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
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-6
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.
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-8
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.
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-10
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
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-11
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
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-12
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
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
8.3 Mid-Level Significant Weather (SIGWX) Chart The Mid-Level Significant Weather (SIGWX) Chart (Figure 8-18) provides a forecast of significant en route weather phenomena over a range of flight levels from 10,000 ft MSL to FL450, and associated surface weather features. The chart depicts a “snapshot” of weather expected at the specified valid time.
The Mid-Level Significant Weather (SIGWX) Chart is available on the Aviation Weather Center web site at: http://aviationweather.gov/products/swm/.
Figure 8-18. Mid-Level SIGWX Chart Example
8.3.1 Content The Mid-Level Significant Weather (SIGWX) Chart depicts numerous weather elements that can be hazardous to aviation.
8.3.1.1 Thunderstorms The abbreviation CB is only included where it refers to the expected occurrence of an area of widespread cumulonimbus clouds, cumulonimbus along a line with little or no space between individual clouds, cumulonimbus embedded in cloud layers, or cumulonimbus concealed by haze. It does not refer to isolated or scattered cumulonimbus not embedded in cloud layers or concealed by haze.
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-14
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Each cumulonimbus area is identified with CB and characterized by coverage, bases and tops.
Table 8-3. Mid-Level SIGWX Chart Cumulonimbus Coverage
CODED CHARACTERIZATION MEANING ISOL Isolated Less than 1/8th coverage OCNL Occasional 1/8 th to 4/8ths coverage FRQ Frequent More than 4/8ths coverage EMBD Embedded CBs concealed by other cloud layers, haze, dust, etc.
Coverage, Table 8-3, is identified as isolated (ISOL) meaning less than 1/8th, occasional (OCNL) meaning 1/8th to 4/8ths, and frequent (FRQ) meaning more than 4/8ths coverage.
Isolated and occasional CBs are further characterized as embedded (EMBD). The chart does not display isolated or scattered cumulonimbus clouds unless they are embedded in other clouds, haze, or dust.
The vertical extent of cumulonimbus layer is specified by top and base heights. Bases that extend below 10,000 feet (the lowest altitude limit of the chart) are encoded XXX.
Cumulonimbus clouds (CBs) are depicted by enclosed (red) scalloped lines (Figure 8-19).
The identification and characterization of each cumulonimbus area appears within or adjacent to the outlined area. If the identification and characterization is adjacent to an outlined area, an arrow points to the appropriate cumulonimbus area.
On significant weather (SIGWX) charts, the inclusion of CB or the thunderstorm symbol (Figure 8-3) should be understood to include all weather phenomena normally associated with cumulonimbus or thunderstorm, namely, moderate or severe icing, moderate or severe turbulence, and hail.
Figure 8-19. Mid-Level SIGWX Chart Thunderstorm Examples
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-15
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
8.3.1.2 Surface Frontal Positions and Movements Surface fronts are depicted using the standard symbols found on the Surface Analysis Chart.
(Figure 8-2). An arrow identifies the direction of frontal movement with the speed indicated in knots plotted near the arrow head (Figure 8-20).
Figure 8-20. Mid-Level SIGWX Chart Surface Frontal Position and Movement Example
8.3.1.3 Jet Streams A jet stream axis with a wind speed of more than 80 knots is identified by a bold green line (Figure 8-21). An arrowhead is used to indicate wind direction. Double-hatched, light green lines positioned along a jet stream axis identify 20 knot wind speed changes.
Symbols and altitudes are used to further characterize a jet stream axis. A standard wind symbol (light green) is placed at each pertinent position to identify wind velocity. The flight level “FL” in hundreds of feet MSL is placed adjacent to each wind symbol to identify the altitude of the jet stream axis.
Jet stream vertical depth (jet depth) forecasts are included when the maximum speed is 120 knots or more. Jet depth is defined as the vertical depths to the 80 knot wind field above and below the jet stream axis using flight levels.
Figure 8-21. Mid-Level SIGWX Chart Jet stream Example.
Forecast maximum speeds of 100 knots at FL310 at one location and 120 knots at FL290 at another location.
At the latter location, the base of the 80 knot wind field is FL210, and the top of the 80 knot wind field is FL340.
AC 00-45F, CHG 2 Section 8: Forecast Charts Page 8-16