upper air observations taken at 0000Z and 1200Z. Up through 12,000 feet are true altitudes; at and above 18,000 feet are
pressure altitudes. Wind direction is always in reference to true north, and wind speed is given in knots. The temperature is
given in degrees Celsius; no winds are forecast when a given level is within 1,500 feet of the station elevation. Similarly,
temperatures are not forecast for any station within 2,500 feet of the station elevation. If the wind speed is forecast to be
greater than 100 knots but less than 199 knots, the computer adds 50 to the direction and subtracts 100 from the speed. A
sample FD report is shown in Figure 4-36.
Figure 4-36. Sample FD report.
To decode this type of data group, the reverse process must be accomplished. For example, when the data appears as
“731960,” subtract 50 from the 73 and add 100 to the 19; the wind would be 230° at 119 knots with a temperature of –60°C.
If the wind speed is forecast to be 200 knots or greater, the wind group is coded as 99 knots. When the data appears as
“7799,” subtract 50 from 77 and add 100 to 99; the wind is 270° at 199 knots or greater. When the forecast wind speed is
calm or less than 5 knots, the data group is coded “9900,” which means light and variable.
Aviation Routine Weather Report (METAR)
METAR is an observation of current surface weather reported in a standard international format. While the METAR code
has been adopted worldwide, each country is allowed to make modifications to the code. This discussion of METAR will
cover elements used in the United States.
Example: METAR KGGG 161753Z AUTO 14021G26 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK
PRESFR
A typical METAR report contains the following information in sequential order:
1. Type of report—the first of two types of METAR reports is the routine METAR report that is transmitted every hour.
The second is the aviation selected special weather report (SPECI). This is a special report that can be given at any
time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.
2. Station identifier—each station is identified by a four-letter code as established by the International Civil Aviation
Organization (ICAO). In the 48 contiguous states, a unique three-letter identifier is preceded by the letter “K.”
For example, Gregg County Airport in Longview, Texas, is identified by the letters “KGGG,” K being the country
designation and GGG being the airport identifier. In other regions of the world, including Alaska and Hawaii, the
first two letters of the four-letter ICAO identifier indicate the region, country, or state. Alaska identifiers always
begin with the letters “PA” and Hawaii identifiers always begin with the letters “PH.” A list of station identifiers can
be found at an FSS or NWS office or on the NOAA’s website.
3. Date and time of report—are depicted in a six-digit group (e.g., 161753Z). The first two digits of the sixdigit group
are the date. The last four digits are the time of the METAR, which is always given in Coordinated Universal Time
(UTC). A “Z” is appended to the end of the time to denote the time is given in Zulu time (UTC) as opposed to local
time.
4. Modifier—denotes that the METAR came from an automated source or that the report was corrected. If the notation
“AUTO” is listed in the METAR, the report came from an automated source. It also lists “AO1” or “AO2” in the
remarks section to indicate the type of precipitation sensors employed at the automated station. When the modifier
“COR” is used, it identifies a corrected report sent out to replace an earlier report that contained an error (for
example: METAR KGGG 161753Z COR).
5. Wind—reported with five digits (e.g., 14021) unless the speed is greater than 99 knots, which requires six digits.
The first three digits indicate the direction of the wind is blowing in tens of degrees with 0/360 from the north, 90
from the east, 180 from the south, and 270 from the west. If the wind is variable, it is reported as “VRB.” The last
two digits indicate the speed of the wind in knots (KT) unless the wind is greater than 99 knots, which requires
three digits. If the winds are gusting 5 knots or greater over the sustained speed, the letter “G” follows the wind
speed. After the letter “G,” the peak gust recorded is provided (e.g., 21G26). If the wind varies more than 60° and
the wind speed is greater than 6 knots, a separate group of numbers, separated by a “V ,” will indicate the extremes
of the wind directions.
6. Visibility—the prevailing visibility (e.g., 3/4 SM) is reported in statute miles as denoted by the letters “SM.” It
is reported in both miles and fractions of miles. At times, runway visual range (RVR) is reported following the
prevailing visibility. RVR is the distance a pilot can see down the runway in a moving aircraft. When RVR is
reported, it is shown with an R, then the runway number followed by a slant, then the visual range in feet. For
example, when the RVR is reported as R17L/1400FT, it translates to a visual range of 1,400 feet on runway 17 left.
7. Weather—broken down into two different categories: qualifiers and weather phenomenon (e.g., +TSRA BR). First,
the qualifiers of intensity, proximity, and the descriptor of the weather will be given. The intensity may be light (–),
moderate ( ), or heavy (+). Proximity depicts only weather phenomena that are in the airport vicinity. The notation
“VC” indicates a specific weather phenomenon is in the vicinity of 5 to 10 miles from the airport. Descriptors
are used to describe certain types of precipitation and obscurations. Weather phenomena may be reported as
being precipitation, obscurations, and other phenomena such as squalls or funnel clouds. Descriptions of weather
phenomena as they begin or end, and hailstone size are also listed in the remarks sections of the report.
8. Sky condition—always reported in the sequence of amount, height, and type or indefinite ceiling/height (vertical
visibility) (e.g., BKN008 OVC012CB). The heights of the cloud bases are reported with a three-digit number in
hundreds of feet above the ground. Clouds above 12,000 feet are not detected or reported by an automated station.
The types of clouds, specifically towering cumulus (TCU) or cumulonimbus (CB) clouds, are reported with their
height. Contractions are used to describe the amount of cloud coverage and obscuring phenomena. The amount of
sky coverage is reported in eighths of the sky from horizon to horizon.
9. Temperature and dew point—always given in degrees Celsius (e.g., 18/17). Temperatures below 0 °C are preceded
by the letter “M” to indicate minus.
10. Altimeter setting—reported as inches of mercury in a four-digit number group, and is always preceded by the
letter “A” (e.g., A2970). Rising or falling pressure may also be denoted in the remarks sections as “PRESRR” or
“PRESFR” respectively.
11. Remarks—comments may or may not appear in this section of the METAR. The information contained in this
section may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure
information, and various other information deemed necessary. An example of a remark regarding weather
phenomenon that does not fit in any other category would be: OCNL LTGICCG. This translates as occasional
lightning in the clouds, and from cloud to ground. Automated stations also use the remarks section to indicate the
equipment needs maintenance. The remarks section always begins with the letters “RMK.”
Example: METAR BTR 161753Z 14021G26 3/4SM -RA BR BKN008 OVC012 18/17 A2970 RMK PRESFR
Explanation:
• Type of Report Routine METAR.
• Location: Baton Rouge, Louisiana.
• Date: 16th day of the month.
• Time: 1753 Zulu.
• Modifier: None shown.
• Wind Information: 140° at 21 kts gusting to 26 kts.
• Visibility: 3/4 statute mile.
• Weather: light rain and mist.
• Sky Conditions: Broken 800 ft, overcast 1,200.
• Temperature: 18 °C, dew point 17 °C.
• Altimeter: 29.70 "Hg".
• Remarks: Barometric pressure is falling.
Terminal Aerodrome Forecasts (TAF)
A terminal aerodrome forecast (TAF) is a report established for the five statute mile radius around an airport. TAF reports
are usually given for larger airports. Each TAF is valid for a 24- hour period, and is updated at a minimum of four times
a day at 0000Z, 0600Z, 1200Z, and 1800Z. TAF utilizes the same descriptors and abbreviations as used in the METAR
report.
The terminal forecast includes the following information in sequential order:
1. Type of report—TAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).
2. ICAO station identifier—The station identifier is the same as that used in a METAR.
3. Date and Time of Origin—reported in a six-digit code. The first two indicate the date, the last four indicate the time.
Time is always given in UTC as denoted by the “Z” following the number group.
4. Valid period date and time—the valid forecast time period is reported in a six-digit number group. The first two
numbers indicate the date, followed by the two-digit beginning time for the valid period, followed by the two digit
ending time.
5. Forecast Wind—the wind direction and speed forecast are reported in a five-digit number group. The first three
digits indicate the direction of the wind in reference to true north. The last two digits state the windspeed in knots,
as denoted by the letters “KT.” 4-39 As in the METAR, winds greater than 99 knots are given in three digits.
6. Forecast visibility—reported in statute miles, in whole numbers or fractions. If the forecast visibility is greater than
6 miles, it will be coded as “P6SM.”
7. Forecast significant weather—weather phenomenon is coded in the TAF reports in the same format as the METAR.
If no significant weather is expected during the forecast time period, the denotation “NSW” will be included in the
“becoming” or “temporary” weather groups.
8. Forecast sky condition—reported in the same manner as the METAR. Only cumulonimbus (CB) clouds are forecast
in this portion of the TAF report as opposed to CBs and towering cumulus in the METAR.
9. Forecast change group—for any significant weather change forecast to occur during the TAF time period, the
expected conditions and time period are included in this group. This information may be shown as From (FM),
Becoming (BECMG), and Temporary (TEMPO). “From” is used when a rapid and significant change, usually
within an hour, is expected. “Becoming” is used when a gradual change in the weather is expected over a period of
no more than 2 hours. “Temporary” is used for temporary fluctuations of weather, expected to last for less than an
hour.
10. Probability forecast—a given percentage that describes the probability of thunderstorms and precipitation occurring
in the coming hours. This forecast is not used for the first 6 hours of the 24-hour forecast.
Example:
TAF KPIR 111130Z 111212 15012KT P6SM BKN090
TEMPO 1214 5SM BR
FM1500 16015G25KT P6SM SCT040 BKN250
FM0000 14012KT P6SM BKN080 OVC150 PROB40
0004 3SM TSRA BKN030CB
FM0400 1408KT P6SM SCT040 OVC080 TEMPO0408
3SM TSRA OVC030CB
BECMG 0810 32007KT=
Explanation: Routine TAF for Pierre, South Dakota on the 11th day of the month, at 1130Z valid for 24 hours from 1200Z
on the 11th to 1200Z on the 12th wind from 150° at 12 knots visibility greater than 6 statute miles, broken clouds at 9,000
feet, temporarily, between 1200Z and 1400Z, visibility 5 statute miles in mist. From 1500Z, winds from 160° at 15 knots,
gusting to 25 knots, visibility greater than 6 statute miles, clouds scattered at 4,000 feet and broken at 25,000 feet. From
0000Z wind from 140° at 12 knots; visibility greater than 6 statute miles, clouds broken at 8,000 feet, overcast at 15,000
feet between 0000Z and 0400Z, there is 40 percent probability of visibility 3 statute miles thunderstorm with moderate rain
showers clouds broken at 3,000 feet with cumulonimbus clouds. From 0400Z winds from 140°at 8 knots visibility greater
than 6 miles clouds at 4,000 scattered and overcast at 8,000 temporarily between 0400Z and 0800Z visibility 3 miles,
thunderstorms with moderate rain showers clouds overcast at 3,000 feet with cumulonimbus clouds. Becoming between
0800Z and 1000Z wind from 320° at 7 knots end of report (=).
Area Forecasts (FA)
The aviation area forecast (FA) gives a picture of clouds, general weather conditions, and visual meteorological conditions
(VMC) expected over a large area encompassing several states. There are six areas for which area forecasts are published
in the contiguous 48 states. Area forecasts are issued three times a day and are valid for 18 hours. This type of forecast
gives information vital to en route operations as well as forecast information for smaller airports that do not have terminal
forecasts.
In-flight Weather Advisories
In-flight weather advisories are forecasts provided to en route aircraft, and detail potentially hazardous weather. These
advisories are also available to pilots prior to departure for flight planning purposes.
Airman’s Meteorological Information (AIRMET)
AIRMETs (report type designator WA) are issued every 6 hours with intermediate updates issued as needed for a particular
area forecast region. The information contained in an AIRMET is of operational interest to all aircraft, but the weather
section concerns phenomena considered potentially hazardous to light aircraft and aircraft with limited operational
capabilities. An AIRMET includes forecast of moderate icing, moderate turbulence, sustained surface winds of 30
knots or greater, widespread areas of ceilings less than 1,000 feet and/or visibilities less than 3 miles, and extensive
mountain obscurities. Each AIRMET bulletin has a fixed alphanumeric designator, and is numbered sequentially for easy
identification, beginning with the first issuance of the day. SIERRA is the AIRMET code used to denote IFR and mountain
obscuration; TANGO is used to denote turbulence, strong surface winds, and low-level wind shear; and ZULU is used to
denote icing and freezing levels.
Example:
DFWT WA 241650
AIRMET TANGO UPDT 3 FOR TURBC… STG SFC
WINDS AND LLWS V ALID UNTIL 242000 AIRMET
TURBC… OK TX…UPDT FROM OKC TO DFW TO SAT
TO MAF TO CDS TO OKC OCNL MDT TURBC BLO 60
DUE TO STG AND GUSTY LOW LVL WINDS. CONDS
CONTG BYD 2000Z
Significant Meteorological Information (SIGMET)
SIGMETs (report type designator WS) are in-flight advisories concerning nonconvective weather that is potentially
hazardous to all aircraft. They report weather forecasts that include severe icing not associated with thunderstorms, severe
or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms, dust storms, or sandstorms that
lower surface or in-flight visibilities to below 3 miles, and volcanic ash. SIGMETs are unscheduled forecasts that are valid
for 4 hours, but if the SIGMET relates to hurricanes, it is valid for 6 hours.
A SIGMET is issued under an alphabetic identifier, from November through Yankee, excluding Sierra and Tango. The first
issuance of a SIGMET is designated as a UWS, or Urgent Weather SIGMET. Re-issued SIGMETs for the same weather
phenomenon are sequentially numbered until the weather phenomenon ends.
Example:
SFOR WS 100130 SIGMET ROME02 V ALID UNTIL
100530 OR WA FROM SEA TO PDT TO EUG TO SEA
OCNL MOGR CAT BTN 280 AND 350 EXPCD DUE TO
JTSTR. CONDS BGNG AFT 0200Z CONTG BYD 0530Z.
Convective Significant Meteorological Information (WST)
A Convective SIGMET (WST) is an in-flight weather advisory issued for hazardous convective weather that affects
the safety of every flight. Convective SIGMETs are issued for severe thunderstorms with surface winds greater than 50
knots, hail at the surface greater than or equal to ¾ inch in diameter, or tornadoes. They are also issued to advise pilots
of embedded thunderstorms, lines of thunderstorms, or thunderstorms with heavy or greater precipitation that affect 40
percent or more of a 3,000 square mile or greater region.
Convective SIGMETs are issued for each area of the contiguous 48 states but not Alaska or Hawaii. Convective SIGMETs
are issued for the eastern (E), western (W), and central (C) United States. Each report is issued at 55 minutes past the hour,
but special Convective SIGMETs can be issued during the interim for any reason. Each forecast is valid for 2 hours. They
are numbered sequentially each day from 1–99, beginning at 00Z. If no hazardous weather exists, the convective SIGMET
is still issued; however, it states “CONVECTIVE SIGMET…NONE.”
Example:
MKCC WST 221855 CONVECTIVE SIGMET 21C V ALID
UNTIL 2055 KS OK TX
VCNTY GLD-CDS LINE NO SGFNT TSTMS RPRTD
LINE TSTMS DVLPG BY 1955Z WILL MOV EWD 30-35
KT THRU 2055Z HAIL TO 2 IN PSBL
Pilot Weather Reports (PIREPs)
Pilot weather reports (PIREPs) provide valuable information regarding the conditions as they actually exist in the air, and
cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear
and turbulence, and the location of in-flight icing. If the ceiling is below 5,000 feet, or visibility is at or below 5 miles,
ATC facilities are required to solicit PIREPs from pilots in the area. When unexpected weather conditions are encountered,
pilots are encouraged to make a report to an FSS or ATC. When a pilot weather report is filed, the ATC facility or FSS will
add it to the distribution system to brief other pilots and provide in-flight advisories.
PIREPs are easy to file, and a standard reporting form outlines the manner in which they should be filed. Figure 11-4 shows
the elements of a PIREP form. Item numbers 1 through 5 are required information when making a report, as well as at least
one weather phenomenon encountered. PIREPs are normally transmitted as an individual report, but may be appended to a
surface report. Pilot reports are easily decoded and most contractions used in the reports are self-explanatory.
Example:
UA/OV GGG 090025/ M 1450/ FL 060/ TP C182/ SK 080
OVC/ WX FV 04R/ TA 05/ WV 270030/ TB LGT/ RM
HVY RAIN
Explanation:
• Type: Routine pilot report.
• Location: 25 NM out on the 090° radial, Gregg County VOR.
• Time: 1450 Zulu.
• Altitude or Flight Level: 6,000 feet.
• Aircraft Type: Cessna 182.
• Sky Cover: 8,000 overcast.
• Visibility/Weather: 4 miles in rain.
• Temperature: 5° Celsius.
• Wind: 270° at 30 knots.
• Turbulence: Light.
• Icing: None reported.
• Remarks: Rain is heavy.
Chapter Summary
A thorough understanding of the weather is a “make or break” item for the balloon pilot; without a complete picture of the
weather, a pilot may make an ill-advised decision to launch that may result in injury, damage to the balloon, or worse. It is
imperative that a pilot use as many resources as he can, understanding the variables potentially affecting flight, and making
an informed decision to conduct a safe flight.
Perhaps the most valuable point to be made is that the balloon pilot must use and exercise common sense. When flying
a balloon, the most desirable conditions are good visibility, light winds, and no precipitation. Anything other than that
scenario should be reason to pause and consider the possible outcome of a launch. There is never an absolute requirement
to fly—there is always the possibility of making the decision to try again another day.