Training Guide in Surface Weather Observations - Multiple Choices

. Invert the overflow can and force it down through the snow. The rim will cut a cylindrical
vertical sample. If the snow is very deep, it may be necessary to push the can part way to the
ground. Then, remove and empty the snow into a container, and insert the can in the same hole
to obtain the rest of the snow.
c. Slip a piece of sheet metal or thin wood beneath the mouth of the can to prevent the snow from
falling out.
d. Take the snow indoors, melt the contents of the can (by adding an accurately measured amount
of warm water), then pour the liquid into the funnel and smaller inner measuring tube of the rain
gauge and measure the amount to the nearest .01 inch. Subtract the amount of warm water added
from the total liquid measurement to get your final liquid water equivalent of the snow on the
ground.
If the melted water equivalent (including any added warm water) exceeds 2 inches (the amount
the measuring tube holds), empty the full measuring tube and pour the remaining liquid from the
large 8-inch can into the emptied measuring tube. Add the multiple measurements.
Do not measure the melted precipitation directly in the overflow can of the 8-inch gauge. Make sure the
inner measuring tube cannot fall over when pouring the liquid into it.
8.3 Measuring Precipitation
The most common types of gauges used to measure liquid precipitation are the 8-inch non-recording
gauge and the universal recording weighing gauge. These provide acceptable accuracy when used to
measure liquid precipitation. Measuring the most common type of solid precipitation, snow, is more
difficult. You will have to use good judgement when measuring the depth of snow and its water
equivalent. The problem is compounded by the tendency of snow to drift.
8.3.1 8-Inch Non-Recording Gauge
This gauge (see Figure 8-1) consists of a large diameter outer can, a smaller diameter measuring tube
inside it, a funnel that connects them, a measuring stick, and a support. The outer can and top of the
funnel are 8 inches in diameter. The funnel directs precipitation into the measuring tube, which is 20
inches tall and holds exactly 2 inches of liquid precipitation (additional rainfall will flow into the
overflow can). This ten-to-one ratio makes it possible to read rainfall amounts to the nearest hundredth
of an inch. The measuring stick is marked at .01 inch intervals.
To measure rainfall, remove the funnel and insert the measuring stick into the bottom of the measuring
tube, leaving it there for two or three seconds. The water will darken the stick. Remove the stick and
read the rainfall amount from the top of the darkened part of the stick. Example: if the stick is darkened
to three marks above the 0.80 inch mark, the rainfall is .83 inch.
If the measuring tube is full (indicating at least two inches of rain), empty the tube carefully to avoid
spilling any water back into the overflow can. Allow a few seconds for all the water to drain from the
tube, then pour the water from the overflow can into the measuring tube. Measure this amount and add
it to the two inches already emptied from the tube. If more than four inches of rain has fallen, the
measuring tube will be filled at least twice.
8-5