1) Cold frontal systems tend to become quasi-stationary
through central Mississippi, southeastern Louisiana, and southeastern Texas
when the air mass behind the system has a trajectory down the Mississippi
Valley to central Kansas, and then eastward. The Bermuda Ridge has
pushed westward. Another indication that a frontal system is going
to become stationary west of the local area is digging of the jet stream
westward along the West Coast, which produces a cut-off low or a retrograding
trough along the California coast.
Prolonged quasi-stationary frontal systems in the local area have a
similar pattern. A continental polar/arctic air mass moves down the
Mississippi Valley to northern Arkansas and then east-southeast into western
Georgia and becomes stationary. The cold frontal system moves into the
Gulf where the front then becomes stationary. At the same time, a westward
extension of the Bermuda High moves into the north central Gulf.
2) The atmospheric conditions are similar to that of a cold frontal
passage with prolonged postfrontal cloudiness. However, wiith a quasi-stationary
front, short waves move eastward through the axis of the long wave trough.
They continue eastward and produce open waves along the front. Close monitoring
is needed to detect low pressure development so that timely warnings and
forecasts can be made.
About 24 hours after the front becomes stationary, weak short waves
at the 700/500 mb level begin to move along the frontal system. This
produces stable waves on the surface that ripple along the frontal zone.
The open waves that ripple along the surface frontal system produce
an increase in rain showers at and northward of the frontal wave.
Radar is helpful in detecting the associated shower activity.
Severe weather is often associated with the development of an unstable
wave or closed low on the frontal system. A strong short wave trough with
associated positive vorticity advection moving off the Texas coast just
south of Galveston will trigger a closed surface wave development on the
Depending on the upper-air pattern, this wave may continue to develop
as it moves east and northeast, producing thunderstorm activity that has
a high potential of being severe as it passes through KNPA's area of