snip
It will be wrong when the lapse rate is different from standard, itself a
significant indicator that something is afoot. When I read a METAR I often
compare the observed ceiling to the surface temp to see if it's close to the
2C/1000 rule or not. If they're lower than they "should be" then you can bet
there's a good chance of convection, turbulence, and generally fast-changing
conditions. At least in New England this really only holds during the warmer
months though.

-cwk.


Would you elaborate on this please? Are you talking about comparing the temp/dewpoint spread to the ceiling at
2C/1000?

I think he's suggesting a comparison between the observed ceiling and the number
of feet you get by dividing the temp/dewpoint difference by 2 and multiplying by
1000. (AGL in both cases.)

If the actual and predicted ceilings are different then the lapse rate is not 2
-- not standard. If the bases are lower, then the lapse rate is deduced to be
larger than 2. And vice versa.