8/15/19 12/31/20 AIM Abbreviation/ Acronym Meaning VR ........ VFR Military Training Route V$_{REF}$ ....... The reference landing approach speed, usually about 1.3 times V$_{so}$ plus 50 percent of the wind gust speed in excess of the mean wind speed. V$_{SO}$ ........ The stalling speed or the minimum steady flight speed in the landing configuration at maximum weight. VTF ....... Vector to Final VV ........ Vertical Visibility VVI ....... Vertical Velocity Indicator V$_{Y}$ ........ Speed for best rate of climb V$_{YI}$ ........ Instrument climb speed, utilized instead of V$_{Y}$ for compliance with the climb requirements for instrument flight WA ........ AIRMET WAAS ..... Wide Area Augmentation System Abbreviation/ Acronym Meaning WFO....... Weather Forecast Office WGS − 84.... World Geodetic System of 1984 WMO ...... World Meteorological Organization WMS . . Wide − Area Master Station WMSC ..... Weather Message Switching Center WMSCR .... Weather Message Switching Center Replacement WP ........ Waypoint WRA ...... Weather Reconnaissance Area WRS....... Wide − Area Ground Reference Station WS ........ SIGMET WSO ...... Weather Service Office WSP ....... Weather System Processor WST ....... Convective Significant Meteorological Information WW ....... Severe Weather Watch Bulletin Abbreviations/Acronyms Appendix 3 − 5