METEOROLOGY — FORECASTING 239 
plan position indicator [PPI] scope appearance of 
ground clutter return. The oscilloscope screen was 
assuined segmented into eight 45° sectors, and the 
maximum range on a ground target in each sector was 
noted hourly during periods of operation. In an at- 
tempt at correlating the radar performance with the 
existing meteorological conditions, a classification 
system was devised in which each distinguishable 
propagation condition was assigned a single number. 
After collecting observations for some time from each 
unit the data were examined, and an average of the 
normal pattern was chosen as the standard, or class 
1, type of propagation. Averages of reported increased 
ranges in various sectors were calculated, while the 
azimuthal variations due to shadow effects of sur- 
rounding terrain, coast line and obstructions were 
Ficure 3A. Typical Class 1 pattern, P-band SCR-271, 
Crystal River. Grid squares are approximately 5 miles 
on a side. 
Ficure 3B. Typical Class 2 pattern, P-band SCR-271, 
Crystal River. 
Ficure 4A. Class 3 pattern, SCR-271, Crystal River. 
Coast line well painted in. 
Ficure 4B. Typical Class 4 pattern, SCR-271, Crystal 
River 
considered. The consistency with which various in- 
creased range averages were attained determined the 
number of classes of propagation assumed for each 
unit. On the assumption that the meteorologist could 
forecast and correlate M-curve types corresponding 
with four types of propagation, four such propaga- 
tion classes were chosen for the S-band V beam and 
the P-band SCR-271 at Crystal River. Figures 3 and 
4 show the four classes of propagation as defined for 
the SCR-271 at Crystal River. The class 4 picture 
definitely shows the Florida coast-line detail painted 
in. Observations from most of the other units, how- 
ever, were classed only as 1 (standard) and 2 (non- 
standard) propagation because of the radar shadows 
of certain topographical features near their sites. Due 
possibly to the peninsular situation of Florida, it was 
