Old-time saying? Yes, but this age-old bit of weather lore is nonetheless a fairly accurate predictor.
The clear full moon as it rose over the Blue Ridge Mountains Tuesday night.
Moonlit nights are clear nights. Clear nights mean no cloud cover to hold in daytime warmth which results in a rapid temperature drop through the night. Sunday night we had a beautiful, bright, almost full moon and by Monday morning, the temperature had dropped into the low 20′s. We awoke to a beautiful hoar frost covering everything.
Hoar frost, also called true frost, forms when water vapor in the air turns directly to ice crystals without first condensing into water droplets (dew). This occurs on nights when the temperature drops below freezing before the water vapor begins to condense. Ice crystals will form on any cold surface creating a frosty white wonderland that is quite a beautiful sight. Sometimes, when the air is very moist, a covering of hoar frost can become so thick, it can be mistaken for snow!
Miscanthus plume covered with delicate ice crystals.
This is what we woke up to on Monday morning. Because the air had been so saturated from the recent misty rain and the moonlit night had become so crisp and cold, a fairly heavy hoar frost had formed on every exposed surface – plants, shrubs, berries, grass, trees, and even rocks.
A beautiful frosty morning!
I couldn’t help going out to snap a picture or two. Well, a picture or two turned into a 45 minute photo session as I discovered more and more fascinating crystal covered bits of nature! The further I wandered from the house, the heavier the layer of frost became.
Too bad I didn’t think to put my jacket on!
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Here are a few of the “cool” frosty photos I took.
Closer to the house where it was more protected, the frost was lighter. My Helleborus flowers were frost covered and nodding.
The blueberry buds and branches were white with frost crystals.
A wild honeysuckle vine with needle-like ice crystals projecting from the leaves and stem
Hoar frost covers the scale-like needles of a cedar branch.
Frost covered an old flower stem
A colorful heuchera leaf is edged in white ice crystals.
Even this spider web was covered with jewel-like ice formations.
The spider web shown above may have been protected enough that a heavy dew formed first and then froze forming ice droplets rather than frost crystals. This is what happens when water vapor in the air condenses and forms dew before the temperature drops below freezing – you get frozen dew rather than true frost (hoar frost). So interesting!
Until next time – Happy Gardening!
Thank you for your very pleasurable read about frost–how and when the different types form. I, too, noticed the heavy frost on Monday, but did not associate it with the incredibly clear sky the night before. Your photos made me realize that I really must stop and look closely at the wonderful frost that outlines and covers the leaves and seedheads of plants that I can only glance at as I rush to take my daughter to school in the morning. I need to leave time for BOTH of us to stop, look, and wonder.