Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
8.1.1 Content COLD FRONT • COLD FRONTOLYSIS
WARM FRONT WARM FRONTOLYSIS
STATIONARY FRONT STATIONARY
OCCLUDED FRONT FRONTOLYSIS
OCCLUDED FRONTOLYSIS
CHANGE OF FRONT TYPE
COLD FRONTOGENESIS HIGH PRESSURE CENTER
WARM FRONTOGENESIS LOW PRESSURE CENTER
STATIONARY TROPICAL (TRPL) WAVE
FRONTOGENESIS TROUGH (TROF) OR L xxx TROPICAL DEPRESSION
OUTFLOW BONDARY (OUTFLOW BNDRY)
TRPCL STORM TROPICAL STORM
DRYLINE XXX
RIDGE HURCN HURRICANE
SQUALL LINE XXX Figure 8-2. Surface Prog Chart Symbols
8.1.1.1 Pressure Systems Pressure systems are depicted by pressure centers, troughs, isobars, drylines, tropical waves, tropical storms and hurricanes using standard symbols (Figure 8-2). Isobars are denoted by solid thin gray lines and labeled with the appropriate pressure in millibars. The central pressure
8.1.1.2 Fronts Fronts are depicted using the standard symbols in Figure 8-2.
8.1.1.3 Squal Lines Squall lines are denoted using the standard symbol in Figure 8-2.
8.1.1.4 Precipitation Rain (light, moderate, heavy) Snow (light,moderate, heavy) RR K Thunder (with rain, snow,no precipitation) Shower (rain, snow) Drizzle ~ Freezing rain, Freezing drizzle Ice pellets/Sleet Fog (shallow.deep) 00 Haze AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-2
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 8-3. Surface Prog Chart Precipitation Symbols
Precipitation areas are enclosed by thick, solid, green lines (Figure 8-4). Standard precipitation symbols are used to identify precipitation types (Figure 8-3). These symbols are positioned within or adjacent to the associated area of precipitation. If adjacent to the area, an arrow will point to the area with which they are associated. A mix of precipitation is indicated by the use of two pertinent symbols separated by a slash (Figure 8-4). A bold, dashed, grey line is used to separate precipitation within an outlined area with contrasting characteristics (Figure 8-4). For instance, a dashed line would be used to separate an area of snow from an area of rain.
Figure 8-4. Surface Prog Chart Precipitation Example
Precipitation characteristic are further described by the use of shading (Figure 8-5). Shading or lack of shading indicates the expected coverage of the precipitation. Shaded areas indicate the precipitation is expected to have more than 50% (broken) coverage. Unshaded areas indicate 30-50% (scattered) coverage.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 8-5. Surface Prog Chart Precipitation Coverage
8.1.2 Issuance Short-Range Surface Prognostic (Prog) Charts are issued by the Hydrometeorological Prediction Center (HPC) in Camp Springs, MD. Table 8-1 provides the product schedule. The 12- and 24-Hour Surface Prognostic (Prog). Charts are issued four times a day and are termed “Day 1” progs. The 36- and 48- Hour Surface Prog Charts are issued twice daily and are termed “Day 2” progs. They are available on the HPC web site at:
http://adds.aviationweather.noaa.gov/progs/.
Table 8-1. Short-Range Surface Prog Charts Schedule Issuance Time (UTC) ~1720 ~2310 ~0530 ~0935 Valid Time (UTC) 12-Hour Surface Prog 0000 0600 1200 1800 24-Hour Surface Prog 1200 1800 0000 0600 36-Hour Surface Prog 0000 NA 1200 NA 48-Hour Surface Prog 1200 NA 0000 NA
8.1.3 Use Short-Range Surface Prognostic (Prog) Charts can be used to obtain an overview of the progression of surface weather features during the next 48 hours. The progression of weather is the change in position, size, and intensity of weather with time. Progression analysis is accomplished by comparing charts of observed conditions to the 12-, 24-, 36-, and 48-hour progs. Short-Range Surface Prognostic (PROG) Charts make the comprehension of weather details easier and more meaningful. For example, in Figures 8-6 through 8-9, the cold front located from the eastern Great Lakes to Missouri is forecast to move southeastward and the High pressure center just north of the Minnesota/North Dakota boarder is also forecast to move southeast and weaken.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) .2-HR FOST OF FRONTS/PRESSURE AND WEATHER VALID: 0000Z FRI DEC 17 2004 H H 1031 H /TROF ISSUED: 16317 THU DEC 16 200 Figure 8-6. 12-hour Surface Prog Chart Example AND WEATHER VALID: 1200Z FRI DEC * * H §40 1042 TROF TROF ISSUED: 16327 THU DEC 16 2004 Figure 8-7. 24-hour Surface Prog Chart Example AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-5
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 8-8. 36-hour Surface Prog Chart Example
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 8-9. 48-hour Surface Prog Chart Example AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-7
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
8.2 Low-Level Significant Weather (SIGWX) Charts The Low-Level Significant Weather (SIGWX) Charts (Figure 8-10) provide a forecast of aviation weather hazards primarily intended to be used as guidance products for pre-flight briefings. The forecast domain covers the 48 contiguous states and the coastal waters for altitudes 24,000 ft MSL (Flight Level 240 or 400 millibars) and below. Each chart depicts a “snapshot” of weather expected at the specified valid time.
Figure 8-10. 12-Hour Low-Level SIGWX Chart Example
8.2.1 Content Low-Level Significant Weather (SIGWX) Charts depict weather flying categories, turbulence, and freezing levels (Figure 8-11). Icing is not specifically forecast.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
FLIGHT PLANNING ONLY
SEE TAF S FOR SPECIFIC
TERMINAL FORECAST CETLINBILESS IESS 1AAN S MALESOR AND/OR VISIBILITY CEILING 1000-3000 -5 MILES INC INCLUSTY
MODERATE OR GREATER
TURBULENCE
AVY FREEZING LEVEL AT SURFACE
- FREEZING LEVEL ABOVE MEAN SEA LEVEL _ MODERATE TURBULENCE TOP (Hundreds of feet MSL) _ SEVERE TURBULENCE 240/100 Base (Hundreds of feet MSL)
EXTREME TURBULENCE Figure 8-11. Low-Level SIGWX Chart Symbols
8.2.1.1 Flying Categories Instrument Flight Rules (IFR) areas are outlined with a solid red line, Marginal Visual Flight Rules (MVFR) areas are outlined with a scalloped blue line, Visual Flight Rules (VFR) areas are not depicted (Figure 8-12).
Figure 8-12. Low-Level SIGWX Chart Flying Categories Example
8.2.1.2 Turbulence Areas of moderate or greater turbulence are enclosed by bold, dashed, yellow lines (Figure 8-
13). Turbulence intensities are identified by standard symbols (Figure 8-11). The vertical extent of turbulence layers is specified by top and base heights separated by a slant. The intensity AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-9
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) symbols and height information may be located within or adjacent to the forecasted areas of turbulence. If located adjacent to an area, an arrow will point to the associated area.
Turbulence height is depicted by two numbers separated by a solidus /. For example, an area on the chart with turbulence indicated as 240/100 indicates the turbulence can be expected from the top at FL240 to the base at 10,000 feet MSL. When the base height is omitted, the turbulence is forecast to reach the surface. For example, 080/ identifies a turbulence layer from the surface to 8,000 feet MSL. Turbulence associated with thunderstorms is not depicted on the chart.
Figure 8-13. Low-Level SIGWX Chart Turbulence Forecast Example
8.2.1.3 Freezing Levels The freezing level at the surface is depicted by a blue, saw-toothed symbol (Figure 8-11). The surface freezing level separates above-freezing from below-freezing temperatures at the Earth's surface.
Freezing levels above the surface are depicted by fine, green, dashed lines labeled in hundreds of feet MSL beginning at 4,000 feet using 4,000 foot intervals (Figure 8-11). If multiple freezing levels exist, these lines are drawn to the highest freezing level. For example, 80 identifies the 8,000-foot freezing level contour (Figure 8-14). The lines are discontinued where they intersect the surface.
The freezing level for locations between lines is determined by interpolation. For example, the freezing level midway between the 4,000 and 8,000 foot lines is 6,000 feet.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 8-14. Low-Level SIGWX Chart Freezing Level Forecast Example
Multiple freezing levels occur when the temperature is zero degrees Celsius at more than one altitude aloft. Multiple freezing levels can be forecasted on the Low-Level Significant Weather Prog Charts in situations where the temperature is below-freezing (negative) at the surface with multiple freezing levels aloft.
Figure 8-15. Low-Level SIGWX Chart Multiple Freezing Levels Example
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) On the chart, areas with multiple freezing levels are located on the below-freezing side of the surface freezing level contour and bounded by the 4,000 foot freezing level. Multiple freezing levels are possible beyond the 4,000 feet freezing level (i.e., below 4,000 feet MSL), but the exact cutoff cannot be determined (Figure 8-15).
8.2.2 Issuance Low-Level Significant Weather (SIGWX) Charts are issued four times per day by the Aviation Weather Center (AWC) in Kansas City, Missouri (Table 8-2). Two charts are issued; a 12-hour and a 24-hour prog. Both are available on the AWC web site:
http://aviationweather.gov/products/swl/.
Table 8-2. Low-Level SIGWX Chart Issuance Schedule Issuance Time ~1720Z ~2310Z ~0530Z ~0935Z Chart Valid Time 12-Hour Prog 00Z 06Z 12Z 18Z 24-Hour Prog 12Z 18Z 00Z 06Z
8.2.3 Use The Low-Level Significant Weather (SIGWX) Charts provide an overview of selected aviation weather hazards up to 24,000 feet MSL (FL240 or 400 millibars) at 12- and 24-hours into the future.
Figure 8-16. 12-Hour Low-Level SIGWX Chart Example
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 8-17. 24-hour Low-Level SIGWX Chart Example AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-13