758 
on the Texas coast. Further deductions can be made 
from the distribution of clouds and precipitation. 
The solenoidal field on the east coast of contents, 
in the Northern Hemisphere, is favorable for wave 
development in connection with stationary fronts. Tech- 
niques for handling cyclogenesis of this type have been 
described by Miller [35]. Byers postulates that no really 
primary cyclone forms entirely independently of other 
nearby disturbances and this appears to be correct for 
extratropical regions. The arrival of even a weak fall in 
pressure over a stationary front will almost always 
result in strong cyclogenesis. 
Cyclogenesis tends to occur where there is a concen- 
tration of isotherms aloft (5000—15,000 ft) which pro- 
vides considerable potential energy, and the wind field 
is favorable (7.e., the wind blows across the isobars). 
Cyclogenesis (anticyclogenesis) tends to occur on the 
warm (cold) side of an area where isotherms are packed. 
Baum [2] has described the Scherhag divergence 
theorem and states, on the basis of some informal ex- 
perimentation with it, that it merits a trial by fore- 
casters in the United States. 
Anticyclogenesis can be detected by the pressure 
tendencies. For the forecasting of anticyclogenesis up- 
stream, the transition from a cold to a warm high with 
resultant blocking should be carefully watched. 
Frontogenesis and frontolysis are not, as a rule, 
particularly troublesome although there is, perhaps, a 
tendency to expect frontolysis too quickly. Over land 
areas, the forecaster must frequently deal with warm 
frontogenesis dynamically induced in the lee of mountain 
ranges and, less frequently, developing between two 
highs. The latter usually has some previous history. 
Important cold frontogenesis will occur in polar re- 
gions with the development and initial southward surge 
of arctic air masses. 
The prognosticator finally completes the approxi- 
mations of the future positions of fronts and the posi- 
tions and intensities of the pressure centers. He then 
tests the consistency of these approximations with the 
upper-air synoptic and prognostic charts and the indi- 
cated extrapolation of mean isotherms between the 1000- 
and 700-mb surfaces. If inconsistencies appear, one or 
more of the factors used in the preparation of the 
surface charts has been incorrectly calculated or inter- 
preted. Inconsistencies must be resolved by further 
checking or by according the greatest weight to the 
factors of greatest certainty. 
In an effort to derive an objective method of fore- 
casting the surface pressure pattern, Haurwitz and col- 
laborators [28] investigated a number of procedures 
based on advection. Isopyenic lines were drawn for five 
levels between sea level and 14 km and forecasts of the 
density changes at these levels were prepared on the 
hypothesis that air moves with the geostrophic wind 
velocity, preserving its density. After allowance had 
been made for the thickness of each layer, the density 
changes were added together to obtain the sea-level 
pressure change. Vertical motions were not considered 
in the study. Correlation coefficients of significance were 
not obtained. This does not imply, however, that the 
WEATHER FORECASTING 
subjective evaluation of advection in forecasting pres- 
sure change is not a helpful procedure. More recent re- 
search by Houghton and Austin [30], while furthering 
our knowledge of the mechanism of pressure changes, 
has failed, so far, to provide new tools for forecasting 
pressure changes. 
No purely objective techniques are available for the 
preparation of prognostic charts and thus procedures 
remain generally subjective. 
Vederman [55] has listed the techniques used in the 
preparation of prognostic charts and includes (1) verti- 
cal extent of highs and lows, and (2) temperature and 
height changes at various constant-pressure surfaces in 
addition to those discussed in this section. Some other 
procedures developed by American meteorologists have 
been described by Fulks and collaborators [23]. 
STEPS IN FORECASTING THE WEATHER 
Preforecast Study. The organization of forecasting at 
a district forecast center should provide for at least 
two days’ study of past maps each month. There are 
important month-to-month and seasonal variations in 
weather sequences, frequency of certain weather types, 
depth of surface heating, effect of nearby water areas, 
and many other similar influences which the forecaster 
must keep in mind. The forecaster can best integrate 
them in his mind by, for example, at the end of the 
month, running through several past years’ charts for 
the followmg month and preparimg practice forecasts 
for one or two areas or cities in his district. 
Preliminary Steps in Forecasting. A certain amount 
of preparatory work is required for a forecaster when 
coming on duty. This may include: 
1. Inspection of weather charts prepared since he 
was last on duty, or if he has been absent for an extensive 
period, for the last four to seven days, in order that he 
may bring himself up to date on the gneve bing type of 
weather. 
2. Briefing by the forecaster gomg off duty, who 
describes and explains the weather now in progress, the 
forecasts in effect and the basis for them. 
3. Analysis of radiosonde observations from stations 
in the forecast district and in adjacent areas from which 
weather is approaching, for the purpose of ascertaming 
stability, cloud decks, freezing level, temperature and 
moisture changes, structure of moist layers, and indi- 
cated maximum temperature. 
4. Inspection of the 850-mb chart for moist tongues, 
the general moisture pattern, advection of warm and 
cold air, and upslope areas. 
5. Amalreis of the 700-mb chart for depth of moisture, 
trends toward increased zonal or meridional flow, in- — 
tensification of troughs and ridges, possible develop- 
ment of closed circulations, advection of colder and 
warmer air, pools of warm and cold air, and steering; 
checking the 700-mb prognostic chart from the weather 
central and modifying it as indicated. 
6. Checking of the 500-mb and 200-mb charts, par- 
ticularly the 500-mb, for the same features as given 
above for the 700-mb chart, except for moisture, which 
is not especially significant at the higher elevations. A 
Le 
