INFO ON ICWF PRODUCTS FROM THE ETA MODEL

        Here is some information about the so-called supplemental fields from
     the early Eta and Meso Eta.  They have been requested by the ICWF
     folks and can be used as an alternative starting point (the previous
     ICWF forecast or a gridded NGM MOS are the other 2 options) for ICWF.
     The gridded fields can be ingested directly into the ICWF from their
     Lambert conic-conformal grid.  I prefer to call them sensible weather
     guidance fields from the Eta Model.
    
        These were first generated from the 10km Nested Eta runs performed for
     the 1998 Summer Olympic games and used as an alternative starting point
     in the ICWF processing for venue specific forecasts.  For the
     Olympics, the fields were on a 10 km grid #218 (Lambert conic
     conformal).  For temperature, the dependence of surface temperatures
     on elevation came out very nicely.  These fields have been generated
     from the early Eta (on 40 km grid #212) and from the Meso Eta (on 20
     km grid #215) for about a year now.  These fields have been available
     on NCEP's NIC server and more recently on the OSO server.  DRG RC#2111
     put them into the main AWIPS distribution stream.   Since then, ICWF
     output has been added on Alaskan grids #216 and #217.
    
     Here are the fields, which are available every 3 hours throughout the
     forecast period, and a few comments on how they are generated:
    
        Surface wind speed and direction - This is a diagnosed wind from the
     Eta Model at 10 m above model terrain.  Except that it is in the form
     of direction & speed, it is IDENTICAL to the surface wind coming out
     of the Eta Model in the form of u & v components.  ICWF requested that
     the surface wind field be in that form.

        Surface temperature and dew point - These are diagnosed from the Eta
     Model at 2 m above model terrain.  The temperature is IDENTICAL to the
     surface temperature coming out of the Eta Model now.  Except that it
     is in the form of dew point, this surface moisture field is IDENTICAL
     to the 2 m specific humidity coming out of the Eta Model.  Again, ICWF
     requested the field be in this format.

        Maximum temperature - This is the maximum temperature at the 2 m level
     above model terrain.  At 12z, the max temperature is set to the 12z
     temperature.  Between 12z and 00z, the max temperature is reset every 3
     hours if the current temperature exceeds the previous max temperature.
     Between 00z and 12z, the max temperature is unchanged.

        Minimum temperature - This is the minimum temperature at the 2 m level
     above model terrain.  At 00z, the min temperature is set to the 00z
     temperature.  Between 00z and 12z, the min temperature is reset every 3
     hours if the current temperature is less than the previous min temperature.
     Between 12z and 00z, the min temperature is unchanged.

        Cloud Cover - This comes straight from looking 'upward' at the Eta Model
     cloud fields carried/predicted at each Eta layer and is the total cloud
     'cover' in percent.

        QPF - 3 hour total precipitation accumulation (m).  This is also IDENTICAL
     to the current Eta Model output field.

        Snow - This is the 3 hour snow accumulation (m).  This is made by assuming
     a fixed snow-to-water ratio of 10-1 and using the snow water equivalent
     carried in the Eta Model land-surface package.

        Precip Probability (%) - This field is a place holder for ICWF and has no
     value added over the QPF field.  The POP field is simply a scaled
     representation of the 3-hour QPF.  Wherever the QPF is less than .01mm, POP
     is set to 0%; wherever the QPF is greater than 6mm, POP is set to 100% and
     POP is scaled linearly in between.

        Thunderstorm Probability (%) - This field is computed from the Eta Model
     surface based Lifted Index based on a linear fit of a summer's worth (1995)
     of data for thunderstorm frequency versus LI (Jason Taylor): P(thunder)=
     -12.76 x LI + 29.33 with values constrained to be between 0 and 100%.

        Probability of frozen precipitation - This field is NOT a probability.  It
     is set to 100% if the Eta Model decision-tree (Mike Baldwin) for precip
     type indicates snow or sleet.  It is 0%, otherwise.

        Probability of freezing precipitation - This field is NOT a probability.
     It is set to 100% if the Eta Model decision-tree (Mike Baldwin) for precip
     type indicates freezing rain.  It is 0%, otherwise.