03 January 2015

Thunderstorms Part I

No chit-chat this time, let's get started.

Reference ACWM Chapter 15

Requirements for development of a thunderstorm:
  • high relative humidity
  • steep lapse rate
  • lifting force / triggering action

Life cycle of a thunderstorm (1 - 3 hours):
  • cumulus stage: only updrafts are present in the cloud
  • mature stage: starts at onset of precipitation at the surface; updrafts and downdrafts
  • dissipating stage: presence of downdrafts throughout nearly the whole cell

Classification of thunderstorms:
  • airmass: form within a warm, moist air mass; isolated
  • frontal: warm front (embedded in stratiform layer; least severe), cold front (form in continuous line; quite severe), trowal (rapid lifting of warm, moist air; moderate severity)
  • squall line: most severe, may include heavy hail, destructive winds, tornados; often form 100-200 miles ahead of fast-moving cold fronts
  • convective: formed by heating from below or by convergence of wind flow
  • orographic: wind forces moist, unstable air up mountain slopes
  • nocturnal: unusually warm air aloft, frequently occurs at night or early morning in Midwest / Central Plains

POP QUIZ!
You've inadvertently just flown into a thunderstorm cell.  What do you do?

Discussion of tornados, hurricanes and hazards to follow.

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