Sometimes it's pretty obvious what you're looking at on a satellite image. Most hurricanes or those classic tornado outbreaks in the Midwest leave no question as to their identity. But there are some features that make you think for a minute. This is one of those cases.
My friend Dan Satterfield posed a question to the readers of his blog, Dan's Wild Wild Science Journal, to see if they could "think like a forecaster" when looking at this satellite image and figure out what's causing the clear strip of skies from Virginia Beach to the west through the Piedmont region of Virginia.
I've highlighted in red the clear strip of skies in question. Can you figure it out?
You'll notice that the clear stripe of skies acts like a dividing line between a thick deck of clouds towards the north and a broken field of clouds towards the south.
The thick deck of clouds is actually dense fog stretching across much of the Mid-Atlantic, dropping the visibility to near-zero in some locations. The broken field of clouds below the fog deck is where the sun was beating down on the ground most of the morning and afternoon, allowing the surface to heat up and parcels of air to rise. As the air rose, it condensed into puffy cumulus clouds and created the fields of cumulus you see along and south of the Virginia/North Carolina border.
The clear strip was caused by fog that "burned off" as the heating of the day took over. Fog forms when the temperature and the dew point meet, creating 100% humidity and allowing the water vapor in the air to condense. As the air temperature starts to rise and climb away from the dew point, the humidity drops, allowing the clouds to dissipate.
At the time of the satellite image, the fog had dissipated but there wasn't enough heating to create rising air and fill in the sky with cumulus clouds, so it left an area of clearing between the two sets of clouds.
Weather is awesome.