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3.7.1.2.9 Ceiling (CIG).
Ceiling is the height from the base of the lowest layer aloft covering more than one-half of the sky. Additionally, vertical visibility into a total surface-based obscuration is defined as a ceiling. For a METAR report, the first broken (BKN) or overcast (OVC) layer is the ceiling. For example, if the METAR sky condition element is SCT030 BKN060 OVC090, the ceiling is 6,000 ft.
For a total surface-based obscuration, no ceiling is plotted and the METAR must be consulted.
If the sky cover is clear, few, or scattered, no ceiling is plotted.
The ceiling is plotted to the lower right of the station circle. Ceilings are reported as hundreds of feet AGL. If no ceiling is present, the code 999 will be plotted.
3.7.1.2.10 Present Weather (WX).
Present weather symbols are entered to the left of the station. Note that the older Surface Aviation Observation (SAO) code is used instead of surface analysis chart symbols or the modern METAR code.
3-75 Table 3-10. AAWU Surface Observation Precipitation Symbols Symbol Meaning T Thunderstorm R Rain RW Rain Shower L Drizzle ZR Freezing Rain ZL Freezing Drizzle A Hail IP Ice Pellets IPW Ice Pellet Showers S Snow SW Snow Showers SP Snow Pellets SG Snow Grains IC Ice Crystals
3-76 Table 3-11. AAWU Surface Observation Obstruction to Visibility Symbols Symbol Meaning BD Blowing Dust BN Blowing Sand BS Blowing Snow BY Blowing Spray D Dust F Fog GF Ground Fog H Haze IF Ice Fog K Smoke Table 3-12. AAWU Surface Observation Precipitation Intensity Symbols Symbol Meaning
- Light (No symbol) Moderate + Heavy
3.7.1.3 Use.
AAWU Surface Observations provide an overview of weather flying categories and other adverse weather conditions for the valid time shown on the graphic display. This product often does not completely represent the en route conditions because of terrain variations and the possibility of weather occurring between reporting stations. This product should be used in addition to the latest METAR/SPECIs, PIREPs, and radar and satellite imagery for a complete look at the latest flying conditions.
3.7.2 METARs on Aviationweather.gov.
3.7.2.1 Issuance.
Surface observations (METAR and SPECI) are provided on https://www.aviationweather.gov in several formats. The formats range from traditional text (referred to as the raw format) to different types of map displays. The two types of map displays are interactive (see Figure 3-41, Surface Observations-Aviationweather.gov METAR Interactive Display Example) and static (see Figure 3-44).
3.7.2.1.1 Interactive Display.
The interactive display includes zoom and pan. Increasing the zoom allows more METARs to be displayed.
Figure 3-41. Surface Observations-Aviationweather.gov METAR Interactive Display Example
ADDS METARS INFO METAR Display at valid at 0129 UTC 17 Apr 2015 CW NZ KEUG 006 9805) Map: Plot Options: Data Options: Overlays:
OLight All •Temp •Wind DAlt Latest D Time • Highways ODark • Decoded • Top Jetroutes
• Vis aWx Cover Ceil
•Simple None •Dew aWgst Old OTAF CARTCC/FIR Bounds Data layers:
Satellite • • Data density
• Radar Metric •Hover 1 € Scale Temp - 28021 966~Alt Vis-0.5 W×- KRFD~1d —Ceil Wind @Calm —ø 15knt I -• 60knt FIt Cat: •MVFR • IFR • LIFR Dew~ Windbarb 3-77
3-78 “Plot Options” allows users to choose the weather elements displayed
(e.g., view only ceilings and visibilities). The following parameters can be displayed using a station plot model (see Figure 3-42, Interactive Display Station Plot Example):
Figure 3-42. Interactive Display Station Plot Example
• Temp: Temperature in Fahrenheit. Celsius is also available, if metric is selected.
• Alt: Atmospheric pressure reduced to MSL.
o Where expressed in inches of mercury (Hg) or altimeter setting, the value is expressed in hundredths of an inch where the leading 2 or 3 is omitted (e.g., 982 would be 29.82 in, 025 would be 30.25 in). When trying to determine whether to add a 2 or 3, use the number that will give you a value closest to 30.00 in.
o Where expressed in millibars, the value is expressed in tenths of a millibar with the leading 9 or 10 omitted (e.g., 998 would be 999.8 mb, 164 would be 1,016.4 mb). When trying to determine whether to add a 9 or 10, use the number that will give you a value closest to 1,000 mb.
• Ceil: Cloud ceiling in hundreds of feet (BKN, OVC, and OVX only).
• Id: The four-letter ICAO identifier for the airport.
• Windbarb: The stick points in the direction the winds are coming from.
Wind speed is in knots. Red represents wind gusts.
• Dew: Dewpoint in Fahrenheit. Celsius is also available, if metric is selected.
• Vis:
Visibility in miles. Kilometers (km), if metric is selected. Visibility value on the chart may not represent actual value reported in the METAR or SPECI, and may be fractionally lower than shown. (e.g., 2½ in the METAR is shown as 3 on the surface plot) (see Table 3-12, Rounding of Actual METAR Visibility Values for Depiction on Aviat ionweather.gov/AWC METAR Display).
• Wx: Weather symbol representing current weather.
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• Sky: Cloud cover s ymbol (see Figure 3-43, Station Plot Sky Symbols) is plotted in the center. The amount the circle is filled represents the amount of cloud cover. The color of the circle represents one of the following weather categories (see Table 3-14, Station Plot Weather Categories):
o Green: VFR, o Blue: MVFR, o Red: IFR, or o Purple: Low instrument flight rules (LIFR).
A click on the station circle displays the raw METAR in a separate text window. When the Hover option is selected, the raw METAR text window appears by merely placing the cursor over the station circle. If the Decoded option is set, the METAR appears in plain language instead of METAR code.
If the TAF option is set, the latest Terminal Aerodrome Forecast (TAF) will be appended to the information in the text window.
Table 3-13. Rounding of Actual METAR Visibility Values for Depiction on Aviationweather.gov/AWC METAR Display Visibility Reported in METAR Visibility, as depicted on surface plot 0, 1/16, 1/8, 3/16, 1/4, 3/8 0.3 ½ 0.5 ¾ 0.8 1½, 1¾, 2 2½, 3 3
3-80 Table 3-14. Station Plot Weather Categories Category* Color Ceiling Visibility LIFR (Low IFR) Magenta Below 500 feet AGL and/or Less than 1 mile IFR Red 500 to below 1,000 feet AGL and/or 1 mile to less than 3 miles MVFR (Marginal VFR) Blue 1,000 to 3,000 feet AGL and/or 3 to 5 miles VFR Green Greater than 3,000 feet AGL and Greater than 5 miles *These categories are not flight rules and should not be confused with the flight rules provided in Part 91, including those for Basic VFR Weather Minimums. Rather, these categories were created for weather charts as a means to visually enhance the products.
Figure 3-43. Station Plot Sky Symbols
Automated stations report “CLR” when clouds may exist above 12,000 ft, so a square is used to represent this uncertainty, whereas an unfilled circle is used for “SKC,” when a human reports the sky is completely clear overhead. The abbreviation “OVX” is unofficial, but AWC uses it to indicate the sky is obscured, which is the case when a METAR reports vertical visibility and no cloud information.
“Miss” means the sky condition is missing.
3.7.2.1.2 Static Display.
Static display products are provided on the AWC’s website for 19 select regions plus the CONUS. Each product is updated every 5 minutes using the latest METAR or SPECI information. The Web page automatically refresh every 15 minutes.
The static display has fewer features than the interactive display. Primarily, the static display does not provide ceiling height. Also, the static display does not have the functionality to display separately the raw METAR or TAF, or change units to metric.
3-81 Figure 3-44. Surface Observations—Aviationweather.gov METAR Static Display Example
Fi gure 3-45. Static Display Station Plot Example St ation plot descriptions are:
• Temp: Temperature in Fahrenheit (F).
• Windbarb: The windbarb. The stick points in the direction the winds are coming from.
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• Alt: Last three digits of the altimeter setting in inches of mercury. For example, 032 represents 30.32 in Hg.
• Id: The last three letters of the ICAO identifier for the airport.
• Dew: The dewpoint temperature in Fahrenheit.
• Vis: The visibility in statute miles.
• Wx: Weather symbol representing current weather.
• Sky: The cloud cover symbol is plotted in the center. The amount the circle is filled represents the amount of cloud cover. The color of the circle represents one of the following weather categories:
o Green: VFR, o Blue: MVFR, o Red: IFR, or o Purple: LIFR.
3.7.2.2 Use.
Graphical depictions of surface observations, both interactive and static display, provide an overview of weather flying categories and other adverse weather conditions for the valid time shown on the graphic display.
3.8 Aviation Weather Cameras.
3.8.1 FAA Aviation Weather Cameras.
The FAA’s Aviation Weather Camera network (see Figure 3-46, Map of FAA’s Aviation Weather Camera Network in Alaska) consists of more t han 220 camera facilities in Alaska. Each site has up to four cameras. The direction of each camera (see Figure 3-47, Sectional Chart Depicting Shungnak (SHG), Alaska Camera Orientations) is provided with reference to a Secti onal Chart. A clear day image (see Figure 3-48, “Clear Day” Image from Aviation Weather Camera Image at Shungnak (SHG), Alaska) is provided for reference and co mparison with the latest image (see Figure 3-49, Aviation Weather Camera Image at Shungnak (SHG), Alaska).
3.8.2 Issuance.
Camera images are available on the FAA’s Aviation Weather Camera website. Images are generally updated every 10 minutes. The time of the last update is indicated on each image. Actual site conditions may differ from displayed images due to a variety of reasons (e.g., rapidly changing weather conditions, image update frequency, optical distortion).
3-83 Figure 3-46. Map of FAA’s Aviation Weather Camera Network in Alaska
F igure 3-47. Sectional Chart Depicting Shungnak (SHG), Alaska Camera Orientations
3-84 Figure 3-48. “Clear Day” Image from Aviation Weather Camera Image at Shungnak (SHG), Alaska
F igure 3-49. Aviation Weather Camera Image at Shungnak (SHG), Alaska
3.8.3 Use.
The images should only be used for flight planning and to improve situational awareness (SA). They are not to be used to comply with regulatory requirements (e.g., to determine weather minimums for IFR flight).
4-1 CHAPTER 4. ANALYSIS The second of three distinct types of weather (meteorological) information are analyses.
Analyses of weather information are an enhanced depiction and/or interpretation of observed weather data. Prior to the 1990s, most analysis charts were hand drawn by forecasters. Today’s analyses are automated, and depending on the weather information provider (i.e., NWS, commercial weather services, and flight planning services), the appearance and content of these analyses will vary.
Chapter 4 will only focus on those analyses produced by the NWS and made available on various websites, including the Aviation Weather Center (AWC), the Weather Prediction Center (WPC), the Ocean Prediction Center (OPC), and the Alaska Aviation Weather Unit (AAWU).
4.1 Surface Analysis Charts.
Surface analysis charts are analyzed charts of surface weather observations. The chart depicts the distribution of several items, including sea-level pressure; the positions of highs, lows, ridges, and troughs; the location and type of fronts; and the various boundaries such as drylines. Pressure is referred to in mean sea level (MSL) on the surface analysis chart while all other elements are presented as they occur at the surface point of observation.
Figure 4-1. NWS Surface Analysis Chart Example