|WAA VS. LOCAL HEATING ON THE
850 MB FORECAST MODELS
METEOROLOGIST JEFF HABY
There is a fundamental difference between
WAA and local heating. WAA is the movement of warmer air into a region.
(diabatic heating) is warming of temperature at a fixed location without movement. WAA is common behind
warm fronts and when a strong southerly wind transports warmer temperatures to the north. Local heating is caused by
the sun's energy striking the earth's surface. Clear skies, long days, light wind and
dry air maximize local heating.
Low level WAA causes a
dynamic lifting of air (due to column stretching) and can increase
Local heating can increase thermodynamic instability but does not cause significant dynamic
lifting by itself. When using the models,
WAA is denoted in a region where wind vectors are crossing through the temperature gradient from warm toward colder
temperatures. The movement of the temperature gradient causes WAA if warmer air is being blown
toward a fixed location.