MONTGOMERY, Ala. (WSFA) - It has been a foggy week across a chunk of the Deep South and Gulf Coast. That was especially true Friday morning right here in Central Alabama.
Dense fog developed Thursday night and only got worse into Friday morning. It took until about lunchtime for the entire region to be entirely fog-free -- something that doesn’t happen all too often.
So what’s up with that?
Fog requires a few basic ingredients to form and sustain itself: clear skies, calm wind, sufficient moisture near the ground, a slight push of air from a warm source like the Gulf of Mexico, and temperatures that cool down to the dew point.
These ingredients most often come together during autumn here in the Southeast. That’s because we can get frequent set-ups of calm wind, clear skies and cool temperatures as high pressure systems move through about once weekly.
But we can also thank our earlier sunsets and longer nights. When the sun sets in the fall, temperatures drop fast. They continue to fall overnight as they approach the dew point, resulting in an increase in moisture (relative humidity).
That increase in moisture causes condensation to occur on tiny particles floating through the air near ground level. The result? The formation of fog! This also happens to be the way clouds form up in the sky (fog is just a cloud, after all).
It’s not necessarily a requirement for fog to form, but we did have an ever-so-subtle push of air from the Gulf last night into this morning. With the Gulf being a source of warmth and especially moisture, we had our already good recipe for dense fog turn into a perfect recipe for dense fog all across Central Alabama.
Put simply, as air from the Gulf moves in, the increase in moisture raises our dew points, thus making it easier for our temperatures to reach the dew point!
It’s also important to note that fog tends to form more often and be more dense in valleys, low-lying rural areas and near bodies of water. This may explain why some mornings feature dense fog in Montgomery, Millbrook, Coosada, and Wetumpka, but not really anywhere else.
More from the National Weather Service on all types of fog here.