AIM 

4/20/23 

4.  Modifier (As Required). 

“AUTO” identifies a METAR/SPECI report as an automated weather report 

with no human intervention. If “AUTO” is shown in the body of the report, the type of sensor equipment used 

at the station will be encoded in the remarks section of the report. The absence of “AUTO” indicates that a report 

was made manually by an observer or that an automated report had human augmentation/backup. The modifier 

“COR” indicates a corrected report that is sent out to replace an earlier report with an error. 

NOTE

−

 

There are two types of automated stations, AO1 for automated weather reporting stations without a precipitation 

discriminator, and AO2 for automated stations with a precipitation discriminator. (A precipitation discriminator can 

determine the difference between liquid and frozen/freezing precipitation). This information appears in the remarks section 

of an automated report. 

5.  Wind. 

The wind is reported as a five digit group (six digits if speed is over 99 knots). The first three digits 

are the direction the wind is blowing from, in tens of degrees referenced to true north, or “VRB” if the direction 

is variable. The next two digits is the wind speed in knots, or if over 99 knots, the next three digits. If the wind 

is gusty, it is reported as a “G” after the speed followed by the highest gust reported. The abbreviation “KT” is 

appended to denote the use of knots for wind speed. 

EXAMPLE

−

 

13008KT 

−

 wind from 130 degrees at 8 knots 

08032G45KT 

−

 wind from 080 degrees at 32 knots with gusts to 45 knots 

VRB04KT 

−

 wind variable in direction at 4 knots 

00000KT 

−

 wind calm 

210103G130KT 

−

 

wind from 210 degrees at 103 knots with gusts to 130 knots 

If the wind direction is variable by 60 degrees or more and the speed is greater than 6 knots, a variable group consisting 

of the extremes of the wind direction separated by a “v” will follow the prevailing wind group. 

32012G22KT 280V350 

(a)  Peak Wind. 

Whenever the peak wind exceeds 25 knots “PK WND” will be included in Remarks, 

e.g., PK WND 28045/1955 “Peak wind two eight zero at four five occurred at one niner five five.” If the hour 

can be inferred from the report time, only the minutes will be appended, e.g., PK WND 34050/38 “Peak wind 

three four zero at five zero occurred at three eight past the hour.” 

(b)  Wind shift. 

Whenever a wind shift occurs, “WSHFT” will be included in remarks followed by the 

time the wind shift began, e.g., WSHFT 30 FROPA “Wind shift at three zero due to frontal passage.” 

6.  Visibility. 

Prevailing visibility is reported in statute miles with “SM” appended to it. 

EXAMPLE

−

 

7SM 

−

 seven statute miles 

15SM 

−

 fifteen statute miles 

1

/

2

SM 

−

 one

−

half statute mile 

(a)  Tower/surface visibility. 

If either visibility (tower or surface) is below four statute miles, the lesser 

of the two will be reported in the body of the report; the greater will be reported in remarks. 

(b)  Automated visibility. 

ASOS/AWOS visibility stations will show visibility 10 or greater than 10 

miles as “10SM.” AWOS visibility stations will show visibility less than 

1

/

4

 statute mile as “M

1

/

4

SM” and 

visibility 10 or greater than 10 miles as “10SM.” 

NOTE

−

 

Automated sites that are augmented by human observer to meet service level requirements can report 0, 1/16 SM, and 1/8 

SM visibility increments. 

(c)  Variable visibility. 

Variable visibility is shown in remarks (when rapid increase or decrease by 

1

/

2 

statute mile or more and the average prevailing visibility is less than three miles) e.g., VIS 1V2 “visibility variable 

between one and two.” 

(d)  Sector visibility. 

Sector visibility is shown in remarks when it differs from the prevailing visibility, 

and either the prevailing or sector visibility is less than three miles. 

7

−

1

−

68 

Meteorology