Calculating LCL on plan-view plot

Shawn Delaney sd19surf at GMAIL.COM
Thu May 1 08:06:27 EDT 2008

```Dan,

Do you run your own WRF model or are you obtaining the GRIB files
from else where.   The reason that I ask is there is a variable called
"hgtadcl" that can be enabled and it would solve your LCL caluculation
problems quickly.  I am currently working on something similar and here's
what I am using.

'set gxout stat'
'set stat on'
'd tmp2m-273.16'
ret=sublin(result,9)
temp=subwrd(ret,5)
'd dpt2m-273.16'
ret=sublin(result,9)
dewp=subwrd(ret,5)
'd pressfc/100'
ret=sublin(result,9)
pres=subwrd(ret,5)
lclp = Preslcl(temp,dewp,pres)
lclp = math_format(fmt,lclp)

Where Preslcl is the function from Bob Hart's plotskew.gs
**************************************************************************

function Preslcl(temp,dewp,pres)

*-------------------------------------------------------
* Calculate press of LCL given temp & dewp in C and pressure
*-------------------------------------------------------

Tlclk=Templcl(temp,dewp)+273.15
tempk=temp+273.15
theta=tempk*pow(1000/pres,0.286)
plcl=1000*pow(Tlclk/theta,3.48)
return(plcl)

**************************************************************************

I am using the pressfc/100 and this gets me within ~10mb of the BUFKIT LCL
pressure.

This is rough code and hasn't been rehacked. I apologize for the slop in

Shawn
www.expweather.com

On Wed, Apr 30, 2008 at 10:33 PM, Dan Leins <theedge981 at gmail.com> wrote:

> All,
>
> I am trying to calculate and plot LCL heights (in millibars) across an
> entire WRF model domain. I am already accomplishing this on a point-by-point
> basis using Bob Hart's plotskew.gs program, but would like to show the
> heights on a plan-view plot.  Has anyone accomplished this?  I dug pretty
> deep into the plotskew.gs code to determine how Bob calculated LCL heights
> and I was able to adapt a portion of his script for my needs. Here is what
> I've got so far...
>
> 'define tempk=tmpsfc+273.15'
> 'define dewpk=dptprs(lev=1013)+273.15'
> 'define Parta=1/(dewpk-56)'
> 'define Partb=log(tempk/dewpk)/800'
> 'define Tlcl=1/(Parta+Partb)+56'
>
>
> 'define Tlclk=Tlcl'
> 'define tempk=tmpprs+273.15'
> 'define theta=tempk*pow(1000/990,0.286)'
> 'define plcl=1000*pow(Tlclk/theta,3.48)'
> 'd plcl'
>
> This seems to match up "poorly" with the LCL heights indicated on my
> skew-T images, and is just plain horrendous when compared to the LCL heights
> shown in Bufkit. Not that Bufkit is considered the correct solution, but I
> expect to be within the ballpark with my calculations. In some spots I was
> off by over 200mb.
>
> Any thoughts on how I might be able to accomplish this?
>
> Thanks,
> Dan
>
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