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20011024: GEMPAK Wind Chill again

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  • Subject: 20011024: GEMPAK Wind Chill again
  • Date: Wed, 24 Oct 2001 17:08:05 -0600
>From: Daryl Herzmann <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200110242213.f9OMDV122314

>Hi,
>       In regards to:
>http://www.unidata.ucar.edu/glimpse/gempak/4634
>http://www.unidata.ucar.edu/glimpse/gempak/4607
>
>       The NWS is using a different formulation then the one in GEMPAK
>for wceq.  I got an email today from the NWS about a Wind Chill plot I
>have.  They are concerned with the discrepancy between my plot on the web
>and what they will be issuing.  Is this an issue with NCEP, or not knowing
>what the new formula is?  I am not sure myself.  I can try to find it if
>you wish.  My abilities are lacking to create my own formulation and then
>patch GEMPAK with it, so I am seeking divine help.  If I provided the
>formula, could you create a patch to use it in GEMPAK?
>
>Thanks,
>       Daryl
>
>-- 
>/**
> * Daryl Herzmann (address@hidden)
> * Program Assistant -- Iowa Environmental Mesonet
> * http://mesonet.agron.iastate.edu
> */
>

Daryl,

The next release of GEMPAK (5.6.E) has a new SFPARM called
WCHT: Revised wind chill temperature in Fahrenheit
computed using the following formula: 

        FUNCTION PR_WCHT ( tmpf, sknt )
C************************************************************************
C* PR_WCHT                                                              *
C*                                                                      *
C* This function computes WCHT, the wind chill temperature from TMPF    *
C* and SKNT.  The input values will first be converted to miles per     *
C* hour.  The output will be calculated in Fahrenheit.                  *
C*                                                                      *
C* WCHT is the temperature with calm winds that produces the same       *
C* cooling effect as the given temperature with the given wind speed.   *
C*                                                                      *
C* The following equation is used:                                      *
C*                                                                      *
C*      PR_WCHT = 35.74 + ( .6215 * TMPF ) - 35.75 * WCI ( V ) +        *
C*                0.4274 * TMPF * WCI ( V )                             *
C*                                                                      *
C*              where:  WCI ( V ) = ( V ** 0.16 )                       *
C*                      V: Wind Speed (mph)                             *
C*                                                                      *
C* REAL PR_WCHT ( TMPF, SKNT )                                          *
C*                                                                      *
C* Input parameters:                                                    *
C*      TMPF            REAL            Air temperature in deg F        *
C*      SKNT            REAL            Wind speed in knots             *
C*                                                                      *
C* Output parameters:                                                   *
C*      PR_WCHT         REAL            Wind Chill temperature in deg F *
C**                                                                     *
C* Log:                                                                 *
C* T. Lee/SAIC           9/01                                           *
C* T. Lee/SAIC           9/01   Set windchill <= air temp               *
C************************************************************************


I will be making a release of this distribution soon.

Steve Chiswell