Air Pressure decides whether or not clouds will form. Low pressure brings cold air up usually making clouds and then once the clouds too heavy the rain falls. With a high pressure system usually cold air stays down. With temps can mean if it'll be snow, rain, sleet, and such. Tornado's and Thunderstorms usually happen in warmer weather because of warmer air coming up which is because of a low pressure system since warm air rises it goes up. Hope it answers your question. Ask away...
