November 16, 2021 - Fog in California

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Winter moisture and cool weather created a dense fog over California’s
Central Valley on November 13, 2021. The Moderate Resolution Imaging
Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a
true-color image of the morning fog on that same day.

This fog, known as tule (too-lee), is a frequent feature of winter in
the Central Valley. Although gorgeous to view from space, the thick low
cloud (fog) can be hazardous for people on the ground. According to
local media, the National Weather Service issued a special “very high
transportation risk” alert on the morning of November 13. The alert
warned drivers to be prepared for traffic delays, reduce speed, use low
beams, and allow extra space between vehicles.

The formation of tule fog requires three ingredients: wet ground, still
air, and cold temperatures. Conditions are ripe after the ground has
become damp from a recent rain. During the day, the warmth of the Sun
causes the moisture to evaporate into the air. After sunset, air
temperature slowly drops. Because cool air can hold less moisture than
warm air the many tiny moisture droplets suspended in the air during
the day combine into large droplets, creating “low cloud”, or fog. Tule
fog tends to form—often rapidly— after sunset, become thickest just
before dawn, then slowly thins as the air warms in the morning. Tule
fog season typically begins in December and ends in February.

Image Facts
Satellite: Terra
Date Acquired: 11/13/2021
Resolutions: 1km (521.8 KB), 500m (1.4 MB), 250m (995.1 KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2021-11-16

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