Training Guide in Surface Weather Observations - Multiple Choices

8.2.2.2 24-Hour Precipitation Amount
The 24-hour precipitation amount, 7R24R24R24R 24,
is included in the 1200 UTC report (or other
designated time) whenever more than a trace of precipitation (water equivalent) has fallen in the past 24
hours. The amount of precipitation is coded using the tens, units, tenths, and hundredths of inches. For
example, 10.45 inches of precipitation (water equivalent) in the past 24 hours would be coded 71045;
0.10 inches of precipitation (water equivalent) in the past 24 hours would be coded 70010. If more than
a trace (water equivalent) has fallen and the amount cannot be determined, the group is coded 7////. If
only a trace or no precipitation occurred in the past 24 hours, the group is omitted.
8.2.2.3 Snow Depth on the Ground
The total snow depth on the ground group, 4/sss, is coded in the 0000 and 1200 UTC observation
whenever there is more than a trace of snow on the ground. It is also coded in the 0600 and 1800 UTC
observations if there is more than a trace of snow on the ground and more than a trace of precipitation
(water equivalent) occurred within the past 6 hours. Report snow depth to the nearest whole inch,
rounding up when one-half-inch increments are reached. For example, a snow depth of 0.4 inches would
be considered a trace amount, the group would be omitted; a snow depth of 33.5 inches would be coded
4/034.
Snow depth on the ground is taken by measuring the total depth of snow on exposed ground by means
of a permanently mounted snow stake or by taking the average of several depth readings at or near the
normal point of observation with a measuring stick. When using a measuring stick, make sure the stick
is pushed vertically into the snow until the bottom rests on the ground. Do not mistake an ice layer or
crusted snow as “ground.” The measurement should reflect the average depth of snow, sleet, and glaze
ice on the ground at your usual measurement site (not disturbed by human activities). Measurements
from rooftops, paved areas, and the like should not be made.
When strong winds have blown the snow, take several measurements where the snow was least affected
by drifting and average them. If most exposed areas are blown free of snow while others have drifts, try
to combine visual averaging with measurements to make an estimate.
8.2.2.4 Water Equivalent of Snow on the Ground
The water equivalent of snow on the ground group, 933RRR, is coded each day in the 1800 UTC report
if the average snow depth is 2 inches or more. This group is the water equivalent of snow (i.e., snow,
snow pellets, snow grains, ice pellets, ice crystals, and hail) on the ground. The water equivalent is
coded using the tens, units, and tenths of inches, using three digits. If the water equivalent of snow
consists entirely of hail, the group shall not be coded. A water equivalent of 4.7 inches of snow would
be coded 933047; a water equivalent of 17.3 would be coded 933173.
This measurement is made by taking a “snow core” of the snow on the ground with the use of the
overflow can of your station’s 8-inch non-recording rain gauge. Use the following procedure to obtain
this measurement:
a. Find an area where drifting is minimal. This will usually be a flat area away from obstructions
such as trees and buildings, although obstructions at some distance can help drifting.
8-4