NYC/PHL 12/21-12/27 Forecast Threats

[eduggs]

Its possible but not based on the synoptic setup shown by the 18Z GFS....the biggest problem is the positioning of the ridge out west, its likely too far east but also the overall degree of phasing and ridging pumping ahead of the system seems strange. The 12/15/89 bust was modeled similar to this early but it severely overphased, in that case though the ridge was positioned well to the west and the system had already undertaken a negative tilt back over the Oh Valley...in this case the system would have a tough time amplifying that fast given there is some confluence to the pattern.

Interesting comparison to '89 and I think I agree with your sentiment. But I decided a long time ago that weather models are better at predicting what is physically possible than I am. So if a model says a s/w trof can buck the confluence, I consider it a possibility.

[tombo82685]

didn't see this posted but here is the 12z euro ens

[LVblizzard]

NAM wants to bring snow into PA on Wednesday night? Yeah, I don't think so. If it somehow did verify, though, that would be one impressive Norlun event:

[LVblizzard]

didn't see this posted but here is the 12z euro ens

Very good agreement with the GFS ensembles.

[Collegestudent11]

I wonder what the effects of an extended snowfall as per NAM would have on the medium range forecast for the christmas storm.

[tombo82685]

NAM wants to bring snow into PA on Wednesday night? Yeah, I don't think so. If it somehow did verify, though, that would be one impressive Norlun event:

i would honestly die if this happened, that would be a sick norlun. Sne gets clobbered. Assuming the 0z nam post 60 hrs is correct.

[supermeh]

I don't think any other model has this, but I could be mistaken in terms of that NAM Norlun event.

[MJO812]

Hour 78 and 84 on the 0z Nam are really interesting.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_ref_078l.gif

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_ref_084l.gif

[Stormlover74]

But 12/15/89 was forecast to be a major snowstorm just hours prior...nobody mentioned the possibility of it turning to rain

Its possible but not based on the synoptic setup shown by the 18Z GFS....the biggest problem is the positioning of the ridge out west, its likely too far east but also the overall degree of phasing and ridging pumping ahead of the system seems strange. The 12/15/89 bust was modeled similar to this early but it severely overphased, in that case though the ridge was positioned well to the west and the system had already undertaken a negative tilt back over the Oh Valley...in this case the system would have a tough time amplifying that fast given there is some confluence to the pattern.

[Zelocita Weather]

Hour 78 and 84 on the 0z Nam are really interesting.

http://www.nco.ncep....am_ref_078l.gif

http://www.nco.ncep....am_ref_084l.gif

Yup sim radar on the 84 hour has pretty goos snows still at the end of the period from E NJ/NYC and East.

[SnowGoose69]

But 12/15/89 was forecast to be a major snowstorm just hours prior...nobody mentioned the possibility of it turning to rain

Well we didn't have the modeling then that we have now...Will posted the setup on here when Alex mentioned it 2-3 months back and its remarkable how the models missed it.

[SnowGoose69]

Why the 00Z NAM is likely out to lunch....a similar scenario to 2/25/90 it depicts, but notice the massive PVA and dynamics at 500 in the 1990 event...thats non-existent for this week at 500 and is too far south.

http://www.meteo.psu.edu/~gadomski/NARR/1990/us0225.php

[tombo82685]

Why the 00Z NAM is likely out to lunch....a similar scenario to 2/25/90 it depicts, but notice the massive PVA and dynamics at 500 in the 1990 event...thats non-existent for this week at 500 and is too far south.

http://www.meteo.psu...1990/us0225.php

the nam has been atrocious lately. Yesterday it was still showing a sne hit up to the 6z runs this morning from the ots storm. I would love to see the verification scores for it against other models....anyways gfs time...no wammies!

[Isotherm]

Updated a new post on my website regarding the upcoming storm potential and the January pattern (which shouldn't reverse to a blowtorch IMO).

http://www.lightinthestorm.com/archives/312

[SnowDemon]

GFS has launched. Out to 12.

[Stormlover74]

of course. That storm still stings though. 4 to 8" of snow followed by an arctic outbreak 9 days before Christmas. I remember temps in the upper 20s when the snow began. About an hour later it was near 40 and pouring outside. It finally went back to snow after midnight but back that point it was too late for anything. Of course then it was bitterly cold with alot of dustings before the major warmup/flip ensued

Well we didn't have the modeling then that we have now...Will posted the setup on here when Alex mentioned it 2-3 months back and its remarkable how the models missed it.

[eduggs]

Near the end of its run, the NAM shows something like a 1000 mile easterly fetch at 300mb near 40-45 degrees latitude. That's pretty unusual.

[Rainshadow]

What stood out to me is that the Euro yesterday had the 500mb low in Canada sort of suppressing the track since it was a stronger feature than the GFS had it yet the GFS was only about 50 miles north of the Euro without the big 500mb low, that to me meant for sure it was too far south with the track if the Canada vortex was not as big of a player...I don't like the American models on SW flow or semi-SW flow type events and to me thats what this is, a slightly suppressed SW flow event....I warned everyone the NAM was going to be way south on it when it got in its range, the NAM is notorious for suppressing those more than any models, I remember when it had the 12/18/08 event tracking over DC 2 days out, in the end it was over NYC more or less.

It didn't look like there was much Rocky Mountain ridging though with that event. That being said its still 5-6 days away, so there are not many solutions that are off the table at this point.

[tombo82685]

yea gfs is totally against the nam's norlun idea

[_AR_]

yea gfs is totally against the nam's norlun idea

I could see the higher resolution NAM catching onto a Norlun trough first, but I would also suspect that it would tend to over-do it. I believe the NAM has caught onto Norlun events in the past.

[Rainshadow]

yea gfs is totally against the nam's norlun idea

Unless the nam is similar to the Canadian regional gem through its entire run, I haven't found too many viable nam solutions up to that forecast point or beyond.

[tombo82685]

hr 87 has 1008 low in far se colorado, 50/50 low is a lot stronger, the dige out ahead of storm is a little weaker thus far

[tombo82685]

out to hr 99 sub 1012 low over ne oklahoma a good bit flatter than the 18z solution at hr 105

[mattinpa]

out to hr 99 sub 1012 low over ne oklahoma a good bit flatter than the 18z solution at hr 105

Wouldn't we want flatter than the 18z, though?

[tombo82685]

northern mo and central ill getting hammered at hr 105, sub 1012 over north central ark

[tombo82685]

Wouldn't we want flatter than the 18z, though?

yes thats what im saying its flatter meaning better in this case

[gkrangers]

Wouldn't we want flatter than the 18z, though?

Yes. We want what the 18z GFS did, by wrapping up the storm, we just want it to happen a bit further south and east. Flatter through 90+ hours is a good way to get there.

[tombo82685]

notable difference at hr 108, 50/50 is locked in whereas 18z had it out of the picture, storm is also further south

[eduggs]

Wouldn't we want flatter than the 18z, though?

Not too flat though. Majority of guidance has been slightly too flat past few days. I'd prefer sharp as 18z but further south with the s/w, i.e. more digging.

[tombo82685]

hr 114 has a sub 1008 low in western ten northern stream starting to get involved