The Trend Technique

  • If a phenomenon is in steady state, or is moving at constant speed, the trend technique can be used.
  • rate x time = distance
  • so if distance traverse by cold front is known over a given time period, its position can be extrapolated in time.
  • more accurate on shorter time scales (minutes to hours)
  • a short term forecast is called a "nowcast"

QUESTION FOR THOUGHT:

Suppose that is is presently warm and raining. A cold front will pass your area in three hours. Behind the front it is cold and snowing. Make a persistence forecast for your area 6 hours from now. Would you expect this forecast to be correct? Explain. Now, make a forecast for your area using the steady-state, or trend method.

image from Meteorology Today by C. Donald Ahrens  1994 West Publishing Company