Welcome to ARPS
CAPS has served the meteorological community since 1997 by continuously
providing real-time numerical analyses and forecasts, initially as part
of a collaboration with American Airlines known as Project Hub-CAPS
(Carpenter, et al., 1999).
During Special Operational Periods, increased resolutions with more
sophisticated configurations are often employed, making use of
supercomputing resources at NCSA or PSC. The Advanced Regional
Prediction System (ARPS) of CAPS and its data analysis system (ADAS) are used.
From mid-May to the end of June of 2002, ARPS ran in support of Internation
Water Project (IHOP
2002), a major field experiment occurring over the US contral plain. Triple
nested 27/9/3 km grids were employed, with the 27 km grid covering the CONUS
domain. Up to 256 Compaq Alpha CPUs on the PSC
Terascale Computing System
and/or up to 512 processors of a Pentium III Linux cluster at
were used. Data analyses was performed locally on a Pentium 4 Linux cluster.
In more recent years, CAPS has participated in spring experiments with the
Storm Prediction Center,
Currently, the 20-km CONUS is run daily starting from 00 UTC and forecast for 84 hours.
00 UTC NAM run will be used for the initial-condition first guess and
for providing the boundary conditions. The 9-km nested grid starts at 12Z
and runs for 24 hours, getting its boundary conditions from the 20
3 km forecast starting at 00 UTC and runs for 6 hours. All forecasts use the
Guide to Interpreting the
Products (not all products listed are available).
NOTE - Some information is out of date. Click on
News for latest info.
Description of the Forecast System
Note: Consult the Data Status page of each forecast run to see how many
observations of each data type were actually used.
- NAM model: Used for boundary conditions and as a first guess for initial
- Rawinsonde: Used on forecasts and national grid analyses only.
- Wind Profiler: All grids.
- MDCRS (aircraft observations): All grids.
- METAR (surface observations): All grids.
- Oklahoma Mesonet: Southern Plains grids.
- Satellite: IR cloud-top temperature used in cloud analysis. VIS data is also used
- NIDS (coarsely discretized radar data) and full volume data WSR-88D data:
Reflectivity used in cloud analysis grids. Radial velocity is not used
at the current time.
- CASA radar data is used in the
Sample ARPS Configuration
ARPS Version 5.0 is used with the following options:
- Vertically-stretched terrain-following grid. Lowest level is 10 m AGL. Model
top is 20 km MSL, 53 vertical levels, with grid spacing at the model top approaching
1 km. Rayleigh damping is applied to the upper 1/3 of the domain.
- Nonhydrostatic dynamics using mode-split and vertically-implicit time integration
- 4th-order advection, simple positive definite scheme for water and TKE.
- 3 ice-phase microphysics (Lin-Tao)
- Kain-Fritsch cumulus parameterization (27 and 9 km grids)
- NCSA Atmospheric Radiative Transfer scheme
- 1.5-order TKE-based subgrid scale turbulence closure and PBL Parmeterization
(Sun & Chang 1986 JCAM)
- 2-layer soil and vegetation model
- 4th-order Computational Mixing
Maintained by Kevin W. Thomas.
Your comments, inquiries, problem reports, and
suggestions are welcome.