3-61 determine hail potential. The three lowest elevation angles are available, with a maximum range of 48 NM.
3.4.9.1.2 Digital Base Velocity (TV0, TV1, TV2/182).
A measure of the radial component of the wind either toward the radar (negative values) or away from the radar (positive values). Cool colors (green) represent negative values and warm colors (red) represent positive values.
These products are used to estimate wind speed and direction, locate boundaries, locate severe weather signatures, and identify suspected areas of turbulence. The three lowest elevation angles are available, with a maximum range of 48 NM.
3.4.9.1.3 Long Range Digital Base Reflectivity (TZL/186).
Digital Reflectivity data are measured at an elevation angle of 0.6 degrees with a maximum range of 225 NM.
3.4.9.1.4 Composite Reflectivity (NCR/37).
A display of maximum reflectivity for the total volume within the range of the radar. This product is used to reveal the highest reflectivity in all echoes, examine storm structure features, and determine intensity of storms.
3.4.9.1.5 Vertically Integrated Liquid (NVL/57).
The water content of a 2.2 x 2.2 NM column of air, which is color-coded and plotted on a 124-NM map. This product is used as an effective hail indicator, to locate most significant storms, and to identify areas of heavy rainfall.
3.4.9.1.6 Echo Tops (NET/41).
An image of the echo top heights color-coded in user-defined increments. This product is used for a quick estimation of the most intense Convection and higher echo tops, as an aid in identification of storm structure features, and for pilot briefing purposes.
3.4.9.1.7 VAD Wind Profile (NVW/48).
A graphic display of windbarbs plotted on a height staff in 500-ft or 1,000-ft increments. The current (far right) and up to 10 previous plots may be displayed simultaneously. This product is an excellent tool for meteorologists in weather forecasting, severe weather, and aviation.
3.4.9.2 Precipitation Products.
Precipitation products are estimated ground accumulated rainfall. Estimates are based on a reflectivity and rainfall rate relationship called Z-R (https://www.weather.gov/tae/research-zrpaper).
3.4.9.2.1 One-Hour Precipitation (N1P/78).
A display of estimated 1 hour precipitation accumulation on a 1.1-NM x 1-degree grid using the Precipitation Processing System (PPS) algorithm. This product is used to assess rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.
3-62
3.4.9.2.2 Storm Total Precipitation (NTP/80).
The estimated storm total precipitation accumulation on a 1.1-NM x 1-degree grid continuously updated since the precipitation event began. This product uses the PPS algorithm. This product is used to locate flood potential over urban or rural areas, estimate total basin runoff, and provide rainfall data 24 hours a day.
3.4.9.2.3 Digital Precipitation Array (DPA/81).
An array format of estimated 1-hour precipitation accumulations on the 1/4 Lyon Federal Maybery (LFM) (4.7625 km Hydrologic Rainfall Analysis Project (HRAP)) grid. This is an 8-bit product with 255 possible precipitation values. This product is used to assess rainfall intensities for flash flood warnings, urban flood statements, and special weather statements.
3.4.9.3 Overlay Products.
Overlay products provide detailed information for identified storm cells.
3.4.9.3.1 Storm Structure (NSS/62).
A table displaying information on storm attributes, which include maximum reflectivity, maximum velocity at lowest elevation angle, storm overhang, mass weighted storm volume, storm area base and top, storm position, and storm tilt.
3.4.9.3.2 Hail Index (NHI/59).
A product designed to locate storms that have the potential to produce hail.
Hail potential is labeled as either probable (hollow green triangle) or positive (filled green triangle). Probable means the storm is probably producing hail and positive means the storm is producing hail.
3.4.9.3.3 Digital Mesocyclone Detection Algorithm (NMD/141).
This product is designed to display information regarding the existence and nature of rotations associated with thunderstorms. Numerical output includes azimuth, range, and height of the mesocyclone.
3.4.9.3.4 Tornadic Vortex Signature (NTV/61).
A product that shows an intense gate-to-gate azimuthal shear associated with tornadic-scale rotation. It is depicted by a red triangle with numerical output of location and height.
3.4.9.3.5 Storm Tracking Information (NST/58).
A product that shows a plot of the past hour’s movement, current location, and forecast movement for the next hour or less for each identified thunderstorm cell. This product is used to determine reliable storm movement.
3.4.9.4 Radar Messages.
Radar messages provide information about the radar status and special product data.
3-63
3.4.9.4.1 General Status Message (GSM/2).
A text message describing the status of the radar site. A reason may be provided if the radar is not transmitting.
3.4.9.4.2 Free Text Message (FTM/5).
A text message describing an upcoming, ongoing, or completed event at the radar site, including downtime, maintenance, and more.
3.4.9.4.3 Radar Status Log (RSL/152).
A running daily log of status, errors, and messages from the Radar Product Generator (RPG) and Radar Data Acquisition (RDA) processing systems.
Discussion Credit: NOAA/NCEI/ROC.
Figure 3-27. WSR-88D vs. TDWR (Image Credit: NWS)
3-64 Figure 3-28. TDWR Site Locations (Image Credit: MIT Lincoln Labs)
The image below is a classic thunderstorm producing a microburst. The TDWR radar picture on the left is a vertical cross section of a storm’s core. The image on the right is a visual photograph of a similar storm that produced a microburst.
Figure 3-29. Thunderstorm Producing a Microburst (Image Credit: MIT Lincoln Labs)
3-65
3.5 Satellite.
3.5.1 Description.
Satellite is perhaps the single most important source of weather data worldwide, particularly over data-sparse regions, such as countries without organized weather data collection and the oceans.
The NOAA’s Geostationary Operational Environmental Satellite (GOES) imagery can be found on the AWC’s website, as well as all NWS WFO websites. Additional satellite imagery for Alaska can be found on the NWS Alaska Aviation Weather Unit (AAWU) website.
3.5.2 Imagery Types.
Three types of satellite imagery are commonly used: visible, infrared (IR), and water vapor. Visible imagery is only available during daylight hours. IR and water vapor imagery are available day or night.
3.5.2.1 Visible Imagery.
Visible imagery (see Figure 3-30, Visible Satellite Image—U.S. Example) displays reflected sunlight from the Earth’s surface, clouds, and particulate matter in the atmosphere. Visible satellite images, which look like black and white photographs, are derived from the satellite signals. Clouds usually appear white, while land and water surfaces appear in shades of gray or black.
The visible channel senses reflected solar radiation. Clouds, the Earth’s atmosphere, and the Earth’s surface all absorb and reflect incoming solar radiation. Since visible imagery is produced by reflected sunlight (radiation), it is only available during daylight.
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.
3-66
3-67
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.
3-72