The following procedures were developed from previous National Weather Service procedures and
input from a broad array of expertise from climatologists, snow specialists, weather observers, and
data users. Some of the materials have been extracted from "The Snow Booklet" by Nolan J.
Doesken and Arthur Judson, CSU, 1996).
Each season before the first snows come: Review these instructions for measuring snow. It is
easy to forget what needs to be measured, especially in those parts of the country where snow falls
At the beginning of each snowfall/freezing season, remove the funnel and inner
measuring tube of the eight-inch manual rain gauge to expose the 8-inch diameter overflow
can so that it can more accurately catch frozen precipitation.
Put your snowboard(s) out and mark their location with a flag or some other indicator so they
can be found after a new snowfall. They should be located in the vicinity of your station in an open
location (not under trees, obstructions, or on the north side of structures in the shadows). Once
your equipment has been readied for winter you are prepared for taking snowfall measurements.
Observers should determine three values when reporting solid precipitation. They
Snowfall: Measure and record the snowfall (snow, ice pellets ) since the
previous snowfall observation (24 hours). (See Snowfall section below for details)
Snow Depth: Determine the depth of the new and old snow remaining on the
ground at observation time. (See Snow Depth section below for details)
Water Equivalent of Snow: Water equivalent of melted snow collected in the
gauge since the last observation. (See Water Equivalent section below for details)
Measure and record the greatest amount of snowfall that has accumulated on your
snowboard (wooden deck or ground if board is not available) since the previous snowfall observation.
This measurement should be taken minimally once-a-day but can be taken up to four times a day,
(every 6 hours) and should reflect the greatest accumulation of new snow observed (in inches and
tenths, for example, 3.9 inches) since the last snowfall observation. Snowfall amounts can
be measured hourly or at any interval as long as the snow measurement board is NOT cleared more
frequently than once every 6 hours. If you are not available to watch snow accumulation at all times
of the day and night, use your best estimate, based on a measurement of snowfall at the scheduled
time of observation along with knowledge of what took place during the past 24 hours. If you are not
present to witness the greatest snow accumulation, input may be obtained from other people who were
near the station during the snow event. If your observation is not based on a measurement, record in
your remarks that the "snow amount based on estimate". Remember, you want to report the
greatest accumulation since the last observation. If snowfall occurred several times during
the period, and each snowfall melted either completely or in part before the next snowfall, record
the total of the greatest snowdepths of each event and enter in your remarks "snowfall
melted during the OBS period". For example, three separate snow squalls affect your station
during your 24-hour reporting day, say 3.0, 2.2, and 1.5 inches. The snow from each event melts off
before the next accumulation and no snow is on the ground at your scheduled time of observation. The
total snowfall for that reporting 24-hour day is the sum of the three separate snow squalls, 6.7
inches, even though the snow depth on your board at observation time was zero.
Snow often melts as it lands. If snow continually melts as it lands, and the
accumulation never reaches 0.1 inches on your measuring surface, snowfall should be recorded as a
trace (T) and record in your remarks that the "snow melted as it landed".
It is essential to measure snowfall (and snow depth) in 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 numerous opportunities for
error. In open areas where windblown snow cannot be avoided, several measurements may often be
necessary to obtain an average depth and they should not include the largest drifts. In heavily
forested locations, try and find an exposed clearing in the trees. Measurements beneath trees are
inaccurate since large amounts of snow can accumulate on trees and never reach the ground.
If your daily schedule permits, you may wish to make a snowfall observation every 6-hours,
beginning with your regularly scheduled time of observation. This is the procedure followed by
National Weather Service Forecast Offices. Follow the same rules for a once-a-day observation, but
the snow accumulation reported will be the greatest for the previous six hours instead of 24 hours.
If you take your observations at this frequency, make sure that you clear your snowboard (or
other measuring surface) no more than once every 6 hours. Record the frequency of
observations during the day in the comments section of your report. Never sum more than
four, six-hourly observations to determine your 24-hour snowfall total. If you use more
than four observations, it would falsely increase snowfall totals.
Freezing rain (glaze ice) should never be reported as snowfall. This precipitation type is
liquid precipitation and should be reported as such.
Determine the total depth of snow, ice pellets, or ice on the ground. This observation
is taken once-a-day at the scheduled time of observation with a measuring stick. It is
taken by measuring the total depth of snow on exposed ground at 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 of the stick rests on the ground. Do not mistake an ice layer or crusted snow
as "ground". The measurement should reflect the average depth of snow, ice
pellets, 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.
Note: Hail accumulation is not entered with snow and ice pellets. Hail accumulation is
entered in the ?/remarks/? section with the amount and diameter (inches and tenths) of the stones.
Report snow depth to the nearest whole inch, rounding up when one-half inch increments
are reached (example 0.4 inches gets reported as a trace (T), 3.5 inches gets reported as 4 inches).
Frequently, in hilly or mountainous terrain, you will be faced with the situation where no
snow is observed on south-facing slopes while snow, possibly deep, remains in shaded or north-facing
areas. Under these circumstances, you should use good judgment to visually average and then measure
snow depths in exposed areas within several hundred yards surrounding the weather station. For
example, if half the exposed ground is bare and half is covered with six inches of snow, the snow
depth should be entered as the average of the two readings, or three inches. When in your judgment,
less than 50 percent of the exposed ground is covered by snow, even though the covered areas have a
significant depth, the snow depth should be recorded as a trace (T). When no snow or ice is on the
ground in exposed areas (snow may be present in surrounding forested or otherwise protected areas),
record a "0".
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 either blown free of snow while
others have drifts, again try to combine visual averaging with measurements to make your
Water Equivalent of Snowfall:
Measuring the water equivalent of snowfall since the previous day's observation.
This measurement is taken once-a-day at your specified time of observation. Melt the contents of
your gauge (by bringing it inside your home or adding a measured amount of warm water) and
then pour the liquid into the funnel and smaller inner measuring tube and measure the amount to the
nearest .01 inch (use NWS provided measuring stick) just as you use for measuring rainfall. Do not
measure the melted precipitation directly in the large 8-inch outer cylinder. Make sure the inner
measuring tube can't fall over when pouring the liquid back into it. If the melted water
equivalent (including any added warm water) exceeds two inches and cannot fit into the measuring
tube all at one time, then empty the full measuring tube and pour the remaining liquid from the
large 8-inch outer cylinder into the emptied measuring tube. Then, add and record the water
equivalent of the multiple measurements.
If you added warm water to the gauge to melt the snow, make sure you accurately measure
the amount of warm water added before pouring it into the gauge. Then, when you take your
liquid measurement, subtract the amount of warm water added from the total liquid
measurement to get your final liquid water equivalent of the snowfall.
As winds increase, gauges collect less and less of the precipitation that actually falls.
Generally speaking, the stronger the wind and the drier the snow, the less is captured in the gauge.
If you notice that less snow is in the gauge than accumulated on the ground, you should first empty
any existing snow from inside the 8-inch cylinder, then use it to take a snow sample, sometimes
referred to as "take a core" or "cut a biscuit" from your snow board with the
8-inch overflow can. Melt the biscuit of snow, pour the liquid into the small measuring tube to
measure the water equivalent.