Tuesday and Wednesday’s weather was a little different. Middle Keys residents and visitors awoke to a thick fog. It ebbed and flowed all day on Tuesday and occurred again on Wednesday morning before burning off.
“It doesn’t happen that often. And to the extent that we got this one, it was very surprising,” said Elizabeth Vickery, meteorologist at the National Weather Service’s office in Key West.
Vickery said the Middle Keys experienced an advection fog (see sidebar). She said it’s pretty common over the Gulf of Mexico. Prevailing winds pushed the pockets of fog over the islands.
On Tuesday morning, Grassy Key was completely clear. However, motorists approaching Marathon experienced a wall of fog at the Coco Plum Drive intersection at 7 a.m. Later in the morning, the fog creeped north and east, enveloping the Grassy Key stretch. Other areas of the Middle Keys also experienced the come-and-go fog throughout the day.
Vickery said she fielded plenty of questions on those two days.
“Mostly, they wanted to know when it was going to go away,” she said, laughing.
There’s no fog forecast next week. Expect the highs to be
During the day the hot ground and the sun above erode the fogs in between and it evaporates it.
Next week’s forecast does not include fog. Instead, expect balmy temperatures in the upper 70s. Gusty winds will rotate clockwise around the islands, starting from a northerly direction on Friday and ending on Thursday from a southerly direction.
Advection fog is the result of condensation. The condensation is caused by the horizontal movement of warm moist air over a cold surface.
Sea fogs are always advection fogs, because the oceans don’t radiate heat in the same way as land and so never cool sufficiently to produce radiation fog. Fog forms at sea when warm air associated with a warm current drifts over a cold current and condensation takes place. Sometimes such fogs are drawn inland by low pressure.