There are still problems with 12z NAM

[ALhurricane]

As has been the case, the forecast surface low positions on the 12Z NAM still do not synoptically make since in my opinion.

First let's take a look at the model initialization...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _000.shtml

As HPC has already mentioned, the NAM failed once again to initialize the surface low correctly. It's at least 4 mb too weak. Bad initialization usually means a troubled model forecast...

Now let's go to 24 hrs...
http://www.nco.ncep.noaa.gov/pmb/nwprod ... _024.shtml

Focus on the jet structure and the favorable left exit region of the jet. In this case, the surface low position is in a decent location given the position of the upper jet. Unfortunately the NAM has problems coming up...

36 hrs...
http://www.nco.ncep.noaa.gov/pmb/nwprod ... _036.shtml

The position of the jet and the surface low do not match up synoptically at all. Given the jet position, I would expect to see the low somewhere just off the NC/VA coast. Instead, the NAM has the low up over Maryland and occluding... if you were to take a look at the 500 mb...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _036.shtml

You would see the NAM has the system vertically stacked already... not likely in my opinion.

Now let's go to 48 hrs...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _048.shtml

Jet structure once again tells me the low should be somewhere just off the NJ/NY coast...but the NAM has it inland over NYC.

In all the 12z NAM still doesn't add up. If you were to believe the NAM upper air, then that would support a more coastal track. Given all the other model guidance, I am still leaning toward a coastal hugger.

[jkt21787]

Hey AL, great to see you back on! Its been a while.

Not much going on here, so like you watching this east coast system. And as you said, the NAM is not handling it well. You highlighted some major problems that are being depicted in 12z run, and certainly needs some serious thought. I think its going to be a major storm for the big cities. They still could change to a mix or even rain, but still 6+ looks likely to me.

[ALhurricane]

Hey JKT,

It looks like we in Memphis will get some light rain this evening, but that is about it. It will turn markedly colder for the first half of the week. I still think guidance is too warm, but we shall see.

New 12z GFS coming in is much closer to what I thought. It implies a big snow for the I-95 corridor. Could be a brief changeover in places like NYC, but snow for the majority of the time. Big event developing as we speak!

[jkt21787]

Hey JKT,

It looks like we in Memphis will get some light rain this evening, but that is about it. It will turn markedly colder for the first half of the week. I still think guidance is too warm, but we shall see.

New 12z GFS coming in is much closer to what I thought. It implies a big snow for the I-95 corridor. Could be a brief changeover in places like NYC, but snow for the majority of the time. Big event developing as we speak!

Yeah, we'll see a little rain tonight it looks like, then much colder. I agree that guidance is warm, I believe they are being biased by climo and the fact that its almost March. The first half of the week will probably have below freezing lows and 40s or low 50s for highs. I was hoping for maybe a winter weather threat while the cold makes a return the first half of the month, but not much chance as it looks right now. I guess I am ready for severe weather season, we already had an early visit last week!

The GFS is more realistic, and implies heavy snows for the I-95 cities. It also says you won't have to go too far west before there is little if anything to talk about. A tight accumulation gradient looks likely.

With the rain further south than orginally forecast (we were supposed to be seeing it right now), does that imply the more southern and eastern track that is key for the Northeast?

[jkt21787]

Also of note is the Tornado watch back in central FL right now. This shows how powerful this system is already becoming. How often do storms that potentially produce tornadoes in FL becoming major snow storms in the northeast? I know the superstorm in 93 did, but did it happen in any others?