FNMOC provides a large number of charts for
dissemination to shore and fleet units. These include
analysis and prognostic charts ranging from
subsurface oceanographic charts to depictions of the
troposphere, as well as a number of specialized
charts. A complete listing of the these charts is
contained in The Numerical Environmental Products
Manual, volume III (Environmental Products),
APPLICATION OF SATELLITE IMAGERY
As a further aid, satellite imagery can also be used
in preparing prognostic charts. The availability of
useful satellite data will vary with time and area.
LEARNING OBJECTIVES: Evaluate various
objective forecasting techniques, including
relationships for the movement of troughs and
ridges. Forecast intensity of troughs and ridges.
Forecast the movement of upper level features.
Forecast the intensity of upper level and
associated surface features. Lastly, forecast the
formation of upper level and associated surface
Experience in itself is not always enough to forecast
the movement and/or intensity of upper air systems, but,
couple the forecasters experience with basic objective
techniques and a more accurate product will be
FORECASTING THE MOVEMENT OF
TROUGHS AND RIDGES
Techniques covered in this section apply primarily
to long waves.
Some of the techniques will be
applicable to short waves as well. A long wave is by
definition a wave in the major belt of westerlies, which
is characterized by large length and significant
amplitude. (See the AG2 TRAMAN, volume 1, for a
discussion of long and short waves.) Therefore, the first
step in progging the movement and intensity of long
waves is to determine their limits. There are several
basic approaches to the progging of both long and
short waves. Chiefly, these are extrapolation,
isotherm-contour relationship, and the location of the jet
maximum in relation to the current in which it lies.
The past history of systems affecting an area of
interest is fundamental to the success of forecasting.
Atmospheric systems usually change slowly, but,
continuously with time. That is, there is continuity in
the weather patterns on a sequence of weather charts.
When a particular pressure system or height center
exhibits a tendency to continue without much change, it
is said to be persistent. These concepts of persistence
and continuity are fundamental forecast aids.
The extrapolation procedures used in forecasting
may vary from simple extrapolation to the use of more
complex mathematical equations and analog methods
based on theory. The forecaster should extrapolate past
and present conditions to obtain future conditions.
Extrapolation is the simplest method of forecasting both
long and short wave movement.
Simple extrapolation is merely the movement of the
trough or ridge to a future position based on past and
current movement and expected trends. It is based on
the assumption that the changes in speed of movement
and intensity are slow and gradual. However, it should
be noted that developments frequently occur that are not
revealed from present or past indications. However, if
such developments can be forecast by other techniques,
allowances can be made.
Extrapolation for short periods on short waves is
The major disadvantage of
extrapolating the long period movement of short waves
or long waves is that past and present trends do not
This can be seen when we
consider a wave with a history of retrogression. The
retrogression will not continue indefinitely, and we must
look for indications of its reversal; that is, progressive
The forecaster should always examine the long
waves for the isotherm-contour relationships, and then
apply the rules for the movement of long waves. These
rules are covered in the AG2 TRAMAN, volume 1.
These rules are indicators only, but if they confirm or
parallel other applied techniques, they have served their
purpose. A number of observations and rules are stated
regarding the progression, stationary characteristics, or