1) As a supplement to an existing SIGMET, Convective SIGMET or AIRMET.
2) 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.
3) 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.
b) 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.
4. Categorical Outlooks
4.1 Categorical outlook terms describing general ceiling and visibility conditions for advance planning purposes are used only in area forecasts. They are defined as follows:
4.1.1 LIFR (Low IFR) . Ceiling less than 500 feet and/or visibility less than 1 mile.
4.1.2 IFR . Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.
4.1.3 MVFR (Marginal VFR) . Ceiling 1,000 or 3,000 feet and/or visibility 3 to 5 miles inclusive.
4.1.4 VFR . Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.
4.2 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.
LIFR CIG.low IFR due to low ceiling.
IFR FG.IFR due to visibility restricted by fog.
MVFR CIG HZ FU.marginal VFR due both to ceiling and to visibility restricted by haze and smoke.
IFR CIG RA WIND.IFR due both to low ceiling and to visibility restricted by rain; wind expected to be 25 knots or greater.
FIG GEN 3.5.8
G.AIRMET Graphical Product
5. Telephone Information Briefing Service (TIBS)
5.1
TIBS, provided by automated flight service stations (AFSSs), is a continuous recording of meteorological and aeronautical information, avail-able by telephone. Each AFSS provides at least four route and/or area briefings. In addition, airspace procedures and special announcements (if applica-ble) concerning aviation interests are also available. Depending upon user demand, other items may be provided; i.e., METAR observations, terminal airport forecasts, winds aloft, and temperatures aloft forecasts.
6.
Inflight Weather Broadcasts
6.1 Weather Advisory Broadcasts. ARTCCs’ broadcast a Severe Weather Forecast Alert (AWW), Convective SIGMET, 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 contain SIGMET or CWA identification and a brief description of the weather activity and general area affected.
EXAMPLE.
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.
EXAMPLE.
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.
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