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Training and Safety Tip: When weather happens between reporting points

In aviation routine meteorological reports (METARs) and terminal aerodrome forecasts (TAFs), the terms VC (vicinity) and DSNT (distant) mean that the reported or forecast weather is between 5 to 10 nautical miles (VC) and beyond 10 nm (DSNT) from the reporting station.

Photo by Mike Fizer.

But what happens when next to METARs and TAFs at your departure and destination airports there’s only one reporting station along your route?

That happened to one pilot who relied on reported weather along the route to be only marginal VFR near that one reporting point about two-thirds into the route. Unfortunately, that wasn’t the case and the pilot unintentionally flew under visual flight rules (VFR) into instrument meteorological conditions (IMC)—a real emergency. Don’t take this lightly as most pilots who fly VFR into IMC don’t survive. While this pilot survived by climbing through the clouds, the NASA Aviation Safety Reporting System (ASRS) report indicates that the pilot didn’t have a clear understanding of how thick the cloud layer was. Fortunately, the layer turned out to be only a few thousand feet thick, and the airplane broke out on top and flew to the destination without further incident. The pilot also wasn’t clear about weather products and tools reviewed in the online briefing and subsequent telephone update briefing.

Here’s an excellent tool to see forecast weather conditions over a wide area: the Aviation Weather Center’s Graphical Forecasts for Aviation (GFA). Enter your route using the flight path tool, and once your route is depicted on the map, zoom in to see the details. Menu buttons at the top allow you to look at each weather condition that might affect your flight, and a sliding timeline shows you the forecast conditions expected for your flight’s duration. One feature that would have helped the pilot who filed the ASRS report is the “Clouds” forecast. Zooming into the flight route, you’ll see forecast cloud bases and tops. Each menu option provides a specific key so you can readily understand what you’re looking at.

The GFA information makes it easier to stay VFR and avoid becoming a VFR-into-IMC accident statistic. Just take the time to compare your route of flight with the forecast conditions. Weather can change, but you’ll be better prepared to deal with it when it does. Consider providing a pirep (pilot weather report) to help out your fellow pilots as well.

John Collins

Aviation Safety Programs
John Collins is the AOPA Air Safety Institute's chief flight instructor and manager of aviation safety programs. Before joining ASI, John was AOPA's manager of airport policy. He earned his flight instructor certificate in 1996 and enjoys seeing students light up when they put it all together and nail a maneuver.
Topics: Training and Safety, Student, Flight School
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