Training Guide in Surface Weather Observations - Multiple Choices

5. When a balloon is used for determining vertical visibility in a surface-based obscuration,
the value shall be the height at which the balloon completely disappears.
c. Convective Cloud Height Diagram. Use this diagram only to estimate the height of cumulus
clouds formed in the vicinity of your station. It is not used at stations in mountainous or hilly
terrain, or to determine the height of other than cumulus clouds. This diagram is more accurate
when used to determine the height of cloud bases below 5,000 feet. Obtain the estimated
height of a cloud base above the point of observation as follows:
1. Locate the point of intersection of the vertical line corresponding to the observed dewpoint
temperature, and the sloping line corresponding to the observed dry-bulb
temperature.
2. From the point of intersection move horizontally to the height scale printed in feet on the
right side of the chart. This value is a good estimation of the height of the cloud base.
d. Pilot Report. A cloud base or ceiling height reported by a pilot (converted from height above
mean sea level to height above surface) may be used in determining cloud heights.
e. Known Heights. The known heights of unobscured portions of natural landmarks or objects
(buildings, towers, etc.) in contact with the cloud base or ceiling layer may be used in
determining cloud and ceiling heights.
f. Experience. Cloud and ceiling heights may be determined on the basis of an observers
observational experience.
5.4 Maintenance of Cloud Height Equipment
Determining cloud and ceiling heights are an important part of the weather observation. The cloud
height equipment your station uses to aid you in making this determination needs to be maintained at
a proper operating level. The following maintenance checks will help you to do this.
a. Ceiling Light
1. Daily Checks. At least once each day, turn on the lamp. If it is shut off by a timer,
determine if it is operational. During daylight hours, the operation of the lamp can be
observed from the office if a metal reflector is placed at the top edge of the cover. Replace
the lamp if it is determined to be defective.
2. Weekly Checks. Clean the outside of the cover glass with water and detergent once each
week or more often if the local conditions require it.
3. Monthly Checks. Clean the mirror and the inside of the cover glass using water and
detergent. Wipe both surfaces completely dry using a soft lint-free cloth. CAUTION -The
concentrated rays of the sun can burn the skin or injure the eyes of personnel and may
damage equipment. Therefore, if direct rays of the sun reach the mirror, take precautions
to shade the projector. If the projector has drainage holes in the mirror or housing, clean
the holes to ensure adequate drainage and ventilation. With the light turned off, inspect
its condition and if the envelope has darkened appreciably, replace it.
5-20