RT-FDDA Frequently Asked Questions
What is does RT-FDDA stand for?
RT-FDDA stands for Real Time Four Dimentional Data Assimilation.
What is RT-FDDA?
RT-FDDA is a mesoscale forecasting system based on either MM5 or WRF and employs a time-continuous assimilation of a variety of synoptic and asynoptic observation data including:
* METAR observations (includes "Specials")
* Ship/buoy observations
* Local surface observations
* WMO rawinsonde observations
* NESDIS satellite-derived winds
* ACARS aircraft observations
These data sets have time frequencies varying from 5 min to 3 h, and are assimilated into the RT-FDDA system at their particular valid time. This allows the model to be nudged closer to observations before the next forecast cycle commences. Please refer to our page describing RT-FDDA for more information.
When does RT-FDDA work best?
RT-FDDA works best when there are a large amount of observations available for assimilation.
How do I read the forecast graphics?
What does forecast cycle mean?
A forecast cycle is the time in UTC the model starts running again. There is usually analysis of the previous 6 hours of model output and assimilation of observations that have become available for this time. The model then begins its forecast. The forecast period can last for up to 36 hours. For this particular implementation of the system, the forecast cycles run every 6 hours at 00, 06, 12, and 18 UTC. If you see graphics up there with a forecast cycle time more than 12 hours old, consider the forecast to be somewhat stale.
What is a cold start?
A cold start is when the RT-FDDA system uses model grids other than it's own to start a forecast cycle. These grids are commonly Eta, GFS, Ruc, etc.
Where can I find out more about the parameterizations used for this forecast?
This system is based on the MM5 model. Please see the MM5 users documentation for more information. You may find this at: http://www.mmm.ucar.edu/mm5/mm5-home.html. A direct link to the discussion about model physics is: http://www.mmm.ucar.edu/mm5/documents/MM5_tut_Web_notes/MM5/mm5.htm
How can I learn more about RT-FDDA?
Please refer to our page describing RT-FDDA for more information.