Lake Tahoe weather: Foggy Martis mornings more likely in winter
February 15, 2016
TRUCKEE, Calif. — It's early morning, and while skies may be clear elsewhere in the Truckee-Tahoe region, visibility in the Martis Valley area near Truckee Tahoe Airport is obscured by fog.
Have you ever wondered why this weather phenomenon exists?
When asked why fog forms more frequently in that particular spot, Shane Snyder, a meteorologist for the National Weather Service in Reno, said the area has three key elements for fog formation — a water source (Martis Creek), cold temperatures and calm air.
Fog, which is a cloud of tiny water droplets suspended in the atmosphere at or near the Earth's surface, generally occurs when relative humidity is at 100 percent, he said, meaning the air is saturated and cannot hold additional moister.
As a result, water vapor will fall out of the air as water droplets, forming fog.
With colder temperatures, the air can't hold as much moisture, Snyder said. Since cold air sinks, it tends to settle in low-lying areas such as valleys, making fog there more common.
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During the winter, when temperatures are colder, nights are longer and there are more moisture sources (considering Truckee's snowpack), fog is more likely to form in Martis Valley, rather than in the summer.
More specifically, for the month of January, the chance of fog forming overnight and being present the following morning in the valley is more than 10 percent, Snyder said, versus about 1 percent in the heart of summer (July and August).
As it gets later in the day, the sun indirectly warms the air, allowing it hold more moisture, and so, the water droplets are absorbed back, in causing the fog to dissipate. Wind can also disrupt fog by mixing the air.
When driving through fog — which typically begins not far from the Northstar intersection off Highway 267 when heading toward Truckee — Snyder advises motorists to take it slow and use low beam headlights, as the light from high beams will reflect back, causing glare and further decreasing visibility.
Visit wrh.noaa.gov/rev to learn more from the National Weather Service in Reno, including forecasts specific to Truckee and North Lake Tahoe.
Also, visit truckeetahoeairport.com to learn more about Truckee Tahoe Airport, and to view web cams and to subscribe to weather alerts.