Winter weather patterns explained

The warm weather we’ve been experiencing over the last several weeks came abruptly to an end on Thursday, and that serves as a perfect reminder that winter is right around the corner.The National Weather Service designated Nov. 10 as Winter Weather Awareness Day in central Iowa, and we want you to be prepared for the upcoming season here with KCCI Storm Team 8.Central Iowa is no stranger to significant winter weather, so we wanted to look at some common weather patterns that bring us winter weather. The first setup is called a “Colorado Low” in which an area of low pressure develops on the foothills of the Rocky Mountains. Typically, these form in southeastern Colorado, but can also originate in other locations just downstream of the Rockies. Once the low pressure forms and can move east, it advects, or transports moisture northward from the Gulf of Mexico, and that moisture is lifted over a pre-existing cold air mass over the Midwest and Northern Plains leading to the formation of clouds and precipitation.These Colorado Lows typically move slowly and can produce some of our largest winter storms because of their access to plentiful moisture. Forecasting these systems can be a challenge as the path the low takes is crucial for snowfall amounts. One wobble north or south can shift where the heaviest snowfall amounts occur here in central Iowa. The second setup is called a “Clipper System.” These form in the Canadian Provinces of Alberta and Saskatchewan and are often called “Saskatchewan Screamers” or “Alberta Clippers.” Unlike the Colorado Lows, these typically don’t have as much access to moisture and move much faster, resulting in lighter yet still impactful snowfall amounts. Ultimately, the type of winter precipitation we receive during the late fall, winter, and early spring highly depends on the temperature profile of the atmosphere. The temperature profile throughout the atmosphere is not uniform, so this can lead to some interesting and impactful forms of precipitation.When the temperature from the ground to just below the cloud bases is above freezing, this results in just rain. If there is a shallow layer of sub-freezing temperatures at the surface, with a large warmer layer above the surface to just below the clouds, we get freezing rain. Freezing rain can form a glaze of ice that coats objects and surfaces and can even lead to structural damage if there’s enough of it. If there is a deeper layer of sub-freezing temperatures and only a small layer of warmer air in between the cloud bases and the surface, then this leads to sleet. Melted raindrops have time to refreeze into little ice pellets that bounce around and accumulate.Lastly, when the entire column from the cloud bases to the ground is below freezing, this results in snow. There are cases where snow can mix with rain when temperatures near the ground are above freezing, but the temperature in the atmosphere aloft must be very cold to allow this to happen. We hope this explainer helps and makes you more weather aware as we head into this winter.

DES MOINES, Iowa —

The warm weather we’ve been experiencing over the last several weeks came abruptly to an end on Thursday, and that serves as a perfect reminder that winter is right around the corner.

The National Weather Service designated Nov. 10 as Winter Weather Awareness Day in central Iowa, and we want you to be prepared for the upcoming season here with KCCI Storm Team 8.

Central Iowa is no stranger to significant winter weather, so we wanted to look at some common weather patterns that bring us winter weather.

The first setup is called a “Colorado Low” in which an area of low pressure develops on the foothills of the Rocky Mountains. Typically, these form in southeastern Colorado, but can also originate in other locations just downstream of the Rockies. Once the low pressure forms and can move east, it advects, or transports moisture northward from the Gulf of Mexico, and that moisture is lifted over a pre-existing cold air mass over the Midwest and Northern Plains leading to the formation of clouds and precipitation.

These Colorado Lows typically move slowly and can produce some of our largest winter storms because of their access to plentiful moisture. Forecasting these systems can be a challenge as the path the low takes is crucial for snowfall amounts. One wobble north or south can shift where the heaviest snowfall amounts occur here in central Iowa.

The second setup is called a “Clipper System.” These form in the Canadian Provinces of Alberta and Saskatchewan and are often called “Saskatchewan Screamers” or “Alberta Clippers.” Unlike the Colorado Lows, these typically don’t have as much access to moisture and move much faster, resulting in lighter yet still impactful snowfall amounts.

Ultimately, the type of winter precipitation we receive during the late fall, winter, and early spring highly depends on the temperature profile of the atmosphere. The temperature profile throughout the atmosphere is not uniform, so this can lead to some interesting and impactful forms of precipitation.

When the temperature from the ground to just below the cloud bases is above freezing, this results in just rain. If there is a shallow layer of sub-freezing temperatures at the surface, with a large warmer layer above the surface to just below the clouds, we get freezing rain. Freezing rain can form a glaze of ice that coats objects and surfaces and can even lead to structural damage if there’s enough of it. If there is a deeper layer of sub-freezing temperatures and only a small layer of warmer air in between the cloud bases and the surface, then this leads to sleet. Melted raindrops have time to refreeze into little ice pellets that bounce around and accumulate.

Lastly, when the entire column from the cloud bases to the ground is below freezing, this results in snow. There are cases where snow can mix with rain when temperatures near the ground are above freezing, but the temperature in the atmosphere aloft must be very cold to allow this to happen.

We hope this explainer helps and makes you more weather aware as we head into this winter.

Winter weather patterns explained

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