Section 5. Aircraft Rescue and Fire Fighting Communications Section 2. Barometric Altimeter Errors and Setting Procedures Paragraph Page 6-5-1. Discrete Emergency Frequency 6-5-1 ........................................ 6-5-2. Radio Call Signs 6-5-1 .................................................... 6-5-3. ARFF Emergency Hand Signals 6-5-1 ....................................... 7-1-1. National Weather Service Aviation Weather Service Program 7-1-1 .............. 7-1-2. FAA Weather Services 7-1-2 ............................................... 7-1-3. Use of Aviation Weather Products 7-1-2 ..................................... 7-1-4. Graphical Forecasts for Aviation (GFA) 7-1-5 ................................ 7-1-5. Preflight Briefing 7-1-7 .................................................... 7-1-6. Inflight Aviation Weather Advisories 7-1-9 ................................... 7-1-7. Categorical Outlooks 7-1-16 ................................................ 7-1-8. Inflight Weather Advisory Broadcasts 7-1-17 .................................. 7-1-9. Flight Information Services (FIS) 7-1-19 ...................................... 7-1-10. Weather Observing Programs 7-1-23 ........................................ 7-1-11. Weather Radar Services 7-1-31 ............................................. 7-1-12. ATC Inflight Weather Avoidance Assistance 7-1-35 ............................ 7-1-13. Runway Visual Range (RVR) 7-1-36 ........................................ 7-1-14. Reporting of Cloud Heights 7-1-38 .......................................... 7-1-15. Reporting Prevailing Visibility 7-1-38 ........................................ 7-1-16. Estimating Intensity of Rain and Ice Pellets 7-1-38 ............................ 7-1-17. Estimating Intensity of Snow or Drizzle (Based on Visibility) 7-1-39 .............. 7-1-18. Pilot Weather Reports (PIREPs) 7-1-39 ...................................... 7-1-19. PIREPs Relating to Airframe Icing 7-1-40 .................................... 7-1-20. Definitions of Inflight Icing Terms 7-1-41 .................................... 7-1-21. PIREPs Relating to Turbulence 7-1-44 ....................................... 7-1-22. Wind Shear PIREPs 7-1-45 ................................................ 7-1-23. Clear Air Turbulence (CAT) PIREPs 7-1-45 .................................. 7-1-24. Microbursts 7-1-45 ....................................................... 7-1-25. PIREPs Relating to Volcanic Ash Activity 7-1-56 .............................. 7-1-26. Thunderstorms 7-1-56 .................................................... 7-1-27. Thunderstorm Flying 7-1-57 ............................................... 7-1-28. Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report  (METAR) 7-1-59 ........................................................ 7-1-29. International Civil Aviation Organization (ICAO) Weather Formats 7-1-61 ....... 7-2-1. General 7-2-1 ............................................................ 7-2-2. Barometric Pressure Altimeter Errors 7-2-1 .................................. 7-2-3. Altimeter Errors 7-2-1 .................................................... ix Table of Contents AIM 12/31/20 Chapter 7. Safety of Flight Section 1. Meteorology