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Jan 20-22 Threat Potential Part 3


ag3

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Lol, I brought up December 26th as something that you were comparing it to..because you keep saying that the storm was poor and underdeveloped. What I was saying was that not every storm was going to be like that.

Again, I think you're just going right over the top of the argument. The point was that if the phase occurred earlier and in a better position, we could get a significant snowstorm as precipitation developed on the northwest side of a rapidly deepening surface low. The models aren't stupid. The NAM was producing that type of precipitation because when you have those type of upper air dynamics you're going to get heavy precipitation regardless of if it's a well developed cold conveyor belt with closed H7 and H85 lows. Of course our location wasn't perfect. But to say that the phase wasn't a major player in getting more rapid development is rather silly.

The modeled phase was never early enough to generate the negative tilt, tucked PVA, and mid-level center that would slow the low center and generate wraparound precipitation etc... That's why I believe the NAM runs were very deceptive. They were always unimpressive in the low/mid levels. Maybe you are correct that I am overstating my position. Because for sure a few models/runs actually managed to deepen the SLP pretty rapidly and crank out a slug of very impressive UVVs. I guess I just saw the glass half empty for the past few days when others saw it half full. I enjoy tracking especially in cases where a phase could produce a robust storm. I never quite saw that possibility here.

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The modeled phase was never early enough to generate the negative tilt, tucked PVA, and mid-level center that would slow the low center and generate wraparound precipitation etc... That's why I believe the NAM runs were very deceptive. They were always unimpressive in the low/mid levels. Maybe you are correct that I am overstating my position. Because for sure a few models/runs actually managed to deepen the SLP pretty rapidly and crank out a slug of very impressive UVVs. I guess I just saw the glass half empty for the past few days when others saw it half full. I enjoy tracking especially in cases where a phase could produce a robust storm. I never quite saw that possibility here.

The surface low is not that important here, the 500 trough is more so...if we can get that to dig further south it can generate decent snow of its own...I mentioned the 12/30/93 event...note the 500mb trough at 03Z has its base near the panhandle of WV...the surface low is 1005mb if that offshore but it was snowing quite well at that point in the evening...this event that 500mb trough axis would seem to argue the snows would be more north...I'd like to see it about 100 miles south of where its shown now when its over OH/PA....it basically hammers home the idea I mention alot...forecasters in the NE US and MA miss the 500 features very often since we tend to get strong systems where the surface low often masks what is going on....you dont need that deep surface low all the time.

http://www.meteo.psu...1993/us1230.php

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It's a perfect illustration as to why the phasing is a major component in getting the storm to develop faster and further southwest, which you argued earlier was not an issue at all. The 06z NAM bufkit gave many areas 10 or more inches. That's a significant snowstorm...so I don't really get why you're completely backing away from that original argument.

I think the source of our disagreement is well hashed out now, but bufkit output doesn't really contribute to the debate. It has regularly printed out over 30" for KSWF and KPOU this year. For sure a few NAM runs produced significant QPF but that doesn't tell the whole story.

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I didn't mean to be diagnosing anything. And that's probably the wrong word I used. I just think the difference between a perfect and imperfect phase in this case had relatively minor implications because of the larger synoptic features and our geographical location. That's not to say this is true in every case. I thought the NAM went overboard in illustrating the upper end of potential by printing out too much QPF over a short period. And I get frustrated when I read a conclusion that things went down the ****ter because it "didn't phase." In fact we have a partial phase, it will snow, and an ocean gale with form eventually anyway.

You're probably right though. I didn't focus on the intricacies because I didn't think we ever got to that point. At no point did I think subtle shortwave interactions could modify the height field sufficiently. I never saw this as anything but a glancing blow. And yes I do believe you can get a glancing 8" of snow.

A couple noteworthy comments. The NAM QPF was ridiculous verbatim, but the threat potential wasn't greater/less based off the NAM QPF. Models aren't supposed to be taken verbatim, especially something so heavily parametrized including the cloud microphysics and the other sub-grid scale interactions.

The lack of a full phase is what it is--and it is why the storm threat is not as significant as it may have been. Do remember 3-4 days ago we spanned the spectrum of nothing at all (ECM) vs a moderate SECS (NAM). The tiny details regarding the western wave and its phase potential are hugely important--and this forecast is just one example. There was never a "misdiagnoses" regarding the upper air features with this event--so you should consider your wording before you suggest that.

While you may not think 2" or 8" is different and that an 8" snow amount within 6-10 hours is a simple glancing blow, meteorologists can not make the same careless assessments since the societal impacts can be significant.

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The surface low is not that important here, the 500 trough is more so...if we can get that to dig further south it can generate decent snow of its own...I mentioned the 12/30/93 event...note the 500mb trough at 03Z has its base near the panhandle of WV...the surface low is 1005mb if that offshore but it was snowing quite well at that point in the evening...this event that 500mb trough axis would seem to argue the snows would be more north...I'd like to see it about 100 miles south of where its shown now when its over OH/PA.

http://www.meteo.psu...1993/us1230.php

Agreed. And I would too.

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A couple noteworthy comments. The NAM QPF was ridiculous verbatim, but the threat potential wasn't greater/less based off the NAM QPF. Models aren't supposed to be taken verbatim, especially something so heavily parametrized including the cloud microphysics and the other sub-grid scale interactions.

The lack of a full phase is what it is--and it is why the storm threat is not as significant as it may have been. Do remember 3-4 days ago we spanned the spectrum of nothing at all (ECM) vs a moderate SECS (NAM). The tiny details regarding the western wave and its phase potential are hugely important--and this forecast is just one example. There was never a "misdiagnoses" regarding the upper air features with this event--so you should consider you wording before you suggest that.

While you may not think 2" or 8" is different and that an 8" snow amount within 6-10 hours is a simple glancing blow, meteorologists can not make the same such careless assessments since the societal impacts can be significant.

Okay I think I can agree with most of this.

I thought the excessive NAM QPF output masked the fact that this threat had some critical factors going against it. I interpreted the succession of high QPF NAM runs to represent a good threat for a moderate to perhaps significant short duration snowstorm for the corridor. I did not interpret it as a 12" - 18" snowfall. But if one were to interpret it as such, you might get the impression that a "phase" could have meant a blizzard and now here we are with a likely "partial phase" probably only getting a few inches. The lack of a perfect phase will not prevent us from the major snowstorm that was otherwise destined to impact us.

And yes, I agree with the forecasting part. Though I am not trying to make a forecast, especially a short term one. I've been thinking mostly in terms of basic synoptic threat assessment until the details hash themselves out to make the specifics worth pinning down.

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Latest day 2 threat from HPC. I'm awfully suprised they wen't as bullish as they did with > 4" amounts. They must be thinking 0.35-0.4 QPF with 15-1 ratios sounds like a good possability.

Keep in mind moderate is defined as a 40% probability, so it does not appear as outlandish as first thought.

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There is no magical meteorology going on here--and it was clear the cold air was displaced aloft in the upper trough. Without sufficient development of the upper level cold front downward, this trough would have been DOA--doesn't matter how far S it amplifies. The southern wave was necessary for the development of an active dynamic tropopause and rapid development. You have no idea what you are talking about. If so, I suggest you post images and dynamically break down the forecast. Trough amplification alone does not equate to rapid development.

I just noticed this post from earlier. I can't tell for sure if I agree, but it sounds very interesting regardless. I think there might be something to learn here if you elaborate on this point.

I don't know what you mean by dead on arrival. A northern stream trof with modestly large vorticity diving south into the strong thermal gradient/baroclinicity we have across the US should be plenty sufficient to initiate cyclogenesis. No? I know why an additional s/w wave could help, but I don't understand why it is absolutely necessary. Thereafter, all the usual processes - surface convergence/upper level divergence, moist warm inflow, latent heat etc... should theoretically continue the development process (possibly rapid). I don't see why this hypothetical scenario precludes the possibility of a strong DT anomaly and rapid deepening, especially with a strong jet streak nearby.

It kind of seemed to me you were trying to use technical terms to jumble and conceal a relatively straightforward point. Namely that ideal conditions are necessary for unusual events like rapidly deepening surface lows, tropopause folds, extreme dynamics etc... Granted. But I'm unclear as to why multiple shortwave interactions are essential for a decent storm.

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:lol:

I can't bring this discussion any further.

This sounds like a snide remark.

D.I. was using technical terms that some people are not even familiar with like active DT to make an assertive statement without necessarily providing a basis for the underlying assumptions. Sometimes people do this to talk down to other people or to preclude a counter argument, even when making a fairly obvious statement. Tio, who I also enjoy reading, comes to mind.

But he seems like a sincere guy and I don't think he was doing this. I really want to know why he didn't think the upper level front would translate down and why wave interaction is a necessary condition for storm development.

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Looks like a modest snowfall event. My current thinking is 2-4 inches for CT, slightly more for NYC and LI and more as well for eastern Massachusetts. With model LE precip forecasts only around 0.25 or slightly higher and good ratios, it seems like a decent forecast. With the storm moving so fast, too many things have to come together for amounts to be much higher. A nice way to whiten up the slush and brown spots, as conditions turn much colder for the weekend.

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I just noticed this post from earlier. I can't tell for sure if I agree, but it sounds very interesting regardless. I think there might be something to learn here if you elaborate on this point.

I don't know what you mean by dead on arrival. A northern stream trof with modestly large vorticity diving south into the strong thermal gradient/baroclinicity we have across the US should be plenty sufficient to initiate cyclogenesis. No? I know why an additional s/w wave could help, but I don't understand why it is absolutely necessary. Thereafter, all the usual processes - surface convergence/upper level divergence, moist warm inflow, latent heat etc... should theoretically continue the development process (possibly rapid). I don't see why this hypothetical scenario precludes the possibility of a strong DT anomaly and rapid deepening, especially with a strong jet streak nearby.

It kind of seemed to me you were trying to use technical terms to jumble and conceal a relatively straightforward point. Namely that ideal conditions are necessary for unusual events like rapidly deepening surface lows, tropopause folds, extreme dynamics etc... Granted. But I'm unclear as to why multiple shortwave interactions are essential for a decent storm.

Yeah I like to hear myself talk. rolleyes.gif

In reality, most analysis often times relies on far too simplistic of a reasoning--which is what you are doing here. Tossing around "modestly large vorticity" and saying "plenty sufficient to initiate cyclogenesis" etc. is, once again, being far too simplistic. If you have any understanding of the chaotic nature of the atmosphere, you would be more willing to understand that things are never so straight-forward.

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This sounds like a snide remark.

D.I. was using technical terms that some people are not even familiar with like active DT to make an assertive statement without necessarily providing a basis for the underlying assumptions. Sometimes people do this to talk down to other people or to preclude a counter argument, even when making a fairly obvious statement. Tio, who I also enjoy reading, comes to mind.

But he seems like a sincere guy and I don't think he was doing this. I really want to know why he didn't think the upper level front would translate down and why wave interaction is a necessary condition for storm development.

It was a snide remark because your replies have been absolutely insincere and without any verifiable proof to back up your silly claims and accusations. You are "frustrated" because, in your opinion, meteorologists are "misdiagnosing" the threat and don't know what a phase is, then when asked to provide your own dynamical/synoptic assessment of the situation, you have nothing but old-wives tales and simplistic met 101 explanations. You accuse earthlight and others of "IMBY" wish-casting for no particular reason other than what must be your own misunderstandings and "frustrations", and when confronted with evidence which discredits your own claims, you back-track and try to cover your own rear-end by saying "I never saw this as anything but a glancing blow. And yes I do believe you can get a glancing 8" of snow." Then when meteorologists do provide evidence and discussion of the particular pattern at hand, which you requested, you say we are trying to complicate a simplistic forecast by saying "It kind of seemed to me you were trying to use technical terms to jumble and conceal a relatively straightforward point." axesmiley.png

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