Meteorology: Weather & Station Models
Air pressure and wind, reading station models and isobars, fronts and air masses, and what makes weather stormy or clear.
Air pressure, highs, and lows
- Low pressure (L) — air rises, cools, and condenses → clouds, precipitation, stormy weather. In the Northern Hemisphere, winds spin counterclockwise and inward.
- High pressure (H) — air sinks → dry, clear, fair weather. Winds spin clockwise and outward.
- Cold, dry air is denser and sinks (higher pressure); warm, humid air is less dense and rises (lower pressure).
Isobars and wind
Isobars are lines connecting points of equal air pressure (in millibars). The closer together the isobars, the steeper the pressure gradient and the stronger the wind — just like tightly spaced contour lines mean a steep slope. Pressure is lowest at the center of a set of nested isobars marked L.
Reading a wind barb
On a station model, the wind is shown as a staff with feathers. The crucial rule: the staff points in the direction the wind is coming FROM, and the feathers (barbs) show speed. A staff pointing to the northeast means a northeast wind — air moving from the NE toward the SW. Winds are always named for where they come from.
Fronts and air masses
An air mass takes on the character of where it forms: maritime (m, humid) or continental (c, dry); tropical (T, warm) or polar (P, cold). A front is the boundary where two air masses meet:
- Cold front — cold air shoves under warm air; brief, intense storms, then clearing.
- Warm front — warm air rides over cold air; long, steady precipitation.
Moisture in the air
Air holds water vapor until it cools to its dew point — the temperature at which it becomes saturated and vapor condenses into clouds, dew, or fog. When the air temperature equals the dew point, relative humidity is 100%.