help! maybe it's a simple question for the experienced, but it puzzled me

[stardust]

Greetings,
I am a beginner for WRF, and last month I successfully run a real case with help of User's Guide(http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V4/WRFUsersGuide.pdf), ARW Online Tutorial(http://www2.mmm.ucar.edu/wrf/OnLineTutorial/) and some tutorial from youtube.
And I have a question (maybe it looks obvious for you, but it really puzzled me for a week) as below.
Since I can download some meteology data from rda.ucar directly, why do I run the model to get the simulated data?
That is, for example, I want to simulate from 20181201_12:00:00 to 20181203_12:00:00，I have to set the start time and end time in namelist.wps and namelist.input, of courese, and in WPS, I have to download grib data from 20181201_12:00:00 to 20181203_12:00:00( ARW Online tutorial pointed that "you need input data for the entire time you plan on running the WRF model."). Since I have these data, what the objective to run WRF model ? It seems like proving a conclusion by itself. Or maybe there are some mistakes in my understanding? :?: :?: :?:
Can anyone catch my idea? Please give me some suggestion and thanks a looooooooooooooooooot for your warm help!

 

[Ming Chen]

The input data you can download from RDA or other websites are coarse-resolution data either from analysis/reanalysis products or from other global/regional model outputs. Running WRF will yield high-resolution simulation of weather and climate that contains more detailed (and often more accurate) picture of the weather /climate one is concerned.

 

[stardust]

The input data you can download from RDA or other websites are coarse-resolution data either from analysis/reanalysis products or from other global/regional model outputs. Running WRF will yield high-resolution simulation of weather and climate that contains more detailed (and often more accurate) picture of the weather /climate one is concerned.

I get it, really appreciate for your help~!