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AIM

10/12/17

7−1−41

Meteorology

3. Heavy. Rapid accumulation on ground.

Visibility reduced by ice pellets to less than 3 statute

miles.

7−1−19. Estimating Intensity of Snow or

Drizzle (Based on Visibility)

a. Light. Visibility more than 

1

/

2

 statute mile.

b. Moderate. Visibility from more than

1

/

4

statute mile to 

1

/

2

 statute mile.

c. Heavy. Visibility 

1

/

statute mile or less.

7−1−20. Pilot Weather Reports (PIREPs)

a. FAA air traffic facilities are required to solicit

PIREPs when the following conditions are reported

or forecast: ceilings at or below 5,000 feet; visibility

at or below 5 miles (surface or aloft); thunderstorms

and related phenomena; icing of light degree or

greater; turbulence of moderate degree or greater;

wind shear and reported or forecast volcanic ash

clouds.

b. Pilots are urged to cooperate and promptly

volunteer reports of these conditions and other

atmospheric data such as: cloud bases, tops and

layers; flight visibility; precipitation; visibility

restrictions such as haze, smoke and dust; wind at

altitude; and temperature aloft.

c. PIREPs should be given to the ground facility

with which communications are established; i.e.,

FSS, ARTCC, or terminal ATC. One of the primary

duties of the Inflight position is to serve as a

collection point for the exchange of PIREPs with en

route aircraft.

d. If pilots are not able to make PIREPs by radio,

reporting upon landing of the inflight conditions

encountered to the nearest FSS or Weather Forecast

Office will be helpful. Some of the uses made of the

reports are:

1. The ATCT uses the reports to expedite the

flow of air traffic in the vicinity of the field and for

hazardous weather avoidance procedures.

2. The FSS uses the reports to brief other pilots,

to provide inflight advisories, and weather avoidance

information to en route aircraft.

3. The ARTCC uses the reports to expedite the

flow of en route traffic, to determine most favorable

altitudes, and to issue hazardous weather information

within the center’s area.

4. The NWS uses the reports to verify or amend

conditions contained in aviation forecast and

advisories. In some cases, pilot reports of hazardous

conditions are the triggering mechanism for the

issuance of advisories. They also use the reports for

pilot weather briefings.

5. The NWS, other government organizations,

the military, and private industry groups use PIREPs

for research activities in the study of meteorological

phenomena.

6. All air traffic facilities and the NWS forward

the reports received from pilots into the weather

distribution system to assure the information is made

available to all pilots and other interested parties.

e. The FAA, NWS, and other organizations that

enter PIREPs into the weather reporting system use

the format listed in TBL 7−1−7. Items 1 through 6 are

included in all transmitted PIREPs along with one or

more of items 7 through 13. Although the PIREP

should be as complete and concise as possible, pilots

should not be overly concerned with strict format or

phraseology. The important thing is that the

information is relayed so other pilots may benefit

from your observation. If a portion of the report needs

clarification, the ground station will request the

information. Completed PIREPs will be transmitted

to weather circuits as in the following examples:

EXAMPLE−

1. KCMH UA /OV APE 230010/TM 1516/FL085/TP

BE20/SK BKN065/WX FV03SM HZ FU/TA 20/TB LGT
NOTE−

1. One zero miles southwest of Appleton VOR; time

1516 UTC; altitude eight thousand five hundred; aircraft

type BE200; bases of the broken cloud layer is six thousand

five hundred; flight visibility 3 miles with haze and smoke;

air temperature 20 degrees Celsius; light turbulence.
EXAMPLE−

2. KCRW UV /OV KBKW 360015−KCRW/TM

1815/FL120//TP BE99/SK IMC/WX RA/TA M08 /WV

290030/TB LGT−MDT/IC LGT RIME/RM MDT MXD

ICG DURC KROA NWBND FL080−100 1750Z
NOTE−

2. From 15 miles north of Beckley VOR to Charles-

ton VOR; time 1815 UTC; altitude 12,000 feet; type

aircraft, BE−99; in clouds; rain; temperature minus

8 Celsius; wind 290 degrees magnetic at 30 knots; light to

moderate turbulence; light rime icing during climb

northwestbound from Roanoke, VA, between 8,000 and

10,000 feet at 1750 UTC.