Training Guide in Surface Weather Observations - Multiple Choices

layer aloft will be considered as midway between the time the balloon begins to fade until the time the
balloon completely disappears.
Once you have determined the amount and height of each layer present at the station you will know what
layer the ceiling will be. If you have learned to evaluate the sky cover and record it correctly, then
determining the ceiling is relatively easy. The ceiling is the lowest layer reported as broken or overcast,
or if the sky is totally obscured, the height of the vertical visibility shall be the ceiling.
When the cloud height is varying rapidly while you are trying to obtain a height, report the average of
all observed values as the height of the layer. If it is the ceiling layer and the average height is less than
3,000 feet and the amount of change is according to the criteria given in your station’s WSOH, a remark
shall be included in column 14 of MF1M-10 giving the range of variability. For example, “CIG
005V010” would indicate a ceiling that was varying between 500 and 1,000 feet.
5.3.1 Methods Used When Determining Cloud and Ceiling Heights
Determination of heights should be supplemented by visual observations and not left solely to
instruments themselves. To determine the height of layers aloft and the vertical visibility into surfacebased
phenomena, the following methods can be used.
a. Ceiling Light and Clinometer. At night, sky cover height and vertical visibility values may be
determined with a clinometer and a projector by using the following procedures:
1. Allow the pendant to swing freely; sight through the clinometer centering the intersection
of the cross-hair:
(a) Upon the brightest portion of the light beam spot when the sky cover layer is aloft (see
Figure 5-13), or
(b) On the upper limit of the light beam penetration when the sky is completely obscured
by a surface-based layer (see Figures 5-12 and 5-14).
2. When the pendant has come to rest, lock it in position without moving the clinometer.
3. Read the indicated angle to the nearest whole degree and release the pendant clutch.
4. Repeat steps 1 through 3 three times, then determine an average angular reading.
5. Refer to a table appropriate for the baseline used for the equivalent height value of this
average reading.
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