12z Model Guidance 12/9

[benfica356]

Nam out to 6, waiting for miracle

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[ChescoWx]

The 6z model run and my Wxsim module indicated a wintry solution for the NW Philly burbs but with less liquid equiv (under 0.5") Temps here in NW Chesco never get above 35 and a mix of IP/SN and rain becomes all snow in the PM with a 1 or 2 inch accum.....of course this 12z run...will have yet another solution.

[ag3]

Sref's...Seems like it has a secondary pretty far south:

[earthlight]

The NAM is definitely a good bit deeper with the shortwave over the Great Lakes at 21 hours, and it's lowering heights there as a result of that.

[earthlight]

Through 27 hours...now considerably lower with heights over the Northeast and Great Lakes thanks to the deeper clipper shortwave noted earlier. The shortwave entering the Pac NW seems slower.

[earthlight]

Going to be very interesting to see what happens this run, at the surface, considering the changes we have seen aloft through 33 hours.

[gkrangers]

Through 27 hours...now considerably lower with heights over the Northeast and Great Lakes thanks to the deeper clipper shortwave noted earlier. The shortwave entering the Pac NW seems slower.

We want a deeper clipper, right?

[nynjpaweather]

Now this is getting very interesting. I've been maintaining the idea of a secondary low and wintery solution of the interior, but more influence from this clipper is going to create a more complicated forecast just away from the coast as well if the first 36 hours of the NAM is correct.

[tornadojay]

Going to be very interesting to see what happens this run, at the surface, considering the changes we have seen aloft through 33 hours.

maybe now that the system is getting ready to enter the west, the models will be able to start handling it better from the starting point.

[SnoSki14]

Wouldn't a stronger clipper allow for an earlier phase since it pulls down the PV further south.

[benfica356]

Now this is getting very interesting. I've been maintaining the idea of a secondary low and wintery solution of the interior, but more influence from this clipper is going to create a more complicated forecast just away from the coast as well if the first 36 hours of the NAM is correct.

steve, do I count as just away from the coast in Roselle Park, NJ?

[earthlight]

Wouldn't a stronger clipper allow for an earlier phase since it pulls down the PV further south.

Doesn't have much to do with the PV, but what it could do is pump up the heights back to the west across the Central US, and with the slower shortwave entering the Pac NW, allow for a further north solution.

[benfica356]

looks like the system is further south at 39 hr than 6z nam at 45 hr

[SnoSki14]

One thing is that the lack of a SE ridge will not allow the storm to pump very warm air out ahead of it. We might not get out of the 40s even with the storm cutting far to the west of us. It's also the reason why we're seeing more a transfer solution but unfortunately it's transferring too far to the north and we don't have a cold air mass locked to help us.

[psv88]

One thing is that the lack of a SE ridge will not allow the storm to pump very warm air out ahead of it. We might not get out of the 40s even with the storm cutting far to the west of us. It's also the reason why we're seeing more a transfer solution but unfortunately it's transferring too far to the north and we don't have a cold air mass locked to help us.

NWS has rain snow for sunday night and monday, and says a brief period of accumulating snow monday morning for the city...

[nynjpaweather]

steve, do I count as just away from the coast in Roselle Park, NJ?

I think you are mostly rain at this point. What I should have said is that more of northwestern NJ and the NW suburbs of Philadelphia may be in the game now.

[nynjpaweather]

NWS has rain snow for sunday night and monday, and says a brief period of accumulating snow monday morning for the city...

Very reasonable approach.

[earthlight]

Looks far north with the primary through 57

[ag3]

Looks far north with the primary through 57

[nynjpaweather]

Looks far north with the primary through 57

The key is that short wave over the Upper Mid West. If that disturbance does not phase with the disturbance over Canada, than the trough goes negative, coastal forms and NW interior gets an icy mess. If the disturbance begins to phase with that disturbance over Canada, the primary remains over the St. Lawrence River Valley and everyone is eventually rain.

By the way, as I suspected the CAD is starting to show up nicely as we get closer for NE PA, NW NJ, and the Hudson Valley.

[Yeoman]

Looks like rain for Chicago

[CooL]

Also nam has the primary much stronger than say, the gfs. Which in the end is probly bringing in even more of a SW flow.

[nynjpaweather]

Considering the strength and location of the strongest PVA is over the Southeast, I would question the magnitude of the surface low, not the location, up to this point over the Great Lakes. If the guidance was showing a phase with the disturbance over Canada, I'd buy it. However, there is clear separation here. So I like the position, just not the strength of the low.

I also expect the coastal to start taking shape by Sunday evening with heights/cold air crashing east as the secondary low starts to gain steam. Just to be clear, still rain along the coast, focus should be over the NW interior. Just don't want anyone to confuse what I'm saying as advocating a snow storm for NYC or anything of that nature.

[bluewave]

It looks like SREF mean is moving toward the more amplified 0z Euro.

[benfica356]

me thinks that the NAM could have been closer to Euro but since its a stronger primary, that isn't the case. Secondary is developing still though and cold air coming in

[_AR_]

ooo Im liking the SREF mean.

[benfica356]

12z nam at 500 looks somewhat similar to 18z GFS yesterday at 500

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[earthlight]

12z nam at 500 looks somewhat similar to 18z GFS yesterday at 500

Not really, the NAM is way, way, way more amplified on the east coast and way more phased with the Polar Vortex.

[NorEaster27]

Considering the strength and location of the strongest PVA is over the Southeast, I would question the magnitude of the surface low, not the location, up to this point over the Great Lakes. If the guidance was showing a phase with the disturbance over Canada, I'd buy it. However, there is clear separation here. So I like the position, just not the strength of the low.

I also expect the coastal to start taking shape by Sunday evening with heights/cold air crashing east as the secondary low starts to gain steam. Just to be clear, still rain along the coast, focus should be over the NW interior. Just don't want anyone to confuse what I'm saying as advocating a snow storm for NYC or anything of that nature.

I still think it will be hard for the adirondacks to have a mostly snow event out of this, looking more like a mix to maybe some backside snow. I dont see any potential right now closer to the coast, even if we are talking about NW NJ or the lower HV. Getting snow on the backside as the cold moves in is very tricky and often overforecasted by the models.

[ParanormalWx]

I still think it will be hard for the adirondacks to have a mostly snow event out of this, looking more like a mix to maybe some backside snow. I dont see any potential right now closer to the coast, even if we are talking about NW NJ or the lower HV. Getting snow on the backside as the cold moves in is very tricky and often overforecasted by the models.

Very true. With the negitive tilt, dry air usually comes in right after the front and kills the precip. then we're waiting for some LES.