B5-26 
PREPARATION OF CHARTS 
Project the lifting condensation point found in(b)up the moist 
pseudo-adiabatic curve which passes through it to the 500 mb 
level. Read the temperature (to the nearest tenth of degree) 
corresponding to that point on the curve. 
Subtract algebraically the temperature found in (c) from the 
temperature of the sounding at the 500 mb level. The differ- 
ence represents the stability index. Record this value to the 
nearest whole degree, with appropriate algebraic sign, to the 
right of Data Block "A'' on WBAN-31A and just below the 500 
mb constant pressure data block. Draw a circle around the 
value. 
NOTE: When the temperature found in (c) is lower than the tem- 
perature the sounding at 500 mb., the index is positive; when it is 
higher the index is negative. 
e. 
Examples: 
a. 
The 
1-1-69 
Code the index in accordance with separate instructions. 
If; station altitude 360 gpm 
base level 850 mb. 
dewpoint 6.8° 
temperature 7.4° 
raob temperature at 500 mb -15.4° 
computed condensation temperature 6.6° 
temperature on pseudo-adiabatic curve at 500 mb -19.6° 
stability index is then: 
-15.4° - (-19.6°) = +4.2°or+4°tothe nearest whole degree and 
entered 
If: station altitude 1619 gpm 
base level 750 mb 
dewpoint 7.1° 
FMH#3 
