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Prognostic Charts

Introduction:

  • Found at http://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
Figure 1: Aviation Weather Prognostic Charts

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

Code Descriptions
0 Quasi-stationary at surface
2 Warm front at surface
4 Cold front at surface
6 Occlusion
7 Instability line

Intensity of Front

Code Descriptions
0 No specification
1 Weak, decreasing
2 Weak, little, or no change
3 Weak, increasing
4 Moderate, decreasing
5 Moderate, little, or no change
6 Moderate, increasing
7 Strong, decreasing
8 Strong, little, or no change
9 Strong, increasing

Character of Front

Code: Descriptions:
0 No specification
5 Forming or existence expected
6 Quasi-stationary
7 With waves
8 Diffuse

Prognostic Chart Symbols
Figure 1: Prognostic Chart Symbols 1

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

Prognostic Chart Symbols
Figure 2: Prognostic Chart Symbols 2

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)

Typical 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

Conclusion:

References: