Wednesday, March 11, 2015

Fog Blog

FOG /fôɡ,fäɡ/
Water that has condensed close to ground level, producing a cloud of very small droplets that reduces visibility to less than 1 km, or 0.625 miles.

Fog on Anderson Rd. in Bowling Green, OH; Photo Credit: Samantha Kirby
As meteorologists, we report fog in many circumstances; most of which occur when visibility is not below 0.625 miles. Fog can be a very flexible term used to describe several different types of weather conditions, resulting in many different categories of fog.

  • Radiation Fog sounds dangerous, but is a harmless concept. Under clear skies with calm winds at night, temperatures cool rapidly at the surface, causing a deep layer of condensation near the ground. This is very common in NW Ohio and SE Michigan.
  • We experienced a few instances of Freezing Fog this past winter in which surfaces are coated in a layer of ice by supercooled water droplets suspended in the air. Under incredibly cold conditions, Ice Fog and/or Diamond Dust may even occur and limit visibility. 
  • Valley Fog or Upslope Fog, rarely occur in Toledo-- for obvious reasons. For this to develop, light winds must force air up an embankment (hillside, mountain, valley, etc) to a level where the air becomes saturated and condensation occurs. Valley fog can also be a form of Radiation Fog where the air condenses in a low lying area. 
What we will deal with primarily at this time of year is known as Advection Fog. Also the result of condensation, advection fog occurs when warm, moist air moves over a cold surface. Say, a surface layer of snow and ice, for example?

Picture from Twitter
As the snow-melt process continues over the next few weeks, we will experience many advection fog events. Many mornings with school delays. Many opportunities to 'use the low beams'. Many days with slow-moving traffic and hard-to-see tail lights. 

If you're not sure, our StormTrack Weather Team will always be on-air with your most up-to-the-minute information.

If the National Weather Service issues a Dense Fog Advisory, we'll be here to tell you.

                                                                                   With maps like these, we can show you the lowest levels of visibility around our region, what you're about to drive into and what you may be driving out of. This is #FogSeason and until the ground and lake temps warm up to match the air, we'll be dealing with this for weeks and months to come. 

Perry's Monument in the fog at Put-In-Bay; Photo Credit @TeachPIB