Ceilings are always above ground level.
The Synopsis is a brief statement of frontal and pressure systems affecting the route during the forecast valid period. The TWEB route forecasts and synopses are issued by the WFOs three times per day. Route forecasts are valid for 15 hours. This schedule provides 24-hour coverage with most frequent updating during the hours of greatest aviation activity. SYNS - Synopsis for the area covered by the route forecasts.