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12Z Guidance Discussion 12/23/2010


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alll very good points...

3. according to then GFS and GGEM.... but this is kind of circular reasoning no?

your point is right but you are looking at those Models that show storm or one that is not close enough ... to show thee is no storm that is close enough?

No, you're right ... some models are more progressive with this streak than others

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Here are my thoughts:

There are significant differences even at initialization for both the NAM and GFS at 12Z. Looking at the 500 hPa initialization charts, the NAM seems like everything is shifted a bit west compared to the GFS. With regards to the western Atlantic low, the NAM shows a stronger low with more of a elongated trough to the SW, the vorticity maxima around the low are stronger. The vorticity maxima in NW Arizona is displaced about 50 miles west of the GFS and it is stronger.

At H+24 the trend persists, the western Atlantic low is shifted west with the NAM but also a bit weaker than the GFS. The vort max has moved ESE to the Texas Panhandle where the NAM is a bit further west, a bit slower and a bit stronger.

At H+48 the trend persists, but not only that the GFS & NAM begin diverging significantly. In my view, the NAM has a perturbation problem at initialization which becomes a positive feedback loop throughout the entire model run. The NAM has the vort max southwest of Galveston Bay, TX and the northern stream energy around Kansas City, MO. Meanwhile, the GFS is a bit less amplified with both the southern and northern streams, however the vort max in the southern stream is much more progressive. At H+48 the 500 hPa vorticity maxima is around Baton Rouge, that is a difference of about 250 miles and is extremely significant in my view at H+48 when we consider the phasing need which others have discussed.

A lot happens after H+48 so I’ll go to H+60. The NAM is not phasing because it is slower with the southern stream vorticity max. The northern and southern streams are clearly separated with the vort max well south of New Orleans, while with the GFS the streams are beginning to phase, the separation of the northern and southern streams are clearly less identifiable, the trough is displaced further west and is beginning to become more amplified.

At H+72 the the NAM is beginning to phase put the initial piece of southern energy is driven down to West Palm Beach, FL? The GFS is more phased and the upper-level trough is more amplified.

After 72 hours I wouldn’t trust either model so I’ll patiently wait for the ECMWF ensembles to come out, but in a nut-shell I believe the NAM is suffering from initialization issues. I'm very interested to see the ECMWF's interpretation of the initialization and speed of the energy in the southern stream.

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What does this say about the Euro if the NAM and GFS end up right?

That the Euro is a piece of ****and needs an update. What an awful UKMET coup- I don't think it had us getting any precip at all. And congrats as well to the JMA, KMA, NOGAPS, etc. The southern shortwave is now being better sampled and it is not at all what it had been modeled to be. It just dies out, which doesn't allow any significant phase really with the northern stream. This by the way, makes complete sense in a La Nina. The Euro will completely fold in a matter of hours.

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To my untrained eye, it seems like we're not missing this by much at all.

The 66 hr pane of the GFS shows that the s/w's catch each other and phase, but you don't get the trough turning negative quite in time.

Sort of looks that way. Close, but the northern stream is just not catching the southern shortwave now. I suppose how "close" it looks to happening still keeps it kind of intriguing despite how it's depicted in the 12Z NAM and GFS.

We get some kind of very light overrunning in the MA late on the 25th according to this, and that's about it.

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What does this say about the Euro if the NAM and GFS end up right?

what it tells me is this... The gfs is garbage 7+ days out b/c it teases us with multiple runs of a snowstorm then in the mid range the euro picks up on it - we all get excited in the 5-6 day range and then slowly the nam and gfs start to crummble. We all sit and hope that the euro is right as the American models begin to sniff out the fact that this isn't going to be the blizzard of the century. At the end of the day the euro is not king bur just a tease. Lastly we shouldn't get to excited over threats 100+ hours out.

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