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WEATHER U: Rime… and reason for ice fog.

Winter fog can be as beautiful as it is dangerous.  Cathy and Rodney Hickey submitted this photo taken earlier this month in Long River PEI.
Winter fog can be as beautiful as it is dangerous. Cathy and Rodney Hickey submitted this photo taken earlier this month in Long River PEI. - Contributed

My mother was a school teacher before she decided to start a family and work on the farm with dad.  I believe we had the best of both worlds – a very intelligent mom who was never too far away.  When I was young, I wanted to be a teacher; mom often talked about how rewarding it was.  Perhaps that’s why I love to answer your weather questions.

This one crossed my desk earlier this month:

“My husband and I disagree on what this photo is.  It was taken in Long River, P.E.I., on February 11 at 9:30 a.m. when the temperature was –10 C.  Any help would be appreciated and may get me dinner at my favourite restaurant.”


Cathy Hickey


Great question! It might help if I told you that the subject line was “fog or frost.” When fog forms in temperatures that are below freezing, the tiny water droplets in the air remain as a liquid.  They become supercooled water droplets – not frozen – even though they exist in below-freezing temperatures.  Cloud droplets and liquid precipitation can remain liquid even when the air temperature is below freezing.  This occurs because the liquid needs a surface on which to freeze. The liquid droplets will freeze without a nuclei surface if the temperature drops low enough.  As a general rule, liquid cloud or precipitation drops between 0 and –10 C will remain liquid.  When the temperature drops to below –40 C, all liquid droplets will solidify.

When droplets from freezing fog come into contact with cold objects, a coating of ice eventually forms.  This ice is called rime ice.  If you look closely you’ll find that the freezing fog is creating ice on the branches in the photo.  There are two kinds of rime ice, soft and hard.  Hard rime forms when there is some wind; temperatures can be as cold as –10 C.  Soft rime forms on a windless night when temperatures are between –3 C and –8 C.  It’s quite beautiful; it can appear sugary with feathery spikes.

So I wonder who bought supper?



Cindy Day is the chief meteorologist for SaltWire Network


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