Training Guide in Surface Weather Observations - Multiple Choices

APPENDIX D - ORDER OF OBSERVING ELEMENTS
I. Elements Evaluated Outdoors
A. Location where the sky and horizon are visible, determine:
1. Height of clouds (to hundreds of feet).
2. Amount of sky covered by clouds or obscured by other phenomena (smoke, fog, mist,
etc.) in eighths.
3. Visibility, i.e., the distance that you can see horizontally (in statute miles).
4. Type of precipitation or obscuration (fog, mist, haze, smoke, etc.).
B. At the instrument shelter, obtain:
1. Dry- and wet-bulb temperatures (to nearest 0.1°C)
a. Moisten the wet-bulb wick with clean water.
b. Ventilate the thermometer by facing into the wind and whirling a sling
psychrometer while holding it in front of you at arm’s length, or by the motor
driven aspirator, for approximately 10 seconds, then read both thermometers (the
wet-bulb first).
c. Repeat step b until the lowest wet-bulb temperature has been reached. The
readings at this time are used in the official observation.
II. Elements Evaluated Indoors
A. After recording the above data (on MF1M-10), read and record similarly:
1. Dew-point temperature: Obtain the difference between the dry- and wet-bulb
thermometers, termed “depression.” Using this difference and the wet-bulb
temperature, compute the dew-point temperature on the psychrometric calculator.
(Instructions for the use of the calculator are printed on it.)
2. Observe the wind indicator(s) for a two-minute period and determine:
a. The average direction, report in tens of degrees using three digits. Enter “000"
when the wind is calm.
b. The average speed to the nearest knot.
3. Altimeter setting:
a. If an altimeter setting indicator is used, read the altimeter setting directly to the
nearest 0.005 inch, estimating values between the graduations. Algebraically add
this reading to the posted correction, then round down the value to the next
reportable value. Record this value in column 13 of MF1M-10.
D-1