6.5  The United States provides an Area Forecast (FA) in place of a GAMET. AIRMETs are issued every 6 hours on a scheduled basis. The FA and AIRMET are valid from the surface to FL450. The FA and AIRMET formats differ from Table A5.4 and Table 6.1. Specifically, the FA are issued three times a day in the United States, with the exception of Alaska and Hawaii where they are issued four times a day. They are valid for a 12.hour period beginning 1 hour after issuance and have an 18.hour outlook. This is also applicable to Part 1: 7.2, Part II, Appendix 5: 4, Part II, Appendix 6:2.1, and Part II, Appendix 8: 4.1.2 (use of templates.) 
Chapter 7  SIGMET and AIRMET Information, Aerodrome Warnings and Wind Shear Warnings 
7.2.3  United States practice is to issue an AIRMET every six hours on a scheduled basis. The United States is developing capabilities to issue an AIRMET on a scheduled basis every 3 hours, which would exceed the SARP standard that an AIRMET is not to be issued more than every 4 hours. 
7.4.1  The United States does not provide wind shear warnings. The United States believes wind shear alerts are timelier to flight crews in landing and takeoff than wind shear warnings and thus provide a greater level of safety. In addition, the information is duplicative in nature in that wind shear warnings could be delayed while wind shear alerts are provided via automated systems that allow for immediate data link to flight crews through ATS systems. This difference is also applicable to App 6: 6.2. 
Chapter 9  Service for operators and flight crew members 
9.2.3 & 9.2.4  United States meteorological offices have no means to communicate directly to flight crews if there is a divergence in the forecast from what is provided in the flight document folder. 
9.3.3  United States meteorological offices have no means to provide updates to flight document folders or to contact the operator. 
PART II  APPENDICES and ATTACHMENTS 
APPENDIX 3  Technical specifications related to meteorological observations and reports 
2.2  The United States does not use the term CAVOK in meteorological reports.  This difference is also applicable to Table A3.2, METAR and SPECI. 
2.3.1 c)  The U.S. does not prepare SPECI for changes in air temperature. 
2.3.2 a)  U.S. practices require SPECI for wind shift when wind direction changes by 45 degrees or more in less than 15 minutes and the wind speed is 10 knots or more throughout the wind shift. 
2.3.2 b)  U.S. practices do not require SPECI for increases of mean surface wind speed. 
2.3.2 c)  U.S. practices require SPECI for squall, where squall is defined as a strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots and is sustained at least 22 knots or more for at least one minute. 
2.3.2d)  U.S. practices do not require SPECI for wind direction changes based on local criteria. 
2.3.2f)  SPECI are not prepared for the equivalents in feet of 150, 350, or 600 meters. United States military stations may not report a SPECI based on RVR. 
2.3.2 g/h)  Practices do not require SPECI for the onset, cessation, or change in intensity of: . freezing fog. . moderate or heavy precipitation (including showers thereof). . low drifting dust, sand or snow. . blowing dust, sand or snow (including snowstorm). . duststorm. . sandstorm. 

2.3.2 i) and j)  The United States provides a SPECI when a layer of clouds or obscurations aloft is present below 1000 ft and no layer aloft was reported below 1000 ft in the preceding report. A SPECI is also reported when the ceiling decreases or increases at these markers: 3000, 1500, 1000, 500ft or lowest published instrument approach procedures. SPECI is made when the ceiling (rounded off to reportable values) forms or dissipates below, decreases to less than, or if below, increases to equal or exceed: 3,000 feet, 1,500 feet, 1,000 feet, 500 feet or lowest standard instrument approach procedure minimum published in the National Ocean Survey (NOS) U.S. Terminal Procedures.  If none published, then 200 feet. 
4.1.1.2  The United States does not provide wind representatives for specific runways but does provide a wind representative for the airport. 
4.1.3.1 b)  The United States provides a 2.minute average wind observation for the METAR/SPECI. 
4.1.5.2b)  The wind direction may be considered variable if, during the 2.min evaluation period, the wind speed is 6 KT or less. Also, the wind direction shall be considered variable if, during the 2.min evaluation period, it varies by 60 deg or more when the wind speed is greater than 6 KT. 
4.1.5.2c)  United States practices define wind gust as rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. Wind speed data for the most recent 10 minutes is examined and a gust, the maximum instantaneous wind speed during that 10.minute period, is reported if the definition above is met during that period. 
　
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