CHAPTER 3
FORECASTING SURFACE SYSTEMS
With the upper air prognosis completed, the next
step is to construct the surface prognostic chart Since
more data is available for the surface chart, and this chart
is chiefly the one on which you, the Aerographer’s Mate,
will base your forecast, you should carefully construct
the prognosis of this chart to give the most accurate
picture possible for the ensuing period. The surface
prognosis may be constructed for periods up to 72 hours,
but normally the period is 36 hours or less. In local
terminal forecasting, the period may range from 1 to 6
hours.
Construction of the surface prognosis consists of the
following three main tasks.
1. Progging the formation, dissipation, movement,
and intensity of pressure systems.
2. Progging the formation, dissipation, movement,
and intensity of fronts.
3. Progging the pressure pattern; that is, the
isobaric configuration and gradient.
From an accurate forecast of the foregoing features,
you should be able to forecast the weather phenomena
to be expected over the area of interest for the forecast
period.
FORECASTING THE FORMATION OF
NEW PRESSURE SYSTEMS
LEARNING OBJECTIVES Recognize
features on satellite imagery and upper air
charts conducive to the formation of new
pressure systems.
The central problem of surface prognosis is to
predict the formation of new low-pressure centers. This
problem is so interrelated to the deepening of lows, that
both problems are considered simultaneously when and
where applicable. This problem mainly evolves into
two categories. One is the distribution of fronts and air
masses in the low troposphere, and the other is the
velocity distribution in the middle and high troposphere.
The rules applicable to these two conditions are
discussed when and where appropriate.
For the principal indications of cyclogenesis,
frontogenesis, and windflow at upper levels, refer to the
AG2 TRAMAN, volume 1.
The use of hand drawn analyses and prognostic
charts in forecasting the development of new pressure
systems is in many cases too time-consuming. In most
instances, the forecaster will generally rely on satellite
imagery or computer drawn prognostic charts.
SATELLITE IMAGERY — THE
FORMATION OF NEW PRESSURE
SYSTEMS
To most effectively use satellite imagery, the
forecaster must be thoroughly familiar with imagery
interpretation. Also, the forecaster must be able to
associate these images with the corresponding surface
phenomena.
The texts, Satellite Imagery Interpretation in
Synoptic and Mesoscale Meteorology, NAVEDTRA
40950, and A Workbook on Tropical Cloud Systems
Observed in Satellite Imagery, volume 1, NAVEDTRA
40970, contain useful information for the forecaster on
the subject of satellite interpretation. The Naval
Technical Training Unit at Keesler AFB, Mississippi,
also offers the supplemental 2-week course, Weather
Satellite Systems and Photo Interpretation (SAT
INTERP).
The widespread cloud patterns produced by
cyclonic disturbances represent the combined effect of
active condensation from upward vertical motion and
horizontal advection of clouds. Storm dynamics restrict
the production of clouds to those areas within a storm
where extensive upward vertical motion or active
convection is taking place. For disturbances in their
early stages, upward vertical motion is the predominant
factor that controls cloud distribution. The
comma-shaped cloud formation that precedes an upper
tropospheric vorticity maximum is an example. Here,
the clouds are closely related to the upward motion
produced by positive vorticity advection (PVA). In
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