Snowfall is measured daily at the specified time of observation using a sturdy ruler and a snow board. The observer must attempt to find a protected and representative location for observing snowfall where the effects of wind are minimal. The goal in measuring and reporting daily snowfall is to observe the maximum accumulated depth of new snow since the previous day before melting and settling reduced the depth.
A snowboard laid on the ground or on the surface of old snow allows
for a more precise determination of snowfall. The snowboard must be
flush with the surface or measurements will not be accurate. Hold the
measuring stick vertical and push it gently into the snow until it
reaches the surface of the snowboard or the bottom of the layer of new
snow. Read this depth to the nearest 0.1 inches. This depth is the
daily snowfall that should he recorded unless blowing, drifting,
melting, or settling have significantly altered the accumulation. If
these have occurred, and they often do, the observer must use good
judgment and include additional information to make a better
determination of snowfall. See items one through four below for
determining snowfall under such conditions.
Special concerns and precautions:
1. It is essential to measure snowfall in representative locations
where the effects of blowing and drifting are minimized. Finding a
good location where snow accumulates uniformly simplifies all other
aspects of the observation and reduces the opportunities for error. In
open areas where windblown snow cannot be avoided, an average of
several measurements may often be necessary, not including the largest
drifts.
2. Snow often melts as it lands on the ground. If snow continually
melts as it lands, and no accumulation is ever noted even on grassy
surfaces, snowfall should be recorded as a "trace," and a remark
should be entered, "Snow melted as it landed."
3. If snow partially melts as it lands, but some accumulation takes
place, the snowfall for the day should be recorded as the greatest
accumulation of new snow observed at any time during the day. When
snow accumulates, melts, and accumulates again, the snowfall is the
sum of each accumulation before melting.
4. In addition to melting, snow settles and compacts as it lies on the
ground. The preferred record of daily snowfall should be the maximum
accumulation of new snow observed at any time during the day. Since
volunteer observers are not always available to watch snow
accumulation at all times of the day and night, observers' best
judgment must be used based on a measurement of snowfall at the
scheduled time of observation along with knowledge of what took place
during the day. If the weather observer is not present to witness the
snow accumulation, input should be obtained from other people who were
near the station during the snow event.
5. Never use the sum of frequent snow observations of a cleared
surface to determine daily snowfall. This will invariably inflate the
apparent snowfall and provide unreasonably low ratios of snowfall to
water content.
6. If a snowboard is not available, wooden decks or platforms and
grassy surfaces are usually good alternatives. Beware that snow may
perch on top of a grassy surface. A measuring stick will penetrate
through both snow and the airspace among the blades of grass resulting
in an overestimate of snow.
7. Summer hail is not reported as snowfall. Winter ice pellets and
sleet do count as snowfall.
8. In areas prone to heavy snow, the snowboard should be marked
clearly with a flag or have an attached stake or pipe that is taller
than the maximum expected snowfall. This way, you should never loose
the snowboard in deep snow, and it is easier to handle while taking
snow cores.