METEOROLOGICAL ANALYSIS IN MIDDLE LATITUDES 721 
casting has been under consideration by many investi- 
gators during the past few years [5, 17|. The three 
factors which have been found to be most important 
for precipitation forecasts are the orientation and curva- 
ture of the flow patterns at the altostratus level (about 
700 mb), the location of areas of pressure fall at sea 
level, and the extension of warm-air advection near the 
850-mb level. Since the detection of advection between 
700 mb and the surface ean be accomplished at a glance 
1020 9BUd20 1023 
1035 —~ 
re 
0630Z OCTOBER 24,1949 
AAAACOLD FRONT 
@aaaWARM FRONT 
MyAy stationary Front | / 
aAaA OCCLUDED FRONT i 
i} 
3001014 
AAAAGOLD FRONT ALOFT 
all three of these charts the relation between the two 
sets of isopleths and the weather and cloud data throws 
into full relief the following information: the principal 
activating mechanisms of precipitation and cloudiness, 
the aréal extention of warm and cold air advection, the 
movement and spatial distribution of pressure-fall areas 
on the surface map with respect to the steering flow 
aloft, the relationship between moisture sources and the 
orientation of the upper flow, the likelihood of vertical 
996 7000 
1008 1905( 1002 999 
996 
de EAN 
\s K< —— 
NS aes =i 
w ie mI 
1011 1040@n 1014 ( 
x 
Fre. 2—Combined sea-level and 700-mb analysis for the United States at 0630Z, October 24, 1949. 
when the charts of these two levels are superimposed, 
and since the 700-mb contours represent the air flow at 
the level where most of the altostratus rain clouds are 
centered, the 700-mb chart superimposed on the sea- 
level chart is considered the most useful combination mm 
giving a comprehensive view of the weather prospects 
in stations where issuance of 24- and 48-hr forecasts to 
the general public is the prime function. The authors 
feel that this is such an important subject that some 
examples of the combined analysis of surface and upper- 
level charts are presented here in detail. 
These examples include three consecutive sea-level 
charts with the corresponding 700-mb contours super- 
imposed upon them, constructed for 24-hr intervals. On 
displacement of an air mass above a front, and the 
areas along fronts where the meteorological properties 
of the atmosphere are most conducive to wave for- 
mation. 
The most striking feature on the first of these ex- 
amples (Fig. 2), is the large area of rain in the southern 
Great Plains States. The strong easterly flow indicated 
by the sea-level isobars in this area leads to the tentative 
assumption that the rain is caused by topographic up- 
slope motion of the cold air mass as it moves toward the 
higher land areas of Colorado, western Texas, and 
western Kansas. In view of the configuration of the 
upper flow, however, it seems quite evident that the 
warm moist tropical air from the Gulf of Mexico is 
