Page 69 - AFMAN 15-111, 12 MAR 2019

AFMAN15-111 12 MARCH 2019 69

13.5.5. Pressure Tendency. Determine the pressure tendency by taking a direct reading from
the FBWOS during the 3-hourly observations.

13.5.5.1. If a direct readout of the pressure tendency is unavailable, compute the tendency
using the following procedures:

13.5.5.1.1. Determine the pressure tendency from the 3-hour trend of the ALSTGs.
Using the code figures in Table 13.3, choose the figure which best describes the
character of the change from the trend.

13.5.5.1.2. Determine the difference (without regard to positive or negative) in station
pressure from the 3-hour period to the nearest 0.005-inch by subtracting the current
station pressure from the station pressure from 3 hours ago. Use Table 13.4 to select
the code figure that corresponds to the net change. Note: Limited-duty units can access
the FBWOS software to obtain past pressure information when if available.

13.5.5.2. Consider the 3-hour pressure tendency group (5appp) as indeterminable when
any portion of the group is impossible to determine. Annotate the reason for not reporting
the group in column 90 (e.g. sensor outage).

Table 13.3. Pressure Tendency Character.
General Description Pressure Characterization Code Figure
Increasing, then decreasing 0
Increasing, then steady, or increasing then increasing 1
Atmospheric pressure more slowly
now higher than 3 hours
ago Increasing steadily or unsteadily 2
Decreasing or steady, then increasing; or increasing 3
then increasing more rapidly
Increasing, then decreasing 0
Atmospheric pressure Steady 4
now same as 3 hours ago
Decreasing, then increasing 5
Decreasing, then increasing 5
Decreasing, then steady; or decreasing then 6
Atmospheric pressure decreasing more slowly
now lower than 3 hours Decreasing steadily or unsteadily 7
ago
Steady or increasing, then decreasing; or decreasing 8
then decreasing more rapidly