RUC Frequently Asked Questions

Last modified on Tuesday, 03-Apr-2012 19:54:51 UTC

Q: Is there an FAQ for the Rapid Refresh? (added 4/3/2012)
Answer: Yes, at .

Q: Will the RUC continue to run at NCEP after the Rapid Refresh (RAP) implementation at NCEP occurs? (added 4/3/2012)
Answer: No, the NCEP RUC will be replaced when the NCEP RAP starts to run. The RAP has RUC-look-alike grids so users should be able to use these RUC look-alike grids. The RAP grids are listed under .

Q: What kind of RUC grids can be used for initializing the WRF model?
Answer: Use the native RUC data (RUCB). Be sure to use the vtable.RUCb available from the WRF repository download (along with other vtables). The native RUC data (RUCb) includes hydrometeor and land-surface fields. Do NOT try to use the isobaric RUC data, which does not include hydrometeor fields or land-surface (soil, snow) fields. RUCB/native data is used to initialize the 3km HRRR (version of WRF-ARW) model, for instance.

Q: When are the key dates for changes in horizontal resolution to the NCEP operational RUC?

Q: Why are precipitation fields missing (flagged values) in RUC analysis fields? 11/07/2007
Answer: Precipitation fields only have non-flagged values for forecast output times, not analysis time (f00), since the RUC doesn't analyze precip, so this is as expected. Precip fields should be available from 1h forecasts onward.

Q: What is the actual valid time for RUC fields (e.g., 3h forecast valid at 03z)?
Answer: Well, the forecasts in this case are indeed "valid" at 03z, but since many of the observations assimilated in the RUC (and other NWP models) are centered 10-30 min before the hour, the actual valid time is also offset by 10-30 min. This is discussed in Benjamin et al., 2004, Mon.Wea.Rev. See p. 15 in pdf version and p.503 in MWR version.

Q: What is the difference between the NCEP and NOAA/ESRL/GSD versions of the RUC?

26Jan05 - Q: If the height from the lowest level in the RUC native coordinate matches the RUC model terrain height exactly, how can the winds from the lowest native level be non-zero?
The lowest native level is 5m above the surface, strictly speaking, except for its calculations of heights. In other words, the winds, virtual potential temperature, and water vapor mixing ratio can all be considered as 5m above the surface in regard to the atmospheric/land-water boundary. Note Fig. 6 in the Feb 2004 Monthly Weather Review paper about the RUC model on p.482, which shows 2.5m as the half-point between the actual surface and the 5m first atmospheric level.
Note also that there are 2-m and 10-m winds in the native file, reduced in a post-processing via Monin-Obukhov similarity.

Q: (an old one) What is the difference between RUC and MAPS?
The RUC is the operational version run at NCEP. Versions of the RUC are also run at FSL as a backup to the operational run and as test versions. MAPS is a now-ancient name used in the early-mid 1990s for development versions of the RUC.

Q: What is the history of the operational RUC?

Q: What is the wind direction shown in RUC weather maps?
The wind flags for these maps are the usual convention for weather maps, showing the direction from which the wind is coming. If the wind flag is toward the west, that means that the wind direction is from the west toward the east. Also, note that the RUC grid map projection is not Mercator (it's Lambert conformal), so right-to-left winds are generally not due west (except at 95 deg W). Finally, wind in RUC grids are grid-relative for direction, not lat/lon-relative. (see last FAQ item for information on rotation to lat/lon-relative)

Q: Why do I get forecasts from different runs when clicking the "All Times" button for RUC or WRFRUC products?
This can sometimes happen because early output times from new runs are processed into products while the run is still continuing in order to make available the latest products. Also, sometimes runs may be missing or products may be missing because of computer/disk outages.

Q: Could you please run the RUC model out past 12 hours?
Almost every RUC version run at GSD goes beyond 12h, with the Backup RUC13 out to 48h, and the dev RUC13 out to 72h (for 00z and 12z init times).

Q: Are the mass and velocity values defined at the same grid point in RUC output grids?
The answer is yes. The native RUC model horizontal grid is an Arakawa C grid, in which there is staggering. This is in the model itself. However, all RUC wind output, even in the hybrid-b native vertical coordinate, is unstaggered back onto the mass points. So that is what you are seeing in any output file, unstaggered winds.

Q: Do you have FORTRAN code for converting the u and v wind components aligned to the RUC grid to components with respect to true north (meteorological standard)?
Here is a code snippet that should do the job.

      PARAMETER ( ROTCON_P   =  0.422618      )
      PARAMETER ( LON_XX_P   = -95.0          )
C**                         AND SIN(LAT_TAN_P) FOR LAMBERT CONFORMAL
C**                         IS TRUE (DEG)
      PARAMETER ( LAT_TAN_P  =  25.0          )

        do j=1,ny_p
        do i=1,nx_p
           angle2 = rotcon_p*(olon(i,j)-lon_xx_p)*0.017453
           sinx2 = sin(angle2)
           cosx2 = cos(angle2)
         do k=1,nzp_p
           ut = u(i,j,k)
           vt = v(i,j,k)   
           un(i,j,k) = cosx2*ut+sinx2*vt
           vn(i,j,k) =-sinx2*ut+cosx2*vt
          end if
         end do
        end do
This page prepared by Stan Benjamin