background image

6/17/21 

AIM 

e. 

The probability of lightning strikes occurring to 

aircraft is greatest when operating at altitudes where 
temperatures are between minus 5 degrees Celsius 
and plus 5 degrees Celsius. Lightning can strike 
aircraft flying in the clear in the vicinity of a 
thunderstorm. 

f. 

METAR reports do not include a descriptor for 

severe thunderstorms. However, by understanding 
severe thunderstorm criteria, i.e., 50 knot winds or 

3

/

inch hail, the information is available in the report 

to know that one is occurring. 

g. 

Current weather radar systems are able to 

objectively determine precipitation intensity. These 
precipitation intensity areas are described as “light,” 
“moderate,” “heavy,” and “extreme.” 

REFERENCE

 

Pilot/Controller Glossary

 

Precipitation Radar Weather Descriptions 

EXAMPLE

 

1. 

Alert provided by an ATC facility to an aircraft: 

(aircraft identification) EXTREME precipitation between 
ten o’clock and two o’clock, one five miles. Precipitation 
area is two five miles in diameter. 

2. 

Alert provided by an FSS: 

(aircraft identification) EXTREME precipitation two zero 
miles west of Atlanta V

O

R, two five miles wide, moving 

east at two zero knots, tops flight level three niner zero. 

7

1

27.  Thunderstorm Flying 

a. 

Thunderstorm Avoidance. Never regard any 

thunderstorm lightly, even when radar echoes are of 
light intensity. Avoiding thunderstorms is the best 
policy. Following are some Do’s and Don’ts of 
thunderstorm avoidance: 

1. 

Don’t land or takeoff in the face of an 

approaching thunderstorm. A sudden gust front of 
low level turbulence could cause loss of control. 

2. 

Don’t attempt to fly under a thunderstorm 

even if you can see through to the other side. 
Turbulence and wind shear under the storm could be 
hazardous. 

3. 

Don’t attempt to fly under the anvil of a 

thunderstorm. There is a potential for severe and 
extreme clear air turbulence. 

4. 

Don’t fly without airborne radar into a cloud 

mass containing scattered embedded thunderstorms. 
Scattered thunderstorms not embedded usually can 
be visually circumnavigated. 

5. 

Don’t trust the visual appearance to be a 

reliable indicator of the turbulence inside a 
thunderstorm. 

6. 

Don’t assume that ATC will offer radar 

navigation guidance or deviations around thunder-
storms. 

7. 

Don’t use data-linked weather next genera-

tion weather radar (NEXRAD) mosaic imagery as the 
sole means for negotiating a path through a 
thunderstorm area (tactical maneuvering). 

8. 

Do remember that the data

linked NEXRAD 

mosaic imagery shows where the weather was, not 
where the weather is. The weather conditions 
depicted may be 15 to 20 minutes older than indicated 
on the display. 

9. 

Do listen to chatter on the ATC frequency for 

Pilot Weather Reports (PIREP) and other aircraft 
requesting to deviate or divert. 

10. 

Do ask ATC for radar navigation guidance 

or to approve deviations around thunderstorms, if 
needed. 

11. 

Do use data-linked weather NEXRAD 

mosaic imagery (for example, Flight Information 
Service-Broadcast (FIS-B)) for route selection to 
avoid thunderstorms entirely (strategic maneuver-
ing). 

12. 

Do advise ATC, when switched to another 

controller, that you are deviating for thunderstorms 
before accepting to rejoin the original route. 

13. 

Do ensure that after an authorized weather 

deviation, before accepting to rejoin the original 
route, that the route of flight is clear of thunderstorms. 

14. 

Do avoid by at least 20 miles any 

thunderstorm identified as severe or giving an intense 
radar echo. This is especially true under the anvil of 
a large cumulonimbus. 

15. 

Do circumnavigate the entire area if the area 

has 6/10 thunderstorm coverage. 

16. 

Do remember that vivid and frequent 

lightning indicates the probability of a severe 
thunderstorm. 

17. 

Do regard as extremely hazardous any 

thunderstorm with tops 35,000 feet or higher whether 
the top is visually sighted or determined by radar. 

18. 

Do give a PIREP for the flight conditions. 

Meteorology 

7

1

57