On a typically cold Saturday morning in March, I was planning a 200-nautical-mile flight to my parents’ home in western New York in a Piper Archer II. I would depart from Capital City Airport near Harrisburg, Pennsylvania, and land at Batavia, New York. The northern end of the Appalachian Mountains lies between the airports, with elevations up to 2,300 feet and various antennas and wind turbines perched on their crests.
I did not intend to file IFR because of the risk of icing in the clouds. And flying above a low ceiling over the mountains was not appealing. If a ceiling existed, it would need to be high enough that I could overfly the mountains without unnecessary risk.
The route would take me over the mountains near Williamsport, Pennsylvania, and Elmira, New York. At 7 a.m., Williamsport reported a scattered layer at 4,800 feet msl, while Elmira had a broken ceiling at 4,300 feet msl. This would allow me to maintain 1,500 feet above the highest ground elevations while staying 500 feet below the ceiling. The broken layer at Elmira was forecast to become scattered by 11 a.m. I decided to depart at 10 a.m.
When I called flight service, the briefer confirmed my interpretation of the data, but also mentioned Airmet Sierra for mountain obscuration. I noted this, but I did not give it much thought because the scattered layer was forecast to be well higher than the maximum elevations.
The scattered layer over Williamsport had become broken when I passed at 10:36 a.m. At a reported 5,100 feet msl, it was sufficiently high for me to continue at 4,500 feet.
However, it soon was clear that the ceiling was not the issue. As I flew over each ridge, the visibility was reduced temporarily. The reduction in visibility worsened as I passed each ridge. Then, passing over one ridge, I could not see ahead to the next. I had just learned that ceilings below the mountaintops are not required to create mountain obscuration.
A ridge rising 1,000 feet from its base is capable of creating localized changes in temperature, humidity levels, and airflow. The result is myriad potentially dangerous conditions, including reduced visibility because of mist, haze, and fog. This potential for reduced visibility should have driven me to pay more attention to the Airmet Sierra in effect that morning.
It is possible for airports on either side of a line of mountains to have ceilings well above the mountain peaks simultaneous with instrument meteorological conditions in the mountains.
If mountain obscuration exists in these conditions, then the cause in most cases is fog. On that day, relatively warm weather had caused some melting of snow in the mountains, which provided moisture that could be lifted to the higher, cooler peaks and condense into fog.
I executed a 180-degree turn and landed at Williamsport. Once there, I saw the TAFs indicated clearing would not occur until 2 or 3 p.m. At 2 p.m., I saw a significant improvement and higher ceilings, so I again ventured out.
About 40 nm out of Williamsport, the ceiling was broken and descending, and the mist and fog had returned. I diverted to Elmira to look at the weather information.
The wind was out of the northwest, and extending 300 miles from Lake Huron’s Georgian Bay was a line of clouds continuing to my route. The mountain obscuration was, in part, a result of moisture being picked up by cold arctic air flowing over the relatively warm waters of lakes Huron and Ontario and rising up the slopes of the Appalachians.
At this point Buffalo was reporting overcast at 3,900 feet agl, and Rochester was reporting scattered. As my destination was between these two cities and the terrain would be more docile, I could push on. Soon I was cruising comfortably, with the overcast layer on the left and blue sky to the right. The effort in getting to this point was surely worth it. Just as important was the lesson learned that mountains do not require low clouds to be obscured. They are quite capable of generating conditions to create obscuration all by themselves.
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