When the WARP is not available, a second system, the
narrowband Air Route Surveillance Radar (ARSR) can
display two distinct levels of precipitation intensity that will
be described to pilots as "MODERATE and "HEAVY TO
EXTREME."

ATC facilities that cannot display the intensity levels of
precipitation due to equipment limitations will describe the
location of the precipitation area by geographic position,
or position relative to the aircraft. Since the intensity level
is not available, the controller will state "INTENSITY
UNKNOWN."

ATC radar is not able to detect turbulence. Generally, turbulence
can be expected to occur as the rate of rainfall or intensity of
precipitation increases. Turbulence associated with greater rates
of rainfall/precipitation will normally be more severe than any
associated with lesser rates of rainfall/precipitation. Turbulence
should be expected to occur near convective activity, even in
clear air. Thunderstorms are a form of convective activity that
imply severe or greater turbulence. Operation within 20 miles
of thunderstorms should be approached with great caution,
as the severity of turbulence can be much greater than the
precipitation intensity might indicate.

Weather Avoidance Assistance
To the extent possible, controllers will issue pertinent
information on weather and assist pilots in avoiding such
areas when requested. Pilots should respond to a weather
advisory by either acknowledging the advisory or by
acknowledging the advisory and requesting an alternative
course of action as follows:
• Request to deviate off course by stating the number of
miles and the direction of the requested deviation.
• Request a new route to avoid the affected area.
• Request a change of altitude.
• Request radar vectors around the affected areas.

It should be remembered that the controller's primary
function is to provide safe separation between aircraft. Any
additional service, such as weather avoidance assistance, can
only be provided to the extent that it does not detract from the
primary function. It's also worth noting that the separation
workload is generally greater than normal when weather
disrupts the usual flow of traffic. ATC radar limitations and
frequency congestion may also be a factor in limiting the
controller's capability to provide additional service.