7.1
Supplemental Numerical Weather Prediction Models
For the 2003-2004 MDSS demonstration FSL configured multiple, high-resolution
models to run over the identical area, all centered on Iowa, with identical grid
configurations and execution schedules. FSL elected to use two different local-scale
models, each of which used different physics packages for parameterizing clouds and
precipitation. The configuration consisted of running MM5 and an improved version of
WRF every hour, and using "time-lagged" ensembling techniques. For example, a 6-hr
ensemble forecast used the current 6-hr forecast, the previous 7-hr forecast, and the 8-hr
forecast from the previous model cycles.
There were no obvious alternatives to the FSL method for initializing the local models
(other methods for diabatic initialization are too computationally intensive to use in real
time), so the Local Analysis and Prediction System (LAPS) hot start initialization was
used for all models. A hot start initialization is a method to generate cloud water and
precipitation processes at the start of the model run. This is a new and promising
technique that improves the ability of models to predict clouds and precipitation,
particularly in the 0-6 hr forecast period.
The local-scale models used for the MDSS field demonstration were:
MM5: http://www.mmm.ucar.edu/mm5/mm5-home.html
WRF: http://wrf-model.org/
The lateral boundary model was the Eta model provided by the NWS National Centers
for Environmental Prediction (NCEP). The Eta model was delivered to NWS field offices
and FSL four times daily.
The supplemental modeling configuration used for the Iowa MDSS field demonstration is
summarized in Table 7.1.
Table 7.1. Configuration of the MDSS Supplemental Models
Forecast Model
Boundary Condition
Forecast
Grid
Update
Source
Period
Spacing
Rate
WRF
NWS: Eta
15 hours
12-km
1-hr
MM5
NWS: Eta
15 hours
12-km
1-hr
The mesoscale models (WRF and MM5) were run out to 15 hours ensuring that, with a 3
hour MDSS update cycle, there were forecasts available from the fine scale models out to
12 hours at all times. The fine scale models ran every hour providing a new 15 hour
forecast to the RWFS. The grid spacing used in the fine scale models was 12-km (~7.5
miles). The MM5 and WRF supplemental models run by FSL had a domain centered on
Iowa as shown in Fig. 7.2.
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