Weather Rules of Thumb

All of these have different scales, ranging from hours and a few miles with the mountain breeze to thousands of miles and days to weeks with trade winds. Knowing which circulation normally affects your weather and which is dominant at the moment is what I would call one of the secrets to understanding the forecast. If the wind direction is normally 150 degrees on September afternoons, seeing 120 degrees tells you the wind is driven by something different.

Tim Vasquez

Sunday, September 16, 2018 at 12:00 AM ET

Verified

Key Takeaways:

Understanding meteorological rules of thumb, such as distinguishing true from magnetic winds and analyzing wind drivers, is crucial for accurate aviation forecasting beyond just computer models.
Atmospheric boundaries (convergence or thermal) are key indicators for cloud, shower, and thunderstorm development, with outflow boundary movement signaling storm dissipation.
Expect fog and low clouds under specific conditions, such as after rain with clear skies and light winds (radiation fog) or when local temperatures are cooler than upstream dewpoints (advection fog).
Predict the movement of surface weather systems by relating them to 500 mb winds and use charts like the 5400-meter thickness line to anticipate the rain-snow boundary.

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We’re getting into some of the most predictably pleasant flying conditions in the U.S. That’s not to say we can’t get the occasional hurricane bearing down, or a cloud-filled clipper sweeping down from the Dakotas. But as autumn arrives, days are getting shorter, the broad-scale heat-driven cyclone in the western United States is much less intense, and the onshore wind component between the oceanic highs on both coasts and the inland areas dies down.

Reduced surface heating means that diurnally-driven thunderstorms are less aggressive. And for most of the western and southern U.S., this means lots of VFR conditions, especially early in the day.