18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Tuesday, 31 July 2001: 1:40 PM
Impact of initial conditions on local modeling
Richard H. Grumm, NOAA/NWS, State College, PA; and G. Bryan
Poster PDF (77.8 kB)
Local mesoscale modeling efforts, using NCEP initial conditions have become common throughout the operational meteorological community. At the National Weather Service Office in State College, both the MM5 and workstation Eta model are run four times daily. These models use NCEP Eta model data as inputs for both initial conditions and lateral boundary conditions. One important aspect of these local modeling efforts is to understand the impact of initial conditions on the forecasts produced by these locally run mesoscale models.

In this paper, a comparison of 15-km MM5 runs was made using the Eta as initial conditions for the East Coast snowstorm of 30 December 2000. This case was chosen due to data availability and the apparent impact of the sea-surface temperatures (SST) on the forecasts. The MM5 was run using the Eta with the low-resolution SST data and the Eta with high resolution SST data as initial and lateral boundary conditions.

The MM5 runs initialized off the Eta with the lower resolution SST data showed a trend toward over forecasting the intensity of the surface cyclone. Additionally, the cyclone track was forecast too far to the west of the observed cyclone track.

The MM5 runs, initialized with the NCEP parallel Eta runs, containing the high resolution SST data, forecast a less intense cyclone with a more eastward track. Preliminary results suggest that the low-resolution SST data caused the MM5 to produce too deep a surface cyclone and too much precipitation too far inland. This paper will demonstrate the need for local modelers to be aware of the impact of the initial conditions on their local mesoscale modeling efforts.

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