December 1999 3-5 UUA /OV ABQ090045/TM 1430/FL130/TP BE30/TB SEV/RM BROKE ALL THE BOTTLES IN
THE BAR An urgent UA 45 miles east of Albuquerque, NM, a pilot of a Beech King Air 300 reported severe turbulence at 13,000 feet. The pilot remarked the turbulence was so severe it broke all the bottles in the passenger cabin bar.
UA /OV KMRB-KPIT/TM 1600/FL100/TP BE55/SK BKN024-TOP032/BKN-OVC043-TOPUNKN /TA M12/IC LGT-MOD RIME 055-080 This PIREP is decoded as follows: UA, Martinsburg to Pittsburgh, Pennsylvania (PA), at 1600 UTC at 10,000 feet MSL. Type of aircraft is a Beechcraft Baron. First cloud layer is broken with a base at 2,400 feet MSL broken and tops at 3,200 feet MSL. The second cloud layer is broken to occasionally overcast with a base at 4,300 feet MSL, and tops unknown. Outside air temperature is -12 degrees Celsius. Light to moderate rime icing is reported between 5,500 and 8,000 feet MSL.
UA /OV KOKC090064/TM 1522/FL080/TP C172/SK SCT090-TOPUNKN/WX FV05SM HZ/TA M04/WV 24540KT/TB LGT/RM IN CLR.
This PIREP is decoded as follows: UA, 64 nautical miles east of Oklahoma City VOR at 1522 UTC, flight level 8,000 feet MSL. Type of aircraft is a Cessna 172. There is a scattered cloud layer with bases at 9,000 feet MSL and unknown tops. Flight visibility is restricted to 5 statute miles due to haze.
Outside air temperature is -4 degrees Celsius, wind is 245 degrees at 40 knots, light turbulence, and the aircraft is in clear skies.
UA /OV KLIT-KFSM/TM 0310/FL100/TP BE36/SK SCT070-TOP110/TA M03/WV 25015KT.
This PIREP is decoded as follows: UA between Little Rock and Fort Smith, Arkansas (AR), at 0310 UTC. A Beech 36 is at 10,000 feet MSL. There is a scattered cloud layer with bases at 7,000 feet MSL, and tops at 11,000 feet MSL. The outside air temperature is -3 degrees Celsius. Winds are from 250 degrees at 15 knots.
UA /OV KABQ/TM 1845/RM TIJERAS PASS CLSD DUE TO FG AND LOW CLDS UNA VFR RTN ABQ.
The PIREP is over Albuquerque at 1845 UTC. The remark section indicates the Tijeras pass is closed due to fog and low clouds. The pilot also mentions that she/he could not continue VFR and returned to Albuquerque.
UA /OV KTOL/TM 2200/FL310/TP B737/TB MOD CAT 350-390.
This PIREP is decoded as follows: UA over Toledo, Ohio, at 2200 UTC and flight level 310, a Boeing 737 reported moderate clear air turbulence between 35,000 and 39,000 feet MSL.
Nonmeteorological PIREPs sometimes help air traffic controllers. This “plain language” report stated:
…/RM 3N PNS LARGE FLOCK OF BIRDS HDG GEN N MAY BE SEAGULLS FRMN … This PIREP alerted pilots and controllers to a bird hazard.
December 1999 3-6
RADAR WEATHER REPORT (SD) General areas of precipitation, including rain, snow, and thunderstorms, can be observed by radar. The radar weather report (SD) includes the type, intensity, and location of the echo top of the precipitation.
(The intensity trend of precipitation is no longer coded on the SD.) It is important to remember that all heights are reported above MSL. Table 3-5 explains symbols denoting intensity. Radar stations report each hour at H+35.
Example of an SD:
TLX 1935 LN 8 TRW++ 86/40 164/60 20W C2425 MTS 570 AT 159/65 AUTO
a. b. c. d. e. f. g. h. i.
^MO1 NO2 ON3 PM34 QM3 RL2 =
j.
Above SD report decoded as follows:
a. Location identifier and time of radar observation (Oklahoma City SD at 1935 UTC).
b. Echo pattern (LN in this example). The echo pattern or configuration may be one of the following:
1. Line (LN) is a line of convective echoes with precipitation intensities that are heavy or greater, at least 30 miles long, at least 4 times as long as it is wide, and at least 25% coverage within the line.
2. Area (AREA) is a group of echoes of similar type and not classified as a line.
3. Cell (CELL) is a single isolated convective echo such as a rain shower.
c. Coverage, in tenths, of precipitation in the defined area (8/10 in this example).
d. Type and intensity of weather (thunderstorm [T] with very heavy rainshowers [RW++]).
Table 3-5 Precipitation Intensity Symbol Intensity
- Light (none) Moderate + Heavy ++ Very Heavy X Intense XX Extreme
December 1999 3-7 Table 3-6 Symbols Used in SD Symbol Meaning R Rain RW Rain shower S Snow SW Snow shower T Thunderstorm Example of an SD:
TLX 1935 LN 8 TRW++ 86/40 164/60 20W C2425 MTS 570 AT 159/65 AUTO
a. b. c. d. e. f. g. h. i.
^MO1 NO2 ON3 PM34 QM3 RL2 =
j.
e. Azimuth, referenced to true north, and range, in nautical miles (NM) from the radar site, of points defining the echo pattern (86/40 164/60 in this echo). For lines and areas, there will be two azimuth and range sets that define the pattern. For cells, there will be only one azimuth and range set. (See the examples that follow for elaboration of echo patterns.)
f. Dimension of echo pattern (20 NM wide in this example). The dimension of an echo pattern is given when azimuth and range define only the center line of the pattern. (In this example, “20W” means the line has a total width of 20 NM, 10 miles either side of a center line drawn from the points given in item “e” above.)
g. Cell movement (cells within line moving from 240 degrees at 25 knots in this example). Movement is only coded for cells; it will not be coded for lines or areas.
h. Maximum top and location (57,000 feet MSL on radial 159 degrees at 65 NM in this example).
Maximum tops may be coded with the symbols “MT” or “MTS.” If it is coded with “MTS” it means that satellite data as well as radar information was used to measure the top of the precipitation.
i. The report is automated from WSR-88D weather radar data.
j. Digital section is used for preparing radar summary chart.
To aid in interpreting SDs, the five following examples are decoded into plain language.
GRB 1135 AREA 4TRW+ 9/100 130/75 50W C2425 MT 310 at 45/47 AUTO Green Bay, WI, Automated SD at 1135 UTC. An area of echoes, 4/10 coverage, containing thunderstorms and heavy rain showers. Area is defined by points (referenced from GRB radar site) at 9 degrees, 100 NM and 130 degrees, 75 NM. 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 is 50 NM; i.e., 25 NM either side of the center line. The cells are moving from 240 degrees at 25 knots. Maximum top is 31,000 feet MSL located at 45 degrees and 47 NM from GRB.
December 1999 3-8 ICT 1935 LN 9TRWX 275/80 210/90 20W C2430 MTS 440 AT 260/48 AUTO Wichita, KS, Automated SD at 1935 UTC. A line of echoes, 9/10 coverage, containing thunderstorm with intense rain showers. The center of the line extends from 275 degrees, 80 NM to 210 degrees, 90 NM. The line is 20 NM wide. NOTE: 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 is 20 miles wide, it extends 10 miles either side of your plotted line. The thunderstorm cells are moving from 240 degrees at 30 knots. The maximum top is 44,000 feet MSL at 260 degrees, 48 NM from ICT.
GGW 1135 AREA 3S- 90/120 150/80 34W MT 100 at 130/49 Glasgow, MT, Automated SD at 1135 UTC. An area, 3/10 coverage, of light snow. The area’s centerline extends from points at 90 degrees, 120 NM to 150 degrees, 80 NM. The area is 34 NM wide.
No movement was reported. The maximum top is 10,000 feet MSL, at 130 degrees, 49 NM.
MAF 1135 AREA 2TRW++6R- 67/130 308/45 105W C2240 MT 380 AT 66/54 Midland/Odessa, TX, Automated SD at 1135 UTC. An area of echoes, total coverage 8/10, with 2/10 of thunderstorms with very heavy rainshowers and 6/10 coverage of light rain. (This suggests that the thunderstorms are embedded in an area of light rain.) The area lies 52½ miles either side of the line defined by the two points, 67 degrees, 130 NM and 308 degrees, 45 NM.
When an SD is transmitted but does not contain any encoded weather observation, a contraction is sent which indicates the operational status of the radar.
Example:
TLX 1135 PPINE AUTO It is decoded as Oklahoma City, OK’s, radar at 1135 UTC detects no echoes.
Table 3-7 Operational Status Contractions Contraction Operational Status PPINE Radar is operating normally but there are no echoes being detected.
PPINA Radar observation is not available.
PPIOM Radar is inoperative or out of service.
AUTO Automated radar report from WSR-88D.
All SDs also contain groups of digits.
Example:
^MO1 NO1 ON3 PM34 QM3 RL2 SL1= These groups of digits are the final entry on the SD. This digitized radar information is used primarily in preparing the radar summary chart. However, by using a proper grid overlay chart for the corresponding radar site, this code is also useful in determining more precisely where the precipitation is occurring within an area as well as the intensity of the precipitation. (See Figure 3-1 for an example of a digital code plotted from the Oklahoma City, OK, SD.)
December 1999 3-9 The digit assigned to a box represents the intensity of precipitation as determined by the WSR-88D and is the maximum precipitation intensity found within the grid box. (See Table 7-2 for definitions of precipitation intensities associated with digits 1 through 6.) These digits were once commonly referred to as VIP levels because precipitation intensity, and therefore the digits, was derived using a video integrator processor (VIP). Since the WSR-88D and not the video integrator processor is now used to determine precipitation intensity, it is suggested that the term VIP should no longer be used when describing precipitation intensity. For example, if a specific grid has the number 2 associated with it, that grid would be described as having moderate precipitation, not VIP level 2 precipitation.
A box is identified by two letters, the first representing the row in which the box is found and the second letter representing 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.
When using hourly SDs in preflight planning, note the location and coverage of echoes, the type of weather reported, the intensity, and especially the direction of movement.
It is important to remember that the SD contains information pertaining to the location of particles in the atmosphere that are of precipitation size or larger. It does not display locations of cloud-size particles, and, therefore, neither ceilings nor restrictions to visibility. An area may be blanketed with fog or low stratus, but the SD would not include information about it. Pilots should use SDs along with METARs, satellite photos, and forecasts when planning a flight.
The SDs help pilots plan ahead to avoid thunderstorm areas. Once airborne, however, pilots must depend on contact with Flight Watch, which has the capability to display current radar images, airborne radar, or visual sighting to evade individual storms.
December 1999 HQ N HJ
IG HP HQ HR IK \ IM JG IP
JH IR IS JK JL KG кн KI KJ KK KL JN IJO JP JQ VR JS KN кО КР
ILK LM KQ KA KS
MG LM LN ILO LP
MI MJ LO ILR NI INJ NK MK NL ML NM MMOKC MN MO 1 MP MQ MR MS
OG NO INP
OI NQ INR OK >G PH PJ IPK ON 00 OP 0Q OR TOS
G PN IPO IPP PQ
QK PS PT ON 100 RH RI RJ OR Fos RL OT SH SI SJ 2 RO RP I RQ IRR RS I RT TH TI ITJ TK SP • SQ ISR SS ST Figure 3-1. Digital Radar Report Plotted on a PPI Grid Overlay Chart.
(Note: See Table 7-2 for Intensity Level Codes 1 through 6.)
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December 1999 3-11
SATELLITE WEATHER PICTURES Prior to weather satellites, weather observations were made only at distinct points within the atmosphere and supplemented by PIREPs. These PIREPs gave a “sense” of weather as viewed from above. However, with the advent of weather satellites, a whole new dimension to weather observing and reporting has emerged. There are two types of weather satellites in use by the U. S. today:
Geostationary Operational Environmental Satellite (GOES), which is a geostationary satellite, and the Polar Orbiter Environmental Satellite (POES). Additional satellite imagery is available from the European Meteosat and the Japanese GMS geostationary satellites.
Two U.S. GOES satellites are used for imaging. One is stationed over the equator at 75 degrees west longitude and is referred to as GOES EAST since it covers the eastern U.S. The other is positioned at 135 degrees west longitude and is referred to as GOES WEST since it covers the western U.S.
Together they cover North and South America and surrounding waters. They normally transmit an image of Earth, pole to pole, every 15 minutes. When disastrous weather threatens the U.S., the satellites can scan small areas rapidly so that a picture can be received as often as every 1 minute. Data from these rapid scans are used at NWS offices.
Since the GOES satellite is stationary over the equator, the images poleward of about 50 degrees latitude become greatly distorted. For images above 50 degrees latitude, polar orbiting satellites are employed. The NOAA satellite is a polar orbiter and orbits the earth on a track that nearly crosses the North and South poles. A high resolution picture is produced about 500 miles either side of its track on the journey from pole to pole. The NOAA pictures are essential to weather personnel in Alaska and Canada.
Two types of imagery are available from satellites, and, when combined, give a great deal of information about clouds. Through interpretation, the analyst can determine the type of cloud, the temperature of cloud tops (from this, the approximate height of the cloud can be determined), and the thickness of cloud layers. From this information, the analyst gets a good idea of the associated weather.
One type of imagery is visible (Figure 3-2). A visible image shows clouds and Earth reflecting sunlight to the satellite sensor. The greater the reflected sunlight reaching the sensor, the whiter the object is on the picture. The amount of reflectivity reaching the sensor depends upon the height, thickness, and ability of the object to reflect sunlight. Since clouds are much more reflective than most of the Earth, clouds will usually show up white on the picture, especially thick clouds. Thus, the visible picture is primarily used to determine the presence of clouds and the type of cloud from shape and texture. Due to the obvious lack of sunlight, there are no visible images available at night.
The second type of imagery is infrared (IR) (Figure 3-3). An IR picture shows heat radiation being emitted by clouds and Earth. The images show temperature differences between cloud tops and the ground, as well as temperature gradations of cloud tops and along the Earth’s surface. Ordinarily, cold temperatures are displayed as light gray or white. High clouds appear the whitest. However, various computer-generated enhancements are sometimes used to sharply illustrate important temperature contrasts. IR images measure cloud top temperatures and are used to approximate the height of clouds.
From this, one can see the importance of using visible and IR imagery together when interpreting clouds. IR images are available both day and night.
December 1999 3-12 Satellite images are processed by the NWS as well as by many private companies. Therefore, they can be received from many different sources. Depending upon the source, satellite images may be updated anywhere from every 15 minutes to every hour; therefore, it is important to note the time on the images when interpreting them. By viewing satellite images, the development and dissipation of weather can be seen and followed over the entire country and coastal regions.
NESDIS is developing the capability to provide derived products useful to aviation from satellite data.
These experimental products are available via the Internet and include:
1. Fog and low cloud coverage and depth.
2. Volcanic ash detection.
3. Microburst products.
4. Soundings.
5. Clear air turbulence.
6. Aircraft icing potential.
December 1999 Figure 3-2. Visible Satellite Imagery.
3-13
December 1999 Figure 3-3. Infrared Satellite Imagery.
3-14
December 1999 3-15 RADIOSONDE ADDITIONAL DATA (RADATs) Radiosonde Additional Data (RADATs) information is obtained from the radiosonde observations that are conducted twice a day at 00 and 12Z. The information contained in a RADAT is the observed freezing level and the relative humidity associated with the freezing level. The freezing level is the height above MSL at which the temperature is zero degrees Celsius.
The format associated with the RADAT is as follows:
Stn ID Time RADAT UU (D) (hhh)(hhh)(hhh)(/n) Explanation:
Stn ID and Time - standard three-letter identifier and observation time in UTC.
RADAT - a contraction identifying the data as “freezing-level data.”
UU - relative humidity at the freezing level in percent. When more than one level is identified, “UU” is the highest relative humidity observed at any of the levels transmitted.
(D) - a coded letter “L,” “M,” or “H.” used in the event of multiple freezing levels to identify which level has the highest relative humidity, “L – lowest,” “M – middle,” “H – highest.” This letter is omitted when only one level is coded.
(hhh) – height of the freezing level in hundreds of feet. Up to three freezing levels can be specified in the event of multiple freezing levels. If there are more than three freezing levels, the levels coded are the lowest, highest, and the intermediate level with the highest relative humidity.
(/n) – an indicator to show the number of freezing levels in addition to the three which are coded. The number is omitted when all observed freezing levels are coded (three or less.)
Examples:
SJU 1200 RADAT 87160 The San Juan, Puerto Rico, RADAT indicates that the freezing level was 16,000 feet MSL and the relative humidity was 87% at the freezing level.
Figure 3-4. SJU RADAT.
16,000 0°C Mean Sea Level
December 1999 3-16 OUN 0000 RADAT 87L024105 The Norman, Oklahoma, RADAT indicates that the freezing level was crossed twice. The two crossings occurred at 2,400 feet MSL and at 10,500 feet MSL. The 87L indicates that the relative humidity was 87% at the lowest crossing (indicated by the L).
Figure 3-5. OUN RADAT.
10,500 2,400 0° Surface of ground Mean Sea Level