Most of us have been listening to the TV weather report since we can remember; but even though I remember learning about different kinds of clouds, types of snow and other meteorological conditions in earth sciences in junior high, I don't really know the difference between partly cloudy and mostly sunny — do you? (I suppose over the years, I've kind of made up a version of what I think they mean, but it's based on experience, not learning the definitions.)
Of course, some weather terms are pretty self-evident: polar air is very cold air that comes down (or up, if you live in the Southern Hemisphere) from polar regions (Canada, the Great Lakes region and upstate New York have plenty of experience with this frigid blast). A sandstorm, for our Southwestern cousins, is a windstorm that kicks up sand — which personally sounds way more terrifying than polar air, but I'm a New Yorker, so what do I know?
But plenty of the terms we hear regularly are pretty mystifying. I've dug up the definitions of some of the most confusing terms (but there are hundreds of official weather terms; if you're interested, check out the exhaustive list over at NOAA):
Onshore breeze: This is air that is blowing over the water and onto land; also known as a sea breeze, it's what summer evenings, especially on the East Coast, are made of.
Partly cloudy: When 3/10 to 7/10 of the sky is cloud-covered, weather forecasters will use this term, though it's mostly used to refer to night skies.
Partly sunny: Basically the same thing as partly cloudy, except it's a term most used in the daytime (when the sun would be out — so it emphasizes how much sun there is rather than clouds).
Overcast: When the sky is 9/10 filled with clouds
Isolated storms: This term is used when a storm or storms are moving through an area, but they are only going to affect 10-20 percent of the area. Unlike the definition of scattered storms, below, isolated storms usually indicate that just one storm will pass through, and once it's over, it should be clear.
Scattered storms: This is when thunderstorms are likely to affect 30-50 percent of the area; they are the kind of storms where it will rain like crazy for five minutes, and then the sun will come out; and hour later the whole dramatic episode will start again. These on-and-off storms can go all day or all night. (Here's a lengthier and more complete discussion of isolated vs. scattered storms.)
Severe thunderstorm: A storm with winds in excess of 58 mph (that's 50 knots) and/or hail that's bigger than 3/8-inch round.
Slight risk (of severe thunderstorm): This means there's only a 2-5 percent chance of a tough storm as detailed above — and if you do get such a storm, it's likely to be isolated to a smaller area.
Inversion: An increase in temperature with height (because usually it's the opposite). According to NOAA, these are important because "Temperature inversions trap atmospheric pollutants in the lower troposphere, resulting in higher concentrations of pollutants at ground levels than would usually be experienced."
Muggy: No official definition; this one can be used for a variety of warm and typically humid weather.
Want to learn how to read a weather report? The BBC put together this useful video that explains the terms you'd hear on the news.