Why Do Snowflakes Vary in Size During a Winter Storm?

WOAY-TV (Oak Hill, WV): We look at the dendritic snow growth zone to answer the question.

The snow growth zone is the zone aloft in the atmosphere where the temperature is -15 degrees Celsius or five degrees Fahrenheit and favors snowflakes to become large, fluffy and rapidly accumulate.

Last night, when the storm began in southern West Virginia, we had a low pressure coming in from the Midwest. The added lift and moisture contained within the snow growth zone of the atmosphere fostered large snowflakes.

The snowflakes turned smaller during the day on Friday. The reason for that, the low pressure has passed to our east, so we were losing lift in the snow growth zone.

There is one exception to snowflake size; elevation. Air rising up over our high terrain helps compensate for the large synoptic feature being to our east. So, you still see large snowflakes through most of the duration of the winter storm.

A cross-profile of the atmosphere that meteorologists use to forecast snow shows this illustration. Meteorologists can see if there is lift and moisture in the snow growth zone to forecast upside risk to accumulation. Less moisture and lift in the snow growth zone produces smaller flakes and less efficient snow accumulation rates.

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