Try the following.
'Temp H500' sets the temperatures for the 500 mB level.
If you replace this by 'TEMP H100' the fills will be drawn for the temperatures at the 100 mB level; TEMP H925 for the 925 mB level and so on ...
Otherwise, the code is the same as for Sea Level temperature fills, where you use 'TEMP'.
Good luck,
Les
ERASE
# Store actual temperatures for the 500 mB level
ANALYZE,STOR=1 TEMP H500
#Store ZERO - (TEMP/1000 is approximately ZERO)
analyze,STOR=2 SDVC=1:1000
# Subtract temperature from 0 - converts -T to +T - plot in 'cool' colour
ANALYZE,OVER FILL COLOR=000:239:255 GRTN=0 SDIF=2:1
ANALYZE,OVER FILL COLOR=000:255:209 GRTN=0 SDIF=1:2
ANALYZE,OVER FILL COLOR=000:154:255 GRTN=5 SDIF=2:1
ANALYZE,OVER FILL COLOR=159:255:000 GRTN=5 SDIF=1:2
ANALYZE,OVER FILL COLOR=000:080:255 GRTN=10 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:255:000 GRTN=10 SDIF=1:2
ANALYZE,OVER FILL COLOR=082:000:255 GRTN=15 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:204:000 GRTN=15 SDIF=1:2
ANALYZE,OVER FILL COLOR=179:000:255 GRTN=20 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:161:000 GRTN=20 SDIF=1:2
ANALYZE,OVER FILL COLOR=242:000:242 GRTN=25 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:097:000 GRTN=25 SDIF=1:2
ANALYZE,OVER FILL COLOR=204:000:204 GRTN=30 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:014:014 GRTN=30 SDIF=1:2
ANALYZE,OVER FILL COLOR=153:000:153 GRTN=35 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:110:110 GRTN=35 SDIF=1:2
ANALYZE,OVER FILL COLOR=122:000:116 GRTN=40 SDIF=2:1
ANALYZE,OVER FILL COLOR=255:153:153 GRTN=40 SDIF=1:2
#basemap
ANALYZE,CONT CINT=5 COLOR=100
100 LINE=1
ANALYZE,CONT COLOR=255:255:255 EQUA=0 LINE=1