ALL ABOUT MOISTURE

Tim Vasquez

Friday, March 26, 2021 at 09:59 AM ET

Verified

The GOES satellite water vapor channel detects moisture even in clear air.

Key Takeaways:

Atmospheric moisture, measured by dewpoint, mixing ratio, or precipitable water, is fundamental to understanding visibility, ceilings, and precipitation, as it governs condensation into droplets and haze.
Relative humidity and dewpoint depression are practical indicators for pilots; a small temperature-dewpoint spread (5°C or less) suggests high relative humidity and potential for fog or low clouds, with zero spread indicating saturation.
High low-level dewpoints (e.g., in the 60s and 70s) are significant contributors to atmospheric instability and are closely associated with severe weather phenomena like hail, high winds, and tornadoes.
Fog, whether radiational, advection, or frontal, is a critical manifestation of high moisture conditions when air cools to its dewpoint, severely impacting flight visibility.

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With summer approaching, we often think about those hot temperatures, high density altitudes, and storms. But another factor enters the picture: moisture. High relative humidity brings foggy mornings, and with soaring dewpoints comes the prospect for storms and rain.

With moisture having such a profound impact on flight operations, it’s time to take a closer look. Maybe we can even help you understand that dewpoint you always dutifully copy down from the METAR.