Newman

A lot of times every model can be wrong with the northern extent of the precip shield. Sometimes the radar day of will give you an idea if there's any fighting chance. However, the NW confluent flow is likely going to eat up the northern shield, and if it doesnt, dry air and virga will be an issue with little forcing. I'm pulling for you guys in DC.

Here are some of Isotherm's thoughts. Let's not bridge-jump too soon. Everything's going to plan: Geopotential heights are likely to correct more positive over the PNA, NAO and southern AO domains as an ineluctable consequence of stratospheric alterations ongoing D10-12. By December 15th-16th, the geopotential structure alteration will have overspread most of North America and Greenland, as the stratospheric vortices are perturbed / displaced toward Eurasia. Robust w1 hit will impact the SPV via the felicitous tropospheric precursor pattern, and once the nascent blocking encompasses the NAO region, wave 2 will be enhanced again. This final follow-up w2 hit circa Dec 23-31 will be the primary opportunity to induce a technical SSW. I have thought that we'll come close, but near miss. Regardless, the tropospheric impacts will be quite significant. MJO should circulate should through p3, thereupon, rapidly losing coherency during passage in p4-5 by mid December. GWO should be back into/approaching phase 5 by about the solstice in my opinion. The momentum reversal processes are already beginning, as this negative/removal mini cycle will be efficiently overshadowed / dampened by the background, resuming +AAM state. +EAMT will increase in the coming week, with more rossby wave dispersion events and wly momentum injection. Classic walker cell forcing resumes again by the 18th, and we will see the retrogression of the GOAK trough into an Aleutian low position on or about December 20th/21st. As a consequence of which, temperatures neutralize/near normal by the 18th-19th, supportive of snow in the coastal Northeast as early as around the 18-20th, then cooler than normal air begins developing shortly following the EPO diminution via GOAK retrogression. December 20th-31st is colder than normal and active w/ an undercutting STJ, with SPV perturbation continuing. In other words, everything's on track. There are heterogeneous stances on initiation/timing among our colleagues here, but by and large, I see the disparities as fairly immaterial and we accord on the larger scale forcing mechanisms

Cutter on the 15th ushers in a better pattern, perhaps we can steal a storm around the 18th-20th, but the pattern fully matures around the 23rd and on into January.

12z RGEM:

The ICON gets the outer precip just to DC:

Although that spread is extremely skewed by one or two members that give the area like 10" lol.

I'M STILL HOLDING OUT HOPE lol We got the SREFS on our side.

Just gonna say that the GFS isn't going to budge at this range. It's going to stay locked in where it's at. Shorter range, high resolution models will be the first to pick up on any real changes at this range and, if trends go favorably, the GFS still won't budge until 24 hours out.

The men and women at Mount Holly are on our side with this one: The 12z ECMWF and GFS keep this system well to the south of the region as it progresses off the coast Sunday night. To be blunt, I am not buying what the models are selling, though I do think the sharp gradient in precipitation on the north side makes physical sense (given the strength of the surface high to its north). A perusal of ensemble guidance suggests the trend has been for a slower exit stage east of the southern-stream system, and there are indications that the interaction with the upstream northern perturbation somewhere in the vicinity of the northern plains late this weekend could act to (1) force the southern-stream system farther north with time (as models tend to struggle mightily with at this time range) and (2) act to develop a secondary low somewhere upstream (west) of the southern- stream low. According to the 12z ECMWF, this second low is prevented from moving northward by a digging shortwave in eastern Canada early next week. However, the GFS is much faster with this trough, suggesting that timing uncertainty is very large with this important feature. With so many perturbations and complex interactions at play and large run-to-run variability, I tend to resort to systematic biases of each model as a starting point. At this time range, models often are too aggressive with the northern-stream kicking the southern- stream system offshore before the inevitable northwest-trending tracks within 48 to 72 hours of the event. The 12z CMC is worthy of noting its farther northwest track and has been fairly consistent with this. Given all of the above, it is premature to trim PoPs in our area Sunday afternoon through Monday night. In fact, I spread PoPs northward to account for what I suspect are model biases exhibiting their usual selves. Given the trend this cool season so far, broad-brushing the timing and expanding PoPs well northward of medium-range consensus seems to me the wise choice at this juncture.

That IVT is going to surprise a lot of areas in SE PA and Southern NJ. It was picked up on all models, but not to the extent it is at right now.

Here were the 12z for comparison: Definitely a more consolidated lean to the north on the 18z.

Here were the 18z EPS fwiw: Credit to Tony/Metfan.

Yep that's what I touched on yesterday. Without the confluent flow lifting out, there's no way really for the storm to reach our regions. Also, a healthier phase would be welcomed.

Last 4 Para GFS runs:

Keep that northern confluent energy far enough north or blast it through quicker and it'll allow the heights up the east coast to respond quicker and allow this storm to come further north. If we don't see positive trends with the overall NW confluent flow in the NE and SE Canada then I don't see this storm coming too far north. The flow will just squash the system to the south. Good thing we've seen positive trends today with that regard. You don't want to be in the bullseye of a Miller A six days out. How many of our big Miller A's in the past 20 years have trended back north? These juiced up storms naturally want to pump heights with the latent heat release. Don't get me wrong, the bullseye will likely not be SE PA. Somewhere in VA will get the bullseye, but this storm is not far off from giving DC Philly and NYC a SECS or maybe even a MECS. There's just too much time left to call absolutes.

GEFS mean snowfall 18z vs 12z:

6. Hour. Difference.

We need a northern piece to drop down and phase. The energy is probably still up over the pole with little sampling. Models won't pick it up until 3 to 4 days away. I don't see the storm being as strung out and suppressed as the 6z GFS. The height falls will be up the coast rather than out with the western ridging. The storm has trended up in time now, leaving less room for the cold air to escape. Not to mention a juiced up system will naturally want to come north by pumping it's own heights.

We go through this every winter. The models are right where we want them. Could suppression be a concern? Yeah possibly. Could the storm ride the coast and produce mostly rain? Possibly as well. But in the end the pattern supports a big east coast storm and the ingredients are there. Timing is the big wild card, as it is in almost all of our storms.

I figured I'd share this. I made a list when reading Kocin and Uccellini's Northeast Snowstorms book of "Ingredients to get the Big One" and here are some (not all) similarities right now with this storm to other greats: 1. "West Coast ridge and downstream trough increasing in amplitude and decreasing in wavelength". Check. 2. "Vorticity Maxima passing between NC and NJ, heading northeast". Check. 3. "Possible southern and northern stream energy mergers". Check. 4. "High latitude blocking over Greenland trapping a 50/50 low, resulting in confluence over SE Canada". This one is little trickier. It's not like there's a huge NAO but the confluence is there that we need. 5. "Large increase of wind speed in upper-level jets upwind of trough axis and along the downstream ridge crest. Entrance region of upper-level jet streaks in NE US or SE Canada". This is a big player in the overall solution. How strong and how far north can we stretch that 250mb Jet.? 6. "Heaviest snows occur 50-300km north of the 850 hPa path". It's close. As you can see. This one has the looks of a truly classic snowstorm.

The GFS sucks I know that and it's been flipping every run, but what it showed at 6z is my biggest concern. The energy up in SE Canada is suppressing the flow enough to not allow the storm to gain latitude and gives DC a hecs. Not to mention the strong high pressure system north of the storm. This MSLP look is classic for an east coast snow storm. But is the press going to be too much? Now the models are going to be flipping every run up until we're 2 days out. But the suppression risk is REAL. One thing I hate sometimes when we're tracking is the ignorance to possible setbacks. I understand why we try to ignore the shortfalls in a storm we're tracking, but it can get us in trouble when we assume a storm "must" trend north but in reality the pattern doesn't fit it. Right now our biggest issue, verbatim, would be suppression. From now up until about 84 hours, we need to look at why the storm WON'T be affected, per say, by the suppression. However, just like the Jan 16 storm, sometimes even at 84 hours the models will be clueless. But the synoptic pattern set forth almost guaranteed that the storm (Jan 16) wouldn't be as south as modeled. I know that I'm going to be on the lookout for trends in the high pressure in the great lakes, the 50/50 low, and the possible nuisance energy in SE Canada suppressing the flow. Remember trends can go BOTH ways, good and bad for a storm threat. Don't get me wrong, the overall hemispheric pattern suggests a significant east coast storm. What I'm suggesting is why does it have to be a Philly to NYC storm? This storm is the real deal and I hope we all cash in next weekend.

One last thing I'd like to mention building off of Isotherm's thoughts is that, even with the PAC jet retraction around the 2nd week, it doesn't mean that the storm chances will increase dramatically. The Pacific will take some time to regain a classic NINO look and it'll probably take until after the 2nd week of December for our first "real" threat. That doesn't mean we won't possibly see snow around the 2nd week of December, but the 15th and on will likely be the best time frame to gear up for snow, just in time for Christmas.

The AAM pattern we're in is really creating a hostile Pacific, as the GFS shows above. The jet extension should relax around the 5th-7th of December. Here is Isotherm's thought's on this as well: Angular momentum removal in the sub-tropics via the MJO and GWO progression into suppressed AAM octants (as indicated by udiv propagation into Indian Ocean) will ultimately lead to a jet retraction event by week 2, following this current jet extension. The present negative FT will eventually manifest in the mid-latitude pattern in about 10 days. Implications are that the Pacific wave-train and jet configuration will acquire a somewhat Nina-esque appearance in the first 10 days of December. Blocking will be developing over the NAO/AO domains contemporaneously with a wavier/Aleutian ridge regime in the Pacific in the December 1st-10th period. Colder weather will return to the Northeast in the means by the second week of December due to the amelioration in Arctic/Atlantic signalling; however, the Pacific will be less auspicious initially.

It's the Pacific that's killing us right now heading into the first week of December. The PAC jet extension is breaking down the west coast ridging extensively: That kills any chances for a snowstorm for the 1st to the 5th. Then the jet extension relaxes and we should have a better opportunity around the 7th-12th time frame: Newest GFS shows the chances for a snowstorm around the 6th-7th:

I'm just gonna stop talking and let the models sort themselves out lol. Pattern recognition > models and right now the models are struggling mightily. If the latest GFS is right, we head into a fairly classic -EPO pattern heading into December. I'd like to reiterate what I did way back before the winter started - A favorable Pacific is almost always more welcomed than a favorable Atlantic.