Winter frost, also referred to as “ground frost,” is something that most people come to expect when the temperature drops below freezing. Even if there’s no snow or rainfall, you’re likely to see frost on the grass, trees, and other plants around your yard. It is often mistaken for light snow or sleet, but winter frost is distinguishable in a number of ways.
That said, what exactly is winter frost? What’s the difference between frost and snow? And why does winter frost come back every year? We will explain all of this and more, but first let’s take a look at the science behind winter frost.
What is Winter Frost?
Though it can occur outside of the winter months, winter or ground frost refers to the thin layer of ice that appears on the surface of plants and other outdoor objects. When water vapor is deposited on a given plant or object, several different things can happen. The water might be partially or completely absorbed or evaporated. In the case of winter frost, it changes into a solid form.
Winter frost occurs when temperatures fall below freezing (32 degrees Fahrenheit). The water vapor freezes, creating a thin layer of frost that melts when temperatures rise above freezing again. It is most common to see ground frost in the morning, as temperatures usually drop below freezing at night and then begin to rise when the daylight returns.
There are technically three kinds of winter or ground frost: radiation frost, advection frost, and evaporation frost. These types of frost are distinguished by the way in which the ice particles form. Let’s take a closer look at how these types of winter frost differ:
- Radiation Frost – This typically occurs on cold nights or mornings, when heat radiates into the open air faster than it can be replaced, resulting in ice crystal formation on plants and other objects.
- Advection Frost – When extremely cold winds blow over objects like tree branches, wires, or poles, it can cause ice spikes to form. This type of frost is more common to see on suspended objects, so it does not typically result in ground frost, though it can still be referred to as “winter frost.”
- Evaporation Frost – Evaporation frost forms as a result of dry winds blowing over a moist surface. Due to latent heat loss, the surface moisture cools below freezing, even when wind temperatures are well above freezing.
What’s the Difference Between Frost and Snow?
Snow is different from frost based on where and when it comes into existence. Frost comes about when water vapor freezes on a plant or object. Alternatively, snow refers to ice crystals that form in the atmosphere, typically from within clouds.
When snow falls, it creates a layer of ice on the ground. In smaller amounts, the difference between frost and snow may not be readily apparent. However, their respective formations are the result of very different processes.
Is Winter Frost Common in Pennsylvania?
Since the appearance of frost comes with cold temperatures, you may not see it every year, depending on where you live. In colder climates, it is possible to see ground frost outside of winter months, especially in late fall or early spring. As previously stated, it is most common to see winter frost on the grass, trees, or other plants in the morning, before the sun reaches its peak at noon.
In Pennsylvania, the climate is typically humid in both summer and winter months. This means that there is more moisture in the atmosphere, and more water vapor on the ground. As a result, winter or ground frost is especially common in Pennsylvania and the surrounding states in the north east.
Additionally, temperatures in Pennsylvania tend to drop well below freezing in winter. On average, winter temperatures fall somewhere between 24 and 40 degrees Fahrenheit in Pennsylvania. The temperature is generally at its lowest in January, and it is not uncommon to see frost on a daily basis in many regions throughout the state.
Why Does Winter Frost Come Back Every Year?
Winter frost comes back every year as long as there is moisture on the ground and temperatures at or below freezing. That said, even if you live in a cold climate like Pennsylvania, you may not always see frost, as daytime temperatures can quickly melt thin ice crystals.
As the temperature drops in the fall and winter months, the chances of seeing winter frost increase exponentially. It’s nearly impossible to see ground frost in the late spring or summer, because the temperature does not fall below freezing, meaning that water vapor cannot change to a solid form. However, as soon as the weather starts getting colder, frost returns. So, the next time you wake up early on a cold winter morning, take a look out of your window; you may just see a thin layer of beautiful winter frost on your lawn!