background image

6/17/21 

AIM 

up to a condition where individual drops are easily 
seen. 

2.  Moderate. 

Individual drops are not clearly 

identifiable; spray is observable just above pave-
ments and other hard surfaces. 

3.  Heavy. 

Rain seemingly falls in sheets; 

individual drops are not identifiable; heavy spray to 
height of several inches is observed over hard 
surfaces. 

b.  Ice Pellets 

1.  Light. 

Scattered pellets that do not com-

pletely cover an exposed surface regardless of 
duration. Visibility is not affected. 

2.  Moderate. 

Slow accumulation on ground. 

Visibility reduced by ice pellets to less than 7 statute 
miles. 

3.  Heavy. 

Rapid accumulation on ground. 

Visibility reduced by ice pellets to less than 3 statute 
miles. 

7

1

17.  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

/

statute mile to 

1

/

2

 statute mile. 

c.  Heavy. 

Visibility 

1

/

statute mile or less. 

7

1

18.  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

6. 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: 

Meteorology 

7

1

39