Cap

{
  "id": "MLC-T-MET-000404",
  "term": "Cap",
  "field": "Meteorology and atmospheric science",
  "definitions": [
    "A layer of stable air aloft that inhibits vertical air movement and suppresses the development of deep convection. This stable layer, often characterized by a temperature inversion, acts as a lid, trapping warm, moist air below it. If the cap is eventually broken by sufficient heating or lifting, explosive thunderstorm development can occur.",
    "(also called \"Lid\") A layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.\n\nThe cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development."
  ],
  "synonyms": [
    "lid",
    "Lid"
  ],
  "references": [
    "NWS Glossary"
  ],
  "url": "https://mlchart.com/terminology/meteorology/cap/"
}