Heat Index plots in GRADS

[Kevin M Levey]

THU 10MAY07: 0940PDT



Hi



I was wondering if anyone has done Heat Index (HI) plotting in GRADS? I have
the correct HI formula, but I get erroneous output since GRADS is
calculating the HI at every point for every temp. However, HI should only be
calculated for temps > 80F (26C). So, what happens is, GRADS calculates the
HI for values < 80F (< 26C) when these points should NOT have HI values and
the plot is a mess - showing both valid and non-valid HI values. I am pretty
adept using GRADS, however, I've been working on this for days and can't
seem to figure out how to get GRADS to ignore values below the HI threshold.
Has anyone come across this problem before? I am using GFS data.



Many thanks!



Below is a typical GRADS script for producing HI.



Regards



Kevin M Levey, MSc (University of Cape Town)

Director of Meteorological Operations

CustomWeather, Inc

San Francisco, CA, USA



 <http://www.1stweather.com> http://www.1stweather.com

 <http://www.myforecast.com> http://www.myforecast.com

 <http://www.customweather.com> http://www.customweather.com









*002hr 0 DAY 1

'set mpdset hires'

'set mpt * off'

'set mpt 0 1 1 6'

'set mpt 1 1 1 1'

'set display color white'

'clear'

'open /prod/custom/intModel/GFS/temp/gfs_001.ctl'

'set xsize 800 600'

'set lat -36 -16'

'set lon 10 36'

'set map auto 1 1 6'

'set lev 1000'

'define temp = TMP2M - 273.16'

'define tempF = (temp *1.8) +32'

'define v = VGRDprs*3.6'

'define u = UGRDprs*3.6'

'define windkmh = mag(u,v)'

'define rh = RH2M'

'define HI = ((-42.379 + (2.04901523*tempF) + (10.14333127*rh) -
(0.22475541*tempF*rh) - (0.00683783*pow(tempF,2)) - (0.05481717*pow(rh,2)) +
(0.00122874*pow(tempF,2)*rh) + (0.00085282*tempF*pow(rh,2)) -
(0.00000199*pow(tempF,2)*pow(rh,2)))-32)*5/9'

*draw heat index map

'run /prod/custom/intModel/GFS/scripts/rgbset_HI1.gs'

'set gxout shaded'

'set cint 2.5'

'set cmin 40'

'set csmooth on'

'set grads off'

'd HI'

'set ccolor 0'

'set gxout contour'

'set cint 2.5'

'set cmin 30'

'set csmooth on'

'd HI'

'run /prod/custom/intModel/GFS/scripts/SA_cities.gs'

'run /prod/custom/intModel/GFS/scripts/cbarn'



'draw title HEAT INDEX (C)\INIT: 12UTC 13MAR07
VALID: 02H00 TUE 13 MAR 2007'

'printim /prod/custom/intModel/GFS/temp/GFS_HEAT_INDEX_PLOT1.png png x800
y600'

'reinit'

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