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6/17/21 

AIM 

(b) 

When an Inflight Advisory has not been 

issued but observed or expected weather conditions 
meet SIGMET/AIRMET criteria based on current 
pilot reports and reinforced by other sources 
of information about existing meteorological condi-
tions. 

(c) 

When observed or developing weather 

conditions do not meet SIGMET, Convective 
SIGMET, or AIRMET criteria; e.g., in terms of 
intensity or area coverage, but current pilot reports or 
other weather information sources indicate that 
existing or anticipated meteorological phenomena 
will adversely affect the safe flow of air traffic within 
the ARTCC area of responsibility. 

2. 

The following example is a CWA issued from 

the Kansas City, Missouri, ARTCC. The “3” after 
ZKC in the first line denotes this CWA has been 
issued for the third weather phenomena to occur for 
the day. The “301” in the second line denotes the 
phenomena number again (3) and the issuance 
number (01) for this phenomena. The CWA was 
issued at 2140Z and is valid until 2340Z. 

EXAMPLE

 

ZKC3 CWA 032140 
ZKC CWA 301 VALID UNTIL 032340 
ISOLD SVR TSTM over KCOU MOVG SWWD 
10 KTS ETC. 

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7.  Categorical Outlooks 

a. 

Categorical outlook terms, describing general 

ceiling and visibility conditions for advanced 
planning purposes are used only in area forecasts and 
are defined as follows: 

1.  LIFR (Low IFR). 

Ceiling less than 500 feet 

and/or visibility less than 1 mile. 

2.  IFR. 

Ceiling 500 to less than 1,000 feet 

and/or visibility 1 to less than 3 miles. 

3.  MVFR (Marginal VFR). 

Ceiling 1,000 to 

3,000 feet and/or visibility 3 to 5 miles inclusive. 

4.  VFR. 

Ceiling greater than 3,000 feet and 

visibility greater than 5 miles; includes sky clear. 

b. 

The cause of LIFR, IFR, or MVFR is indicated 

by either ceiling or visibility restrictions or both. The 
contraction “CIG” and/or weather and obstruction to 

vision symbols are used. If winds or gusts of 25 knots 
or greater are forecast for the outlook period, the word 
“WIND” is also included for all categories including 
VFR. 

EXAMPLE

 

1. 

LIFR CIG

low IFR due to low ceiling. 

2. 

IFR FG

IFR due to visibility restricted by fog. 

3. 

MVFR CIG HZ FU

marginal VFR due to both ceiling 

and visibility restricted by haze and smoke. 

4. 

IFR CIG RA WIND

IFR due to both low ceiling and 

visibility restricted by rain; wind expected to be 25 knots or 
greater. 

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8.  Inflight Weather Advisory 

Broadcasts 

a. 

ARTCCs broadcast a Severe Weather Forecast 

Alert (AWW), Convective SIGMET, SIGMET, 
AIRMET, Urgent Pilot Report, or CWA alert once on 
all frequencies, except emergency, when any part of 
the area described is within 150 miles of the airspace 
under their jurisdiction. These broadcasts advise 
pilots of the availability of hazardous weather 
advisories and to contact the nearest Flight Service 
facility for additional details. 

EXAMPLE

 

1. 

Attention all aircraft, SIGMET Delta Three, from Myton 

to Tuba City to Milford, severe turbulence and severe clear 
icing below one zero thousand feet. Expected to continue 
beyond zero three zero zero zulu. 

2. 

Attention all aircraft, convective SIGMET Two Seven 

Eastern. From the vicinity of Elmira to Phillipsburg. 
Scattered embedded thunderstorms moving east at one 
zero knots. A few intense level five cells, maximum tops four 
five zero. 

3. 

Attention all aircraft, Kansas City Center weather 

advisory one zero three. Numerous reports of moderate to 
severe icing from eight to niner thousand feet in a three zero 
mile radius of St. Louis. Light or negative icing reported 
from four thousand to one two thousand feet remainder of 
Kansas City Center area. 

NOTE

 

Terminal control facilities have the option to limit the 
AWW, convective SIGMET, SIGMET, or CWA broadcast as 
follows: local control and approach control positions may 
opt to broadcast SIGMET or CWA alerts only when any 
part of the area described is within 50 miles of the airspace 
under their jurisdiction. 

Meteorology 

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