Louisiana and Southeast Texas
Fog
Research and Modeling
Timothy A. Erickson* National Weather Service Lake Charles, LA
![This picture was taken in the Intracoastal Waterway near the Grand Lake pontoon bridge. This barge unit "PUSH" was moving very slowly due to the dense fog.](images/mvc-024s.jpg)
Picture by Kent Kuyper: This picture was taken in the
Intracoastal Waterway near the Grand Lake pontoon bridge. This barge unit "PUSH"
was moving very slowly due to the dense fog. The fog pictured is "sea fog".
This is obvious by looking at the U.S. flag flying by winds necessary to bring
the fog inland. The picture shows how significant fog is to the marine industry.
Purpose: This research was conducted to help find the cause in fog
development and times of initiation. This research focused mainly on what
conditions were necessary for fog initiation. Better forecasting of these events
may prove to help in time and monetary losses as well as traffic and marine
accidents.
Area of Study: The principal region of study includes the
Lake Charles National
Weather Service Office County Warning Area (CWA); the area it is responsible
for issuing warnings, forecasts, advisories, and statements. In Southeast
Texas, this includes the counties of Jefferson, Orange, Jasper, Newton, Tyler,
and Hardin. In Louisiana, this includes the parishes of Cameron, Vermilion,
Iberia, St. Mary, Upper and Lower St. Martin, Calcasieu, Jefferson Davis,
Acadia, Lafayette, Beauregard, Allen, Evangeline, St. Landry, Vernon, Rapides,
and Avoyelles.
In addition, the fog model produced may be used along the entire northern
gulf coast. The model output should be taken with caution since it has never
been used for locations outside the Lake Charles CWA. The model should be run to
find how viable it would be for a certain area of consideration before using
operationally.
FOG FORECASTING
The fog model developed from this research
indicates that FOG will be defined as water droplets suspended in the air
reducing visibilities to 1/2 mile or less not including visibilities reduced due to
shower or thunderstorm activity.
There are 2 major scales of fog:
1) Widespread (mesoscale)
2) Local (microscale)
Problems with each scale will cause forecasting headaches,
but the local (microscale) fog is almost impossible to forecast. Local fog may
effect only one or two areas with other close-by sites continuing to show minor
to no restrictions in visibility. The problem with trying to forecast this type
is that no model will have such small resolution. Most times this type of fog
shows up as coastal fog that lies along the immediate coast and along the river
and channel systems. Visibilities will be lowered in this fog deck to less than
a 1/4 mile while on either side visibilities may range from as little as 3 to as
much as 10 miles. Even though the width of the fog line is small, it represents
an extreme danger to all traffic moving through this "fog boundary".
Without observations and other equipment, forecasting this type of fog is left
solely to "gut feeling". Some techniques will be discussed to give
some insight into this phenomenon. Widespread fog has its problems in one
area...that is there are an enormous amount of parameters to look at. These
will be broken down into categories making forecasting fog a little easier.
Fog develops under many different and complex atmospheric
conditions. Each kind of fog will materialize as only one type of pattern with
some support from other parameters. This is called pattern recognition. There
are many types of fog to consider:
1) Radiation Fog
2) Frontal Fog
3) Marine Fog ("sea fog")
4) Advection Fog
5) Conglomerate of two or more types
The 5th type occurs most frequently.
Certain atmospheric conditions for producing fog will always
be present during formation.
A) Moisture
B) Negative or Neutral Omega within or just
above the boundary layer
C) Weak or no positive vorticity in the
boundary layer
* Author's Current Affiliation: National Weather Service, New Orleans / Baton Rouge, LA
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