Stally............
I think that's right.
From what I can remember (and I gotta admit it's not much these days), you can also work out cloud base from LCL, but it's a lot more complicated, and the rule of thumb olderairhead quoted works OK. I dug out some of my old met notes, and here's the comparison between the two methods:
Assuming the following conditions:
Surface pressure (hPa) = 1013
Surface T (STc) = 15
Surface Dewpoint T (SDc) = 12
ESTIMATED CLOUD BASE (ft AGL)
(STc - SDc) *400 = 1,200 ft AGL
Now, if you cross-reference this ‘rule of thumb’ to the calculation for Lifted Condensation Level (LCL), you come up with:
LIFTED CONDENSATION LEVEL
LCL ft AGL = 1,200 ft
Because:
PT (LCL Temp in C) = 12
And:
LCLhPa = 973 hPa
From the following formulas:
Lifted Condensation Level Temp (PT) = ((1/(1/((SDc+273.16) 56)+LOG((STc+273.16)/(SDc+273.16))/800))+56)-273.16
Lifted Condensation Level hPa = ((Surface Pressure*1000)*(((PT+273.16)/(STc+273.16))^(3.5)))/1000
LCL ft AGL = (Surface Pressure - LCL hPa)*30
At least, I
think that's the way it's done
