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Transcribed Weather Broadcast

Introduction:

  • Transcribed Weather Broadcasts (TWEBs) are continuous broadcasts of recorded NOTAM and weather information prepared for a 50-nautical mile wide zone along a route and for selected terminal areas
  • TWEBs are recorded on tapes and broadcasted continuously over selected low/medium frequency navigational aids and/or VHF Omni-Directional Range (VOR) facilities
  • TWEBs are provided for Alaska, mentioned in the Aeronautical Information Manual, but have since been removed from Advisory Circular 00-45, Aviation Weather Services, likely due to their limited scope
  • Part of a series of individual taped recordings which are changed as they occur

Transcribed Weather Broadcasts (TWEB) Content:

  • The sequence, source, and content of transcribed broadcast material shall be:
    1. Introduction
    2. Synopsis. Prepared by selected WFOs and stored in Weather Message Switching Center (WMSC)
    3. Adverse Conditions. Extracted from inflight weather advisories, center weather advisories (CWAs), and alert severe weather watch bulletins (AWWs)
    4. TWEB Route Forecasts. Includes the valid time of forecasts prepared by WFOs and stored in the WMSC
    5. Winds Aloft Forecast. Broadcast for the location nearest to the TWEB. The broadcast should include the levels for 3,000 to 12,000 feet, but shall always include at least two forecast levels above the surface
    6. Radar Reports. Local or pertinent radar weather reports (SDs) are used. If there is access to real-time weather radar equipment, the observed data is summarized using the SDs to determine precipitation type, intensity, movement, and height
    7. Surface Weather Reports (METARs). Surface/special weather reports are recorded, beginning with the local reports, then the remainder of the reports beginning with the first station east of true north and continuing clockwise around the TWEB location
    8. Density Altitude. Includes temperature and the "check density altitude" statement for any station with a field elevation at or above 2,000 feet MSL and meets a certain temperature criteria
    9. Pilot Weather Reports (PIREPs). PIREPs are summarized. If the weather conditions meet soliciting requirements, a request for PIREPs will be appended
    10. Alert Notices (ALNOT), if applicable
    11. Closing Statement
  • The information provided varies depending on the type equipment available
  • Forecast is for a 50 NM wide corridor along a line connecting the end points of a route
    • Sustained surface winds (25 knots or greater), visibility, weather and obscuration to vision, sky conditions (coverage and ceiling/cloud heights), mountain obscurement, and non-convective low-level wind shear
    • If visibility of 6 SM or less is forecasted, obstructions to vision and/or weather will be included

Issuance & Validity:

  • TWEB Frequencies Listed in the Chart Supplement U.S.
    TWEB Frequencies Listed in the Chart Supplement U.S.
  • Issued 4 times daily (0200Z, 0800Z, 1400Z, and 2000Z)
  • Valid for 12 hours
  • Frequencies can be found in the Chart Supplement Alaska on local airfields which can receive the service [Figure 1]
  • At selected locations, telephone access to the TWEB has been provided (TEL-TWEB)
    • Numbers are found in the Alaska Supplement of the Chart Supplement Alaska
    • These broadcasts are made available primarily for preflight and inflight planning, and as such, should not be considered as a substitute for specialist-provided preflight briefings
  • Ranges:
    • VOR facilities (108.00 - 117.95 MHZ) have line-of-sight range
    • NDB (L/MF) facilities (190 - 535 kHz) have varying ranges

TWEB Route Forecast Example:

  • 249 TWEB 251402 KISN-KMOT-KGFK. ALL HGTS AGL XCP TOPS. KISN-50NM E KISN TIL 00Z P6SM SKC...AFT 00Z P6SM SCT050 LCL P6SM -TSRA BKN050. 50NM E KISN-KDVL TIL 20Z P6SM SCT070...AFT 20Z P6SM SCT070 LCL SFC WNDS VRB35G45KT 3-5SM TSRA CIGS OVC030-040. KDVL-KGFK TIL 16Z P6SM SCT-BKN020 AREAS 3-5SM BR...AFT 16Z P6SM SCT040

  • 249 - Route number
  • TWEB - TWEB Route Forecast
  • 25 - twenty-fifth day of the month
  • 1402 - Valid 14Z on the twenty-fifth to 02Z on the twenty-sixth (12 hours)
  • KISN-KMOT-KGFK - Route from Williston, ND to Minot, ND to Grand Forks, ND

  • Translation:
    • All heights AGL except cloud tops. KISN-50NM E KISN until 00Z, visibility greater than 6 SM with clear skies. After 00Z, visibility greater than 6 SM with scattered clouds at 5,000' AGL. Local areas of visibility greater than 6 SM, thunderstorm with light rain showers, and broken clouds at 5,000' AGL. 50 NM E KISN-KDVL (Devil's Lake, ND) until 20Z, visibility greater than 6 SM, scattered clouds at 7,000' AGL. After 20Z, visibility greater than 6 SM, scattered clouds at 7,000' AGL, local surface winds variable at 35 gusting to 45 knots, visibility 3-5 SM, thunderstorm with moderate rain showers, overcast ceilings 3,000-4,000' AGL. KDVL-KGFK until 16Z, visibility greater than 6 SM, scattered to broken clouds at 2,000' AGL, areas of visibility 3-5 SM with mist. After 16Z, visibility greater than 6 SM, scattered clouds at 4,000' AGL

TWEB Vicinity Forecast Example:

  • 431 TWEB 021402 LAX BASIN. ALL HGTS MSL XCP CIGS. TIL 18Z P6SM XCP 3SM BR VLYS BKN020...18Z-22Z P6SM SCT020 SCT-BKN100...AFT 22Z P6SM SKC

  • 431 - TWEB vicinity number
  • TWEB - TWEB Forecast
  • 02 - second day of the month
  • 1402 - valid 14Z on the second to 02Z on the third (12 hours)
  • LAX BASIN - The weather conditions in the Los Angeles basin

  • Translation:
    • All heights mean sea level except ceilings. Until 18Z, visibility greater than 6 SM except 3 SM due to mist in the valleys and broken clouds at 2,000' MSL. Between 18Z and 22Z, visibility greater than 6 SM and scattered clouds at 2,000' AGL; also scattered to broken clouds at 10,000' MSL. After 22Z, visibility greater than 6 SM and sky clear
    • A TWEB synopsis forecast is a brief description of the weather systems affecting the route during the forecast valid period. The synopsis describes movement of pressure systems, movement of fronts, upper air disturbances, or air flow

TWEB Synopsis Example:

  • BIS SYNS 250820. LO PRES TROF MVG ACRS ND TDA AND TNGT. HI PRES MVG SEWD FM CANADA INTO NWRN ND BY TNGT AND OVR MST OF ND BY WED MRNG

  • BIS - Bismarck, ND, WFO issuing synopsis and route forecasts
  • SYNS - Synopsis for the area covered by the route forecasts
  • 25 - twenty-fifth day of the month
  • 1402 - Valid from 08Z on the twenty-fifth to 20Z on the twenty-fifth (12 hours)

  • Translation:
    • Low pressure trough moving across North Dakota today and tonight. High pressure moving southeastward from Canada into north-western North Dakota by tonight and over most of North Dakota by Wednesday morning

Conclusion:

References: