The Chautauqua County Water Network
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Evaluating the water quantity in southwest NY...


Precipitation Trends

Precipitation Trends of Chautauqua County
Side view of Chautauqua County looking east, with Lake Erie
in the left foreground and a heavy black line marking the shore

Both rain and snow increase southeastward over the county. This is due to both a shoreline effect ("lake effect") and an orographic effect.

Locally, "lake effect" refers to an increase in rain or snow because as warm Lake Erie water evaporates, it increases the temperature and amount of moisture in the clouds. When the warmer clouds pass over the cooler land it causes the clouds to cool and condense and drop rain or snow. These conditions are common in autumn and prior to ice covering the lake.

The orographic effect is an elevation effect; air is forced upwards simply because a hill is in the way and forces the air to rise. As the air goes up it cools, condenses and rains or snows. The air has to rise 1000 feet just to get from Lake Erie over the edge of the plateau; then as the air travels southeastward across the county it rises another 600 feet or more. These changes in elevation throughout the county are displayed by the illustration at the top of this page.

Thus, climate changes significantly with location from Fredonia to Cassadaga or Westfield to Mayville. The following graph shows monthly snowfalls when data were available in recent years.

Snowfall comparison of Chautauqau County, December 2002 - March 2005

Lastly, note that differences between lake effect and orographic effect are observable. Each year's graphs show peaks early in winter when lake effect is maximum as caused by maximum differences in lake vs. land temperatures. However, even as temperatures between lake and land reach a similar degree (similar snow-ice covered condition), the upland sites have more snowfall (orographic effect). How could this hypothesis be further tested? Perhaps a comparison could be made between the stations we graphed here and a line of weather stations where the ground is somewhat flat; such is closer to Buffalo. Those stations should have little orographic effect.




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Page modified 6/4/14