BOISE, Idaho — Western portions of the Treasure Valley, including Caldwell and Nampa, are still experiencing low visibility due to lingering fog. This is a sharp contrast to eastern portions of the valley, such as Boise, where the sun is shining through a mild haze.
This contrast is caused by a strong high-pressure system, keeping air very stable. The cooler air is confined to areas of slightly lower elevations. There is approximately a 10-degree temperature difference within a few miles. The warm temperatures the valley has seen over the past few days are making the ground significantly warmer than the air that is locked in place. It is enough of a difference for the moisture to condense out and create fog.
Typically, fog will dissipate when the air starts to mix in the afternoon, but the high-pressure system has this cooler portion of air locked in place.
The National Weather Service issued an air stagnation advisory that is in effect until Saturday at 11 a.m. and a dense fog advisory has been added which will be in effect for the lower Treasure Valley and Eastern Oregon until 1 p.m. Saturday.
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