The science behind foggy winter weather in Iowa

The science behind foggy winter weather in Iowa

Iowa Weather: Fog has been heavy across the state this winter. this is the reason.

Meteorologist Trey Fulbright explains why we’ve been seeing so much fog lately and how different types of fog form

Dense fog is a weather hazard that many central Iowans have become familiar with this winter, with several dense fog advisories over the past few weeks. While fog may look the same, there are several different types that form with different processes in the atmosphere. In Iowa, the most common types of fog that occur year-round are radiation, advection, vapor, and freezing. When forecasting fog, meteorologists look for a few key factors that can trigger fog formation: light winds, moist ground, clear skies, and saturated air from the ground to a few thousand feet above the ground. Light winds are important because this allows fog to develop and not mix with the dry air coming from above. Moist ground is important because it provides the moisture needed for fog formation. Fog is a ground cloud that develops, and the presence of low-level humidity can allow the air to become saturated more easily. Saturation occurs when the maximum amount of humidity that air can hold at a given temperature is reached. When the air temperature and dew point temperature are in a very close range, we can assume that we are close to saturation. Finally, clear skies are important because this allows most of the surface heating that builds up during the day to radiate and escape back into the atmosphere, thus efficiently cooling the air closest to the ground. On nights with radiation fog, the sky is clear, and this allows heat that has accumulated during the day near the ground to radiate back into the atmosphere. The surface temperature then cools to approach the dew point temperature but will never fall below the dew point temperature. If there are calm winds, this prevents mixing of drier air from above, and a ground cloud can form once saturation is reached and condensation occurs, which is what we know as fog. Get the latest KCCI forecasts » Download the free KCCI app to get updates on the go: Apple | Google Play Advection fog forms differently than radiation fog. The process begins with cold, snow-covered ground. When winds transport or direct warm, moist air over cold, snowy ground, that air mass then takes on the characteristics of snow-covered ground by cooling, reaching saturation, condensing, and forming a cloud close to the ground (fog). . In cases of advective fog, the winds can be slightly stronger if the air contains enough moisture. Advection fog was the primary type of fog affecting central Iowa the last week of January because we had warm, moist air moving over a slowly melting snowpack. Fog can be dangerous because it reduces visibility while driving and air travel. This can lead to aircraft pile-up or plane crashes in worst-case scenarios. When temperatures are below freezing, supercooled water droplets that form fog can freeze on surfaces, forming a layer of ice. People are advised to slow down, leave extra space and use low-beam headlights if they have to travel in foggy conditions.

Dense fog is a weather hazard that many central Iowans have become familiar with this winter, with several dense fog advisories over the past few weeks.

While fog may look the same, there are several different types that form with different processes in the atmosphere. In Iowa, the most common types of fog that occur year-round are radiation, advection, vapor, and freezing.

When forecasting fog, meteorologists look for a few key factors that can trigger fog formation: light winds, moist ground, clear skies, and saturated air from the ground to a few thousand feet above the ground. Light winds are important because this allows fog to develop and not mix with the dry air coming from above. Moist ground is important because it provides the moisture needed for fog formation. Fog is a ground cloud that develops, and the presence of low-level humidity can allow the air to become saturated more easily. Saturation occurs when the maximum amount of humidity that air can hold at a given temperature is reached. When the air temperature and dew point temperature are in a very close range, we can assume that we are close to saturation. Finally, clear skies are important because this allows most of the surface heating that builds up during the day to radiate and escape back into the atmosphere, thus efficiently cooling the air closest to the ground.

On nights with radiation fog, the sky is clear, and this allows heat that has built up during the day near the ground to radiate back into the atmosphere. The surface temperature then cools to approach the dew point temperature but will never fall below the dew point temperature. If there are calm winds, this prevents mixing of drier air from above, and a ground cloud can form once saturation is reached and condensation occurs, which is what we know as fog.

Get the latest KCCI forecasts

» Download the free KCCI app to get updates on the go: Apple | Google Apps

Advection fog forms differently than radiation fog. The process begins with cold, snow-covered ground. When winds transport or direct warm, moist air over cold, snowy ground, that air mass then takes on the characteristics of snow-covered ground by cooling, reaching saturation, condensing, and forming a cloud close to the ground (fog). . In cases of advective fog, the winds can be slightly stronger if the air contains enough moisture. Advection fog was the primary type of fog affecting central Iowa the last week of January because we had warm, moist air moving over a slowly melting snowpack.

Fog can be dangerous because it reduces visibility while driving and air travel. This can lead to aircraft pile-up or plane crashes in worst-case scenarios. When temperatures are below freezing, supercooled water droplets that form fog can freeze on surfaces, forming a layer of ice. People are advised to slow down, leave extra space and use low-beam headlights if they have to travel in foggy conditions.

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