What's with the fog?

The first week of November there were two days where heavy fog fell over the area, causing schools across Delmarva to open late.

People new to the area who are unfamiliar with Delmarva's climate might be surprised by the amount of fog the peninsula sees, but the reason is anything but hazy. There is water everywhere, from rivers and inland bays to the Atlantic Ocean and Chesapeake and Delaware bays.

"Here there are more chances of having really foggy days because of being surrounded by water bodies," Delaware State Climatologist Dan Leathers said.

The region sees the most fog in the spring and the fall as the weather is transitioning from warm to cold and vice versa, said Jeff Orrock, National Weather Service Meteorologist in Charge.

Fog is caused by a number of factors, essentially forming a cloud on the ground when air reaches the dew point, the temperature at which water droplets can form.

When warm air is blown across a cooler surface, such as a body of water, it creates advection fog.

"That can create some pretty nasty marine fog," Orrock said.

And that fog can then be pushed over land.

There is also radiational fog, which is when the ground is moist and temperatures drop rapidly to the dew point, at which point the fog forms. Radiational fog is more likely to form in places such as open fields or over waterways.

So, why does the fog thin out when you're driving through trees? Trees are able to hold the heat in a little bit, lessening the fog effect.

"One thing that can be kind of unnerving with the fog, you can go from a visibility of a mile, mile-and-a-half and all the sudden you get near a body of water, or a big open field and the (visibility drops)," Orrock said.

That causes drivers to slow down their vehicles rapidly, which could lead to a possible accident.

"Any type of travel is really the big issue with fog," Orrock said.

That includes marine traffic as well.

Delays caused by fog aren't just annoying to parents with school-aged children, the National Oceanic and Atmospheric Administration estimates trucking companies lose between $2.2 and $3.5 million a year due to fog-related shipping issues.

The Maryland Motor Vehicle Administration recommends slowing down when driving through fog, and slowing down even more when you see headlights or brake lights from another vehicle – you should be prepared to stop. It also suggests using low beam headlights or fog lights if you have them, as high beams will reflect back from the fog, further reducing visibility. If you feel you can't drive safely, pull off the road to a  safe location and turn your flashers on.

rpacella@dmg.gannett.com

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On Twitter @rachaelpacella