3-70 useful. Interpretation of the patterns and how they change over time is more important. The legend may vary depending on the satellite image provider.
Figure 3-37. Water Vapor Satellite Image Data Legend
The colors (values) represent temperature in degrees Celsius
3.5.3 Polar Orbiting Environment Satellites (POES).
POES stands for the Polar Orbiting Environment Satellites, although more recently the U.S. polar satellite program has been rechristened the Joint Polar Satellite System (JPSS).
Polar satellites are not stationary. They track along various orbits around the poles.
Typically, they are somewhere between 124 and 1,240 mi above the Earth’s surface. The satellites scan the Earth in swaths as they pass by on their tracks.
3.5.3.1 Benefits.
Because they are so much closer to Earth, you can get very high resolution,
i.e., better than 0.5 km (or ~5/8 mi). This allows for weather and surface features to be seen in much greater detail.
This is particularly useful over the poles and arctic areas. Quality of geostationary satellite data degrades the further you get from the poles, while polar data provides high resolution in those areas.
3.5.3.2 Shortfalls.
By far the most significant shortfall is the latency, or the time between the satellite scanning the area and the time that the data is available to a user.
Because polar satellites are moving, they cannot continuously transmit to a single station. Instead, there are a series of stations around the globe through which the data are collected. Data is then transmitted from those stations to other locations. At times, it can be several hours (or more) old by the time it reaches operational users in the United States (in polar areas it is much quicker). There are some direct ground stations closer to the United States which can cut the latency to ~45 minutes when utilizing the newer polar satellites. For the purpose of the AWC, that is at the limit of usefulness for real-time operations.
Discussion Credit: NOAA/NWS/AWC.
3.6 Upper-Air Observations.
3.6.1 Radiosonde Observations.
Since the late 1930s, the NWS has taken upper air observations with radiosondes attached to weather balloons. Weather data from the radiosonde are foundational to all computer model forecasts produced by the NWS.
3-71 The radiosonde is a small, expendable instrument package (weighing 100 grams (g) to 500 g) that is suspended below a large balloon inflated with hydrogen or helium gas. As the radiosonde rises at about 300 m per minute (about 1,000 ft per minute), sensors on the radiosonde measure profiles of pressure, temperature, and moisture. These sensors are linked to a battery-powered radio transmitter that sends the sensor measurements to a ground tracking antenna. Wind speed and direction aloft are also obtained by tracking the position of the radiosonde in flight using Global Positioning Satellites (GPS).
3.6.1.1 Issuance.
Weather balloons with radiosondes are launched twice a day worldwide from designated locations (see Figure 3-38, U.S. Radiosonde Network, for U.S. locations) at around 1100 UTC and 2300 UTC. It takes approximately 90 minutes for the balloon to reach an altitude of 100,000 ft. The weather data collected is assigned the observation times of 1200 UTC and 0000 UTC.
Special radiosondes may be launched at select times for various reasons, including when severe weather is expected in a region.
Figure 3-38. U.S. Radiosonde Network
3.7 Graphical Depiction of Surface Observations.
3.7.1 AAWU Surface Observations.
A display of color-coded station plots (see Figure 3-39, AAWU Surface Observations Example) from Alaska is produced by the NWS' AAWU. This product shows: surface temperature, dewpoint, celling, visıbılity, and wind direction/speed which have been taken from the METAR report. A key to the station plots is tound on each map.
Figure 3-39. AA WU Surface Observations Example CYPC 1599 38 999 CYUA †EGĘYUB 999- ÄCYEV 15 240 m 52 PAKP / O PARC S9 CZFI 109-199€ : 100 F0 /PADE 48 SG Par Eg 19" 80! PABT PATA PAUN 35 1501 CZFI }S 14657 1220 IEUDU SO PRE • -57 . 18, 70- 54 IPAJN 15*% 12 IMP(dey isoW) USTNID EO SAS 18 PALS Są~ IFR MYFRqVF ~10°999 ST2 FA42 ORSERVATION ED 172 07/14/2005 DEWPT(deg F) CI
3.7.1.1 Issuance.
The charts are issued hourly and can be found on the AAWU website.
3.7.1.2 Legends.
AAWU Surface Observations depict numerous parameters, including the tlying category, sky cover, and wind.
3.7.1.2.1 Flying Category.
Each station plot is color-coded according to the weather flying category reported (see Table 3-9, AA WU Surface Observations Flying Categories and Criteria). Red indicates IFR, blue indicates Marginal Visual Flight Rules (MVFR), and black is plotted for stations reporting Visual Flight Rules (VFR) ceiling and/or visibility conditions.
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3-73 Table 3-9. AAWU Surface Observations Flying Categories and Criteria FLYING CATEGORY CEILING (feet) VISIBILITY (miles) VFR (black) Greater than 3,000 feet Greater than 5 miles MVFR (blue) 1,000 to 3,000 feet 3 to 5 miles IFR (red) Less than 1,000 feet Less than 3 miles
3.7.1.2.2 Station Plot.
METAR elements are plotted for each station in the form of a station plot (see Figure 3-44, Surface Observations—Aviationweather.gov METAR Static Display Example).
Figure 3-40. AAWU Surface Observation Plot Legend
3.7.1.2.3 Sky Cover.
The sky cover symbol is plotted at the station location and is filled according to the summation total of the sky condition element from the METAR report.
For example, if the METAR sky condition element was SCT030 BKN060 OVC090, the sky cover would be overcast and have a completely filled circle.
3.7.1.2.4 Station Identifier (STNID).
The four-letter ICAO station identifier is entered to the upper right of the station.
3.7.1.2.5 Wind.
Wind is plotted the same as the NWS surface analysis charts.
3.7.1.2.6 Temperature (TMP deg F).
Temperature in degrees Fahrenheit is plotted to the upper left of the sky cover symbol.
3.7.1.2.7 Visibility (VIS).
Visibility in statute miles is plotted to the left of the sky cover symbol.
Decimals are used to represent tenths of miles, when necessary.
3.7.1.2.8 Dewpoint Temperature (DEWPT deg F).
Dewpoint temperature, in degrees Fahrenheit, is plotted to the lower left of the sky cover symbol.
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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.