Basic Convergence and
Divergence
Definitions/Concepts
• Convergence is air coming together
• Combination of confluence (air moving together) and
speed convergence (air slowing down over a distance)
– Surface convergence associated with low pressure and
potential for rain, snow, thunderstorms, etc.
– Upper-level convergence associated with sinking air and
therefore surface high pressure
• Fair weather
• Divergence is air spreading apart
• Combination of diffluence (air moving apart) and speed
divergence (air speeding up over a distance)
– Surface divergence associated with high pressure and fair
weather
– Upper-level divergence associated with rising air and
therefore surface low pressure
Traffic Jam Analogy
• Trough axis is the traffic jam.
– Cars slow down approaching the traffic jam
(convergence)
– Cars speed up exiting the traffic jam (divergence)
Recognize on a Upper Air Chart
Intro to the 500mb Map
http://www.spc.noaa.gov/obswx/maps/
Convergence
Divergence
Trough Axis
Note: Divergence and convergence can’t actually be found on a map like this as they
are mathematical quantities, but in general, divergence occurs downstream of a
trough axis and convergence occurs upstream of a trough axis.
• What does this
mean for
forecasting?
• Basically: fair
weather behind
a trough axis
and
clouds/precip
possible ahead
of a trough axis
Precip or no Precip for Oklahoma?