New NAM Flavor to Be Released October 18

Bob Hartig

Bob Hartig

EF5
Joined
Jul 2, 2004
Messages
1,781
Location
Hastings, Michigan
I understand that the NAM is due for an update on October 18. Here's a link:

http://nws.noaa.gov/os/notification/tin11-16nam_changes_aad.htm

Can anyone tell me in simpler English what this means? From what I gather, the NAM-WRF is getting punted out of the picture and will be replaced with this new version. The new NAM has gone through a few developmental headaches that have resulted in the release date being bumped a couple times from earlier in the year, but I suppose that's to be expected. The October 18 date, which is this coming Tuesday, seems pretty solid.

Who knows more about this? What significant improvements is this new iteration of the NAM going to make?
 
Bob Hartig said:
Can anyone tell me in simpler English what this means? From what I gather, the NAM-WRF is getting punted out of the picture and will be replaced with this new version. What significant improvements is this new iteration of the NAM going to make?
Click to expand...

I've been in contact with someone who works for NCEP and has been explaining a few things to me about the new model. The new NAM, which is being called the Nonhydrostatic Multiscale Model on B-grid (NMMB), which as far as I've been told, is completely different from the WRF (apparently NCEP does not like the WRF much), will have a few sets of changes. One set of changes is physics based (improved microphysics, for example). Another is improved dynamics (change in the way boundary condition data is fed into the model). Probably the biggest change is in the configuration. While there will still be a 12 km parent domain, there will be a ton of high-resolution nests, including a 4 km nest covering the CONUS and some fire weather nests using grid spacing as fine as 1.3 km. These hi-res nests will use explicit convection, so the realism in QPF should be very much improved.

The TIN also mentions changing the definition of the tropopause and using the virtual temperature correction in CAPE/CIN/LI computations.

Finally, the TIN mentions improved clock time for the model runs. They expect all runs and nests to be done in 3 hours of initialization time, which is a little earlier than what is currently going on.

I could go into a little more detail, but I'll save my fingers for now. I'm sure others can chime in on the changes, too.
 
It boggles my mind how that can run in under three hours. I am curious as to how much better it would handle with winter precipitation. It seems as if the focus of changes have been towards convection and summer modes (and fires). There doesn't appear to be much difference with scanning over it, to the actual data type and format which is convenient (yay for thunder for GRIB files!). Hopefully this works out well!

Chip
 
Life is full of new acronyms to learn, and the latest here seems to be NEMS-NMMB:

The prediction model used in the NAM run will go from being the strictly regional Nonhydrostatic Mesoscale Model (NMM) to a new extended capability version now known as Nonhydrostatic Multiscale Model on B-grid (NMMB), which can be run either regionally or globally with or without embedded nests. This NEMS-NMMB also will serve as the prediction model running in the NAM Data Assimilation System (NDAS).​

I am uncertain what this means exactly. But my understanding of the NAM is that it's just a slot occupied by a particular mid-range forecast model, and that the model is prone to periodic replacement. In times past, the NAM slot was filled by ETA. Then ETA got replaced by the NMM-WRF, which is the currently reigning model. The way I'm piecing together the above language, we've now got a new kid on the block called the NEMS-NMMB that will replace the NMM-WRF as the operative NAM. That doesn't mean the NMM-WRF will go away; it just won't be the presiding model for the NAM anymore. As of Tuesday, that will be the NEMS-NMMB

Take the above as more of a question than a statement. My grasp of this subject is flimsy, and I'm just trying to sort through this latest gobbledegook. So Rob, if you, or if anyone here, can shed more light on the matter, feel free to correct me.
 
Bob Hartig said:
I am uncertain what this means exactly. But my understanding of the NAM is that it's just a slot occupied by a particular mid-range forecast model, and that the model is prone to periodic replacement. In times past, the NAM slot was filled by ETA. Then ETA got replaced by the NMM-WRF, which is the currently reigning model. The way I'm piecing together the above language, we've now got a new kid on the block called the NEMS-NMMB that will replace the NMM-WRF as the operative NAM. That doesn't mean the NMM-WRF will go away; it just won't be the presiding model for the NAM anymore. As of Tuesday, that will be the NEMS-NMMB.
Click to expand...

I believe that's correct.
 
Ahhh! Thanks Jeff! I was casually looking for it yesterday for WxChallenge and couldn't find anything. Sweet deal!

I do have one quick question, it is probably something dumb, but what does "Shelter" mean? It is with the 2m Tp and Dp.

Chip
 
That's a really good question, Chip. The definition of a shelter variable is not readily available out there. However, from some WRF post-processor code I looked at, it appears that "shelter" refers to a level, much like "surface". I think shelter temperature is probably 2 m temperature. I have also asked wrfhelp about this so I will hopefully get a clear answer soon.
 
I'm bumping up this thread in order to get a sense of where the NAM is at today. Presumably the NEMS-NMMB now presides as the operative NAM in place of the NMM-WRF. So when I consult the NAM on COD or F5 Data or Twisterdata or any other source, the NEMS-NMMB should be what I'm getting. But since I haven't heard any further discussion on the matter, I'm unsure whether that assumption is correct.

Used to be, the acronyms NAM, WRF, NAM-WRF, and NMM-WRF got used interchangeably (to my confusion, I might add). Nowadays I don't hear any similar talk of NAM-NMMB, NEMS, and so on--and now, ironically, what I find confusing isn't the multiple synonyms for NAM but their absence. It makes me wonder what in fact I'm getting these days when I consult the NAM at the usual sources.

Would someone knowledgeable in these matter kindly bring me up to date on the state of the NAM?
 
Last edited by a moderator:
Bob, you can find probably all you want to know about the NAM at this site: http://www.emc.ncep.noaa.gov/index.php?branch=NAM (although it looks like there's some old information even at this link)

I have a friend who works for NCEP, but he doesn't work on the NAM. I've asked him why the 4 km CONUS nest graphics still don't have a "home" site, and he doesn't know. All he knows is NCO, the organization that makes the graphics for the MAG site (http://mag.ncep.noaa.gov/NCOMAGWEB/appcontroller) is either arrogant, lazy, or very bad at communicating, as they haven't really shown any updates to the NAM forecast graphics (although the Rapid Refresh graphics have replaced those of the RUC). So I honestly don't know exactly what is what. I just know the "NAM" is the name given to NCEP's limited-area/mesoscale model to be used for operations in the US. At its core is the NMMB, but several domains are run, including a 12 km North American sized domain, a 4 km nest for just the CONUS, and at least one 1.33 km very small nest for fire weather or severe weather focus.
 
Thanks for the info, Jeff--I appreciate it. After checking out the first link, I'm still unclear, but I guess you are too, and I suppose that the only folks who really know what's going on with the NAM are the inner circle at NCEP and NCO. At this point, I'm left to assume that the NEMS-NMMB now fills the NAM slot, but the popular outlets for NAM are equipped to display only the 12 km domain, not the 4 km convective nests or the 1.33 km fire weather nest.
 
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