11/4/2023 0 Comments Ice fog weather gif![]() This image shows an example of valley fog detected by early-morning visible satellite pictures. As the colder, denser air flows into the valleys, water vapor in the air condenses forming fog. This is just another type of radiation fog. Valley fog is fog that occurs in mountain valleys, river valleys, and other low areas. One of the hazards with this type of fog is that one can encounter rapidly changing visibility, from a few miles to just a few feet, in a short distance while traveling roads and highways. Cool air tends to pool in valleys or lower elevations in the terrain causing fog to be denser in these locations. Ground fog can reduce visibility to near zero at times, but visibility can be highly variable. Since the lowest temperature overnight typically occurs in pre-dawn hours, fog is most common in the early morning.įog as a result of radiational cooling has formed a thin layer close to the ground. If you are outdoors when fog begins to form you may notice that it is first visible as a thin layer or patches near the ground, then gets deeper as the air continues to cool. The fog's thickness depends on the depth of the cool, moist layer of air. Radiation fog can be a few feet deep right near or above the ground, or it can be hundreds of feet deep. When the air cools to the point of saturation (its dew point temperature), fog can develop. The layer of air near the surface cools under clear skies because heat absorbed by the surface during the day is released back (radiates) into the atmosphere at night. ![]() In the spring, summer, and early fall, fog often forms when radiational cooling occurs at night. Fog development is sometimes a complex process, and fog does not always form when the relative humidity is 100 percent. ![]() If more water molecules (vapor) is added or the air cools further, water vapor in the air will begin to condense into small water droplets. At 100 percent saturation (100 percent relative humidity) the air can hold no more water molecules as a gas (vapor). The dew point temperature is the temperature at which the air will become 100 percent saturated. There are a number of ways fog develops, but the underlying process is the same in each case.įog forms when the layer of air near the surface is cooled to its dew point temperature. Fog shrouding Lake Michigan spills over the Chicago Lakefront.įog is a common occurrence throughout the Midwest. Dense fog is most prevalent in the Midwest from October through March in the hours between midnight and mid-morning. Heavy fog is defined as fog that reduces visibility to 0.25 mile or less. However, in general use, the term “fog” is any visible condensation in the air (i.e., cloud), at or near the ground, even at higher visibilities. According to the international definition, fog reduces visibility to less than one kilometer (0.62 mile). Fog is not precipitation, although in the right conditions precipitation (drizzle) can occur. ![]() It is composed of tiny water droplets, or in colder weather, ice crystals. But I just did a search for current_conditions_icon_code_descriptions_e.csv and found someone that had it posted.Ĭurrent_conditions_icon_code_descriptions_e.Fog is visible condensation in the air, at or near the ground - basically a ground-based or low-lying cloud. I was actually looking for a list of what the icon numbers meant.
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