NAM Phase Shift Westward (Too Slow)

[baroclinic_instability]

The NAM can be good at certain times, and it has its uses if used carefully by the forecaster, but for the most part, it is just plain bad. I talk about the NAM "Phase Shift" issue a lot, but I constantly see threads where members are making use of it for their forecast because it shows "potential" to phase, for instance, or are just wondering why it is so slow. I think most experienced mets are well aware of this problem, but it arises under certain weather patterns where the entire height field is "phase shifted" westward, resulting in a far too slow progression of weather features. Sometimes it can rear its ugly head as early as 6-12 hours into the forecast with errors growing with each successive forecast hour through 84 hours. This is not uncommon, but it has been especially atrocious this storm.

Problems? There are differing theories, but one logical explanation is its early runtime (compared to the GFS), therefore it relies on the previous run GFS to initialize its boundary conditions (i.e. a 12Z NAM run is initialized on the boundaries with the 06Z GFS). That still can't explain it all though. Something else is obviously wrong...if anyone has ideas post here.

Of course, it can do some things quite well including rapid and intense marine cyclogenesis and cyclogenesis associated with deep slow progressing and deep PV Anomalies over intense baroclinic zones, surface wind fields, mountain drag, downslope wind storms, lee waves, etc.

Compare the NAM @ 0Z Friday :

Resized to 91% (was 972 x 696) - Click image to enlarge

GFS at the same forecast hour:

Resized to 91% (was 972 x 696) - Click image to enlarge

Note in the NAM, compared to the GFS, how far behind the shortwave over the northern plains is...and how far behind the shortwave over Nevada is.

Then look at the NAM this morning at the same forecast time. Note how it is "corrected" and everything is in phase (faster):

Resized to 91% (was 972 x 696) - Click image to enlarge

Here are the HPC NAM 500 hpa verification fields (red is the forecast which is being verified, blue is the the latest NAM run), notice how the NAM fields are consistently phase shifted W and can only correct themselves within 24 hours:

84 Hours:

72 Hours:

60 Hours:

48 Hours:

36 Hours:

24 Hours:

12 Hours:

Here is the HPC verification page for those interested.

http://www.hpc.ncep....tml#diagnostics

[Cyclonicjunkie]

So would it be safe to say that the NAM is a excellent model for genesis?