Tornadoes are rare west of the I-25 corridor; however, one notable exception was an F3 tornado that struck 4.4 miles south of downtown on June 15, 1988. On the other hand, the suburbs east of Denver and the city's east-northeastern extension (Denver International Airport) can see a few tornadoes, often weak landspout tornadoes, each spring and summer—especially during June with the enhancement of the Denver Convergence Vorticity Zone (DCVZ). The DCVZ, also known as the Denver Cyclone, is a variable vortex of storm-forming air flow usually found north and east of downtown, and which often includes the airport. Heavy weather from the DCVZ can disrupt airport operations. In a study looking at hail events in areas with a population of at least 50,000, Denver was found to be ranked 10th most prone to hail storms in the continental United States. In fact, Denver has received three of the top 10 costliest hailstorms in United States history, which occurred on July 11, 1990; July 20, 2009; and May 8, 2017 respectively.
Denver is in the center of the Front Range Urban Corridor, between the Rocky Mountains to the west and the High Plains to the east. Denver's topography consists of plains in the city center with hilly areas to the north, west and south. According to the United States Census Bureau the city has a total area of 155 square miles (401 km2), of which 153 square miles (396 km2) is land and 1.6 square miles (4.1 km2) (1.1%) is water. The City and County of Denver is surrounded by only three other counties: Adams County to the north and east, Arapahoe County to the south and east, and Jefferson County to the west.