ISENTROPIC ANALYSIS 163 
6 39 SY: Yj 
KEY 
Fic. 3. SYNOPTIC CHART OF SURFACE WEATHER OVER UNITED STATES AT 7:30 
am., EK. S. T., JUNE 24, 1987. (Cold fronts are indicated by heavy solid 
lines, warm fronts by dotted lines, and occluded fronts by alternately 
dashed and dotted lines. The hatching indicates areas where precipita- 
tion is falling at the time of observation. Air-mass symbols are those 
customarily in use in the United States and introduced at the Massachu- 
setts Institute of Technology. Surface observations at or near aerological 
stations [circles] are entered in the customary manner. To the right of 
the circles from top to bottom: temperature and dew point (°F), pressure, 
and precipitation. Winds are indicated by arrows, the numbers of half- 
barbs corresponding to Beaufort numbers of force. To the left of the 
station are the clouds in international symbols, and the pressure char- 
acteristic and change in the preceding three hours.) 
