Moisture in the Air Meets Cool Ground (Image Credits: Pixabay)
Seattle – Residents noticed slick patios and dewy lawns under clear skies this week, a subtle reminder of how atmospheric moisture can mimic rainfall without a single drop falling from above.
Moisture in the Air Meets Cool Ground
The phenomenon began unfolding as a stream of subtropical air swept into the Pacific Northwest, elevating humidity levels across the region. Dew points, which measure the air’s moisture content, climbed into the low to mid-50s Fahrenheit by midday on January 13. This influx created conditions ripe for condensation, where water vapor in the atmosphere transformed into liquid on contact with chilled surfaces.
Cooler ground temperatures, lingering from a chilly late December, played a crucial role. At Seattle-Tacoma International Airport, daily highs and lows hovered below 50 degrees, allowing bricks, grass, and other outdoor elements to drop even further after sunset. When air temperatures matched or fell below these dew points, moisture began to condense, leaving behind a visible sheen that surprised early evening observers.
Understanding the Dew Point Effect
Dew point represents the critical threshold where saturated air releases its water vapor as dew upon cooling. In simpler terms, it indicates how much moisture the atmosphere holds and at what temperature that moisture starts to form droplets. For Seattle, where winter typically brings drier conditions, dew points nearing 55 degrees marked an unusually muggy episode, the highest recorded at local stations like Boeing Field so far this season…