What are the common types of winter frost?
By Thomas deHaas – ANR Educator OSU Extension and Jeff Stachler – North Dakota State University Extension Cropping Systems Specialist at the Carrington Research Extension Center.
Driving to a pesticide training last Thursday morning. It was still dark, but I noticed the trees and shrubs were sparkling. It wasn’t Jack Frost. It was Hoarfrost. So, what is Hoarfrost? And are their different types of frost?
Hoarfrost is a sharp grayish-white crystalline deposit of frozen water vapor formed in clean still weather on vegetation, fences and other cold surfaced objects. It’s taken from the old English adjective ‘hoary’ which means gray or white in appearance.
With the cold still nights we have experienced in northwest Ohio, we have seen frost form in the early morning.
The best time to see this is right at sunrise.
When I arrived at my meeting, and took more pictures, I spoke with Dr. Aaron Wilson, our OSU Climatology Specialist. He reminded me of a fellow ANR Extension Educator by the name of Jeff Stachler, who was previously in Auglaize County, Ohio until 2020. He is now the Extension Cropping Systems Specialist for North Dakota State University but loves to speak of and take photos of frost in his spare time. I asked him to explain frost and under what conditions it is likely to form. The following descriptions and pictures are courtesy of Jeff and the images are gorgeous!
And here is what Jeff Stachler, NDSU Extension Cropping Systems Specialist had to say:
“What are the common types of winter frost?
There are three types of winter frost, hoarfrost (derived from the Old English meaning of frost resembling an old man’s beard),
rime frost or rime ice,
and window frost.
The basic weather conditions for all types of winter frost are temperatures below freezing, high humidity, relatively low wind speeds and dew points low enough to form ice crystals.
According to Dan Kottlowski, AccuWeather Senior Meteorologist, hoarfrost occurs when the water vapor, moisture, in the air goes directly to sharp ice crystals on any object below freezing. Hoarfrost typically forms when the air has sufficient water vapor, the air is nearly calm, and object temperatures are below freezing. Usually, the colder the air the better the chances of amazing hoarfrost development. With my wife and I now living in Cooperstown, ND we get a chance to see hoarfrost multiple times during the winter.
It is so beautiful and amazing. I take pictures with nearly every hoarfrost event. The uniqueness and beauty of the sharp crystals are amazing!
Look as some of the included photos. If the air temperature stays really cold and there is little wind and minimal sunshine, hoarfrost can stay on objects for multiple days. Once the sun shines brightly to allow temperatures to get near or above freezing and/or the wind speed is above about eight miles per hour the hoarfrost will fall off of the objects on which it formed.
As I learn more about frost, since I see it so often and Tom asked me to write about it, the most common winter frost is rime frost, also called rime ice. Rime frost usually occurs when the air is nearly saturated with moisture, such as the presence of fog, windspeed is above zero, but relatively low (at least under 10 miles per hour) and the air and object temperatures are below freezing.
Rime frost occurs when the water droplets attach to the surface of below-freezing objects and turn into ice immediately. Rime frost forms more of a round-shaped ball that sticks together instead of the sharp crystals seen with hoarfrost, however, there can be so much rime frost within a day or even during one night and during multiple days of fog with temperatures significantly below zero, the rime frost can get one to two inches in length on objects.
The other cool thing about rime frost is it usually forms on objects downwind since wind can be present in the formation of rime frost. With the rime frost forming downwind, it usually forms on one side of an object instead of all sides of an object, unless the wind direction changes while fog is still present.
I greatly enjoy taking pictures of rime frost during the day with the sun shining in the early morning or at night with streetlights illuminating the frost on objects. Trees usually have the most and coolest rime frost. It is so amazing to see how rime frost makes different designs for each tree species!
Pine and spruce trees look way different than deciduous trees and each species within the two types of trees are different as well.
Sometimes when the windspeed is close to zero you can get a mixture of rime and hoarfrost at the same time. This past Christmas in Brooks, Alberta, Canada where my wife is from was the first time I’ve seen actual crystals looking like snowflakes. It was just phenomenal!
The last type of frost is window frost. Window frost occurs when there is moisture in the air and the glass on the outside is below freezing and the inside part of the glass is slightly above freezing.
Window frost was very common in many parts of the country including Ohio, however with the invention of double pane windows, it is hard to find single pane windows anymore that allows window frost to occur. Our patio door happens to have a single pane glass and as you can see from the photos the patterns are highly variable. It is just so amazing.
My guess is the eastern half of North Dakota, and the northern half of Minnesota and Michigan gets to see these three types of frost the most often during the winter.
Since herbaceous plants are already dormant and woody plants can handle very cold temperatures, hoarfrost and rime frost will not damage most woody species, unless fog is present for many days and the rime frost collects on woody branches to break them. I have not seen this happen before, but in 2023, the rime frost was so thick, around two inches in length and sometimes longer, I was concerned wood species branches could break if the wind would have gotten stronger at that point in time.
Hoarfrost and rime frost are my most favorite types of winter frost, but the variable conditions at which rime frost can occur, it usually is the prettiest because it can get so thick! God is so great to paint such beautiful and changing winter scenes for us in North Dakota! I sure hope Tom choses some cool photos to share with you of the different types of frost. If want to learn more about winter frosts, you may contact me at jeff.stacher@ndsu.edu.”
Thanks, Jeff, for the fantastic explanation on Frost. I sure learned a lot. I am grateful for the time Jeff Stachler, who previously worked for OSU Extension – Auglaize County, so a fellow Buckeye took to craft this article. He now lives in North Dakota, but he loves describing and photographing hoarfrost. But in North Dakoata, it’s a whole different story.
My pictures look nothing like his pictures. But hoarfrost is a beautiful thing.
As a side note, why do some people like getting a flocked Christmas Tree?
Looks pretty similar to a real frost event!
Will frost hurt plants? No, But……
Most ornamental trees shrubs and plants will tolerate frost just fine.
But, with the cold temperature, some fruit crops, especially grapes,
and fruit trees like peaches
may experience some or significant losses in fruit set. Not due to frost but to the extended cold temperatures
we have had this winter may have damaged the buds.
Peach Buds:
Grape Buds:
But we will have to see in spring just how much damage has occurred.
In the meantime, get out and look for signs of spring in the snow. Some witch hazel
in a variety of flower colors are getting ready to bloom.
Also, Lenten Rose will soon follow.
I know Punxsutawney Phil saw his shadow on Groundhog Day
predicting 6 more weeks of winter. But spring is just around the corner.
