Dear Tom,
What would Chicago’s weather be like if the Rocky Mountains weren’t there?
Jeff Nardas, Moline, Ill.

Dear Jeff,
Familiar landmarks of Chicago’s climate would be absent or significantly diminished if the Rocky Mountains were not there. Frequent, abrupt temperature changes would be greatly reduced. Huge temperature ranges between summer heat and winter cold would vanish. The occasional storms that swirl into the Midwest from their birthplace in the lee of the Rockies would also disappear.

The existence of these weather events is a testament to the capability of the Rocky Mountains to alter the weather. Oriented perpendicular to the prevailing westerlies that dominate the movement of weather systems across the United States, the Rockies inhibit the eastward movement and moderating influence of mild, moist Pacific air and encourage the north/south movement of arctic and Gulf air masses.

In the absence of the Rocky Mountains, Chicago’s climate would be dominated by Pacific air, summer and winter. The weather, consequently, would be much less prone to big temperature swings because warm, moist Gulf air would visit our area much less frequently. Outbreaks of bitterly cold arctic air would also hardly ever occur.