Figure 3-30. Visible Satellite Image-U.S. Example http://adds.aviationwe 9 12 15 18 42 45 51 54 57 60 63 66 72252 4 7 0
3.5.2.1.1 Visible Image Data Legend.
The data legend (see Figure 3-31, Visible Satellite Data Legend) on a visible image displays albedo, or reflectance, expressed as a percentage. For example, an albedo of 12 means 72 percent of the sunlight that struck a feature was reflected back to space.
Figure 3-31. Visible Satellite Data Legend 0 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 02 05 78 01 84 87 00 03 The gray shades (values) represent albedo, or reflectance, expressed as a percentage.
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3.5.2.2 Inf rared (IR) Imagery.
IR images (see Figure 3-32, Infrared (Color) Satellite Image—U.S.
Example, and Figure 3-33, Unenhanced Infrared (Black and White) Satellite Image—U.S. Example) display temperatures of the Earth’s surface, clouds, and p articulate matter. Generally speaking, the warmer an object, the more IR energy it emits. The satellite sensor measures this energy and calibrates it to temperature using a very simple physical relationship.
Clouds that are very high in the atmosphere are generally quite cold
(e.g., -50 ºC), whereas clouds very near the Earth’s surface are generally quite warm (e.g., +5 ºC). Likewise, land may be even warmer than the lower clouds
(e.g., +20 ºC). Those colder clouds emit much less IR energy than the warmer clouds and the land emits more than those warm clouds.
The data measured by satellite is calibrated and colorized according to the temperature. If the temperature of the atmosphere decreases with height (which is typical), cloud-top temperature can be used to roughly determine which clouds are high-level and which are low-level.
When clouds are present, the temperature displayed on the IR images is that of the tops of clouds. When clouds are not present, the temperature is that of the ground or the ocean. A major advantage of the IR channel is that it can sense energy at night, so this imagery is available 24 hours a day.
Figure 3-32. Infrared (Color) Satellite Image—U.S. Example
The scale is in degrees Celsius. Blue/purple colors indicate colder temperatures, while orange/red colors indicate warmer temperatures.
3-68 Figure 3-33. Unenhanced Infrared (Black and White) Satellite Image—U.S. Example
The scale is in degrees Celsius. Lighter gray shades indicate colder temperatures, while darker gray shades indicate warmer temperatures.
3.5.2.2.1 Infrared Image Data Legends.
The data legend (see Figure 3-34, Infrared (Color) Satellite Image Data Legend, and Figure 3-35, Unenhanced Infrared (Black and White) Satellite Image Data Legend) on an IR image is calibrated to temperature expressed in degrees Celsius. The legend may vary based on the satellite image provider.
Figure 3-34. Infrared (Color) Satellite Image Data Legend The colors (values) represent temperature in degrees Celsius.
Figure 3-35. Unenhanced Infrared (Black and White) Satellite Image Data Legend The gray shades (values) represent temperature in degrees Celsius.
3.5.2.3 Water Vapor Imagery.
The water vapor imagery (see Figure 3-36, Water Vapor Satellite Image— U.S. Example) displays the quantity of water vapor generally located in the middle and upper troposphere within the layer between 700 mb (approximately 10,000 ft MSL) and 200 mb (approximately FL390). The actual numbers displayed on the water vapor images correspond to temperature in degrees Celsius. No direct relationship exists between these values and the temperatures of clouds, unlike IR imagery. Water vapor
3-69 imagery does not really “see” clouds, but “sees” high-level water vapor instead.
The most useful information to be gained from the water vapor images is the locations and movements of weather systems, jet streams, and thunderstorms.
Another useful tidbit is aided by the color scale used on the images. In general, regions displayed in shades of red are very dry in the upper atmosphere and may correlate to crisp, blue skies from a ground perspective.
On the contrary, regions displayed in shades of blue or green are indicative of a lot of high-level moisture and may also indicate cloudiness. This cloudiness could simply be high-level cirrus types or thunderstorms. That determination cannot be ascertained from this image by itself, but could easily be determined when used in conjunction with corresponding visible and IR satellite images.
A major advantage of the water vapor channel is that it can sense energy at night, so this imagery is available 24 hours a day.
Figure 3-36. Water Vapor Satellite Image—U.S. Example
The scale is in degrees Celsius. Blue/green colors indicate moisture and/or clouds in the mid/upper troposphere, while dark gray/orange/red colors indicate dry air in the mid/upper troposphere.
3.5.2.3.1 Water Vapor Image Data Legend.
The data legend (see Figure 3-37, Water Vapor Satellite Image Data Legend) on water vapor images is calibrated to temperature expressed in degrees Cels ius. The actual data values on the water vapor images are not particularly
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