snowstorms will dramatically decrease in frequency in the southern portions of the Great Lakes basin
• Changes in the northern portions of the basin may be much less
• These changes are caused almost entirely by warmer temperatures; other conditions favorable for heavy snow do not change much in the climate models
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Conclusions
• What we were not able to examine is the speed with which these changes will take place. Will decreased frequencies begin to occur early in the 21st Century, or later?
• The models do show warming in the early part of the 21st Century, so mid-winter melting events may become more frequent, even if total snowfall does not change
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THE END