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
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4.1.1 WPC Surface Analysis Charts.
The WPC in College Park, MD, produces a variety of surface analysis charts for North America that are available on their website. Figure 4-1, NWS Surface Analysis Chart Example, is one example of several surface analysis products available on their website. WPC’ s surface analysis is also available at https://www.aviationweather.gov.
Some of WPC’s surface analysis charts are combined with radar or satellite imagery (Figure 4-2, NWS Surface Analysis and Radar Composite Example) as well as have different background features (e.g., terrain).
Figure 4-2. NWS Surface Analysis and Radar Composite Example
4.1.1.1 Issuance.
The WPC issues surface analysis charts for North America eight times daily, valid at 00, 03, 06, 09, 12, 15, 18, and 21 Coordinated Universal Time (UTC).
4.1.1.2 Anal ysis Symbols.
Figure 4-3, NWS Surface Analysis Chart Symbols, shows analysis symbols used on NWS surface analysis charts.
Figure 4-3. NWS Surface Analysis Chart Symbols
COLD FRONT COLD FRONTOLYSIS
WARM FRONT WARM FRONTOLYSIS
STATIONARY FRONT STATIONARY
FRONTOLYSIS
OCCLUDED FRONT
OCCLUDED FRONTOLYSIS
CHANGE OF FRONT TYPE
COLD FRONTOGENESIS HIGH PRESSURE CENTER
WARM FRONTOGENESIS LOW PRESSURE CENTER
STATIONARY TROPICAL (TRPL) WAVE
FRONTOGENESIS TROUGH (TROF) OR 1 XXX TROPICAL DEPRESSION
OUTFLOW BONDARY (OUTFLOW BNDRY)
TRPCL STORM TROPICAL STORM
DRYLINE XXX
RIDGE HURCN HURRICANE
SQUALL LINE XXX
4.1.1.3 Station Plot Models.
Land, ship, buoy, and Coastal-Marine Automated Network (C-MAN) stations are plotted on the chart to aid in analyzing and interpreting the surface weather features. These plotted observations are referred to as station models.
Some stations may not be plotted due to space limitations. However, all reporting stations are used in the analysis.
Figure 4-4, NWS Surface Analysis Chart Station Plot Model, and Figure 4-5, NWS Surface Analysis Chart Ship/Buoy Plot Model, contain the most commonly used station plot models used in surface analysis charts.
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Figure 4-4. NWS Surface Analysis Chart Station Plot Model Wind Sea-level pressure Temperature 57 107 Weather -6 56 Pressure trend (mb) Dew Point(F) Sky cover Figure 4-5. NWS Surface Analysis Chart Ship/Buoy Plot Model Wind Sea-level Temperature (F) * Pressure 57 107 Current _Pressure Weather -6 Trend (mb) Station > 41010 56 10605< Wave Identification Information 62 080801 Water Dew Sky Cover Swell Temperature (F) Information Point (F) WPC also produces surface analysis charts specifically for the aviation community. Figure 4-6, NWS Surface Analysis Chart for Aviation Interests Station Plot Model, contains the station plot model for these charts.
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4-5 Figure 4-6. NWS Surface Analysis Chart for Aviation Interests Station Plot Model
4.1.1.3.1 Station Identifier.
The format of the station identifier depends on the observing platform.
• Ship: Typically four or five characters. If five characters, then the fifth will usually be a digit.
• Buoy: Whether drifting or stationary, a buoy will have a five-digit identifier. The first digit will always be a 4.
• C-MAN: Usually located close to coastal areas. Their identifier will appear like a five-character ship identifier; however, the fourth character will identify off which state the platform is located.
• Land: Land stations will always be three characters, making them easily distinguishable from ship, buoy, and C-MAN observations.
4.1.1.3.2 Temperature.
The air temperature is plotted in whole degrees Fahrenheit.
4.1.1.3.3 Dewpoint.
The dewpoint temperature is plotted in whole degrees Fahrenheit.
4.1.1.3.4 Weather.
A weather symbol is plotted if, at the time of observation, precipitation is either occurring or a condition exists causing reduced visibility.
Figure 4-7, NWS Surface Analysis Chart Common Weather Symbols, contains a list of the most common weather symbols.