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Training Guide in Surface Weather Observations - Multiple Choices

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5 = 90° 2 = 90°<br />

3* = 90° 7/8* = 90°<br />

180° 180°<br />

2<br />

Figure 3-1. Prevail<strong>in</strong>g Visibility 3SM Figure 3-2. Prevail<strong>in</strong>g Visibility 7/8SM<br />

1 = 135°<br />

4* = 180° 5/8* = 135°<br />

270°<br />

3.2.1 Sector Visibility<br />

Figure 3-3. Prevail<strong>in</strong>g Visibility 4SM Figure 3-4. Prevail<strong>in</strong>g Visibility 5/8SM<br />

*Indicates Prevail<strong>in</strong>g Visibility<br />

Whenever the visibility is not uniform <strong>in</strong> all directions and the prevail<strong>in</strong>g visibility and/or the sector<br />

2<br />

visibility is less than 3 miles report sector visibility. Report <strong>in</strong> the remarks any sector whose visibility<br />

differs from the prevail<strong>in</strong>g visibility by one or more reportable values. To record this remark, enter the<br />

contraction VIS followed by the sector (us<strong>in</strong>g 8 po<strong>in</strong>ts of the compass) and the visibility <strong>in</strong> that sector,<br />

e.g., VIS NE 2 1/2. If more than one sector needs to be reported, code these sectors <strong>in</strong> a clockwise order<br />

start<strong>in</strong>g with north. For example, the first example (page 3-1) would be coded <strong>in</strong> column 14 as:<br />

VIS E 1 S 1 1/2 SW 2 3/4 W 3/4 NW 1/2<br />

3.2.2 Variable Prevail<strong>in</strong>g Visibility<br />

When the prevail<strong>in</strong>g visibility rapidly <strong>in</strong>creases and decreases by one or more reportable values dur<strong>in</strong>g<br />

the time of the observation, use the average of all determ<strong>in</strong>ed values as the prevail<strong>in</strong>g visibility reported<br />

<strong>in</strong> column 7a of MF1M-10C. If the average is less than 3 miles and the variation between the m<strong>in</strong>imum<br />

and maximum is 1/2 mile or more, report the limits of variability <strong>in</strong> column 14, Remarks. Make the<br />

remark by enter<strong>in</strong>g the contraction VIS followed by the lowest observed visibility, the letter V, and the<br />

highest observed visibility; e.g., VIS 1/4V1, to <strong>in</strong>dicate that the visibility is vary<strong>in</strong>g between 1/4 and 1<br />

mile. S<strong>in</strong>ce the reported visibility is the average of all observed values, it is not necessarily the average<br />

of the two values given <strong>in</strong> the remarks, but it usually turns out that way.<br />

Example: 1 1/2SM (RMK VIS 1V2)<br />

A sector visibility may also be entered if <strong>in</strong> the op<strong>in</strong>ion of the observer it is operationally significant.<br />

3-2

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