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Cloud height
Sky cover
Temperature
Dew point
Altimeter
7−1−13. Weather Radar Services
a. The National Weather Service operates a
network of radar sites for detecting coverage,
intensity, and movement of precipitation. The
network is supplemented by FAA and DOD radar
sites in the western sections of the country. Local
warning radar sites augment the network by operating
on an as needed basis to support warning and forecast
programs.
b. Scheduled radar observations are taken hourly
and transmitted in alpha-numeric format on weather
telecommunications circuits for flight planning
purposes. Under certain conditions, special radar
reports are issued in addition to the hourly
transmittals. Data contained in the reports are also
collected by the National Center for Environmental
Prediction and used to prepare national radar
summary charts for dissemination on facsimile
circuits.
c. A clear radar display (no echoes) does not mean
that there is no significant weather within the
coverage of the radar site. Clouds and fog are not
detected by the radar. However, when echoes are
present, turbulence can be implied by the intensity of
the precipitation, and icing is implied by the presence
of the precipitation at temperatures at or below zero
degrees Celsius. Used in conjunction with other
weather products, radar provides invaluable information
for weather avoidance and flight planning.
8/5/04 AIM
Meteorology 7−1−29
FIG 7−1−9
NEXRAD Coverage
AIM 8/5/04
7−1−30 Meteorology
FIG 7−1−10
NEXRAD Coverage
2/17/05 AIM
Meteorology 7−1−31
FIG 7−1−11
NEXRAD Coverage
AIM 2/17/05
7−1−32 Meteorology
d. All En Route Flight Advisory Service facilities
and AFSSs have equipment to directly access the
radar displays from the individual weather radar sites.
Specialists at these locations are trained to interpret
the display for pilot briefing and inflight advisory
services. The Center Weather Service Units located in
ARTCCs also have access to weather radar displays
and provide support to all air traffic facilities within
their center’s area.
e. Additional information on weather radar
products and services can be found in AC 00−45,
Aviation Weather Services.
REFERENCE−
Pilot/Controller Glossary, Radar Weather Echo Intensity Levels.
AIM, Thunderstorms, Paragraph 7−1−29.
A/FD, Charts, NWS Upper Air Observing Stations and Weather Network
for the location of specific radar sites.
7−1−14. National Convective Weather
Forecast (NCWF)
a. Description.
1. The NCWF is an automatically generated
depiction of: (1) current convection and (2) extrapolated
significant current convection. It is a
supplement to, but does NOT substitute for, the report
and forecast information contained in Convective
SIGMETs (see paragraph 7−1−6d). Convection,
particularly significant convection, is typically
associated with thunderstorm activity.
2. The National Weather Service Aviation
Weather Center (AWC) updates the NCWF based on
input from the Next Generation Weather Radar
(NEXRAD) and cloud−to−ground lightning data.
3. The NCWF is most accurate for long−lived
mature multi−storm systems such as organized line
storms. NCWF does not forecast initiation, growth or
decay of thunderstorms. Therefore, NCWF tends to
under−warn on new and growing storms and
over−warn on dying storms. Forecast positions of
small, isolated or weaker thunderstorms are not
displayed.
4. The NCWF area of coverage is limited to the
48 contiguous states.
b. Attributes.
1. The NCWF is updated frequently (every
5 minutes) using the most current available data.
2. The NCWF is able to detect the existence of
convective storm locations that agree very well with
concurrent radar and lightning observations.
3. The NCWF is a high−resolution forecast
impacting a relatively small volume of airspace rather
than covering large boxed areas. The location, speeds
and directions of movement of multiple convective
storms are depicted individually.
4. The NCWF extrapolation forecasts are more
accurate when predicting the location and size of well
organized, unchanging convective storms moving at
uniform speeds. The NCWF does not work well with
sporadic, explosive cells developing and dissipating
in minutes.
5. In displaying forecast cell locations, the
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