NEWR/WRF EMS - Frequently Asked Questions [FAQ]

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NEWR/WRF EMS - Frequently Asked Questions [FAQ]

Post by meteoadriatic »

FAQ - Collection of frequently asked questions about NEWR and WRF EMS.
[continuously updated]

Q: What is WRF EMS?
A: WRF EMS stands for Weather Research and Forecasting Model - Environmental Modeling System. It is created by NOAA/NWS SOO STRC, from open source WRF software, that is a specific computer program with a dual use for forecasting and research. WRF is the latest numerical program model adopted by NOAA's National Weather Service. WRF EMS package includes the original WRF model code and a series of scripts used to rapidly acquire initial conditions, launch forecasts, and post-process model output into a more readily usable format.

Q: What is NEWR EMS?
A: NEWR EMS stands for NEMS WRF EMS. NEWR EMS is new version of EMS package, scheduled for release in Spring 2012. As STRC webpage said, the name change is necessitated by the inclusion of the NEMS NMM-B model into the EMS package. Consequently, it's no longer a WRF-based system. Yes, the WRF will remain a significant part of the EMS but just not in the name.

Q: What is NMM-B?
A: NMM-B is newest NWP model developed by NCEP, evolved from the WRF NMM. NMM-B stands for Nonhydrostatic Multiscale Model on the B grid.

Q: Is WRF EMS free of charge?
A: Yes. Give a thanks to it's developers!

Q: Where I can get WRF EMS?
A: Please take a look here, at the bottom of the page. You will receive installer script that will download and install WRF EMS on your Linux computer.

Q: Will an old installer script I have work for newer WRF EMS versions?
A: No. For example, installer for version 3.1 will not install version 3.2 correctly. You should get updated installer script. Either way, with a new installer you can't install old version!

Q: Can I install WRF EMS without installer script?
A: It is possible, but if you really want to try out your skills, go on and figure out all things on your own.

Q: Is there a user manual for WRF EMS?
A: Of course, click here.

Q: So, I can run my own weather forecast model at home?
A: Yes, and pretty much easy. Minimal Linux knowledge is required and fun can begin.

Q: How powerful computers are needed to run WRF?
A: It depends on your needs. You can run it on low end desktop PC with Pentium or Athlon CPU and 1 GB of memory, but this will almost certainly be NOT enough for any practical purporse. However, today's desktop computers for office, multimedia use, and especially gaming will be probably sufficient to give you your weather forecast every day. Newest processors on the market like Sandy Bridge (Core I7 second generation) are exceptionally fast in executing WRF code. However, keep in mind this: more RAM you have, better.

Q: Can WRF EMS be run on a cluster of computers over network?
A: Yes, easy. WRF EMS includes precompiled MPICH2 code and all tools needed to distribute processing over network.

Q: Do I need to have PGI (or any other) compiler on my system?
A: No, WRF EMS comes with all stuff statically precompiled so it will work on almost any Linux system.

Q: Which Linux distro is best for WRF EMS?
A: WRF EMS can run on almost any Linux distribution, however, if I have to name one, my choice would be Centos/RedHat.

Q: Any special software dependencies?
A: Not much, but csh/tcsh shell must be installed for system user that will execute WRF EMS.

Q: Do I need root access to install WRF EMS?
A: Not necessary, it can be installed as normal system user in it's home directory.

Q: Do I need X server for WRF EMS?
A: No, everything can be handled from command line, including creating domains. Yes that's right, you don't need to use domain wizard (dwiz), and if you ask me better don't, it is full of bugs.

Q: 32 or 64 bit software?
A: If you have 64-bit CPU than it is strongly suggested that you install 64-bit operating system and 64-bit WRF EMS binaries. It will run faster, and also some things can fail if you use 32-bit software, like postprocessing >2GB grib files in GrADS (32-bit wgrib doesn't support them).

Q: Does WRF EMS need Internet connection to work?
A: If you intend to run real time forecasts then yes. WRF EMS will automatically download GFS data needed for model intialization and atmospheric boundary conditions around your domain during model run.

Q: Can I use WRF EMS for case study simulations?
A: Yes, relatively easy. You just won't use ems_autorun script because it is designed for real time forecasts. You also need to find input data for your case yourself. Also, take a look at here.

Q: My WRF run has been finished. How can I see forecasts now?
A: You need to postprocess your model data. You will first have to run ems_post script on your model data, and then you can use any graphic software or whatever you want to view/generate forecasts. I use GrADS for all my graphic forecast stuff (weather maps, meteograms, skew-t diagrams and so on). Note that GrADS is included in WRF EMS package among many other tools! However, if you didn't used any meteo-graphics tool yet, it will require some learning. These tools are not simple point-and-click type software, but also not very hard to learn, at least, GrADS.

Q: Can I overclock my CPU for faster model run?
A: Yes, but keep in mind that overclocking adds additional stress to your system and thus computer components are more likely to fail (die), so I don't recommend doing that. Rather invest in faster hardware or build a small cluster. If you still don't want to take my warnings seriously, have a look here, I wrote short guide how to tune your computer for faster modelling.

Q: What is difference between NMM and ARW?
A: You can think of them as completely different models, and WRF as software infrastructure needed for them to run. So, NMM and ARW does not share much of their internal algorithms. Different equations, different dynamics, different physics and finally different results, sometimes much different!

Q: Which core is better, NMM or ARW?
A: This is not possible to answer. There is no "better" one, because then everybody would use it and other one will be abandoned. This is not the case, so for somebody NMM will work better, and for other ARW will serve best for his purporses. Note that NMM is almost 2x faster than ARW in running, so this is why vast majority of users chose NMM for realtime forecasts. Researchers tend to use ARW more than NMM.

Q: How to chose which core to start during model run?
A: NMM and ARW models require different domains to run. So, by creating different domains, you will define which core will be run on that domain. You do that in graphical tool domain wizard when selecting domain projection type, or, if you are command line lover than with --core (nmm|arw) switch in script.
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