SnowenOutThere

Yeah more or less thats my thinking. If only we could just get more confluence as that is just a win win.

Love to extend the scroll length of a page by twice its normal amount

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.

Pasting over all of this to the thread, will take some time

I think the big story of the GFS run is how good that initial thump of snow is. That is how we all win from me to Bob Chill to PSU.

Only concern with the de amp is it could mess up our initial thump if things go really poorly but that’s probably an irrational fear.

I know people are blowing off the NAM as crazy, which it probably is, but if it is handling dynamics correctly and it shows that sleet line progress so quickly I wouldn’t bet against it. I was in NYC for the Boxing Day storm and from a couple days out it was hammering a quick changeover that the other models didn’t have and it was completely right.

NAM was better but still the low end totals as it almost misses the thump for places south of NOVA. I for example get 3 inches of snow which would be... not great

I don't know! I just got here. Though I think they do better when it comes to freezing rain and surface cold air but this setup to my knowledge is all based on 850-700mb warm layers which should torch faster the further south. I'm just worried that I end up with a major ice storm of freezing rain.

Interestingly the 12z NAM looks very similar to its 0z run so far as it has the same NS setup. For those who don't remember the 0z run looked to be very good for us all.

What do you think for Cvill. I've been telling people 4-8 low end with an inch of two of sleet and the possibility of .5+ freezing rain or the high end snowfall of 8-14 with an inch or two of sleet.

As for when the NS is sampled I don’t know but @MillvilleWx probably does. As for needing it sampled to know what happens that’s true. We need the whole picture not one half.

https://x.com/MikeTFox5/status/2014175039457829228 Probably should be in banter but Fox model is my new friend.

Thank you guys.

Genuinely do not know your issue with me man. You’ve been on my ass when you yourself offer no commentary on our setups and haven’t been on the forum in years. It’s bullshit. As for the CMC point go back to model runs Monday and tell me which one is the closest to our current runs. It is the CMC as by and far it involved the cleanest phase out west and includes the NS lobe which the others didn’t even have at that point. Either way, you gotta chill out man; as it turns out I’ve changed since you last checked the forum and actually know what I’m talking about now. If you’d like to contest that please refer to the top 2 most popular posts in the old thread and tell me the synoptic faults I made as I am more than willing to concede I’m not perfect.

Oh I agree its a 90% plus likelihood but I think a pathway exists when we have such complex interactions for the models to shift some more. Once again I think all synoptic stuff is settled by tomorrow 12z (which is why I'll make my final analysis then)

Yeah, it won with this storm. It has consistently been the most amped and saw the second NS phase before any other model did. My post way back on Monday analyzing this storm put the CMC in its separate category where I bemoaned how if it pulled of this phase we'd mix. Well, it was right.

Hypothetically we still could avoid it. Would require dramatic shifts by 12z tomorrow (and even worse the GFS to be mostly right) but theres enough weirdness in the NS where I wouldn't write it off completely.

CMC so far looking more eastward with its phasing of the NS and SW. Otherwise similar.

For those wondering how the GFS did it. The GFS had better confluence, a low that ejected a bit further south and resisted the phase, a less powerful NS, and a more eastern NS. If the Euro shows any one of these things we should hopefully get a further south solution.

For now assume all my posts are made with me being at UVA

Storm exiting

QDF bomb

Snow total though hour 93 (which is when I mix)

Its quite the front end thump though the second part of the storm is going to mix hard imo