Guide

Look closerWeather

Snowflake shapes on a dark sleeve

December to March

Catch falling snow on a dark sleeve or mitten and look closely at single crystals. Their shape reflects the temperature and humidity of the cloud where they grew.

Why this time of year

Whenever snow is falling and the air is cold enough for flakes to stay crisp, single crystals land on a dark sleeve and can be read by eye.

How to notice it

  1. Hold out a dark sleeve, mitten or glove while snow is falling. Dark fabric makes the crystals easy to see.
  2. Look fast, before they melt, with your eyes or a cheap magnifier. Look for flat six-armed stars and tiny six-sided plates.
  3. Look for small columns or needles too, but they are small and easy to miss, so look closely.
  4. Notice that big fluffy flakes are clumps of many crystals stuck together, not one crystal.

Try this with kids: Hold out your dark mitten and count the arms on the biggest star you can find. Is it six?

Phrase to know: A “stellar dendrite” is a flat, star-shaped snow crystal with branching arms.

Sources

  • snowcrystals.comKenneth Libbrecht (Caltech physics professor), primary reference site. Stellar crystals grow near -15 C (5 F); plates near -15 C; needles and columns near -6 C (21 F); six-fold symmetry; shape depends on temperature and humidity in the cloud. Quotes: 'the largest, most photogenic stellar snow crystals only grow in a narrow temperature range around -15 C (5 F)'; 'Needles and columns are best found around -6 C (21 F)'; 'Snow crystals display that characteristic six-fold symmetry we are all familiar with.'
  • snowcrystals.comSame author, observing guide. Dark fabric helps spotting stellar dendrites; best specimens when weather is quite cold near -15 C (+5 F); columns near -6 C (21 F) are small and easy to miss; bring a magnifier. Quotes: 'especially if you are wearing a dark fabric'; 'The best specimens usually appear when the weather is quite cold'; 'consider it a challenge to get a magnifier, go outside'.
  • nsidc.orgNSIDC (federally funded university-based data center). Flakes can be single six-sided crystals or clumps. Quotes: 'Snow may fall as symmetrical, six-sided snowflakes, or it may fall as larger clumps of flakes.'; 'Snowflakes are accumulations of many snow crystals.'
  • ncei.noaa.govNOAA NCEI 1991-2020 monthly normals, Boston Logan (USW00014739), opened by the refute pass 2026-10-30: mean monthly snowfall Nov 0.7 in, Dec 9.0, Jan 14.3, Feb 14.4, Mar 9.0, Apr 1.6. Coastal station; inland totals may differ. Backs the months.

Checked against these sources on October 30, 2026.

In the guide for December, January, February, March

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