Fog will end by later this week, for a while, as drier air enters Tampa Bay region

Heavy fog this week is expected to give way to the patchy variety or none at all by Friday.

Parts of Tampa Bay had visibility of less than a quarter-mile Sunday and Monday.

It will return, though, said Rodney Wynn of the National Weather Service in Ruskin.

December is often the beginning of a fog season that typically runs through February across Tampa Bay, Wynn said.

“You talk to people and they think the type of fog we’ve had is atypical,” Wynn said. “But this is the season for it and it’s nothing out of the ordinary. It’s just been a while since we last had the fog.”

Fog comes and goes depending on a number of factors, including cloud cover, humidity and wind speeds. Clear skies and humid air, as Tampa Bay has experienced during the past week, increase chances. So do weak winds.

The two types of fog most common across the region are radiation fog and sea fog, Wynn said. Just as it sounds, sea fog forms over the Gulf of Mexico and can push into coastal areas with a wind that blows east. Radiation fog forms over land when the air temperature cools sharply to match the dew point overnight and is most prevalent during the long nights of winter.

How long fog sticks around depends on how fast temperatures rise in the morning, Wynn said.

It won’t be as dense as this week, but more fog could form as soon as late Friday into Saturday morning, Wynn said: “Don’t count on it being away long.”