A popular shorthand in fiction is to use snow as a direct indicator of how cold the weather is, and the amount of snow indicates the amount of refrigeration. The reasoning is that snow falls when the temperature is cold, so when the temperature is very cold there should be lots of snow. This is not how it works in real life - the colder it gets, the less likely significant snowfall is. In fiction, though? When the temperature drops, get ready for a blizzard.
This trope usually appears in fictional works in one of two ways:
An area with moderate or warm climate experiences a sharp drop in temperature, whereupon it gets hit with a sudden appearance of snow, such as a blizzard with gale-force winds. If the Big Bad uses his Weather Control Machine to chill the planet, expect to see a snow-draped Miami complete with icicle-covered palm trees.
Snowfall is used as a visual indicator of how cold something is. This typically happens for comedic effect, such as a Funny Animal opening a refrigerator door and getting blasted by a flurry of snow. If the temperature drops further, the amount of snow will increase accordingly. This is a case of Reality Is Unrealistic, as snow generally only occurs around the freezing point. It won't snow at all if it's bitterly cold out.
Nearly every occurrence of Batman villain Mr. Freeze ever. If he's generating sub-zero temperatures, expect lots of snow and ice to instantly appear, even if it's in the middle of the Atacama Desert or the vacuum of outer space.
Averted in The Incredibles; Frozone can't generate ice in a burning building because of the lack of humidity. Of course, in normal conditions, he's able to summon impressive amounts of ice from thin air, possibly because he lives in a coastal city and can also use some of the water in his body. This is another example of Reality Is Unrealistic: a major byproduct of most combustion is H2O; Frozone should not have a problem finding water in a burning building.
Unless he absorbs water at an accelerated rate and uses his internal stores to make the ice. Can't breathe in the H2O-laden smoke, no matter how useful it might be to generate ice in a burning environment.
The scene immediately after that has him drinking a (small) cup of water to produce ice again.
The novelization of Star Trek IV: The Voyage Home averts this. While the probe's blotting out the sun causes snow in many cities, in St. Petersburg, it is too cold to snow.
Subverted in Fantastic Four: Rise of the Silver Surfer, when the Surfer's passage causes snow to fall on the Great Sphinx outside Giza, Egypt ... without a corresponding drop in temperature.
Played very straight in Frozen — when Elsa loses control of her powers in the middle of the summer, the countryside quickly turns cold and snow begins to fall.
In Beakman's World, every episode is begun, ended, and occasionally interrupted by a scene of two talkingpenguins watching the show from the South Pole. It is perpetually snowing during all of their scenes, which is particularly interesting because in one rapid-fire Q&A session, Beakman explicitly points out that the South Pole actually gets very little snow.
To explain: Mrs. Olsen cites the heavy snowfall as proof that "global warming is a crock." Actually, because snowfall occurs due to humidity, excessive snowfall occurs when there's more humidity in the atmosphere, due to increased evaporation of the Earth's oceans and ice packs. Ergo, the heavy snowfall would be evidence for global warming, not against it.
The original Transformers Generation 1 cartoon episode "Fire In the Sky" has the Decepticons tapping the Earth's geothermal energy and chilling the planet. The Autobots become suspicious when it begins snowing in July at their desert base.
In the G.I. Joe miniseries "The Revenge of Cobra", the Joes attack Cobra's desert base to stop the villains from using their rebuilt Weather Dominator. Among Destro's weather attacks is an instant snowstorm.
In the Teenage Mutant Ninja Turtles episode "Take Me To Your Leader," Shredder and Krang use a Solar Siphon to drain the sun's energy and make the Earth cold. The turtles discover something's amiss when it starts snowing in July.
In Sponge Bob Square Pants, it always snows in Sandy's treedome during winter. This appears most prominently in "Survival of the Idiots", but it also pops up briefly in "Bubble Buddy".
In Spider-Man and His Amazing Friends, Spidey and Iceman first met during a Let's You and Him Fight situation. Iceman got Spider-Man's attention by causing a freak blizzard during the summer. Iceman wasn't seen actually throwing snow around to do it (as comic Iceman would likely have to. Making ice constructs and changing weather patterns aren't the same power; he isn't Storm.) but appeared to be just willing it to happen.
An episode of Code Lyoko saw XANA try to bury France in an Endless Winter to get at the protagonists. It was already snowing, but it was there to drive home the point that the temperatures were dropping deep into the negatives; hell, Yumi almost dies of hypothermia in Ulrich's arms, only to be saved by a return to the past.
Whenever a large snowstorm occurs, expect to see members of certain political factions ranting about how "the climate can't be getting warmer because of all this snow!" or something to that effect