NZ Weather Forum

just looking at the following..
why is it that the lapse rate line drawn from the surface temp reading seems to be taken from waaay to high a reading? shouldnt it be drawn from the base of the red temperature line?

I'd like to know that for sure too, I have assumed that is from modelling of the expected Tmax and DPmax for some following period, does seem to be close to the GFS model surface predictions if a little high at times

The BOM site gives the observed sounding. And as Ricky suggests, the surface tt/dp are a forecast and hence the SALR is the forecast. I'm not keen on this methodology. If you are going to apply forecast surface parameters then the upper air sounding needs to be a forecast as well, not an historical observed sounding.

From my understanding it looks correct because the surface temperature intersects (almost) the constant mixing ratio line of the surface dewpoint and then the dry adiabatic follows back to the surface from the intersection... and hence it's around 26-28C which is the convective temperature needed for free convection to occur (dependant on other factors though).

The forecast surface temp/dp being used there is extrapolated from the sounding. But the numbers ended up wrong as our max temp was more like 21C and dewpoint 15C.