ROCHESTER, N.Y. – Tell me if you have heard any of these? There is radiation fog, upslope fog, steam fog or advection fog (just to name a few). These fog events all happen for different reasons, but what they all have in common is they reduce the visibility at the surface of the Earth. That visibility can range from a light haze with maybe four to six miles visibility or a dense fog with visibility restricted to a quarter of a mile or less.

During the middle of the this week portions of Western New York had some foggy problems – especially over the southern tier near the Pennsylvania border. The communities of Olean and Jamestown had zero visibility due to heavy fog.  However, around our “neck of the woods” the fog was not quite as thick. Canandaigua was down to a mile and a half and Batavia the visibility was reduced to three quarters of a mile. A fog advisory was then posted for portions of Western New York. Keep in mind that that degree of visibility will vary from day to day and even hour to hour.

But what type of fog did we have today? This is called advection fog and when it happens there needs a certain set of ingredients. First, you require a very cold surface or a cold landscape. In this particular case that cold surface is a snow cover. That snow acts like the refrigerant and as that very mild, moist air crosses into the snowpack it will cool the air down to the point of saturation. At that point, the moisture becomes visible with condensation. Simply stated, we are looking at a cloud that just happens to be located on the ground. Usually this type of fog happens for us during the late winter or early spring season.