Aviation Weather Services

Weather Depiction Chart ceiling height, weather, and obstructions to visibility, but A weather depiction chart details surface conditions as does not include winds or pressure readings like the surface derived from METAR and other surface observations. The analysis chart. A bracket ( ] ) symbol to the right of the station weather depiction chart is prepared and transmitted by indicates the observation was made by an automated station. computer every 3 hours beginning at 0100Z time and is valid data for the forecast period. It is designed to be used for flight Significant Weather Prognostic Charts planning by giving an overall picture of the weather across Significant weather prognostic charts are available for low- the United States. [Figure 13-12] level significant weather from the surface to FL 240 (24,000 feet), also referred to as the 400 mb level and high-level The weather depiction chart also provides a graphic display significant weather from FL 250 to FL 630 (25,000 to 63,000 of IFR, VFR, and marginal VFR (MVFR) weather. Areas of feet). The primary concern of this discussion is the low-level IFR conditions (ceilings less than 1,000 feet and visibility significant weather prognostic chart. less than three miles) are shown by a hatched area outlined by a smooth line. MVFR regions (ceilings 1,000 to 3,000 The low-level chart is is a forecast of aviation weather feet, visibility 3 to 5 miles) are shown by a nonhatched area hazards, primarily intended to be used as a guidance product outlined by a smooth line. Areas of VFR (no ceiling or ceiling for briefing the VFR pilot. The forecast domain covers the 48 greater than 3,000 feet and visibility greater than five miles) contiguous states, southern Canada and the coastal waters for are not outlined. Also plotted are fronts, troughs, and squall altitudes below 24,000 ft. Low altitude Significant Weather lines from the previous hours surface analysis chart. charts are issued four times daily and are valid at fixed times: 0000, 0600, 1200, and 1800 UTC. Each chart is divided on Weather depiction charts show a modified station model the left and right into 12 and 24 hour forecast intervals (based that provides sky conditions in the form of total sky cover, on the current NAM model available). Figure 13-12. Weather depiction chart. 13-15