12.weather-charts. Aviation Weather Charts
Aviation weather charts are graphical depictions of observed or forecast weather conditions and are an essential component of preflight planning. They allow pilots to visualize the big-picture synoptic situation — fronts, pressure systems, areas of precipitation, icing, turbulence, and convection — that text products such as METARs and TAFs describe only in localized form. Weather charts are produced and disseminated by the National Weather Service (NWS), the Aviation Weather Center (AWC), and the Weather Prediction Center (WPC), and are accessed primarily through aviationweather.gov and through Flight Service (1-800-WX-BRIEF).
Surface Analysis Chart. The Surface Analysis Chart is issued every 3 hours and depicts conditions at the surface across the contiguous United States and adjacent areas. It shows:
- Isobars — solid lines of equal sea-level pressure, drawn at 4-millibar intervals (e.g., 1000, 1004, 1008 mb). Tightly spaced isobars indicate a strong pressure gradient and stronger surface winds.
- Pressure centers marked with H (high) and L (low).
- Fronts — cold (blue triangles), warm (red semicircles), stationary (alternating), and occluded (alternating triangles and semicircles in purple).
- Station models showing temperature, dew point, wind, sky cover, pressure, and present weather at each reporting station.
Ceiling and Visibility Analysis (CVA). The CVA, updated every 5 minutes, displays current ceiling and surface visibility derived from METARs and is color-coded by flight category — VFR (green), MVFR (blue), IFR (red), and LIFR (magenta). It is one of the quickest ways to identify where IMC is occurring along a route.
Weather Depiction Chart. Although phased out as a standalone product, its functions are now served by the CVA and the Graphical Forecasts for Aviation (GFA). It historically summarized observed ceilings, visibilities, and weather, with shaded areas for IFR and contour outlines for MVFR.
Graphical Forecasts for Aviation (GFA). The GFA replaced the textual Area Forecast (FA) for the CONUS. It is a web-based tool on aviationweather.gov that provides a continuous, layered display of observations and forecasts from 14 hours in the past to 18 hours in the future. Layers include clouds, ceiling/visibility, precipitation/weather, winds, turbulence, icing, and PIREPs. The GFA is the primary go-to product for visualizing en route conditions for VFR and IFR flight planning.
Significant Weather (SIGWX) Prognostic Charts. Low-level Significant Weather Prog Charts cover the surface to FL240 and forecast 12 and 24 hours ahead. They depict:
- Areas of forecast IFR (enclosed by solid lines) and MVFR (scalloped lines).
- Areas of moderate or greater turbulence with dashed lines and a peaked-hat symbol, with tops and bases noted.
- Freezing levels as dashed blue lines labeled in hundreds of feet MSL (e.g., 80 = 8,000 ft).
- Forecast positions of fronts and pressure centers.
High-level SIGWX charts cover FL250–FL630 and are used primarily by jet operators.
Convective Outlook (AC). Issued by the Storm Prediction Center, this chart forecasts the probability and severity of thunderstorms (general, slight, enhanced, moderate, high) for Day 1 through Day 8. It is invaluable for anticipating widespread convection.
Winds and Temperatures Aloft Chart (FB / FD). A graphical companion to the FB text product. Wind barbs show direction and speed at standard altitudes (3,000; 6,000; 9,000; 12,000; 18,000; 24,000; 30,000; 34,000; 39,000 ft), with temperatures (°C) plotted alongside. Useful for selecting cruise altitude, computing groundspeed, and identifying wind shear between levels. Note: forecasts are omitted within 1,500 ft of station elevation, and temperatures are omitted at 3,000 ft.
Radar Summary and Composite Reflectivity. Radar mosaics depict the location, intensity, movement, and tops of precipitation echoes. Intensity is shown by color (green → yellow → red → magenta corresponding to light → extreme). Movement vectors show cell direction and speed. Caution: radar shows precipitation, not clouds or turbulence — a clear scope is not a guarantee of clear skies.
Satellite Imagery. Two principal types are used: visible (shows reflected sunlight, only useful in daylight; helpful for identifying cloud type and texture) and infrared (IR) (shows emitted radiation, available 24 hours; brighter/whiter tones indicate colder, higher cloud tops — useful for spotting thunderstorm tops and night convection).
Using Charts Together. No single chart tells the full weather story. A sound preflight briefing layers products: start with the Surface Analysis and Prog Charts for the synoptic picture, drill into the GFA for the route, check radar and satellite for current convection, and finish with METARs, TAFs, PIREPs, and AIRMETs/SIGMETs for verification. Per 14 CFR 91.103, the PIC must become familiar with all available information concerning the flight, and these charts are central to satisfying that duty.