Prognostic Charts
Forecasting how weather systems will evolve is critical for effective flight planning. Understanding prognostic charts helps pilots anticipate the movement of fronts, pressure systems, and significant weather patterns hours into the future.
Introduction to Prognostic Charts
- Found at https://aviationweather.gov/adds/progs/
- Portray forecasts of selected weather conditions at specific times
- The chart is an extension of the day 1 U.S. LLSWPC issued from the same observed data base time
- Displays forecast positions and characteristics of pressure patterns, fronts, and precipitation
- The 36 and 48-Hour Prognostic Chart is a day 2 forecast of general weather for the conterminous United States
Aviation Weather Prognostic Charts
- Aviation Weather Prognostic Charts provide relatively long-term weather forecasts on a large scale to enable future flight planning
Issuance & Validity
- Issued four times daily (00Z, 06Z, 12Z, 18Z)
- Valid for the time specified (12, 24, 36, 48 hrs)
- Data is forecasted
- Information is insufficient for flight planning
- An effective overview of observed and prognostic charts allow the many essential details to fit into place and have continuity
Low-Level Significant Weather Prognostic Chart
- LLSWPC in a day 1 forecast of significant weather in the conterminous United States
- Provides information from the surface to FL240 (400 mbs)
- Altitudes from the surface to 17,999 are referenced using MSL altitudes
- Altitudes from 18,000' to FL240 are referenced using pressure altitude
- Provided in two forecasts, 12 and 24 hours in 4 panels
- Two top panels depict the 12 and 24 hour produced at the Aviation Weather Center (AWC) in Kansas City, Missouri
- Two lower panels depict the 12 and 24 hour produced at the Hydro meteorological Prediction Center (HPC) in Camp Springs, Maryland
High-Level Significant Weather Prognostic Chart
- HLSWPC is a day 1 forecast of significant weather in the conterminous United States
- Provides information from 24,000' to 60,000'
- Covers much of the Northern Hemisphere and a limited portion of the Southern Hemisphere
- Each section covers a specific area and areas sometimes overlap
- Conditions routinely appearing on the chart are jet streams, cumulonimbus clouds, turbulence, and Tropopause heights
- Surface fronts are included to add perspective
- Sometimes tropical cyclones, squall lines, volcanic eruption sites, sandstorms, and dust storms will appear
Surface Pressure Systems
- Depict pressure centers, troughs and on selected panels, isobars
- High and Lows identified by "Hs" and "Ls" respectively
- Pressure troughs are identified by long dashed lines labeled "TROF"
- Isobars are drawn as solid lines to portray pressure patterns
- Isobars are drawn in 8 millibar (mb) intervals instead of 4 mb to provide a less sensitive analysis
- Occasionally, nonstandard isobars will be drawn using 4 mb intervals to highlight patterns with weak pressure gradients
- Nonstandard isobars are drawn as dashed lines
Fronts
- Surface fronts are depicted on each panel
- Formats used are the standard symbols and three-digit characterization code used on the surface chart
-
Type of Front:
CodeDescriptions0Quasi-stationary at surface2Warm front at surface4Cold front at surface6Occlusion7Instability line -
Intensity of Front:
CodeDescriptions0No specification1Weak, decreasing2Weak, little, or no change3Weak, increasing4Moderate, decreasing5Moderate, little, or no change6Moderate, increasing7Strong, decreasing8Strong, little, or no change9Strong, increasing -
Character of Front:
Code:Descriptions:0No specification5Forming or existence expected6Quasi-stationary7With waves8Diffuse
Precipitation
- Solid lines enclose precipitation areas
- Symbols specify the forums and types of precipitation
- A mix is indicated by the use of two pertinent symbols separated by a slash
- Areas of continuous precipitation is shaded as well as precipitation covering more than half of the area
- A bold dashed line is used to separate precipitation with contrasting characteristics
- A dashed line would be used to separate an area of similar characteristics (snow and rain)
Jet Streams
- Jet streams with a maximum speed of more than 80 knots are identified by bold lines
- Arrowheads indicate the orientation of each jet stream
- Double hatched lines identified changes in wind speed
- Speed indicators are drawn at 20-knot intervals and begin with 100 knots
- Standard wind symbol (shaft, pennants, and barbs) is placed at each pertinent position to identify velocity
- The altitude in hundreds of feet prefaced with "FL" is placed adjacent to each wind symbol
Cumulonimbus Clouds
- Cumulonimbus clouds (CBs) are thunderstorm clouds
- Enclosed by scalloped lines
- Isolated or scattered CBs (one-half or less coverage) which are not embedded are not depicted
- Identified with CB and altitude
- Isolated (ISOL)
- Occasional (OCNL)
- Frequent (FRQ)
- Bases that extended below 24,000 are encoded "XXX" (High-Level)
- Thunderstorms imply hazards including turbulence and hail
Tropopause
- Plotted in hundreds of feet
- Heights enclosed by rectangles
- Centers of high and low heights are identified with "H" and "L" respectively with their heights and enclosed by polygons
Weather Flying Categories
- Ceiling and visibility determine the category
- VFR - Visual Flight Rules
- MVFR - Marginal Visual Flight Rules
- IFR - Instrument Flight Rules
- IFR areas are enclosed by solid lines
- MVFR areas are enclosed by scalloped lines
- All other areas are VFR
Freezing Levels
- Depicted by a zigzag line labeled as "SFC" for surface
- Freezing levels aloft are depicted by thin, short dashed lines
- Lines are drawn at 4,000' intervals (80 = 8,000')
- Lines are discontinued where they intersect corresponding altitudes of the Rocky Mountains
- Areas with multiple freezing levels have lines drawn to the highest freezing level
Turbulence
- Areas of moderate or greater turbulence are enclosed by bold, long dashed lines
- Turbulence intensities are identified by symbols
- The vertical extent of turbulence layers are specified by top and base heights
- Areas of thunderstorms do not include indications of turbulence because it is implied
- Added emphasis is included if the turbulence is from the surface to 24,000' or above, having thunderstorms covering more than half of the area
- Intensity symbols and layer altitudes appear within or adjacent to the forecast area
- Heights are pressure altitude
- Bases that extended below 24,000 are encoded "XXX" (High-Level)
Tropical Cyclones
- Positions of hurricanes, typhoons and tropical storms are depicted
- Hurricanes use standard symbol while typhoons are shaded
- When pertinent the name of each storm is positioned adjacent to the symbol
Squall Lines
- Severe squall lines are lines of CBs with 5/8 coverage or greater
- Identified by long dashed lines separated by a V
Volcanic Eruption Sites
- Identified by a trapezoidal symbol
- Dot at the base indicates latitude and longitude of volcano
- Name, latitude, and longitude are noted adjacent
- Reference SIGMETs for more information
Sand and Dust Storms
- Areas of widespread sandstorms and dust storms are labeled by an S
- The S with an arrow depicts areas of widespread sandstorms or dust storms
- The S without an arrow depicts severe sandstorm or dust haze
Prognostic Charts Conclusion
- For more information, a paper copy of Federal Aviation Administration (FAA-H-8083-28) Aviation Weather Handbook [Amazon] is available for purchase
- A digital copy of Federal Aviation Administration (FAA-H-8083-28) Aviation Weather Handbook is available from the FAA's website
- Improve your weather skills with FAA provided (and WINGS credited) resources by going to https://www.faasafety.gov/ and type "weather" into the search bar
- Still looking for something? Continue searching: