Airport Dense Fog Study
by Jan Jackson and Amanda Worrell
The Blacksburg Weather Forecast Office prepares specialized weather forecasts for three airports in Virginia: Roanoke, Lynchburg and Danville; and two airports in West Virginia, Bluefield and Lewisburg. One of our toughest challenges is forecasting dense fog, with visibilities of a quarter mile or less. As the graphic below shows, the southern and central Appalachian mountains and foothills have some of the highest number of days with dense fog per year in the eastern U.S. The average for our area ranges from 40 days in the piedmont, to 80 in the mountains.
In order to help with our forecasting, 30 years worth of data, (1973 - 2003), were studied for each airport to determine how often, and at what time, dense fog was reported. The data was available in four 6 hour periods, from 4:00 am to 10:00 am, 10:00 am to 4:00 pm, 4:00 pm to 10:00 pm, and 10:00 pm to 4:00 am. The following are the results from each of the airports.
- Most of the dense fog at the Bluefield airport occurred in the morning, between 4:00 am and 10:00 am.
- The highest number of days with dense morning fog occurred in the 3 month period from July through September.
- There were no occurrences of dense fog between the hours of 10:00 amd and 10:00 pm in June, July or August.
- In the cool season months of November through March, the number of days with dense fog were fairly evenly spread throughout the hours of the day.
- Dense fog only occurred in the 10:00 pm to 10:00 am time frame in the Summer months of June, July and August.
- By far, most of the dense fog occurred between the hours 4:00 am and 10:00 am.
- The peak month with early morning fog and also total number of fog days, was January.
- In the warm season months of May through August, dense fog only occurred in the 4:00 am to 10:00 am time frame.
- December and January had the highest number of days with dense fog, all time periods combined.
- Lewisburg has the most days with dense fog by far of the 5 airports covered by the Blacksburg Weather Forecast Office.
- The vast majority of dense fog at the Lewisburg airport occurs from May through October in the 4:00 am through 10:00 am time period.
- The high number of days with dense fog in the Summer through early Fall are the result of river fog from the nearby Greenbrier River.
- There was a peak in the early morning dense fog days in July, August and September.
- There was a minimum of dense fog in March and April.
- There was only one occurrence of dense fog in the 10:00 pm to 4:00 am period.
- In every month of the year, the majority of dense fog occurred between the hours of 4:00 am and 10:00 am.
- The highest number of days with early morning (4:00 am to 10:00 am) dense fog occurred from July through November, with the highest in August.
- The highest number of days with dense fog during the rest of the day occurred in the Winter months of November, December and January.
- Most of the dense fog occurred between the hours of 4:00 amd and 10:00 am.
- There is a peak in the early morning (4:00 am to 10:00 am) fog in September.
- The 10:00 pm to 4:00 am period had the second most number of dense fog days.
- Nearly all of the dense fog between the hours of 10:00 am and 10:00 pm occurred in the cool season months from November through March.
- January and February had the highest number of days with dense fog, with the fog spread throughout the four 6 hour time periods.