H o w e v e r, any computer forecast is dependent upon the data used as input. While a
dense network of observations existed over the land areas of the Nort h e rn Hemisphere ,
many remote areas of the globe—particularly the oceans—were not routinely
observed. The satellite era, beginning in the early 1960’s, provided the capability for
global weather observations. These observations further improved computer forecasts.
In the future, advances in observations, computing technology, and remote sensing will
continue to drive advances in forecast meteoro l o g y, particularly in the areas of longer
range (greater than 6 day) forecasts and local, severe weather forecasts. The inform a t i o n
now becoming available from Doppler radars and the new generation of geosynchro-
nous satellites will also improve the theoretical understanding of the atmosphere.
The polar front theory gained general acceptance by World War II because it was able
to explain the observed weather associated with mid-latitude disturbances. In figure
14a, vertical cross-sections through the cold and warm fronts are shown. The cloud
patterns that are associated with the different regions of the disturbance are a function
of the vertical structure of the atmosphere at each location. The cold front is character-
ized by cool, dense air which burrows under warm, moist air. As we will see in more
detail later, rapid lifting and cooling of moist air produces the thunderstorms that fre-
quently accompany frontal passages, and are often large enough to be fully detected
by satellite images. Conversely, the warm front consists of warm air rising gradually
over slightly cooler air. This slowly rising air produces layered, or stratiform, clouds.
figure 14a. GOES image of cyclone, April 12, 1994 0100 CDT.
image courtesy of M. Ramamurt h y, University of Illinois, Urbana/Champaign
C ross sections are A-B (cold front) and C-D (warm front).
ABCD