Louisiana and Southeast Texas
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.
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.
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