ECPC's September 2000 Forecasts

contributed by J. Roads, S. Chen, J. Ritchie

Experimental Climate Prediction Center Scripps Institution of Oceanography UCSD, 0224 La Jolla, CA 92093

ECPC's Global to Regional Atmospheric Forecast System

As previously discussed by Roads et al. (2000a,c), the Scripps Experimental Climate Prediction Center (ECPC) uses the reanalysis I version (Kalnay et al. 1996) of the National Centers for Environmental Prediction's (NCEP's) medium range forecast (MRF) model or global spectral model (GSM; Roads et al. 1999a). These global forecasts (4xdaily-7 days and weekly to 12-weeks) start from the NCEP operational 00UTC global analysis. The GSM then forces a regional spectral model (RSM; Juang and Kanamitsu, 1994; Juang et al. 1997; Chen et al. 1999, Anderson et al. 1999, Roads and Chen 2000) in order to gain increased spatial resolution (50-25 km resolution) at shorter time scales (4xdaily-7 days and weekly to 4-weeks) for several selected regions (US, CA, SW, Brazil). At even smaller space (2-km resolution) and time scales (8xdaily to 2 days) either the NCEP analysis or GSM forces a corresponding nonhydrostatic mesoscale spectral model (MSM; Juang 1999) for the Hawaiian Islands (Stevens et al. 1999). All atmospheric models are based upon the same physics used in the GSM and can, in principle, be updated as the GSM is updated. Output products from the atmospheric models include a fire weather index (FWI, see Roads et al. 1997) and associated variables such as 2m-temperature, relative humidity and 10m-windspeed as well as precipitation and soil moisture. Since the global atmospheric model is now forcing an ocean model (Auad et al. 1999), forcings and corresponding output from the ocean model will be presented in later ELLFB issues.

Preliminary Forecast Skill Evaluations

Two years worth of forecasts (104 forecasts) have been used to develop a GSM forecast climatology dependent upon season as well as lag. This ensemble of forecasts has also been used to evaluate forecast skill. As discussed by Roads et al. (2000c), the GSM provides skillful forecasts of temperature, precipitation, soil moisture and a fire weather index at long forecast ranges. Although the greatest skill occurs initially and then decays toward zero, daily, weekly or monthly forecast skill does not ever reach zero and forecasts averaged into monthly and seasonal averages demonstrate significant skill, which may be comparable to other long-range forecast methodologies. Similar evaluation efforts are underway for the regional forecasts, which currently use the GSM to start the forecasts and the GSM climatology to derive regional anomalies.

Global seasonal GSM forecasts and US monthly RSM forecasts

Figs. 1,2,3,4 show the GSM seasonal anomaly forecast for Sept.-Nov.2000 along with the corresponding RSM monthly anomaly forecast for Sept. 2000 of 2-m surface temperature, precipitation, soil moisture and the FWI. It should be noted that both the GSM and the RSM use the same GSM climatology to calculate the anomalies, which may have a deleterious effect on the RSM anomalies discussed below. We are still trying to develop a more suitable RSM climatology for the RSM simulations.

Above normal seasonal temperatures (Fig. 1) are being forecast to continue for most areas in the Northern Hemisphere, with the exception of central Europe. Lower than normal temperatures are being forecast for most of the southern hemisphere. Over the US, even higher temperatures are being forecast by the RSM during Sept. over the Mississippi River Basin and parts of the US West.

GSM seasonal precipitation forecasts (Fig. 2) have fairly zonal patterns. Southern Europe and the US are being forecast to have above normal precipitation. In the eastern Pacific, an above normal band is forecast from Hawaii to Central America. Strong precipitation is expected along the Asian coast and a corresponding dry region is forecast for the south China sea. More intense features are being forecast over the eastern US during Sept. Wet anomalies are also being forecast over the Northwest and parts of California during Sept. Dryer anomalies are being forecast over the Gulf of Mexico and Caribbean.

Soil moisture (Fig. 3) forecasts are generally coincident with the global and US precipitation and temperature predictions. This reflects the strong influence of precipitation on soil moisture as well as potential feedbacks by the soil moisture on precipitation and temperature. Many potential global dry areas are being forecast for Europe, South Africa, Brazil, and the Central US and Mexico. During Sept. the soil moisture is noticeably low in the central US, Mexico.

The FWI (Fig. 4) is generally coincident with the precipitation and soil moisture but it should be noted that wind speed and relative humidity are the explicit contributors. There appears to be reduced danger just about everywhere, except for perhaps Siberia, South Africa, and Argentina. Over the US, the FWI is being forecast to remain above normal over the West although the seasonal global forecast is suggesting an eventual reduction. The FWI is especially low over the east coast where above normal precipitation is being forecast.

Other experimental GSM and RSM forecast fields (wind speed, relative humidity) and additional forecast months)can be found at: http://ecpc.ucsd.edu/projects/ellfb/. Other forecast ranges and other regions can be found at http://ecpc.ucsd.edu/m2s/m2s_ECPC_forecasts.html/.

References

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

Auad, G., J. Roads, A. Miller, D. Cayan, W. White, 1999: Comparison of wind stresses and surface heat fluxes from the COADS, FSU and NCEP data sets. (submitted)

Chen, S. -C., J.O. Roads, H. -M. H. Juang, M. Kanamitsu, Global to regional simulation of California's wintertime precipitation. J. Geophys. Res., 104(24), 31517-31532, 1999.

Chen, S-C. J. O. Roads, and M. Wu, 2000: ECPC's Asia forecasts. Journal of Terrestrial-Atmosphere-Oceanography (in progress).

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.

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., S. Chen, M. Kanamitsu, H. Juang, Surface water characteristics in NCEP global spectral model reanalysis. J. Geophys. Res., 104, 19307-19327, 1999a

Roads, J., S. -C. Chen, J. Ritchie, 2000a: ECPC's Weekly to Seasonal U.S. Forecasts of FWI, Soil Moisture, and Precipitation. ELLFB, Mar. 2000.

Roads, J. and S. Chen, 2000b: Surface Water and Energy Budgets in the NCEP Regional Spectral Model. J. Geophys. Res. (in press)

Roads, J., S. Chen, F. Fujioka, 2000c: ECPC's Weekly to Seasonal Global Forecasts. Bull. Amer. Meteor. Soc. (submitted)

Stevens, D. D. Funayama, J. Roads, S. Chen, W. Smith, C. McCord, H. Juang, F. Fujioka, 1999: Experimental short-term weather forecasts for Hawaii. MHPCC application briefs 1999. (Available from MHPCC, Kihei, Maui, HI 96753), 19.