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University of Washington Mesoscale Ensemble (UWME) Information

General Information: A group in the Department of Atmospheric Sciences at the University of Washington is running a mesoscale, short-range (0-3 day forecasts) ensemble with the Weather Research and Forecasting (WRF) mesoscale model twice per day (at the 0000 UTC and 1200 UTC cycles) in order to produce skillful probabilistic mesoscale meteorological forecasts for the Pacific Northwest. This effort, supported by a consortium of local, state, and federal agencies, has several goals:

Detailed analysis of results obtained so far can be found on the UWME Publications & Presentations page.

Model Configuration: The WRF mesoscale ensemble forecasts currently feature an outer grid (151x127) of 36 km horizontal grid spacing that covers much of western North America and the northeastern Pacific and a nested grid (163x124) of 12 km grid spacing that covers the entire Pacific Northwest U.S., from central California to central British Columbia, and from 600 miles off the west coast to central Montana. The model utilizes 37 vertical eta levels, and is non-hydrostatic in order to limit pressure gradient force errors in the complex terrain. An upper-radiative boundary condition is used to allow gravity waves to radiate through the model top without being reflected. The sub-grid scale parameterizations include:

Detailed terraind and land use information for each domain was derived from the 1-km U.S.G.S. digital database.

Initial Condition Selection Strategy: MULTIANALYSIS
Initial conditions and lateral boundary conditions for the WRF mesoscale ensemble are currently generated by interpolation of separate global/synoptic-scale model analysis and forecast fields obtained from several operational weather prediction centers worldwide. A current list of these models includes:

See the summary of members.

Hardware: Forecasts are computed on a cluster of computers:

  1. A 16-node (116 Intel Xeon 2.3GHz processors) Linux PC Beowulf cluster

Each 36/12 km 72-hour forecast finishes in approximately 2 hours. Each global/synoptic-scale IC becomes available at a different time after 0000/1200 UTC. Thus, some UWME ensemble members finish before others.

All eight UWME members plus the centroid run (CENT) are usually completed by 1200/0000 UTC (0400/1600 PST) provided all initializations are in on time. Ensemble mean and spread calculations are made at that time.

Future Improvements: The ensemble modeling system is constantly being improved, so expect changes and delays. Among the changes we hope to make in the future are:

Questions and comments should be directed to: Rick Steed

Last Updated: June 1, 2011

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