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Posted at 12:30 PM ET, 01/18/2008

The Cause of Big Flakes

By Jason Samenow

Some pretty big snowflakes were observed in Thursday's snowstorm. Numerous visitors commented on them, and weatherdudeVA asked:

What is making these flakes SO BIG?

Is it the fact that they have a high water content and they're sticking together, or is it something else?

Yes - high water content and stickiness play a big role. . According to meteorologist Jeff Haby of, large snowflakes are formed when temperatures in a layer of the atmosphere are just above freezing, causing the flakes to partially melt:

This produces a liquid film on the snowflake. This makes it much easier for snowflakes to stick together. Thus, it is liquid water that is the "glue" to producing large snowflakes and snow that is easy to make snowballs with.

Because large snowflakes are often associated with warming aloft, they're not a good sign for snow lovers. They often indicate snow is close to mixing with and changing to sleet or rain. Thursday was a classic example.

By the way, the largest snowflake on record, 15 inches wide and 8 inches thick, was reported at Fort Keogh, Montana, on January 28, 1887 according to the Guinness Book of World Records.

You can learn all you ever wanted to learn about snowflakes and more by visiting, created by Cal Tech physics professor Kenneth G. Libbrecht.

By Jason Samenow  | January 18, 2008; 12:30 PM ET
Categories:  Science  
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Next: CommuteCast: Much Easier than Yesterday's


Margusity is still calling for some snow tomorrow.. Few inches just south of town.

Posted by: Anonymous | January 18, 2008 12:37 PM | Report abuse

Why is Dulles still stuck in the fog and 33 degrees? This morning's drive was nerve-wracking enough. I don't need another one tonight. I need that ice to melt off the roadways.

Posted by: Ivan | January 18, 2008 1:01 PM | Report abuse

Wow! Thank you! I get educated AND weather all in the same place, I love it!

Posted by: weatherdudeVA | January 18, 2008 1:05 PM | Report abuse

Most "snowflakes" are aggregates of many snow flakes. You only see individual dentrites, columns, rods, etc. when it is rather cold through out the whole column of the atmosphere. So the "potato chip" flakes yesterday were probably made up of dozens of individual ones. Charlie Knight at NCAR developed a snow camera that I used to document flakes in a study I was involved with when I worked there. It was very simple, but took amazing black and white negatives of flakes so we could ground truth what doppler radar was indicating in order to build a better algorithim to quantify liquid water equivalent of snow only use doppler. One of Charlies snow flake pitctures is emblazoned on the tail of NCAR's C-130 reasearch aircraft.

Posted by: Nader | January 18, 2008 1:24 PM | Report abuse

weatherdudeVA, welcome to life as a capwxgang member! You've hit upon what all the rest of us have discovered, and why we keep coming back. Good to have you with us!

Posted by: ~sg | January 18, 2008 1:25 PM | Report abuse

Dulles is in a basin, and with light to no winds and more snow on the ground than to the east, which continues to melt and evaporate - fog is lingering.

Posted by: Nader | January 18, 2008 1:34 PM | Report abuse

So, why is it that snowflakes are sometimes hard little pellets, that are still snowflake shaped? I've only seen them a couple of times in my life, but they look like snowflake cake sprinkles.

Posted by: Char | January 18, 2008 2:06 PM | Report abuse

hooray for the webcam! thanks, guys--keep up the good work!

Posted by: washingtonydc | January 18, 2008 2:23 PM | Report abuse

Char: I think you have seen flakes that have been covered with rime. Rime ice forms on snowflakes when they go through a layer of very moist or supersaturated air and water dropplets suspended in the air freeze on contact wih the flakes.

Posted by: Nader | January 18, 2008 2:46 PM | Report abuse


I believe you are referring to graupel, or "snow pellets." This form of precip is relatively rare, and is, if I understand correctly, between snow and sleet. The warm layer is not deep enough to melt the snow fully so that it refreezes into sleet, but it IS deep enough to melt the "arms" off the snowflakes leading to a pellet like shape. Graupel basically has a thin ice coating, with snow on the inside!

Graupel looks a lot like those little styrofoam balls used in blow up snowglobles.

Posted by: Jim in Blacksburg | January 18, 2008 2:47 PM | Report abuse

Does anybody forecast using trends and patterns any more? Sure doesn't seem like it. The models left the forecasters up north with poo on their faces about a week ago with the 6-12 inches for NYC that turned out to be a dusting yet, you guys still live and die by them. Even yesterday, the snow hung on longer in points south than most predicted.

Every storm this year coming up from the south has trended further north and west the closer it got to the coast. Does that trend not mean something at all? I haven't even heard that trend mentioned. I think everybody is expecting this cold air mass coming down to push the storm further east. It probably will but, when?

Anybody can learn how to read a model.

Posted by: TJ | January 18, 2008 3:08 PM | Report abuse

It must have been rime on the flakes. They were still snowflake shaped, just much thicker and very solid. I hope next time I have a camera with me.

Thanks for the info!

Posted by: Char | January 18, 2008 3:27 PM | Report abuse

Thanks ~sg! I've actually been reading CapWx for months and months and months and months (I think you get the point...), I decided to comment yesterday though. I really love this blog, I don't trust anyone else (sorry Mrs. Palka, LOL) anymore with the weather!

Sorry for the off topic here...

But yeah, I was in school this morning (two hour delay for us in PWC) and saw my name in the post and had to do a double take. I almost fell out of my chair, HA! I've learned my factoid for the day, I'm happy :)

Posted by: weatherdudeVA | January 18, 2008 4:39 PM | Report abuse

Char, I know exactly what you are talking about. I've only seen them twice in my life. They look pretty cool and I always wondered how they formed.

Posted by: wgomes | January 18, 2008 10:22 PM | Report abuse

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