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Some the hi res models will prob start showing it tomorrow at some point.

100%

Sitting inside the 1" total here in Rutherford. Lord

Synoptic Overview 3 Well, we’ve made it. At this point our synoptic scale features are more or less set in stone and all we will see are some minor shifts; however, small shifts aloft may be the determining factor between who gets 6 inches of snow/sleet and who gets 20 inches of snow. I will start off the review with our key changes since my last outlook two days ago, I will then progress over the synoptic setup of this storm and the relationship it has with our thermals. Additionally, I will mention the features we want to see shift around to get a snowier outcome. This Overview is made with the 12z runs minus the Euro, though atp you can apply it to any model. Important parts of this overview will be bolded. Part 1: Major Changes since Tuesday 1. Further West and Stronger NS 2. Less Confluence 3. Further West Storm Track 1. Further West and Stronger NS This feature has been the largest factor in eliminating our suppression concerns and replacing them with amplification concerns. We have seen a consistent further west progression of our NS vort which phases into our SW sooner and more completely. For example comparing our recent Euro run with one that smoked the whole area without mixing concerns we can see the difference in our NS. Lets start with the old run Clearly this will still be a nearly full phase, yet the westward movement of NS becomes apparent when compared to our recent runs (6z) Honestly, it's not an absolutely huge change but it's more than enough to allow a complete capture of the SW which leads to higher heights out front. We can also see that the western edge of our vort, which runs N to S, is a good bit more intense which only aids in amplification. However, this change out west is only one part of the picture, and on its own it would’ve acted to probably give us a HECS run. Unfortunately, its not the only change that occurred… 2. Less Confluence This is the second piece to our puzzle that explains the relatively rapid shift to our NW that threatens to skunk SW VA and points south-east. Once again lets look at the Euro run comparison but focus our gaze on the Northeast. Once again our old run of the Euro has a pretty major difference. We see the confluence right over Maine thanks to a NS disturbance over Canada. That is a great setup to force our amped storm south. Welp, the latest Euro shows us our problem. Those disturbances which gave us that confluence is pretty much gone. Additionally, we can see that the more powerful NS is able to pretty much dominate the pattern further East as it doesn’t have those disturbances to counteract it. With a run like this we don’t have that same active mechanism to prevent the storm from cutting into the TN valley. At this point its probably too late to get those disturbances back (besides I think their disappearance is in part an absorption into our NS lobe) so we need to hope that instead the overarching 50/50 low comes back west some. Now lets put headlines 1 and 2 together. 3. Further West Storm Track Of course, the two causes I outlined have far more complexity then what I am able to understand, but putting them together gives us a good enough picture of what has happened. Let's look at the old North America 500mb maps We can see our 50-50 low and the block over Greenland. Additionally, we can see the disjointed phase that the storm is undergoing in the plains. With a look like this we were golden as they managed to balance between the southeast ridge which allowed the storm to hit us, and overamplification which would mix in ice. Our new run shows how factors 1 and 2 really hurt us. We have a stronger, more consolidated storm out west which on its own would pump the East coast heights. Then that is combined with a shift east of our 50-50 low due to less blocking over Greenland and well, it's clear why we're going to mix. Additionally, you can see the little disturbance that pokes west of the main 50-50 and how its now up near Greenland instead of further south over Canada, I suspect that this is a sneaky reason for why our confluence has collapsed so much. A vort map shows this sneaky disturbance better. The old run shows a weaker NS and generally the 50-50 low as the dominant factor as there is no secondary disturbance in the flow. Our new run has a stronger NS which on its own would raise heights but we also see a new lobe of vorticity over the Canadian islands. This energy was previously part of our 50-50 and instead it now acts to amplify our storm some (or at the very least does nothing to stop it). As for implications of this shift, let's get into that with our current breakdown of the storm. Part 2: Synoptics and Thermal Impact During The Storm. Let's start with the basics, we are dealing with a warm air intrusion aloft centered from 850-700mb. This means our surface temps don't matter too much, but instead we need to focus on our winds throughout these layers and how synoptics impact those. First Phase and SW Opening (Hours 36-54) This part of our storm is more or less set in stone and rather uninteresting. We see our SW get opened up by an initial influx of NS energy which sets our storm traveling east. The Euro at hour 36 shows us that our SW is still closed, but vorticity over the Pac NW will soon change that At hour 54 this process is complete and we begin to see the second part of our storm period enter the picture. That being the NS dropping south. Second Phase and Initial Thump (54-84) Let's start from the top down in the atmosphere. At hour 63 we can see the changes outlined in our key points taking effect. Our NS is backed up further west and captures our SW further west leading to higher heights in conjunction with the loss of confluence. Now what happens thermally in response? Well all thermal stuff can be traced back to winds induced by cyclogenesis. Look at our recent 6z Euro run and its wind flow at the 850 level (wind is blowing across isotherms as such it is advecting that temperature into the area it is blowing). Compare this to colder runs and its quite apparent what has happened. Our wind field used to be a couple hundred miles south and oriented differently! We need to watch how strong the winds are on the CAMs as we get closer to the event. We want to see a flatter area of high speed 850s from the south. Progressing our storm forward some and we get this H5 map Looking back at our 850 map we can see how the H5 level translates into cyclogenesis East of the H5 low. See the closed isobar already formed, of course, winds will flow cyclogenically which then puts us in its warm sector and eroding our upper level cold air. We need less phasing because it shunts the cyclogenesis south. Or we need more confluence as it prevents the winds from reaching as far north. Now finally, let's connect this to the surface with FGEN and precip. We can see how these winds translate to FGEN, and then subsequently this induces lift and boom! Snow! In order to get this to stay colder we want less intense 850-700mb winds as that will prolong our cold air reserves and still allow for FGEN as we will have WAA regardless. Coastal? (Hour 84 onwards) NGL, I don’t think we score on this one. Even on our best scenario which is the GFS its still really an overrunning event that manages to climb the coast based on the H5 and winds Notice how we don't get a separate coastal low aloft. We don’t really have a great mechanism to flip back to snow without that. However, for the people who are hoping for it we want a further south system with more confluence to force a quicker handoff. Final Thoughts (TLDR) The synoptics of this storm are locked in stone more or less. However, changes can still occur. For example, the GFS and Euro still have quite a different H5 map. Euro top GFS bottom Summing up my whole post we can see why the GFS is so much better. It has a bit less phasing which allows for an extremely strong initial thump before we start flooding our mid-levels with warm air as seen in the 850 wind (Euro top GFS bottom) As we progress towards the event it’ll be time to start looking less from H5 and more from the wind and thermal profiles. By tomorrow it’ll be time to start using the NAM and other CAMs for this purpose. We can still hope for some H5 changes as they may have significant impacts on our lower level winds; however, I think it is reasonable to say that we should expect 6+ inches of snow and several inches of sleet OR 12+ of snow with an inch of sleet for areas near NOVA. Ofc, if you are further north, situation two is more likely and possible you don't see sleet. Areas around where I am in UVA should bank more on scenario 1 happening. Conclusion It's going to snow.

Still showing the freezing rain but different people are saying that freezing rain could be sleet and that the European model doesn't do a good job with the differential. Let's hope so

Right direction being an ice apocalypse in the triangle?

It sucks to waste all this cold air on this. I don’t think I’ve been able to track a successful winter storm since I started having an interest in this field, so I have no clue what to look for aside from textbooks and stuff. It really helps me to have experienced it before.

I mean the trend isn't looking good for the higher amounts.

I think my forecast has it around four or 5° on Sunday night during the heaviest snow. Don’t think I’ve seen that since maybe 2013 or 14.

12z Euro essentially stalls the coastal as the primary ascent from the jet results in redevelopment closer to the coast, long period of high ratio fluff results and gets the entire region above 15".

Euro is much drier, hopefully a blip. But significantly cuts back the thump by .2-.3 LE.

I think Ice Storm warning upstate, NEGA and maybe Transylvania, Henderson. Winter storm warning for foothills and western piedmont.

The actual surface temps seem colder. In my opinion it was a trend in the right direction

00z tonight is going to be interesting around these parts

My thinking about an upcoming significant snowfall in and around New York City remains intact following the 1/22 12z model cycle. Overall, the City remains on course to see its biggest snowstorm in nearly four or five years. The storm will likely attain a Category 3 or, less likely but still possible, Category 4 rank on the Northeast Snowfall Impact Scale (NESIS). NESIS is based on a combination of the area affected by the storm, population in the affected areas, and snowfall amounts. During the height of the storm, the dedridritic growth zone (DGZ) will have temperatures between -17°C and -12°C as per the soundings from multiple models, which is close to ideal for snow growth. The layers below it will be well-saturated, and surface temperatures will be very cold, reducing the risk of melting/riming. As a result, well-accumulating dendrites will be the predominant snowflake. Ratios during this time will probably range from 12:1 to 15:1. A classic paper can be found here: https://www.wpc.ncep.noaa.gov/research/snow2a/snow2a.pdf Later on, warmer air will push into the mid levels (mainly between 650 mb and 800 mb), which will lead to a transition to lower ratios and then sleet for parts of the New York City area, including the City and nearby suburbs. There's a small chance that the storm could end as some freezing drizzle as it pulls away early Monday. Taking into consideration the DGZ conditions, historic data for snowstorms with 1" or greater QPF, the various 12z model solutions, it appears that an good initial estimate for storm total snow and sleet in New York City and nearby areas will fall in the 6"-12" range. Areas to the south and east of New York City and its nearby suburbs could see 4"-8" amounts. Areas with 12"-18" are possible well north and west of New York City, most likely in parts of northeastern Pennsylvania, Orange County, Dutchess County, and Sussex County. A reasonable floor for New York City is 5". A reasonable ceiling is 14". There remains a degree of uncertainty concerning mid-level and surface storm evolution and tracks, and a potential primary-secondary storm handoff. Model skill will improve markedly within another day. Estimates could be revised based on the subsequent guidance, as needed, but the initial estimate is probably a reasonable starting point. Areas north and west of New York City where ratios could be higher for a longer period of time and mixing could be less of an issue, will likely see higher amounts than New York City.

I can remember case studies being planned back in the early 2000s about this when we had want felt like ice storm after ice storm in the SE. Wonder if those ever happened or if nothing could be added to the models to better identify it.

Man that EC AI is a total weenie solution. Days and days and over a foot for all.

Thank you and I really hope that's what happens!

Yes, and in my experience these are not modeled well, partially why precip tends to always begin early. Would not shock me to see this look as we get closer that could at least give areas some flakes that aren’t modeled now but unfortunately this wouldn’t amount to much

Yes, I think it’s starting to finally see the effects of that HP.

Sweetwater could be that line in the sand for the Great Valley. I'm pretty sure the warm nose wins south of there. Sweetwater and Athens are a slightly elevated area relative to CHA and TYS. Could be less certain north of there. Chattanooga local notes: Signal, Lookout, and Flatop are not going to get as warm as KCHA. They are all still locked in for Warning criteria ice. Downtown to maybe East Brainerd, I'm much less concerned - except Saturday. Then Sunday may cut.

I'm not sure we want that... if you disregard the GFS pretty much everything else is about the same in terms of when we lose the mid level thermals...between 15-21z depending on where you are south to north. So we want as much precip before that as possible...

Maybe a step in the right direction.

Wasn't the December 2020 storm a weak low setup that put that insane fronto band over CNE (and then all evaporated with one of the Grinchiest Grinches a few days later)? That setup was different, of course, without the huge storm impacting the SE, and came more up the coast, but might this have some kind of meso front that dumps 30" of fluff somewhere?

Looking forward to those 90th percentile maps, if that's the current expectation.