Inversion brings unusual heavy fog to South Lake Tahoe

SOUTH LAKE TAHOE, Calif. - Fog is normally associated with San Francisco and the coastal cities of California, not with Lake Tahoe.

On Friday and Saturday, a strong inversion was in place at around the 7,000-7,500 foot level, compressing the molecules that normally evaporate off of the lake and keeping them trapped closer to the ground and the lake.

Inversions exist on a fairly common schedule, but the experience the past two days was different for a couple of reasons:

- The inversion wasn't as deep as normal but it was strong and it never broke up as it normally does. The moisture was trapped and never had a chance to escape.

- Above the cloud deck, the air was incredibly dry and the humidity in higher elevations was in the single digits Friday night.

According to National Weather Service SeniorNeterologist Dawn Johnson, both Truckee and the Martis Valley who normally experience fog and can get socked in easily were clear and dry.

Driving Friday night around the South Shore was interesting, to say the least. Street lights were covered in fog, making visibility very short-ranged. As of 1:00 p.m. Saturday, the fog over the lake is starting to break up and people will see the sky start to clear. The fog can affect a five-mile range around the lake. It is also keeping temperatures down in the affected areas.

Johnson said the areas of Markleville and south were seeing 70s Saturday.

The attached video will show how inversions occur. They are caused when the temperatures are rising with height instead of falling. A cold air mass is denser and sinks to the ground. With the warm air on top, it never has a chance to mix up unless there is a wind.

Several social media posts were spread across South Lake Tahoe with people asking "where is the fire?".

There was no fire, it was just fog. If there was a sense of smoke smell is can be caused by smoke from chimneys ...again, the particles are trapped and can't go out into the atmosphere as they normally do.

Changes are coming to Lake Tahoe so the inversion will be breaking up. Winds start Saturday night and will be from the southwest around 10 mph, with gusts as high as 20 mph. On Sunday there is a lake wind advisory from 4:00 a.m. to 7:00 p.m. Sunday. The quick-moving storm will be ahead of a big cold front, one that will drop the high temperature by 30 degrees on Monday. There is also a chance of snow Sunday after 10:00 a.m. with about one-inch at lake level.