Thunderstorms and volcanic ash will always be included regardless of the visibility. Cloud bases can be described either in MSL or AGL (CIGS or BASES). It depends on which statement is used: "ALL HGTS MSL XCP CIGS." or "ALL HGTS AGL XCP TOPS". Use of "AGL", " CIGS", and "BASES" should be limited to cloud bases within 4,000 feet of the ground. Cloud tops, referenced to MSL, should also be forecasted following the sky cover when expected to be below 15,000 MSL using the sky cover contractions FEW, SCT, or BKN. Nonconvective low-level wind shear will be included when the TAF for the airport involved has issued a nonconvective low-level wind shear forecast. Expected areas of icing and turbulence will not be included.
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
All heights AGL except cloud tops. KISN-50NM E KISN until 00Z, visibility greater than 6SM with clear skies. After 00Z, visibility greater than 6SM with scattered clouds at 5,000 feet AGL. Local areas of visibility greater than 6SM, thunderstorm with light rain showers, and broken clouds at 5,000 feet AGL. 50 NM E KISN-KDVL (Devil’s Lake, ND) until 20Z, visibility greater than 6SM, scattered clouds at 7,000 feet AGL. After 20Z, visibility greater than 6SM, scattered clouds at 7,000 feet AGL, local surface winds variable at 35 gusting to 45 knots, visibility 3-5SM, thunderstorm with moderate rain showers, overcast ceilings 3,000-4,000 feet AGL. KDVL-KGFK until 16Z, visibility greater than 6SM, scattered to broken clouds at 2,000 feet AGL, areas of visibility 3-5SM with mist. After 16Z, visibility greater than 6SM, scattered clouds at 4,000 feet AGL.
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
- TTWEB - 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
All heights mean sea level except ceilings. Until 18Z, visibility greater than 6SM except 3SM due to mist in the valleys and broken clouds at 2,000 feet MSL. Between 18Z and 22Z, visibility greater than 6SM and scattered clouds at 2,000 feet AGL; also scattered to broken clouds at 10,000 feet MSL. After 22Z, visibility greater than 6SM 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.
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)
Low pressure trough moving across North Dakota today and tonight. High pressure moving southeastward from Canada into northwestern North Dakota by tonight and over most of North Dakota by Wednesday morning.
