These files are for hours 0-48 every 3 hours for the 3 MM5 domains.
They are little-endian binary.

Stations included all fall with the lat/lon box around Washington
$minlat,$minlon,$maxlat,$maxlon = "45.55,-124.75,49,-116.9"
See station_list for more info.


Since you are writing C, I also include PERL code that reads a line of
the binary file:
    ($id,$init_time,$fcst_time,$fhour
    ,$obs{temp},$model{temp},$model{t2}
     ,$obs{rh},$model{rh},$obs{wsp},$model{wsp},$model{wsp2}
     ,$obs{wdir},$model{wdir},$obs{pres},$model{pres}
     ,$obs{pcpn},$model{pcpn},$obs{pcpn24},$model{pcpn24}
     ,$lat,$lon,$elev,$domxcor,$domycor,$xcor,$ycor) =
	 unpack "a8 i i i f23",$row_data;

Here are the lines from the fortran code that wrote these:

      CHARACTER*8  stnid 
      REAL     real23(23)
      INTEGER   fhour, idate1, idate2
     $     , iline, iend, hour1, hour2
            write(63,rec=newrecl,err=905) stnid(refnum)
     $           ,idate1,idate2,fhour,real23
CC     
CC  Description of Variables:
CC     stnid(1:5): the ID of the observation point
CC     stnid(7:8): the 2-character type of the observation point
CC     idate1:     the initialization date of the run YYYYMMDDHH
CC     idate2:     the actual time of the observation YYYYMMDDHH
CC     fhour:      the forecast hour corresponding to idate2
CC
CC     the 23 elements of real23 are as follows:
CC     real23(1):  observed temperature (Kelvin)
CC     real23(2):  model predicted lowest sigma level temperature
CC     real23(3):  model predicted lowest sigma level temperature average with
CC        the ground temperature
CC     real23(4):  observed relative humidity
CC     real23(5):  model predicted relative humidity
CC     real23(6):  observed wind speed (meters/second)
CC     real23(7):  model predicted lowest sigma level wind speed 
CC     real23(8):  model predicted lowest sigma level wind speed brought down
CC        to 10 meters using log profile
CC     real23(9):  observed wind direction (degrees)
CC     real23(10): model predicted lowest sigma level wind direction
CC     real23(11): observed sea-level pressure (millibars)
CC     real23(12): model predicted sea-level pressure
CC     real23(13): observed 6-hour precipitation (millimeters)
CC     real23(14): model predicted 6-hour precipitation
CC     real23(15): observed 24-hour precipitation (millimeters)
CC     real23(16): model predicted 24-hour precipitation
CC     real23(17): observation latitude
CC     real23(18): observation longitude
CC     real23(19): observation elevation
CC     real23(20): observation x coordinate in dot points on the nest
CC     real23(21): observation y coordinate in dot points on the nest
CC     real23(22): observation x coordinate in dot points on the coarse grid
CC     real23(23): observation y coordinate in dot points on the coarse grid
c     Surface history
            WRITE(bigline,4036) stnid(refnum),
     &           idate1, idate2, fhour, real23
 4036       FORMAT(a8,',',2(i10,','),i4,',',
     $           22(F11.3,','),F11.3)
            nsbl = nospace(bigline)
            call trim(nsbl,iblen)
            write (61,'(a)') nsbl(1:iblen)


      function nospace(word)
      integer nchars
      character *(*) word,nospace
      
      iout = 1
      nchars = len(word)
      do i = 1,nchars
         nospace(i:i) = ' '
      enddo
      do i = 1,nchars
#ifdef OSF1
         if (word(i:i).ne.' '.and.ichar(word(i:i)).ne.0) then
#else
         if (word(i:i).ne.' '.and.word(i:i).ne.' ') then
#endif
            nospace(iout:iout) = word(i:i)
            iout = iout + 1
         endif
      enddo
      return
      end

      subroutine trim (word,ilength)
      character*(*) word
      integer ilength,il,ifirst,ilast
      
      il = len(word)
      ilast = 0
      ifirst = 0
      do ii = 1,il
         if (word(ii:ii) .eq. ' ') then
            if (word(ii-1:ii-1) .ne. ' ') ilast = ii - 1
         else if (ifirst .eq. 0) then
            ifirst = ii
         endif
      enddo
      ilength = (ilast - ifirst) + 1
      ii = 0
      do i = ifirst,ilast
         ii = ii + 1
         word(ii:ii) = word(i:i)
      enddo
      do ii = ilength+1,il
         word(ii:ii) = ' '
      enddo
      return
      end