Weather Rant: Fluff Factor

Nothing makes me cringe more than hearing a meteorologist say “temperatures will be so cold there will be a fluff factor.” It makes me want to scream!

There’s a big difference between dry and light snow that is easy to move and fluffy snow flakes that are able to accumulate fast! A meteorologist friend of mine in New Hampshire used this analogy:

Think of dendrites as a bunch of tree branches thrown into a pile. The pile gets stacked high the more you add as the branch structure traps air in between. Now throw them through a wood chipper and watch how much lower the pile gets. There’s your columns, needles, bullets, and small plates.

Dendrites (the beautiful and ornate crystals) are the flakes that can pile up quickly and result in high ratios of liquid precipitation to snow totals. Snow flakes grow through deposition. Deposition is the process where water vapor changes state to a solid on the ice crystal. This is the dominant process in producing snow.

The deposition process is maximized when temperatures are between -12c and -18c in the cloud. Besides a more efficient growth process dendrites also accumulate more rapidly due to their large suface area adding to extra space in between each individual flake.

Bottom line is that even though it’s in the teens that doesn’t guarantee good snow growth or a fluff factor!! Not even close!!! Having cold temperatures in addition to saturation and strong lift in the dendritic growth zone (-12ºc to -18ºc) is the key to getting a “fluff factor”.

When temperatures are too cold or too warm in the region of best lift you get other types of crystals that don’t form as efficiently and don’t accumulate as efficiently. The latter will reduce snow:liquid ratios. Snowflakes like plates or columns or needles accumulate slowly and produce a “fine” consistency to the snow.

Looking at a surface temperature and saying the snow will accumulate fast is bad meteorology. Use cloud microphysics folks – it’s the only way to forecast snow!


3 thoughts on “Weather Rant: Fluff Factor

  1. Was it cold enough for Storm Alfred to have a good fluff factor? Sorry, had to say it. I can imagine your blood boiling over with that sentence! 😉

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