Up here in Minnesota with lots of diverse weather, it seems that winter storms last longer, are bigger than (area-wise), and move slower than summer storms. I’ve seen lots of winter storms and blizzards that seem to last at least 12 hours and dump snow continuously the entire time. However, I’ve only seen a couple of rainstorms that last that long and rain somewhat consistently. Rainstorms almost always seem to move in a relatively thin band across an area while snow storms hover and are much more spread out on the radar.
Is this just my imagination? If not, why does this happen?
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There are two main types of storms that cause rain or snow: a slow type that happens mostly in the winter, and an intense rapid type that happens in summer.
In a “frontal system”, large-scale wind patterns push warm humid air up over a body of cold air, the cold air acts like a ramp. The rising warm air cools, creating rain or snowfall as long as the winds keep driving he air “up the ramp”. This can go on for days. These storms tend to happen in winter, when you get stronger temperature variations from place to place. They create snow in winter, or long drizzly rainfalls in spring and fall.
In a cumulus / thunderstorm system, *very* moist air near the ground gets warm enough to rise up on its own. As it does so the humidity condenses into rain/snow, but this also releasing heat, which powers even more rising motion. This is a self-amplifying chain reaction, that continues until the humidity supply is exhausted. So the storm grows really fast, is very intense, and dies out fast too. This type of storm happens mostly in the summer (or in the tropics), when the air is especially warm and humid.
Snowstorms seem to last longer because they usually cover much more area than rainstorms. Also, snowflakes fall slower than rain because of their shape, raindrops are nice and circular so they have little air resistance compared to a snowflake.
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