In the winter, when warm, tropical air from the gulf of mexico moves northwestward, cities like denver that are situated along the eastern side of the rocky mountains tend to get prodigious amounts of snow. what is the cause of these storms?

Denver is located between rocky mountains in west and high plain in east. Lies within semiarid climate type.

Explanation:

December is the coldest month of the year, as chinook winds bring in warming effects to this place. The impact of the warm and moist tropical gulf of Mexico moving in northwestwards brings climatic changes to the city of Denver having large and big ranges this mountain tends to have snow through the year. For the Denver F3 type of tornadoes strike the region often have weak land spots in each summer and June as Denver cyclones are a vortex of caused due to the heavy weather disturbances and bring down hail storms as they are the 10th costliest storm that occurs due to the mountain ranges  

Its decreasing because of illnesses

It is the doctrine that the us had the right and duty to expand throughout north america. it just means they believed they had the right to expand westward and they did! they stated with the 13 colonies and then they kept moving gaining different territories throughout the years