|LOCATING A FRONT ON A SOUNDING
METEOROLOGIST JEFF HABY
Fronts such as cold fronts and warm fronts have a surface boundary that moves. A distinct air mass change occurs when transitioning from
one air mass to another. Not only are air mass changes present at the surface but they also occur in the vertical. This is because fronts
have a depth. Fronts tend to be shallower near the surface boundary and deeper farther behind the front. A vertical frontal boundary will
also have a shift in air mass. This has important forecasting implications such as precipitation type.
A sounding is a vertical profile of temperature, dewpoint and wind information with height. As the sounding instruments rise in the atmosphere
they log temperature, dewpoint and wind information. A graph can then be produced that shows how the temperature, dewpoint and wind change
with height. This graph can be used to determine at what elevation a vertical frontal boundary is present. When transitioning from one air
mass to another there can be a sudden change in temperature, dewpoint, wind speed and/or wind direction.
The air associated with cold fronts is cold and dense and thus this air tends to stay at and near the ground surface due to gravity. This
air can be shallow and in that case on the sounding there can be a sudden increase in temperature on the temperature profile. This
indicates the boundary of the vertical cold front. In a warm front situation there can also be a sudden temperature increase with
height when transitioning from the cool air ahead of the warm front to the warmer air aloft. Dry air masses can also be located on
the sounding. In a situation in which very dry air is flowing over warm and moist air, the sounding will show a sudden decrease in
dewpoint with height when transitioning from the moist air to the dry air.