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.
- To test the applicability and effectiveness of multianalysis short-range
ensemble forecasting (SREF; 0-72 hours lead time) at mesoscale ( O(10km) ) grid
- To determine whether mesoscale SREFs have more or less value in
regions of large orography and weak convection (northwestern U.S.) than in
regions with mostly flat topography and more frequent, deep convection.
- To determine whether the mesoscale SREF mean possesses greater skill
than any of its individual members.
- To determine whether the mesoscale SREF spread can be used as a predictor of
both deterministic and probabilistic forecast error.
- To determine whether the mesoscale SREF can be used to produce
skillful probabilistic forecast guidance for surface weather parameters,
especially for temperature, winds, and precipitation.
- To determine the relative skill of the mesoscale SREF members in real-time
and during the recent past to potentially derive appropriate weightings, that when
applied to each ensemble member, would result in more accurate deterministic
and probabilistic weather forecasts.
- To determine whether model error plays a significant role in the prediction of
surface weather parameters for a region subject to large topographic influences.
- To determine whether incorporating model uncertainty into a mesoscale SREF is
worthwhile, even for a region where the mesoscale forecast uncertainty is often dominated
by the synoptic-scale uncertainty.
- To determine whether the multianalysis ensemble size can be expanded using linear
combinations of the synoptic-scale ICs in order to improve the chance of encompassing
truth and to provide more skillful probabilistic forecast guidance.
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:
- Yonsei University planetary boundary layer scheme
(see Hong and Pan, 1996)
- Thompson explicit moisture scheme including mixed phase processes
(see Thompson et al., 2004)
- Kain-Fritsch cumulus parameterization (see Kain and Fritsch, 1993)
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
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:
- 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:
- Adding graphics of near real-time performance and historical verification over extended
periods to the UWME Verification & Performance page.
- Adding an array of post-processed forecast products to the website, including calibrated
(via Bayesian Model Averaging) probability plots and data range products.
Questions and comments should be directed to:
Last Updated: June 1, 2011