Training Guide in Surface Weather Observations - Multiple Choices

OUTLINE
DETERMINING VISIBILITY
From an outside point where all appropriate visibility markers can be observed:
1. Determine the most distant object visible, using the station visibility chart as a guide.
2. Estimate the visibility in the direction of this object as follows:
a. If the object is barely identifiable, consider the visibility to be the same as the distance to
this object.
b. If the outlines of the object are in sharp relief, estimate the distance that can be seen
beyond this object.
3. Check the visibility in other directions to determine if the above value is representative of all
directions.
a. If the visibility is different in other sectors but is relatively uniform within each sector,
estimate the value in each sector in a manner similar to (2) above.
b. If the visibility rapidly increases and decreases by one or more reportable values during the
period of observation, use the average of all observed values as the prevailing visibility.
Entries on MF1M-10:
4. Enter the prevailing visibility in column 7(a) as follows:
a. If the visibility is the same in all directions, enter this value.
b. If the visibility differs in various sectors (3a), select a single value that is the greatest
visibility equaled or exceeded throughout at least half the horizon circle.
c. If the visibility is variable (3b), enter the average value.
5. If the visibility is non-uniform (3a) with the prevailing visibility and/or the sector visibility less
than 3 miles, or variable (3b) with the average visibility less than 3 miles and the variation
between the minimum and maximum 1/2 mile or more, enter remarks in column 14 in
accordance with sector visibility (3a) or variable prevailing visibility (3b).
6. If control tower visibility observations are taken at your station, they are entered in column 7(b)
only when the visibility at the control tower is less than 4 miles and differs from the visibility
at the usual point of observation (surface). The higher visibility value (SFC or TWR) would
also be entered in column 14, Remarks.
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