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/

Trough Axis

DivergenceConvergence

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?