Plane & Pilot
Tuesday, March 6, 2012

Weather Avoidance: Back To Basics

Ten simple steps to enhance your weather planning and avoid Mother Nature’s worst

NTSB statistics show weather as one of the top five accident causes in general aviation, with an 85% fatality rate.
One example is the phrase, "VFR not recommended." FAA research has shown the phrase is offered much too often. The net effect is that many pilots have heard the warning, decided to launch anyway to "take a look," and have found no bad weather along their route, confirming their confidence. So the phrase has lost some of its bite. But experts caution it's still a phrase that should sound an alert to pilots, to prod them to gather more information before making a decision.

It's up to the pilot to interpret the information received in a briefing. For example, many pilots abuse the terminal area forecast (TAF). Dennstaedt explains that most pilots don't realize a TAF is only good for a five-mile radius around the station. "It's a point forecast, and not indicative of the weather along a route," he adds. Pilots get into trouble reading the TAF and mentally expanding its forecast farther out than it should be.

Another part of the standard briefing pilots need to rethink is the winds-aloft forecast (also called "FB winds"). The problem is the report's "resolution," which pilots can think of as "freshness date and accuracy." Winds-aloft forecasts are good for six hours; which is too long in many instances. Also, the readings are taken at the closest grid point to the reporting stations, which are 12 kilometers apart, and they're given at 3,000-foot intervals. "A lot can happen in between those 3,000-foot layers," says Dennstaedt. "Use winds-aloft forecasts in conjunction with other tools to tell the whole story."

Strategic Plan, Tactical Decisions
Weather avoidance is a strategic exercise that consists of acquiring data and making tactical decisions based on that data. Because weather isn't static, a one-time telephone briefing—with its shortcomings—isn't always adequate for making decisions that will affect your and your passengers' lives. Pilots can supplement their current techniques with a multi-step approach to weather planning and avoidance.

1 Spot Trends: Seeing what the weather has been doing in the past several hours is something few pilots do, but is the best indicator of what it probably will do. One tool for this is the surface analysis chart. "One of the best tips I can give pilots is to learn to read a surface analysis chart," says Dennstaedt. The surface analysis is a computer-generated report that's transmitted every three hours and covers the contiguous 48 states and adjacent areas. It shows the areas of high and low pressure, fronts, temperatures, dew points, wind directions and speeds, local weather, and visual obstructions. The chart also shows weather at specific reporting points across the country— each depicted by a "station model" with lots of useful information. Charts are available for previous days.

2 Gather Data: The Internet and cable/satellite television have made weather data gathering a no-brainer. But the overwhelming amount of weather data available has made it confusing for pilots to find what's truly useful.

Pilots should use many sources combined to get the most accurate picture of the weather. For example, the lay person's "Weather Channel" has useful, aviation-specific weather available at by drilling down to "aviation." Even their televised weather is a great place to start. Though not technically FAA approved, they provide compact, packaged summaries to get you started. The National Weather Service's Aviation Weather Center ( is useful, especially their AIRMET and SIGMET watch boxes.


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