The Front Room
The same air mass brings a drizzle over one boundary and a squall line over another, depending on which air is doing the lifting.
Phase 0 · The phenomenon
One air mass, two kinds of weather
Left panel: a gently sloping wedge of cold air with warm air gliding up over it, a long sheet of flat grey layered cloud and light drizzle spread over a wide area. Right panel: a steep, blunt nose of cold air pushing under warm air, with a tall anvil-topped thunderstorm cloud and a narrow band of heavy rain just ahead of the cold air.
A warm, humid air mass sits over the southern plains. On its northern edge, cooler air retreats slowly and the warm air glides up over it: the result is a grey day of low cloud and drizzle that lasts from breakfast until the next morning.
On its western edge, a cold air mass charges in and shoves under the same warm air. There the sky builds a line of towering thunderstorms, gusty wind and a downpour that is over in under an hour.
Same warm air. Same moisture. Two completely different days. In this lab you will find out what the boundary — the front — does to the air above it.
How can the same warm, humid air mass give a long, grey drizzle at one front and a short, violent squall line at another?
What this lab works toward
HS-ESS2-4Use a model to explain how changes in the energy flowing into and out of Earth's systems change climate.HS-ESS2-5Investigate the properties of water and how water changes Earth materials and surface processes.
Plain-English summaries. The course maps these performance expectations to this lab; the official wording is published at nextgenscience.org.
The stations
- Cloud BaseWhat sets the height of the cloud base?
- Front SlopeWhich front lifts the warm air faster, and by how much?
- Stability TestWhen does lifted air keep rising on its own?
- Front RoomWhat happens when the same unstable, humid air meets a warm front versus a cold front?
Each station runs the same loop: predict before you see any data, investigate the model and record runs, reveal what the measurements show, then explain the gap between your prediction and the result. A claim-evidence-reasoning checkpoint and an exit ticket close the lab.
- Air is followed as a single rising parcel that does not mix with its surroundings. Real rising air entrains drier air, which weakens clouds.
- Above cloud base the parcel follows a pseudo-adiabat computed from its temperature and pressure; pressure falls with an 8 km scale height. No ice processes or rain-out are included.
- Fronts are drawn as straight sloping surfaces. Real cold fronts have a steep, blunt nose near the ground — steeper than their average slope — which makes their lifting even more abrupt.
- The surrounding air cools at one steady rate all the way to the tropopause. Real soundings have inversions, dry layers and wind shear, and a steep lapse rate rarely runs through the whole troposphere — so very steep settings give larger storm energies than real air masses usually hold.