Precipitation Forecast and Verification of the NCEP ETA Model

Major Milestones

Ying Lin

12Z 8 Jun 1993:

NCEP implemented the 80km/38-level Eta analysis and forecasting system (Black, 1994) to provide forecast guidance over North America. A one-year comparison of QPF during 1993-94 showed that the Eta model solidly outperformed the Regional Analysis and Forecast System (the model Eta replaced) during both cold and warm seasons (Rogers, 1995).

12Z 12 Oct 1995:

In the pre-implementation parallel tests, each of these four components proved to have a positive impact on the model's precipitation forecast, both individually and when combined with the three other components (Rogers, 1996. Tests were initially made on either the 48km grid or a 40km grid. In the end the 48km grid was chosen for implementation due to computer limitations at the time).

  1. reduced the horizontal grid spacing from 80km to 48km (QPF scores from test 1 and test 2).
  2. used a 12h period of Eta-based data assimilation system (EDAS, with 3-hourly optimal interpolation [OI] analysis updates) to provide initial conditions for each cycle of forecast (QPF scores).
  3. implemented an explicit cloud prediction scheme (Zhao, 1997. QPF scores).
  4. used satellite-based total column water vapor information in the 3-hourly OI analysis (Lin, 1995. QPF scores).

12Z 31 Jan 1996:

Added modern multi-layer soil/vegetation/snowpack model

12Z 18 Feb 1997:

  1. Added bias adjustment to the initial GDAS soil moisture (used by Eta/EDAS as a first guess
  2. Implemented new high resolution seasonal greenness fraction database
  3. New top soil-layer direct evaporation function used
This "bundle" of changes are described in Black (1997. QPF scores for the parallel test).

12Z 9 Feb 1998:

  1. grid resolution increased from 48km/38-level to 32km/45-level (QPF scores for the parallel test).
  2. Soil layers increased from 2 to 4
  3. Eta OI analysis replaced by Eta based 3D variational analysis (3DVAR) (QPF scores for the parallel test).
  4. "Partially cycled" EDAS: rather than starting each cycle of EDAS entirely the first guess obtained from the global model, we now obtain soil moisture/temperature, cloud water and TKE from the previous EDAS cycle.

References: Rogers et al., 1996, 1997.

12Z 3 Jun 1998:
  1. "Full cycling" of EDAS variables (both atmospheric and land) was implemented, and the Eta/EDAS system became independent of the Global Model (QPF scores for cycling vs. non-cycling EDAS under OI and 3DVAR analysis).
  2. Forecast are made 4 times each day (00, 03, 12 and 18Z).
12Z 3 Nov 1998:
Changes to the 3DVAR analysis were made to improve the analysis of surface and lower tropospheric data, particularly moisture. During the winter of 1998-99 it became apparent that the Eta model forecasts had decreased skill from the previous winter (Rogers, 1999):

QPF scores for 1 Dec 1997 - 28 Feb 1998
QPF scores for 1 Dec 1998 - 28 Feb 1999

12Z 13 May 1999:
After extensive tests, the problem in the 3DVAR analysis implemented in the previous November was fixed (Rogers, 1999. QPF scores shown here).
27 Sep 1999, Cray90 outage:
C90 was damaged by a fire on the afternoon of 27 Sep. Currently only the 80-km Eta (from static analysis) is being produced at 00Z and 12Z.

Impact to the QPF due to the production model downgrade (the degradation in the Eta threat scores after September can be seen in the now-smaller advantage Eta has over the AVN and NGM models):

QPF scores for Sep 1999 (90% of cycles are from 32km ETA/EDAS)
QPF scores for 1-21 Oct 1999 (from 80km static ETA)
Black,T, M. Baldwin, K. Brill, F. Chen, G. DiMego, Z. Janjic, G. Manikin, F. Mesinger, K. Mitchell, E. Rogers, and Q. Zhao, 1997: Changes to the Eta forecast systems. Technical Procedures Bulletin, No. 441, NOAA/NWS, [National Weather Service, Office of Meteorology, 1325 East-West Highway, Silver Spring, MD 20910]. On-line version

Black, T., 1994: The new NMC mesoscale Eta model: description and forecast examples. Wea. Forecasting, 9, 265--278.

Lin, Y., K.E. Mitchell, E. Rogers and G.J. DiMego, 1995: Impact of satellite moisture observations on forecasts made by NMC's Eta model. Preprints, 14th Conf on Weather Analysis and Forecasting, Dallas, TX, Amer. Meteor. Soc., 301-302.

Rogers, E., D. Parris and G. DiMego, 1999: Changes to the NCEP operational Eta Analysis. Technical Procedures Bulletin, No.*** (not yet numbered), NOAA/NWS. [ National Weather Service, Office of Meteorology, 1325 East-West Highway, Silver Spring, MD 20910 ]. On-line version

Rogers, E., M. Baldwin, T. Black, K. Brill, F. Chen, G. DiMego, J. Gerrity, G. Manikin, F. Mesinger, K. Mitchell, D. Parrish, Q. Zhao, 1997: Changes to the NCEP Operational "Early" Eta Analysis/Forecast System. Technical Procedures Bulletin No. 447, NOAA/NWS. [ National Weather Service, Office of Meteorology, 1325 East-West Highway, Silver Spring, MD 20910 ]. On-line version

Rogers, E., D. Parrish, Y. Lin and G.J. DiMego, 1996: The NCEP Eta data assimilation system: tests with a regional 3-D variational analysis and continuous cycling. Preprints, 11th AMS Conference on Numerical Weather Prediction, Norfolk, VA, 19-23 August 1996.

Rogers, E., T. L. Black, D. G. Deaven, G. J. DiMego, Q. Zhao, M. Baldwin, N. W. Junker and Y. Lin, 1996: Changes to the operational ``Early'' Eta analysis/forecast system at the National Centers for Environmental Prediction. Wea. Forecasting, 11, 391--413.

Rogers, E., D. Deaven and G. J. DiMego, 1995: The regional analysis system for the operational "early" Eta model: original 80-km configuration and recent changes. Wea. Forecasting, 10, 810--825.

Zhao, Q., T.L. Black and M.E. Baldwin, 1997: Implementation of the cloud prediction scheme in the Eta model at NCEP. Wea. Forecasting, 12, 697--711.