Secondly, moisture is needed to form clouds and precipitation. The Gulf of Mexico is an excellent source of moisture in Missouri. And lastly, a lifting mechanism, such as a frontal boundary, is needed to lift warm moist air over the colder air to form the clouds and precipitation. In Missouri, the major snowstorms usually develop across the southern Rockies and move eastward across the plains. As these storms move east, moisture from the Gulf of Mexico is drawn northward ahead of the system, while arctic air plunges southward into the area from Canada.
Sleet occurs when raindrops freeze while in the atmosphere as ice pellets.
They tend to bounce off of the surface and accumulate on the ground. Freezing Rain on the other hand, occurs when temperatures throughout the atmosphere are above freezing and the surface of the ground is at freezing or below. The raindrops then freeze when coming in contact with the ground and tend to glaze over surface causing very hazardous driving conditions. Snow occurs when temperatures are below freezing in enough of the atmosphere where the snowflake cannot change state. The ground can still be above freezing with snow occurring, however most of the atmosphere above the ground to the cloud producing the snow must be below freezing.