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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.
4-6 Figure 4-7. NWS Surface Analysis Chart Common Weather Symbols
4.1.1.3.5 Wind.
Wind is plotted in increments of 5 knots (kts). The wind direction is referenced to true north and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50 kts), barbs (10 kts) and half-barbs (5 kts) found on the stem.
If the wind is calm at the time of observation, only a single circle over the station is depicted.
Figur e 4-8, NWS Surface Analysis Chart Wind Plotting Model, includes some sample wind symbols.
4-7 Figure 4-8. NWS Surface Analysis Chart Wind Plotting Model
4.1.1.3.6 Ceiling.
Ceiling is plotted in hundreds of feet above ground level (AGL).
4.1.1.3.7 Visibility.
Surface visibility is plotted in whole statute miles (sm).
4.1.1.3.8 Pressure.
Sea-level pressure is plotted in tenths of millibars (mb), with the first two digits (generally 10 or 9) omitted. For reference, 1013 mb is equivalent to
29.92 inches (in) of mercury. Below are some sample conversions between plotted and complete sea-level pressure values.
410 1041.0 mb 103 1010.3 mb 987 998.7 mb 872 987.2 mb
4.1.1.3.9 Pressure Trend.
The pressure trend has two components, a number and a symbol, to indicate how the sea-level pressure has changed during the past 3 hours. The number provides the 3-hour change in tenths of millibars, while the symbol provides a graphic illustration of how this change occurred.
4-8 Figure 4-9, NWS Surface Analysis Chart Pressure Trends, contains the meanings of the pressure trend symbols.
Figure 4-9. NWS Surface Analysis Chart Pressure Trends
4.1.1.3.10 Sky Cover.
The approximate amount of sky cover can be determined by the circle at the center of the station plot. The amount that the circle is filled reflects the amount of sky covered by clouds. Figure 4-10, NWS Surface Analysis Chart Sky Cover Symbols, contains the common cloud cover depictions.
4-9 Figure 4-10. NWS Surface Analysis Chart Sky Cover Symbols
4.1.1.3.11 Water Temperature.
Water temperature is plotted in whole degrees Fahrenheit.
4.1.1.3.12 Swell Information.
Swell direction, period, and height are represented in the surface observations by a six-digit code. The first two digits represent the swell direction, the middle digits describe the swell period (in seconds), and the last two digits are the swell’s height (in half meters).
090703:
09: The swell direction is from 90 degrees (i.e., it is coming from due east) 07: The period of the swell is 7 seconds 03: The height of the swell is 3 half meters (m) 271006:
27: The swell direction is from 270 degrees (due west) 10: The period is 10 seconds 06: The height of the swell is 6 half meters
4.1.1.3.13 Wave Information.
Period and height of waves are represented by a five-digit code. The first digit