JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Using TAFs For Flight Planning
For flight planning purposes, an aviator must consider the worst weather conditions that fall
within the period of 1 hour prior to the planned estimated time of arrival (ETA) up to but not
including 1 hour after ETA, for a total of a 2-hour window. As an example, assume an ETA of
1620Z at NAS Whiting, use the TAF in Figure 6-27, and follow these simple steps:
1. Determine the arrival window, which would be 1520 – 1720Z in this case.
2. Evaluate the whole TAF to determine the forecast time period to which each line applies. If
any part of the 2-hour ETA window falls within the time period of that line, then the
information in that line will be applicable. In this case, lines 2, 3, and 4 each cover part of
the 1520 – 1720Z window.
3. Finally, mix and match the weather from each line for use in flight planning, building a set
of the worst-case scenario for each group: strongest winds, lowest visibility, worst weather,
lowest ceiling, and lowest altimeter.
Another technique is to lay out a timeline in order to dissect and categorize the applicability of
the various lines of a TAF. By drawing labeled brackets around the times to which each line
applies and around the 2-hour ETA window, it becomes easier to see which lines of the TAF are
applicable. This technique is especially useful when planning a mission with numerous
approaches or en route delays, or when the weather will be a deciding factor for the landing time.
Figure 6-28 shows a diagram of this technique for our example.
Figure 6-28 — TAF Timeline Example
This technique also requires the flight crew to apply the 2nd, 3rd, and 4th lines of the forecast.
Using either method, they would look for the worst weather among each of these lines and plan
for:
• Winds 230 degrees at 15 knots gusting to 25 knots (23015G25)
• Visibility 6 miles in haze (9000 HZ)
• Scattered cumulonimbus at 2500' AGL, scattered clouds at 8000' AGL, and broken
clouds at 25,000' AGL, with ceiling at 25,000' (SCT025CB, SCT080, BKN250)
• Altimeter setting 29.96 inches (QNH2996INS)
• Frequent moderate clear air turbulence from the surface up to 4000 feet (530004)
• Rain showers in the vicinity (VCSHRA)
6-26 Version 3.2/Dec 08