Training Guide in Surface Weather Observations - Multiple Choices

8.3.3.1 Depth of New Snow (Snowfall)
The depth of new snow (snowfall), 931nnn, is reported every six hours at 0000, 0600, 1200, and 1800
UTC when any amount of snow has fallen in the past six hours. It is not included in a METAR report,
but it is reported by NWS stations in supplementary climatological data observations. The report
represents the depth of new snow (i.e., snow, snow pellets, snow grains, ice pellets, ice crystals, and hail)
in the past six hours reported in tens, units, and tenths of inches, using three digits. The amount reported
is the actual amount that has fallen, even if some (or all) of it melted by the time of observation. Trace
amounts are reported as 931000. If the depth consists entirely of hail, the group is omitted.
Measure the greatest amount of snowfall that has accumulated on your snow board (wooden deck or
ground if board is not available) since the previous snowfall observation. This measurement should
reflect the greatest accumulation of new snow observed in the past six hours. If snowfall occurred
several times during the six-hour period, and each snowfall melted either completely or in part before
the next snowfall, report the total of the greatest snow depths of each event (i.e., though the report
reflects a six- hour accumulation, to obtain the greatest amount may require you to take several
measurements during this period). Make sure you clear the snow board or other measuring surface no
more than once every six hours. Note the following examples:
a. During the 6-hour period it snowed two times. The first snowfall accumulated 3.7 inches of new
snow. Before the second snow, 3.5 inches of the new snow melts. The second snow adds
another 0.8 inches of new snow. The depth of new snow would be coded 931045.
b. During the 6-hour period it snows only one time but the snowfall ends prior to the observation.
The event is of long duration and adds 16.3 inches of new snow. Between melting and drifting,
there are only 9.4 inches of snow left at the time of observation. The depth of new snow would
be coded 931163.
If snow continually melts as it lands and the accumulation never reaches 0.1 inches on your measuring
surface, record the snowfall as a trace and record in column 65 that the snow “melted as it landed.”
It is essential to measure snowfall in a location 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 numerous opportunities for error. In heavily forested locations, try to find
an exposed clearing in the trees. Measurements beneath trees are inaccurate because large amounts of
snow can accumulate on trees and never reach the ground.
Hourly snowfall measurements may be made for local use (there is no national requirement for this
information), but they are not to be used or totaled for climatological purposes.
8.4 Contractions
Authorized contractions are a shortened form of a word that is used for brevity, to conserve time and
space, and should be used whenever possible. However, in no case should an essential remark be
omitted for the lack of readily available contractions. In such cases, the only requirement is that the
remark be clear. The following is only a partial list of the authorized contractions that can be used in
the remarks section of the aviation weather observation. A larger list of contractions can be found in
Appendix A of your station’s WSOH.
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