The implementation of the 20km RUC into operations at NCEP has been scheduled for 9 April 2002. Questions on the 20km RUC will be handled on a special RUC20 forum at http://ruc.fsl.noaa.gov/forum/eval20. You are welcome to participate in that forum. Please first review the PowerPoint presentation on the web at http://ruc.fsl.noaa.gov/ppt_pres/RUC20-Feb02-summary.htm to learn basic information about the change. We are working on a draft Technical Procedures Bulletin on the RUC20 and will post information on it as soon as it is available.

Below is the Notice of Intent to Change for the RUC20 issued today:
---------------------------------------------
Revision to Notice of Intent to Change – Rapid Update Cycle to 20km (RUC20)
---------------------------------------------

A major change to the Rapid Update Cycle (RUC) has been scheduled for implementation on Monday 9 April 2002. This change includes an increase in resolution from 40km to 20km and 40 to 50 vertical levels, adding assimilation of GOES cloud-top pressure data, modifications to RUC model physical parameterizations, and improvements in post-processing. More information on these changes is provided below and in a web powerpointpresentation at http://ruc.fsl.noaa.gov/ppt_pres/RUC20-Feb02-summary.htm.

Output grids at 40km resolution will still be produced from the RUC-20, identical to those currently being produced. BUFR output files with hourly output broken out by individual stations will now be available, similar to those provided for the Eta model.

--------------------------------------
Summary of RUC20 vs. RUC-2 differences
--------------------------------------

1. Horizontal resolution
The RUC20 has a 20-km horizontal resolution, compared to 40 km for the previous RUC-2. The computation grid has not changed. The RUC20 has a 301x225 horizontal grid, compared to 151x113 for the 40-km RUC-2. (see terrain difference in above RUC20 web link)

2. Vertical resolution
The RUC20 has 50 computational levels, compared to 40 levels for the RUC-2. The RUC20 continues to use the hybrid isentropic-sigma vertical coordinate used in previous versions of the RUC.

3. Improved moist physics
Improved quantitative precipitation forecasts have been a primary focus for changes in the RUC20 model, including a major revision in the MM5/RUC mixed-phase microphysics cloud routine, and a new version of the Grell convective parameterization with an ensemble approach to closure and feedback assumptions. The main effect of the microphysics change is to decrease overforecasting of graupel and ice, and to improve the precipitation type forecast.

4. Assimilation of GOES cloud-top data
The RUC20 includes a cloud analysis which updates the initial 3-d cloud/hydrometeor fields by combining cloud-top pressure data from GOES with the background 1-h RUC hydrometeor field. Cloud clearing and building is done to improve the initial cloud water/ice/rain/snow/graupel fields for the RUC.

5. Better use of observations in analysis
The RUC20 continues to use an optimal interpolation analysis as in the RUC-2 – implementation of a 3d variational analysis has been deferred. The RUC20 assimilates near-surface observations more effectively through improved
algorithms for calculating observation-background differences. Assimilation of surface observations is improved by use of backgrounds for 2-m temperature and dewpoint and 10-m winds and by matching of land-use type for
coastal stations.

6. Improved land-surface physics
The RUC20 land-surface model is changed from that of the RUC-2. It uses detailed land-use and soil texture data, in contrast to 1-degree resolution fields used in the RUC-2. It includes improved cold-season processes and a 2-layer snow model. These changes improve the evolution of surface moisture and temperature and snow cover, leading to improved forecasts of surface temperature and moisture and precipitation.

7. Lateral boundary condition updates
The RUC-2 used lateral boundary conditions specified from the Eta model initialized every 12 h. The RUC20 adds updates from the 0600 and 1800 UTC Eta runs.

8. Improved post-processing
The RUC20 includes more realistic diagnostic techniques for 2-m temperature and dewpoint, 10-m winds, helicity, visibility, convective available potential energy, and convective inhibition.

Most significant improvements in RUC20 fields over those from RUC-2:
- precipitation - both summer and winter - From improved precipitation physics
- all surface fields - temperature, moisture, winds - From improved surface and cloud/precipitation physics
- upper-level winds and temperatures - From higher vertical and horizontal resolution, better physics
- orographically induced precipitation and circulations - From higher horizontal resolution, cloud physics, and better use of surface data near mountains.

For additional information, see

RUC20 PowerPoint presentation at http://ruc.fsl.noaa.gov/ppt_pres/RUC20-Feb02-summary.htm

RUC20 products – http://ruc.fsl.noaa.gov - select ‘test RUC20’

RUC20 evaluation forum – http://ruc.fsl.noaa.gov/forum/eval20
- interactive bulletin board for RUC20 implementation information, questions/answers

Schedule:
March 2002 - field test with RUC20 parallel cycle
after field test - CAFTI meeting
9 April 2002 - operational implementation