Environmental computer systems, such as TESS,
have built in programs that will plot a complete upper-
air observation report on a background representative of
the Skew T, Log P and calculate many values routinely
found by using the diagram. However, the computer
plot does not provide the overall detail provided by a
paper copy of the Skew T chart. An actual DOD-WPC
9-16 Skew T, Log P Diagram should be available at
your command.
Detailed information on plotting, analysis, and
forecasting techniques using the Skew T, Log P
diagram is contained in NAVAIR 50-lP-5, The Use of
the Skew T, Log P Diagram in Analysis and
Forecasting.
DIAGRAM FAMILIARIZATION
The Skew T, Log P diagram is a set of curved and
straight lines that graphically represent the physical
processes that occur in the atmosphere as moist air rises
and descends. In the upper-right comer of each diagram
is a detailed explanation of each set of lines on the
diagram. The Skew T, Log P diagram is printed in
black, pastel green, and light brown. DOD WPC
(Department of Defense, Weather Plotting Chart) 9-16
is the basic chart. Several different variations of the
chart are available and listed in the NIMA Catalog. All
versions have the basic plotting scales discussed below,
superimposed over each other (fig. 4-24). These scales
are used as guides for plotting observed information,
and then for deriving other values when analyzing the
plotted information. The use of the Skew T, Log P
diagram allows analysts to find important values and
indicators without having to preform complex
thermodynamic calculations.
Isobar Scale
Isobars are lines of equal pressure. The scale is a
series of horizontal, solid brown lines spaced
logarithmically at 10-hectopascal intervals from 1050
Figure 4-24.—A portion of a Skew T, Log P diagram (version 9-16-1) showing the superimposed plotting scales.
4-25
