December 1999 1-7 Once the HIWAS broadcast is updated, an announcement will be made once on all communications/NAVAID frequencies except emergency, and En Route Flight Advisory Service (EFAS). In the event that a HIWAS broadcast area is out of service, an announcement shall be made on all communications/NAVAID frequencies except emergency and EFAS.
En Route Flight Advisory Service (EFAS) The en route flight advisory service (EFAS), or “Flight Watch,” is a service from selected FSSs or AFSSs on a common frequency 122.0 mHz below flight level (FL) 180 and on assigned discrete frequencies to aircraft at FL180 and above. The purpose of EFAS is to provide en route aircraft with timely and pertinent weather data tailored to a specific altitude and route using the most current available sources of aviation meteorological information. Additionally, EFAS is a focal point for rapid receipt and dissemination of pilot reports. Figure 1-1 indicates the sites where EFAS and associated outlets are located. To use this service, call for flight watch. Example, “(Oakland) FLIGHT WATCH, THIS IS…” The following paragraphs describe other FAA facilities which provide support to the aviation community.
Air Traffic Control System Command Center (ATCSCC) The Air Traffic Control System Command Center (ATCSCC), also known as “central flow control,” is located in Herndon, Virginia. ATCSCC has the mission of balancing air traffic demand with system capacity. This ensures maximum safety and efficiency for the National Airspace System while minimizing delays. The ATCSCC utilizes the Traffic Management System, aircraft situation display, monitor alert, the follow-on functions, and direct contact with the air route traffic control center (ARTCC) and terminal radar approach control facility (TRACON) traffic management units to manage flow on a national as well as local level.
Because weather is the most common reason for air traffic delays and re-routings, the ATCSCC is supported full-time by Air Traffic Control System Command Center Weather Unit Specialists (ATCSCCWUS). These specialists are responsible for the dissemination of meteorological information as it pertains to national air traffic flow management.
Air Route Traffic Control Center (ARTCC) An air route traffic control center (ARTCC) is a facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft.
En route controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traffic control duties. En route controllers shall advise pilots of hazardous weather that may impact operations within 150 NM of the controller’s assigned sector or area of jurisdiction.
Center Weather Service Unit (CWSU) The purpose of the center weather service unit (CWSU) is to provide weather consultation, forecasts, and advice to managers and staff within ARTCCs and to other supported FAA facilities. The CWSU is a joint agency aviation weather support team located at each ARTCC. The unit is composed of NWS meteorologists and FAA traffic management personnel, the latter being assigned as Weather
December 1999 1-8 Coordinators. The CWSU meteorologist provides FAA traffic managers with accurate and timely weather information. This information is based on monitoring, analysis, and interpretation of real-time weather data at the ARTCC through the use of all available data sources including radar, satellite, PIREPs, and various NWS products such as TAFs and area forecasts, inflight advisories, etc. The flow or exchange of weather information between the CWSU meteorologists and the FAA personnel in the ARTCC is the responsibility of the Weather Coordinator.
Air Traffic Control Tower (ATCT) An air traffic control tower (ATCT) is a terminal facility that uses air/ground communications, visual signaling, and other devices to provide ATC services to aircraft operating in the vicinity of an airport or on the movement area. It authorizes aircraft to land or take off at the airport controlled by the tower or to transit the Class D airspace area regardless of flight plan or weather conditions (IFR or VFR). A tower may also provide approach control services.
Terminal controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traffic control duties. Terminal controllers shall advise pilots of hazardous weather that may impact operations within 150 NM of the controller’s assigned sector or area of jurisdiction. Tower cab and approach control facilities may opt to broadcast hazardous weather information alerts only when any part of the area described is within 50 NM of the airspace under the ATCT’s jurisdiction.
The responsibility for disseminating weather information is shared with the NWS at many ATCT facilities. If the responsibility is not shared, the controllers are properly certified and acting as official weather observers for the elements being reported.
An automatic terminal information service (ATIS) is a continuous broadcast of recorded information in selected terminal areas. Its purpose is to improve controller effectiveness and to relieve frequency congestion by automating the repetitive transmission of noncontrol airport/terminal area and meteorological information.
Direct User Access Terminal Service (DUATS) The direct user access terminal system (DUATS) provides current FAA weather and flight plan filing services to U.S. Coast Guard and certified civil pilots. The computer-based system receives and stores up-to-date weather and NOTAM data from the FAA’s WMSC. Pilots using a personal computer, modem, and a telephone line can access the system and request specific types of weather briefings and other pertinent data for planned flights. The pilot can also file, amend, or cancel flight plans while dialed into the system. Further information about DUATS can be obtained from any AFSS or FAA Flight Standards District Office (FSDO).
OBSERVATIONS Weather observations are measurements and estimates of existing weather conditions both at the surface and aloft. When recorded and transmitted, an observation becomes a report; and reports are the basis of all weather analyses, forecasts, advisories, and briefings. The following paragraphs briefly describe the observation programs of the NWS and the FAA. More detailed information on each program follows.
December 1999 1-9 SURFACE AVIATION WEATHER OBSERVATIONS (METARs) Surface aviation weather observations (METARs) include weather elements pertinent to flying. A network of airport stations provides routine up-to-date surface weather information. For more information on surface aviation observation, see Section 2.
UPPER-AIR OBSERVATIONS Upper-air weather data is received from sounding balloons (known as radiosonde observations) and pilot weather reports (PIREPs). Upper-air observations are taken twice daily at specified stations. These upper-air observations furnish temperature, humidity, pressure, and wind data, often to heights above 100,000 feet. In addition, pilots are a vital source of upper-air weather observations. In fact, aircraft in flight are the only means of directly observing turbulence, icing, and height of cloud tops. For more information on PIREPs, see Section 3. Recently some US and other international airlines have equipped their aircraft with instruments that automatically send weather observations via a satellite downlink.
These are important observations which are used by NCEP in their production of forecasts.
RADAR OBSERVATIONS The weather radar provides detailed information about precipitation, winds, and weather systems.
Doppler technology allows the radar to provide measurements of winds through a large vertical depth of the atmosphere, even within “clear air.” This information helps support public and aviation warning and forecast programs. Figure 7-2 shows the weather radar network across the United States.
FAA terminal doppler weather radars (TDWRs) are being installed near a number of major airports around the country. The TDWRs will be used to alert and warn airport controllers of approaching wind shear, gust fronts, and heavy precipitation which could cause hazardous conditions for landing or departing aircraft.
Also installed at major airports are the FAA airport surveillance radars. With this radar, specific locations of six different precipitation intensity levels are available for the routing of air traffic in and about a terminal location. However, the radar’s primary function is for aircraft detection.
LOW-LEVEL WIND SHEAR ALERT SYSTEM (LLWAS) The low-level wind shear alert system (LLWAS) provides pilots and controllers with information on hazardous surface wind conditions (on or near the airport) that create unsafe landing or departure conditions. LLWAS evaluates wind speed and direction from sensors on the airport periphery with center field wind data. During the time that an alert is posted, air traffic controllers provide wind shear advisories to all arriving and departing aircraft.
SATELLITE IMAGERY Visible, infrared (IR), and other types of images (or pictures) of clouds are taken from weather satellites in orbit. These images are then made available on a near-real-time basis to NWS and FAA facilities.
Satellite pictures are an important source of weather information. For more information on satellite products, see Section 3.
December 1999 1-10
COMMUNICATION SYSTEM High speed communications and automated data processing have improved the flow of weather data and products through the nation’s weather network. The flow of weather information within and between agencies is becoming faster as computers and satellites are being used to facilitate the exchange of data.
A new computer-based advanced weather interactive processing system (AWIPS) workstation is being deployed for the NWS. This system is replacing the current system and will allow quicker dissemination of weather information. AWIPS will be linked with the weather radars to provide better detection, observing, and forecasting of weather systems, especially severe weather.
The flow of alphanumeric weather information to the FAA service outlets is accomplished through leased lines to computer-based equipment. The NWS and FAA service outlets exchange weather information through the use of graphic products and alphanumeric information. Graphic products (weather maps) are received by FAA service outlets from NCEP through a private sector contractor.
Alphanumeric information exchanged through telecommunication gateways at NWS and FAA switching centers serves to pass data between the various FAA facilities, NWS, and other users.
USERS The ultimate users of the aviation weather service are pilots and dispatchers. Maintenance personnel may use the service to keep informed of weather that could cause possible damage to unprotected aircraft. Pilots contribute to, as well as use, the service. Pilots should send PIREPs to help fellow pilots, briefers, and forecasters. The service can be no better or more complete than the information that goes into it.
In the interest of safety and in compliance with Title 14, Code of Federal Regulations, all pilots should get a complete weather briefing before each flight. It is the responsibility of the pilot to ensure he/she has all the information needed to make a safe flight.
OBTAINING A GOOD WEATHER BRIEFING When requesting a briefing, pilots should identify themselves as pilots and give clear and concise facts about their flight:
1. Type of flight (VFR or IFR)
2. Aircraft identification or pilot’s name
3. Aircraft type
4. Departure point
5. Proposed time of departure
6. Flight altitude(s)
7. Route of flight
8. Destination
9. Estimated time en route (ETE)
December 1999 1-11 With this background, the briefer can proceed directly with the briefing and concentrate on weather relevant to the flight. The weather information received depends on the type of briefing requested. A “standard” briefing should include:
1. Adverse conditions. Meteorological or aeronautical conditions reported or forecast that may influence a pilot to alter the proposed flight.
2. VFR flight not recommended (VNR). VFR flight is proposed and sky conditions or visibilities are present or forecast, surface or aloft, that, in the judgment of the AFSS/FSS briefer, would make flight under visual flight rules doubtful.
3. Synopsis. A brief statement describing the type, location, and movement of weather systems and/or air masses which might affect the proposed flight.
4. Current conditions. A summary from all available sources reporting weather conditions applicable to the flight.
5. En Route forecast. A summary from appropriate data forecast conditions applicable to the proposed flight.
6. Destination forecast. Destination forecast including significant changes expected within 1 hour before and after the ETA.
7. Winds aloft. Forecast winds aloft for the proposed route; temperature information on request.
8. NOTAMs. Provides NOTAMs pertinent to the flight.
9. ATC delays. Informs the pilot of any known ATC delays and/or flow control advisories that may affect the proposed flight.
10. Request for PIREPs. A request is made if a report of actual inflight conditions would be beneficial or when conditions meet the criteria for solicitation of PIREPs.
11. EFAS. Informs pilots of the availability of Flight Watch for weather updates.
12. Any other information the pilot requests; e.g., military training routes, etc.
An “abbreviated” briefing will be provided at the user’s request:
1. To supplement mass disseminated data.
2. To update a previous briefing.
3. To request that the briefing be limited to specific information.
An “outlook” briefing will be provided when the proposed departure is 6 hours or more from the time of the briefing. Briefing will be limited to applicable forecast data needed for the proposed flight.
The FSS/AFSS’s purpose is to serve the aviation community. Pilots should not hesitate to ask questions and discuss factors they do not fully understand. The briefing should be considered complete only when the pilot has a clear picture of what weather to expect. It is also advantageous for the pilot to make a final weather check immediately before departure if at all possible.
December 1999
MKG DET CH
GRB NR IRK Figure 1-1. EFAS Sites and Communication Outlets.
(DEN) GGW (ABC GUP
CDC) FLIGHT WATCH CONTROL COMMUNICATIONS OUTLETS
LEGEND STATIONS (FWCS) SBF 1-12
December 1999 2-1 Section 2
AVIATION ROUTINE WEATHER REPORT (METAR) The aviation routine weather report (METAR) is the weather observer’s interpretation of the weather conditions at a given site and time. The METAR is used by the aviation community and the National Weather Service (NWS) to determine the flying category - visual fight rules (VFR), marginal VFR (MVFR), or instrument flight rules (IFR) - of the airport, as well as produce the Aviation Terminal Forecast (TAF). (See Section 4.)
Although the METAR code is being adopted worldwide, each country is allowed to make modifications or exceptions to the code for use in that particular country. The U.S.A. reports temperature and dew point in degrees Celsius and continues to use current units of measurement for the remainder of the report.
The elements in the body of a METAR report are separated with a space. The only exception is temperature and dew point that are separated with a solidus (/). When an element does not occur, or cannot be observed, the preceding space and that element are omitted from that particular report. A METAR report contains the following elements in order as presented:
1. Type of report
2. ICAO station identifier
3. Date and time of report
4. Modifier (as required)
5. Wind
6. Visibility
7. Runway visual range (RVR) (as required)
8. Weather phenomena
9. Sky condition
10. Temperature/dew point group
11. Altimeter
12. Remarks (RMK) (as required) The following paragraphs describe the elements in a METAR report. A sample report will accompany each element with the subject element highlighted.
TYPE OF REPORT METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 There are two types of reports: The METAR and the aviation selected special weather report (SPECI).
The METAR is observed hourly between 45 minutes after the hour till the hour and transmitted between 50 minutes after the hour till the hour. It will be encoded as a METAR even if it meets SPECI criteria. The SPECI is a non-routine aviation weather report taken when any of the SPECI criteria have been observed. The criteria are listed in Table 2-1, “SPECI Criteria.”
December 1999 2-2 Table 2-1 SPECI Criteria Report Element Criteria Wind Wind direction changes by 45 degrees or more in less than 15 minutes and the wind speed is 10 knots or more throughout the windshift.
Visibility Surface visibility as reported in the body of the report decreases to less than, or if below, increases to equal or exceeds: 3,2, or 1mile or the lowest standard instrument approach procedure minimum as published in the National Ocean Service U.S Instrument Procedures. If none is published use ½ mile.
RVR Changes to above or below 2,400 feet Tornado, Funnel Cloud, Waterspout When observed or when disappears from sight (ends) Thunderstorm Begins or ends Precipitation When freezing precipitation or ice pellets begin, end, or change intensity or hail begins or ends Squalls When they occur Ceilings The ceiling forms or dissipates below, decreases to less than, or if below, increases to equal or exceeds: 3,000, 1,500, 1,000, or 500 feet or the lowest standard instrument approach procedure minimum as published in the National Ocean Service U.S Instrument Procedures. If none is published use 200 feet.
Sky Condition A layer of clouds or obscuring phenomenon aloft that forms below 1,000 feet Volcanic Eruption When an eruption is first noted Aircraft Mishap Upon notification of an aircraft mishap, unless there has been an intervening observation Miscellaneous Any other meteorological situation designated by the agency, or which, in the opinion of the observer, is critical
ICAO STATION IDENTIFIER METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 The METAR code uses International Civil Aviation Organization (ICAO) four-letter station identifiers that follow the type of report. In the conterminous United States, the three-letter identifier is prefixed with K. For example SEA (Seattle) becomes KSEA. Elsewhere, the first one or two letters of the ICAO identifier indicate in which region of the world and country (or state) the station is located.
Pacific locations such as Alaska, Hawaii, and the Mariana Islands start with P followed by an A, H, or G respectively. The last two letters reflect the specific reporting station identification. If the location’s three-letter identification begins with an A, H, or G, the P is added to the beginning. If the location’s three-letter identification does not begin with an A, H, or G, the last letter is dropped and the P is added to the beginning.
December 1999 2-3 Examples:
ANC (Anchorage, AK) becomes PANC.
OME (Nome, AK) becomes PAOM.
HNL (Honolulu, HI) becomes PHNL.
KOA (Keahole Point, HI) becomes PHKO.
UAM (Anderson AFB, Guam) becomes PGUA.
Canadian station identifiers start with C.
Example:
Toronto, Canada, is CYYZ.
Mexican and western Caribbean station identifiers start with M.
Examples:
Mexico City, Mexico, is MMMX.
Guantanamo, Cuba, is MUGT.
Santo Domingo, Dominican Republic, is MDGM.
Nassau, Bahamas, is MYNN.
The identifier for the eastern Caribbean is T, followed by the individual country's letter.
Example:
San Juan, Puerto Rico, is TJSJ.
For a complete worldwide listing, see ICAO Document 7910, “Location Indicators.”
DATE AND TIME OF REPORT METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 The date and time the observation is taken are transmitted as a six-digit date/time group appended with Z to denote Coordinated Universal Time (UTC). The first two digits are the date followed with two digits for hour and two digits for minutes. If a report is a correction to a previously disseminated erroneous report, the time entered on the corrected report shall be the same time used in the report being corrected.
MODIFIER (AS REQUIRED) METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 The modifier element, if used, follows the date/time element. The modifier, AUTO, identifies a METAR/SPECI report as an automated weather report with no human intervention. If AUTO is shown in the body of the report, AO1 or AO2 will be encoded in the remarks section of the report to indicate the type of precipitation sensor used at the station. A remark of AO1 indicates a report from a station that does not have a precipitation discriminator, and an AO2 remark indicates a report from a station
December 1999 2-4 which has a precipitation discriminator. The absence of AUTO indicates that the report was made manually or the automated report had human augmentation/backup.
The modifier, COR, identifies a corrected report that is sent out to replace an earlier report with an error.
Example:
METAR KLAX 140651Z COR… WIND METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 The wind element is reported as a five-digit group (six digits if speed is over 99 knots). The first three digits are the direction from which the wind is blowing in tens of degrees referenced to true north.
Directions less than 100 degrees are preceded with a zero. The next two digits are the average speed in knots, measured or estimated, or if over 99 knots, the next three digits.
Example:
340105KT If the wind speed is less than 3 knots, the wind is reported as calm, 00000KT. If the wind is gusty, 10 knots or more between peaks and lulls, G denoting gust is reported after the speed followed by the highest gust reported. The abbreviation KT is appended to denote the use of knots for wind speed.
Other countries may use kilometers per hour or meters per second.
If the wind direction is variable by 60 degrees or more and the speed is greater than 6 knots, a variable group consisting of the extremes of the wind directions separated by V will follow the wind group.
Example:
08012G25KT 040V120 The wind direction may also be considered variable if the wind speed is 6 knots or less and is varying in direction (60-degree rule does not apply). This is indicated with the contraction VRB.
Example:
VRB04KT
WIND REMARKS At facilities that have a wind recorder or at automated weather reporting systems, whenever the peak wind exceeds 25 knots, PK WND will be included in the Remarks element in the next report. The peak wind remark includes three digits for direction and two or three digits for speed followed by the time in hours and minutes of occurrence. If the hour can be inferred from the report time, only the minutes are reported.
December 1999 2-5 Example:
PK WND 28045/15 When a windshift occurs, WSHFT will be included in the Remarks element followed by the time the windshift began (with only minutes reported, if the hour can be inferred from the time of observation).
A windshift is indicated by a change in wind direction of 45 degrees or more in less than 15 minutes with sustained winds of 10 knots or more throughout the windshift. The contraction, FROPA, may be entered following the time if the windshift is the result of a frontal passage.
Example:
WSHFT 30 FROPA
VISIBILITY METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Prevailing visibility is reported in statute miles followed by a space, fractions of statute miles, as needed, and the letters SM. Other countries may use meters or kilometers. Prevailing visibility is considered representative of the visibility conditions at the observing site. Prevailing visibility is the greatest visibility equaled or exceeded throughout at least half the horizon circle, which need not be continuous. When visibilities are less than 7 miles, the restriction to visibility will be shown in the weather element. The only exception to this rule is that if volcanic ash, low drifting dust, sand, or snow is observed, it is reported, even if it does not restrict visibility to less than 7 miles.
VISIBILITY REMARKS If tower or surface visibility is less than 4 statute miles, the lesser of the two will be reported in the body of the report; the greater will be reported in the Remarks element.
Example:
TWR VIS 1 1/2 or SFC VIS 1 1/2 Automated reporting stations will show visibility less than 1/4 statute mile as M1/4SM and visibility 10 or greater than 10 statute miles as 10SM.
For automated reporting stations having more than one visibility sensor, site-specific visibility (which is lower than the visibility shown in the body) will be shown in the Remarks element.
Example:
VIS 2 1/2 RWY 11 When the prevailing visibility rapidly increases or decreases by 1/2 statute mile or more during the observation, and the average prevailing visibility is less than 3 statute miles, the visibility is variable.
Variable visibility is shown in the Remarks element with the minimum and maximum visibility values separated by a V.
December 1999 2-6 Example:
VIS 1/2V2 Sector visibility is shown in the Remarks element when it differs from the prevailing visibility and either the prevailing or sector visibility is less than 3 miles.
Example:
VIS NE 2 1/2
RUNWAY VISUAL RANGE (RVR) (AS REQUIRED) METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Runway visual range (RVR) follows the visibility element. RVR, when reported, is in the following format: R identifies the group; followed by the runway heading and, if needed, the parallel runway designator; next is a solidus (/); last is the visual range in feet (meters in other countries) indicated by “FT.” RVR is shown in a METAR/SPECI if the airport has RVR equipment and whenever the prevailing visibility is 1 statute mile or less and/or the RVR value is 6,000 feet or less. When the RVR varies by more than one reportable value, the lowest and highest values are shown with V between them.
Example:
R35L/4500V6000FT When the observed RVR is above the maximum value which can be determined by the system, it should be reported as P6000 where 6,000 is the maximum value for this system. When the observed RVR is below the minimum value which can be determined by the system, it should be reported as M0600 where 600 is the minimum value for this system.
Example:
R27/P6000FT and R12C/M0600FT
WEATHER PHENOMENA METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Weather phenomena is broken into two categories: qualifiers and weather phenomena.