Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-47
Rain (R) Rain shower (RW) Snow (S) Snow shower (SW) Thunderstorm (T)
Multiple precipitation types can be reported within a configuration.
3.3.1.6 Precipitation Intensity Four precipitation intensities can be reported as shown in table 3-11.
Table 3-11. SD/ROB Reportable Intensities Symbol Intensity dBZ
- Light 0-29 (no entry) Moderate 30-40 + Heavy 41-45 ++ Heavy 46-49 X Extreme 50-56 XX Extreme 57 or more
Examples:
7R- 7/10 coverage of light rain 3R-6S 3/10 coverage light rain, 6/10 coverage moderate snow, 9/10 total coverage 2TRWX4R- 2/10 coverage thunderstorms, extreme rain showers, 4/10 coverage light rain, 6/10 total coverage
3.3.1.7 Location An area is coded with two end points and a width that defines a rectangle. Each end point is defined by an azimuth and range (AZRAN).
A line is also coded with two end points and a width that defines a rectangle. Each end point is defined by an AZRAN.
A cell is coded as a single point with a diameter (D). This point is defined by an AZRAN.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 3-48 Section 3: Observed Text Products
Figure 3-13. SD/ROB AREA, Line (LN), and CELL Location Examples The “+” denotes the radar location.
3.3.1.8 Maximum Top Maximum top (MT or MTS) denotes the altitude and location of the top of the highest precipitation echo.
All radar heights are estimates and assume standard atmosphere conditions and, thus, standard radar wave propagation. MT denotes radar data alone was used to determine the maximum top. MTS denotes both satellite and radar data were used to estimate the maximum top.
The maximum top is coded as a three-digit number in hundreds of feet MSL. Location is coded as an azimuth and range (AZRAN) relative to the radar site. If echo tops are uniform in altitude, the letter “U” precedes the altitude with no AZRAN provided.
Examples:
MT 150 19/32 Maximum top 15,000 feet MSL at 19 degrees, 32 nautical miles MT 340 182/98 Maximum top 34,000 feet MSL at 182 degrees, 98 nautical miles MTS 520 5/121 Maximum top with satellite data 52,000 feet MSL at 5 degrees, 121 nautical miles
3.3.1.9 Cell Movement Cell movement is the average motion of all the cells within a configuration. It is coded in the following format: the cell movement group is indicated by the letter C followed by four digits.
The first two digits represent the direction the cell(s) is (are) moving from in tens of degrees referenced to true north. The last two digits represent the speed of the configuration in knots.
Movement of areas and lines is not coded.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-49
Examples:
C0209 Cell movement from 20 degrees at 9 knots C2043 Cell movement from 200 degrees at 43 knots C3616 Cell movement from 360 degrees at 16 knots
3.3.1.10 Remarks Remarks contain information about the radar’s status and type of report. Currently, all weather radar reports are automated.
Table 3-12. Weather Radar Report Remarks and Meaning
REMARK MEANING PPINE Equipment normal and operating, but no echoes observed PPINA Observation not available PPIOM Radar out for maintenance AUTO Report derived from an automated weather radar
3.3.1.11 Digital Section The information contained in the digital section is used primarily to create the Radar Summary Chart. However, with the proper grid overlay chart for the corresponding radar site, the digital section code can also be used to determine precipitation location and intensity. (See Figure 3- 14 for an example of a digital code plotted from the Oklahoma City, Oklahoma, Weather Radar Report.)
Each digit represents the maximum precipitation intensity found within a grid box as determined by the weather radar. Light intensity is denoted by a 1, 2 is for moderate, 3 and 4 is for heavy, 5 and 6 is used for extreme precipitation. These digits were once commonly referred to as VIP levels because precipitation intensity, and therefore the digit, was derived using a video integrator processor (VIP). Whereas the old WSR-57 and WSR-74 weather radar video integrator processors displayed six data levels, the WSR-88D weather radar displays sixteen data levels. The data levels are still converted back to six levels for use in the Radar Weather Report. To avoid confusion, the term VIP should no longer be used to describe precipitation intensity. For example, if a grid box is coded with the number 2, it would be described as “moderate” precipitation,” not “VIP 2” or “level 2” precipitation.
A grid box is identified by two letters. The first represents the row in which the box is found and the second letter represents the column. For example MO1 identifies the box located in row M and column O as containing light precipitation. A code of MO1234 indicates precipitation in four consecutive boxes in the same row. Working from left to right: box MO = 1, box MP = 2, MQ = 3, and box MR = 4.
A Weather Radar Report contains data about precipitation echoes only. It does not contain information about important non-precipitation echoes such as clouds, fronts, dust, etc., which can be detected by weather radar under certain circumstances.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) HQ N HI HJ HP HQ HR JG IP -Ja IR
KG JK JL JMA JN JO JP
KK JR JS KL KN LG КР KQ
MG LK LM LM LN LO LP KS
ILO LA
MK MIL MO INJ NK INL NM NN 1 MR †MS / 0g гон NO 1 INP NQ NR PI IPJ lOK OL OM ON 100 / Op 0Q OR ros PL ак 3 PN 4 PO PP IPQ ¡PR IPS 1 PT ON RH RI Jap OR RM RN
SH SI SJ RP RO JAR IRS RT SM SN
TH TI TJ TK TL TM S SQ ISR SS ST
I TO / TP Figure 3-14. SD/ROB Digital Section Information Plotted on a PPI Grid Overlay Example (See Table 3-11 for Intensity Level Codes 1 through 6.)
3.3.2 Examples GRB 1135 AREA 4TRW+ 9/101 133/76 54W MT 310 45/47 C2428 AUTO Green Bay, Wisconsin, automated Radar Weather Report at 1135 UTC. An area of echoes, 4/10 coverage, contained thunderstorms and heavy rain showers. Area is defined by points (referenced from GRB radar site) at 9 degrees, 101 nautical miles and 133 degrees, 76 nautical miles. These points, plotted on a map and connected with a straight line, define the center line of the echo pattern. The width of the area was 54 nautical miles; i.e., 27 nautical miles either side of the center line. Maximum top was 31,000 feet MSL located at 45 degrees and 47 nautical miles from Green Bay. Cell movement was from 240 degrees at 28 knots.
ICT 1935 IN 9TRWX 274/84 216/93 22W MTS 440 260/48 C2131 AUTO Wichita, Kansas, automated Radar Weather Report at 1935 UTC. A line of echoes, 9/10 coverage, contained thunderstorm with intense rain showers. The center of the line extended Page 3-50 Section 3: Observed Text Products
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-51 from 274 degrees, 84 nautical miles to 216 degrees, 93 nautical miles. The line was 22 nautical miles wide.
To display graphically, plot the center points on a map and connect the points with a straight line; then plot the width. Since the thunderstorm line was 22 nautical miles wide, it extended 11 nautical miles either side of your plotted line.
The maximum top is 44,000 feet MSL at 260 degrees, 48 nautical miles from Wichita. Cell movement was from 210 degrees at 31 knots.
GGW 1135 AREA 3S- 95/129 154/81 34W MT 100 130/49 0805 AUTO
Glasgow, Montana, automated Radar Weather Report at 1135 UTC. An area, 3/10 coverage, of light snow. The area’s centerline extended from points at 95 degrees, 129 nautical miles to 154 degrees, 81 nautical miles from Glasgow. The area was 34 nautical miles wide. The maximum top was 10,000 feet MSL, at 130 degrees, 49 nautical miles from Glasgow. Cell movement was from 80 degrees at 5 knots.
JGX 2235 AREA 2TRW++6R- 67/130 308/45 106W MT 380 66/54 C2038 AUTO
Atlanta, Georgia, automated Radar Weather Report at 2235 UTC. An area of echoes, total coverage 8/10, with 2/10 of thunderstorms with very heavy rain showers and 6/10 coverage of light rain (This suggests that the thunderstorms were embedded in an area of light rain). The area was 53 nautical miles either side of the line defined by the two points, 67 degrees, 130 nautical miles and 308 degrees, 45 nautical miles from Atlanta. Maximum top was at 38,000 feet and was located on the 66 degree radial of JGX at 54 nautical miles. Cell movement was from 200 degrees at 38 knots.
HKM 0235 CELL TRW+ 19/22 D5 MT 270 18/23 C0414 AUTO
Kohala, Hawaii, automated Radar Weather Report at 0235 UTC. A cell, containing thunderstorms with very heavy rain showers, 5 miles in diameter, was located 19 degrees, 22 nautical miles from Kohala. Maximum top was 27,000 feet located at 18 degrees, 23 nautical miles from Kohala. Movement was from 40 degrees at 14 knots.
TLX 0435 PPINE AUTO
Oklahoma City, Oklahoma, automated Radar Weather Report at 0435 UTC, detected no echoes.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) KCBW KMSX KCCW * KMBX CA KMVX KDLH OKTFX OKBIS СУХ KELX KABR O КМРУ O KGRB ( КМАХ « КСВХ KUDX KARY
KSEX KRIW KF SD O KBBX KUŘX KNIX KCYS KOAX O * KDMX KOTNA KLOT KI WX KCLEO ·ccх CADIX KDAX OKRGE ÖKUEX KILI O OKILN KRLX KDOX * KMUX KFTGO O KGLD OKEAK KIND ICKO ©KAKQ KICK КРИХ © KDDCO OKIC OKSGF ORES KRAKO 2KмHX KVBX O OKVTX KEYX O © KNKX KYUX KIWA KF SX КЕМХ KABX KHIX CREPZ KMAF © KDYXO OKLBB OKFDE OKTLX OKFWS OKSHY KLZK KGWÖ KJAN AKNOA KHIS квих KMXX O KE ОХО *коні KEFC KeSP OKCAE O KVA KJCx KGRK O RICH кихСя КМОв LPLA OKMLB
KOFX KEWX KHCK KIEWO
PAEC PAPD OKCRP KERO KBYX
PHO T CER POTA 6 RKIK Figure 3-15. WSR-88D Weather Radar Network Sites Page 3-52 Section 3: Observed Text Products
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 4: Radar and Satellite Imagery Page 4-1 4 RADAR AND SATELLITE IMAGERY
4.1 Radar
4.1.1 Description Radar images are graphical displays of precipitation and non-precipitation targets detected by weather radar. WSR-88D Doppler radar displays these targets on a variety of products which can be found on the internet on the National Weather Service (NWS) Doppler Radar Images web site at: http://radar.weather.gov/ridge/
4.1.2 Modes of Operation The WSR-88D Doppler radar has two operational modes, Clear Air and Precipitation.
4.1.2.1 Clear Air Mode In Clear Air Mode, the radar is in its most sensitive operation. This mode has the slowest antenna rotation rate which permits the radar to sample the atmosphere longer. This slower sampling increases the radar's sensitivity and ability to detect smaller objects in the atmosphere.
The term "clear air" does not imply "no-precipitation" mode. Even in Clear Air Mode, the WSR- 88D can detect light, stratiform precipitation (e.g., snow) due to the increased sensitivity.
Many of the radar returns in Clear Air Mode are airborne dust and particulate matter. The WSR- 88D images are updated every 10 minutes when operating in this mode.
4.1.2.2 Precipitation Mode Precipitation targets typically provide stronger return signals to the radar than non-precipitation targets. Therefore, the WSR-88D is operated in Precipitation Mode when precipitation is present although some non-precipitation echoes can still be detected in this operating mode.
The faster rotation of the WSR-88D in Precipitation Mode allows images to update at a faster rate approximately every 4 to 6 minutes.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 4-2 Section 4: Radar and Satellite Imagery
4.1.3 Echo Intensities
Figure 4-1. WSR-88D Weather Radar Echo Intensity Legend
The colors on radar images represent different echo reflectivities (intensities) measured in dBZ (decibels of Z). The dBZ values increase based on the strength of the return signal from targets in the atmosphere. Each reflectivity image includes a color scale that represents a correlation between reflectivity value and color on the radar image. Figure 4-1 depicts these correlations.
The scale ranges from -30 to greater than 75 dBZ. The scale also include ND correlated to black which indicates no data was measured.
Reflectivity is correlated to intensity of precipitation. For example, in Precipitation Mode, when the dBZ value reaches 15, light precipitation is present. The higher the indicated reflectivity value, the higher the rainfall rate. The interpretation of reflectivity values is the same for both Clear Air and Precipitation Modes.
Reflectivity is also correlated with intensity terminology (phraseology) for air traffic control purposes. Table 4-1 defines this correlation.
Table 4-1. WSR-88D Weather Radar Precipitation Intensity Terminology Reflectivity (dBZ) Ranges Weather Radar Echo Intensity Terminology <30 dBZ Light 30-40 dBZ Moderate >40-50 dBZ Heavy 50+ dBZ Extreme
Values below 15 dBZ are typically associated with clouds. However, they may also be caused by atmospheric particulate matter such as dust, insects, pollen, or other phenomena. The scale
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 4: Radar and Satellite Imagery Page 4-3 cannot be used to determine the intensity of snowfall. However, snowfall rates generally increase with increasing reflectivity.
4.1.4 Products The NWS produces numerous radar products of interest to the aviation community. The next section will discuss Base Reflectivity and Composite Reflectivity both available through National Weather Service (NWS) Doppler Radar Images web site at: http://radar.weather.gov/ridge/
4.1.4.1 Base Reflectivity Base Reflectivity is a display of both the location and intensity of reflectivity data. Base Reflectivity images encompass several different elevation angles (tilts) of the antenna. The Base Reflectivity image currently available on the ADDS website begins at the lowest tilt angle
(0.5°), more specifically 0.5° above the horizon.
Both a short range (Figure 4-2) and long range (Figure 4-3) image is available from the 0.5º Base Reflectivity product. The maximum range of the short range Base Reflectivity product is 124 NM from the radar location. This view will not display echoes farther than 124 NM from the radar site, although precipitation may be occurring at these greater distances. Other options to view precipitation beyond 124 NM from the radar site include selecting the long-range view which increases coverage out to 248 NM, selecting adjacent radars, or viewing a radar mosaic.
Figure 4-2. WSR-88D Weather Radar Short Range (124 NM) Base Reflectivity Product Example
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) DBZ Radar Image from National Weather Service: KPAH 19:03 UTC 04/29/2005 + Kankakee + Fort Wayne 75 Lamoni Peoria + Logansport * Lima 70 + Kirksville + Champaign.
+ Quinci Springfield taindianapolis -65 + Terre Haute 60 + Bloomington Columbia 55 50 Evansvile i Louisville 45 + Springfield Pomar Bl some green 65 * propson -30 oversbur hville + Crossville 25 + Lawrénceburg 20 + Memphis + Chattanboga HOttle Rock Forence « Hunts vie + Pine Blufg:* + Oxford Tupelo + Rome 10 + Gadşden Columbus + Bimingham Greenville + El Dorado + Tuscaloosa J IND Radar Image from National Weather Service: KPAH 19:03 UTC 04/29/2005 Figure 4-3. WSR-88D Weather Radar Long Range (248 NM) Base Reflectivity Product Example
4.1.4.1.1 Base Reflectivity Use The Base Reflectivity product can be used to determine the location of precipitation and nonprecipitation echoes, the intensity of liquid precipitation, and the general movement of precipitation when animating the image.
If the echo is precipitation, the product can be used to determine if it is convective or stratiform in nature. Stratiform precipitation (Figure 4-4) has the following characteristics:
• Widespread in areal coverage,
• Weak reflectivity gradients,
• Precipitation intensities are generally light or moderate (39 dBZ or less),
• Occasionally, precipitation intensities can be stronger
• Echo patterns change slowly when animating the image.
Page 4-4 Section 4: Radar and Satellite Imagery
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 4: Radar and Satellite Imagery Page 4-5
Figure 4-4. WSR-88D Weather Radar Stratiform Precipitation on the 0.5ºBase Reflectivity Product Example
Hazards associated with stratiform precipitation include possible widespread icing above the freezing level, low ceilings and reduced visibilities.
Convective precipitation (Figure 4-5) can be described using the following characteristics:
Figure 4-5. WSR-88D Weather Radar Convective Precipitation on the 0.5ºBase Reflectivity Product Example
Echoes tend to form as lines or cells, Reflectivity gradients are strong,
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 4-6 Section 4: Radar and Satellite Imagery Precipitation intensities generally vary from moderate to extreme, o Occasionally precipitation intensities can be light Echo patterns change rapidly when animating the image
Numerous hazards are associated with convective precipitation. They include: turbulence, lowlevel wind shear, strong and gusty surface winds, icing above the freezing level, hail, lightning, tornadoes and localized IFR conditions with heavy precipitation.
4.1.4.1.2 Strengths of Base Reflectivity The strengths of the Base Reflectivity product include:
The location of precipitation and non-precipitation echoes is depicted, and The intensity and movement of precipitation is relatively easy and straight forward to determine.
4.1.4.1.3 Limitations of Base Reflectivity Limitations associated with the Base Reflectivity product include:
The radar beam may overshoot targets, and The image may be contaminated by:
o Beam blockage o Ground clutter o Anomalous Propagation (AP) and o Ghosts.
4.1.4.1.3.1 Radar Beam Overshooting Radar beam overshooting may occur because the radar beam (typically the 0.5 degree slice) can be higher than the top of precipitation. This will most likely occur with stratiform precipitation and low-topped convection. For example, at a distance of 124 NM from the radar, the 0.5º Base Reflectivity radar beam is at an altitude of approximately 18,000 feet; at 248 NM the beam height is approximately 54,000 feet. Any precipitation with tops below these altitudes and distances will not be displayed on the image. Therefore, it is quite possible that precipitation may be occurring where none appears on the radar image.
4.1.4.1.3.2 Beam Blockage Beam blockage (Figure 4-6) occurs when the radar beam is blocked by terrain and is particularly predominant in mountainous terrain. This impacts both the Composite Reflectivity and Base Reflectivity images.
Beam blockage is most easily seen on the 0.5º Base Reflectivity images where it appears as a pie-shaped area (or areas) perpetually void of echoes. When animating the imagery, the beam blockage area will remain clear of echoes even as precipitation and other targets pass through.