44, TECHNICAL SURVEY 
RADAR FORECASTING 
The forecasting of propagation conditions for early 
warning radars is of great operational significance be- 
cause ranges for airplane as well as ship targets often 
vary by as much as a factor of 2 or more depending 
on the weather conditions. Forecasting is based on 
the general meteorological principles presented above 
which can be organized into a system of standard 
procedures for the prediction of propagation in a 
given area.?44/253,295 Jt is usually quite difficult to 
make a quantitative forecast of such parameters as 
duct height, but this has been tried with a fair 
degree of success. 
A radio forecast is made by first taking the general 
synoptic weather situation as presented on a weather 
map and including such upper air data as may be 
available. Usually one forecast cannot be applied to 
more than a limited area of specific local conditions; 
fortunately such a forecast is in general adequate for 
the area covered by one or a few radar sets. The 
formation of ducts depends principally on the tem- 
perature difference between the air and the ground 
or sea surface and on the humidity.of the air. Data 
on sea temperature, which is usually fairly constant, 
are collected while over land it is necessary to obtain 
data an the diurnal variation of the soil temperature. 
Wind velocities may be gathered from the weather 
map, and the trajectory of the air previous to and 
during the forecast period can then be determined. 
If the relative humidity of the air is known, it is 
possible from the theories at hand to draw estimated 
curves of the temperature and moisture variation 
in the lowest layers. From these an estimated M 
curve is obtained. The success of this method depends 
to a large degree upon the familiarity of the fgrecaster 
with local conditions. 
The forecasting of advective ducts over the ocean 
is the main problem in which radio forecasting 
requires other tools than those used for ordinary 
weather forecasting; but most other problems’ are 
closely similar to those presented by conventional 
practice, among which are the forecasting of subsi- 
dence from upper air meteorological data, the 
forecasting of nocturnal temperature inversions in 
dry climates, and the forecasting of standard 
propagation conditions. 
In order to facilitate weather forecasting in the 
Pacific, where data have been very scanty during 
the war, a system has been worked out whereby 
localities in the Pacific area are compared to those 
of closely similar climatic and meteorological charac- 
ter in the Atlantic. A rough estimate of propagation 
conditions to be expected may be derived there- 
from. ?>>215 
