In a recent article, Fosberg and Fujioka (1987) described the use of national

ECPC’s U.S. Forecasts
J. Roads, S. -C. Chen, J. Ritchie

Experimental Climate Prediction Center

Scripps Institution of Oceanography

UCSD, 0224

La Jolla, CA 92093

http://meteora.ucsd.edu/ecpc/

1. ECPC’s Atmospheric Forecast System

The Scripps Experimental Climate Prediction Center's (ECPC's) atmospheric forecast system was previously described by Roads et al. (1998a,b,c,d). At the largest space and time scales, ECPC’s system uses the National Centers for Environmental Prediction’s (NCEP’s) medium range forecast (MRF) model or global spectral model (GSM; Kalnay et al. 1996, Roads et al. 1999a). A high-resolution regional spectral model (RSM; Juang et al. 1994,1997; Chen et al. 1999; Anderson et al. 1999a,b), is nested within the GSM, which provides initial and low spatial resolution global model parameters for the RSM. A mesoscale spectral model (Juang et al., 1997, Juang 1999), which uses the nonhydrostatic equations, can then be nested within the RSM or can be initialized and bounded by the global model. The MSM is being used to display high-resolution products for the Hawaii Islands (see Roads et al. 1999c and http://www.mhpcc.edu/~wswx).

These global to regional and daily to seasonal forecasts are currently displayed at ECPC's site (http://meteora.ucsd.edu/ecpc/). Output includes products from the global (200-km) at daily to monthly time scales, and daily to weekly products from U.S. (50km), U.S. Southwest (25 km), and California (25 km) RSM forecasts. Products include a fire weather index (FWI, see Roads et al. 1997, 1999b) and associated variables such as 2m-temperature, relative humidity and 10m windspeed as well as precipitation and soil moisture for several regions. Since the atmospheric models are now forcing ocean and land surface models, we are also beginning to display surface water and energy forcings in conjunction with ocean and land models and these will be presented in later ELLFB issues.

2. GSM Forecast Skill Evaluations

As discussed by Roads et al. (1998a,b,c), still limited forecast samples suggest that the GSM appears to provide more skillful forecasts of temperature, precipitation, soil moisture, and fire weather index than persistence, even at long forecast ranges. Although the greatest skill occurs initially and then decays toward zero, daily or weekly or monthly forecast skill does not ever reach absolute zero and the residual weekly forecast skill when averaged into monthly and seasonal averages have skills that may be significant and comparable to other long-range forecast methodologies.

Separating out the systematic biases as well as evaluating the true forecast skill from the limited numbers of forecasts is frustrating and we have to be patient in developing comprehensive evaluations. It is especially important that we evaluate many additional years of forecasts to get the appropriate background climatologies and probability distributions for the forecasts. The current background climatology comes from the NCEP reanalysis (Kalnay et al. 1996) and does not take into account the significant biases that these models produce. For example, over the US there is a negative forecast temperature bias, on the order of a few degrees, that is comparable to the standard deviation of the temperature variations. This negative temperature bias is also reflected in a high relative humidity bias (forecast RH > than observed RH) and a low FWI bias (forecast FWI > analysis FWI). We have considered making an empirical correction to these temperature and relative humidity forecasts. However, we should mention that with the introduction (beginning in July 1998) of NCEP's higher resolution global forecasts (T170L31), the forecast biases became much larger for both the GSM and the persistence forecasts. We are thus waiting to see if the systematic biases will decrease now that NCEP has moved back to the previous lower resolution analysis system.

3. Dec. 1998 forecasts

Table 1 (http://meteora.ucsd.edu/ecpc/projects/ellfb) provides the ECPC entry to the ELLFB US forecast products. A secondary table (Table 2) now provides the entry to individual images for each of the monthly forecasts. In separate locations, which are not shown here but are accessible through http://meteora.ucsd.edu/ecpc/) are forecasts of these same variables for individual days and weeks as well as for other global regions. Forecasts of other variables, such as net surface heating, wind stress and surface currents) are also being evaluated and displayed on a page devoted to a beginning ocean forecasting effort.

As an example of the current ELLFB forecasts, Fig. 1 shows the anomalous FWI forecast (from the global model) for the U.S. for the period Feb.27-Mar. 27, 1999 and Mar. 27-Apr. 24, 1999. The US West continues to be of some concern (see Roads et al. 1998c). This increased FWI potential is largely due to reduced relative humidity, although increased wind speed is still contributing. Temperature effects have less influence on FWI variations. Fig. 2 shows the anomalous soil moisture forecast for the U.S. for the same periods. The soil moisture anomalies are quite similar to the FWI anomalies. This relative dryness may change soon in the east. Fig. 3 displays the precipitation forecast anomalies, which are similar to the forecast soil moisture and FWI only over the US west. Above normal precipitation is appearing further to the east.

References

Anderson, B.T., J. O. Roads, S. -C. Chen, and H. -M. Huang, 1999a: Regional Modeling of the Low-level Monsoon Winds Over the Gulf of California and Southwest United States: Simulation and Validation, (submitted).

Anderson, B.T., J. O. Roads, S. -C. Chen, and H. -M. Huang, 1999b: Model Dynamics of Low Level Monsoon Winds and Surge Events over the Gulf of California and Northwest Mexico. (submitted).

Chen, S. -C., J. O. Roads, H. H. -M. Juang, and M. Kanamitsu, 1999 Global to Regional Simulations of California Wintertime Precipitation. J. Geophys. Res. (in press, special precipitation issue)

Juang, H. -M. H., and M. Kanamitsu, 1994: The NMC nested regional spectral model. Mon. Wea. Rev., 122, 3-26.

Juang, H.-M. H., S.-Y. Hong and M. Kanamitsu, 1997: The NCEP regional spectral model: an update. Bulletin Amer. Meteor. Soc., 78, 2125-2143.

Juang, H. -M. H., 1999: The EMC/NCEP mesoscale spectral model: A revised version of the nonhydrostatic regional spectral model. Mon. Wea. Rev., submitted.

Kalnay, E. et al., 1996: The NMC/NCAR reanalysis project, Bull. Am. Meteor. Soc., 77, 437- 471, 1996.

Roads, J.O., S. -C. Chen, F.M. Fujioka, H. Juang, and M. Kanamitsu. 1997. Global to Regional Fire Weather Forecasts. Int. Forest Fire News, 33-37.

Roads, J., Chen, S. -C., Ritchie, J., 1998a: Evaluation of the Experimental Climate Prediction Center’s global to regional and daily to seasonal prediction system. Proceedings of the 23^rd Annual Climate Diagnostics Meeting. Miami, Florida

Roads, J., S. -C. Chen, J. Ritchie, 1998b: ECPC’s Weekly to Seasonal U.S. Forecasts of FWI, Soil Moisture, and Precipitation. ELLFB bulletin, Sept. 1998

Roads, J., S. -C. Chen, J. Ritchie, 1998c: ECPC’s Weekly to Seasonal U.S. Forecasts of FWI, Soil Moisture, and Precipitation. ELLFB bulletin, Dec. 1998

Roads, J. O., S. -C. Chen, M. Kanamitsu, H. Juang, 1999a: Surface Water Characteristics in NCEP’s Reanalysis and Global Spectral Model. J. Geophys. Res.-Atmos. (in press, special GCIP Issue)

Roads, J. O., S. -C. Chen, J. Ritchie F. Fujioka, H. Juang, M. Kanamitsu, 1999c: ECPC's global to regional fireweather forecast system. Proceedings of the 79 Annual AMS Meeting, Dallas TX Jan. 10-16, 1999.

Roads, J., S. Chen, D. Stevens, C. McCord, H. Juang, F. Fujioka, 1999c: Weather and climate analyses and forecasts at MHPCC. Seventh International Conference on High Performance Computing and Networking. Amsterdam, The Netherlands, April 12-14, 1999.

Table. 1 ECPC's ELLFB table entry (http://meteora.ucsd.edu/ecpc/projects/ellfb/) to monthly U.S. forecasts of FWI, windspeed, temperature, relative humidity, precipitation and soil moisture. Additional products regions and timescales are available at http://meteora.ucsd.edu/ecpc/m2s/m2s_ECPC_forecasts.html/

Table. 2 The ELLFB table entries to GSM monthly U.S. forecasts. Both total and anomaly forecast fields for the current and past forecasts are available for perusal and can be compared to observations (operational analyses).

Fig. 1. Monthly FWI anomaly forecasts for the U.S. region for Feb.27-Mar. 27, 1999 and Mar. 27-Apr. 24, 1999.

Fig. 2 Monthly soil moisture anomaly forecasts for the U.S. region for Feb.27-Mar. 27, 1999 and Mar. 27-Apr. 24, 1999.

Fig. 3. Monthly precipitation moisture flux anomaly forecasts for the U.S. region for Feb.27-Mar. 27, 1999 and Mar. 27-Apr. 24, 1999.