The freak dictionary
Every term I throw around, defined in one breath. Alphabetized, because chaos belongs in the atmosphere, not the reference material.
These are working definitions — what the term actually means when a forecaster uses it, not the textbook version with nine caveats. When a definition needs more room, it links to the full lesson.
- Anvil
- The flat spreading top of a thunderstorm where it hits the tropopause and gives up climbing. full lesson →
- Blocking pattern
- A stuck upper-air pattern. Whatever weather you have, you now have it for a week.
- Bombogenesis
- A low deepening 24 millibars in 24 hours. The atmosphere doing something quickly enough to earn a name.
- Cap
- The warm layer that stops rising air. Breaks or it does not, and the whole day hinges on it. full lesson →
- CAPE
- Convective Available Potential Energy. The fuel gauge for thunderstorms, and no guarantee anyone lights the match. full lesson →
- Clipper
- A fast, moisture-starved low that sprints out of Canada and leaves four inches and a wind chill behind.
- Deformation zone
- The stretched, pinched flow north of a low where snow rates go vertical.
- Derecho
- A long-lived, fast-moving windstorm from a convective line. A hurricane's angry inland cousin.
- Dew point
- The temperature at which air gives up and makes water. The only humidity number worth reading. full lesson →
- Dryline
- The boundary where humid Gulf air meets desert air. Where the Plains keeps its severe weather.
- Ensemble
- One model run many times with slightly different starting points, so you can see the spread instead of one confident guess. full lesson →
- Freezing rain
- Rain that stays liquid all the way down and then turns to ice on contact. The worst one. Not close.
- Frontogenesis
- The process of a temperature gradient tightening. Where the heavy snow band tends to set up.
- Heat index
- What the temperature feels like once humidity stops your sweat from working.
- Hodograph
- A plot of how the wind vector turns with height. Curvature here is why some storms rotate.
- Inversion
- A layer where temperature rises with height. It caps storms and traps everything else.
- Lake-effect
- Cold air crossing warm water and unloading downwind. Twenty miles decides everything. full lesson →
- Model run
- One execution of a forecast model. Four a day, and I have opinions about all of them. full lesson →
- Nowcast
- A forecast for the next thirty minutes, made mostly by extrapolating what radar is already doing.
- Overshooting top
- A bump above the anvil. The updraft was strong enough to punch through the ceiling. full lesson →
- QLCS
- Quasi-Linear Convective System. A squall line with a research budget.
- Reflectivity
- How much radar energy came back. Not rainfall, no matter how the app colours it. full lesson →
- Shear
- How much the wind changes with height. It is what turns a tall storm into an organised one.
- Snow ratio
- How many inches of snow you get per inch of liquid. Ten to one is a myth that will ruin your forecast.
- Sounding
- A vertical profile of the atmosphere. The single most information-dense chart in weather.
- Supercell
- A thunderstorm with a persistent rotating updraft. The apex predator of convection. full lesson →
- Trended east
- The forecast moved and so did the storm, usually about six hours before it mattered. The recurring villain of this website.
- Velocity couplet
- Adjacent inbound and outbound radar returns. Rotation, and the reason a warning gets issued. full lesson →
- Virga
- Rain that evaporates before it lands. Radar sees it, you do not. full lesson →
- Wind chill
- What the temperature feels like once wind strips the warm layer off your skin.
- Wintry mix
- All of winter's precipitation types taking turns disappointing you.
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