The Return of the 12/5 Snowstorm

[bncho]

18z EPS shows an even stronger signal than 12z.

[CAPE]

2 minutes ago, SnowenOutThere said:

Thank you! We finally got to the actual H5 Jet stream ageostrophic etc part of my course last month! Of course, it wasn't anything crazy but its given me just enough tools to begin identifying how the upper air connects to the surface. That said, I'm very confident that this is very much a Dunning-Kruger effect where I know just enough to make broad forecasts and identify what I we need models to trend and make predictions from an earlier hour to but I am unable to "correct" model behavior as I just don't have the confidence (wait till Spring 2027 and Synoptic met for that) to do so. So with that said please feel free to correct any mistakes I make as it literally might save my grade!

You doing good friend. I used to be the one to bore everyone with all the 500 mb vorticity interactions/analysis. Now you can do it lol. It's largely what dictates our sensible weather at the surface as you are discovering. Good stuff!

[SnowenOutThere]

1 minute ago, CAPE said:

You doing good friend. I used to be the one to bore everyone with all the 500 mb vorticity interactions/analysis. Now you can do it lol. It's largely what dictates our sensible weather at the surface as you are discovering. Good stuff!

I edited my previous post to give you a shoutout for those posts as they are what got me largely to where I'm at! Thank you for them. BTW the best part about being a student is that while doing these breakdowns is procrastinating it feels infinitely better than doom scrolling as I can rationalize it as learning for future classes. 

[Maestrobjwa]

1 hour ago, CAPE said:

Strong upper jet streak induces stretched/elongated vorticity ribbon underneath. Not going to get a widespread or major event with this, but rather a possible narrow corridor of decent lift that could produce a light to moderate event. Hard to say exactly where that might occur at this juncture but it appears it will be somewhere in our region or maybe even a bit south. Given the h5 look on the Euro it *should* be cold enough for a bit of snow.

If I gambled I'd bet a lot on that being the outcome, lol

[Terpeast]

28 minutes ago, SnowenOutThere said:

To be honest the upper winds is where my knowledge gets confused as we went over how the jet forms (I can tell you why the jet increases on the northward heading side of an upper low and decreases when heading south) but didn't go over the practical effect on the surface. I'm currently trying to research it on my own but generally it confuses me as my intuition says that areas of lift should form where winds are accelerating in the upper atmosphere (as it induces lower level lift as air is pulled into the upper flow) yet I know from the 4 quadrant model that understand I have is flawed. Additionally, I would've expected that stronger upper winds generally encourages cyclogenesis and didn't consider that it could actually hurt consolidation (which admittedly does make sense). Basically, what upper wind profile would actually be conductive to forming a strong surface low pressure? 

Left exit and right entrance regions, where upper level flow diverges. Conservation of mass and surface boundary dictates that air must lift to replace the diverging flow. 

[SnowenOutThere]

5 minutes ago, Terpeast said:

Left exit and right entrance regions, where upper level flow diverges. Conservation of mass and surface boundary dictates that air must lift to replace the diverging flow. 

That makes sense, but as Cape alluded to with the flow stretching the vorticity apart is it best for a developing low to be displaced from the strongest winds? I know that oftentimes the jet isn't able to "round the base" of a trough and once it does it indicates a matured/max developed storm and is that the logic behind it or am I mistaken?

[Solution Man]

Damn, great stuff tonight folks, thanks

[Terpeast]

50 minutes ago, SnowenOutThere said:

That makes sense, but as Cape alluded to with the flow stretching the vorticity apart is it best for a developing low to be displaced from the strongest winds? I know that oftentimes the jet isn't able to "round the base" of a trough and once it does it indicates a matured/max developed storm and is that the logic behind it or am I mistaken?

I was a little confused by your question, so I had to reread a few times. 

Correct me if I’m wrong, but I think what you are asking is why the low doesn’t develop right under the strongest winds of a jet stream. You’d be correct in your observation that it usually develops downstream of a trough where upper level winds diverge, air lifts, and surface pressure decreases.

When the vorticity “stretches”, we get an elongated region of positive vorticity advection as opposed to concentrated into a tight vort max over one area. That spreads upper level forcing for lifting over a large area, thereby “diluting” the tendency for a surface low to form.

So it’s not so much the sfc low doesn’t “prefer” to be away from the strongest winds, but more like it tends to deepen where that elongated band of vorticity overlaps the divergence (left exit/right entrance regions) and the baroclinic gradient. While vorticity alone isn’t enough to develop a storm, that combined with upper level support will do it - there needs to be both.

The displacement you’re noticing is really a reflection of where the total forcing (vorticity and upper level divergence) both line up, which often ends up a bit downstream and to the left of the jet streak, not directly under the strongest winds.

Now when the jet core “rounds the base” of the trough, you’re right that we’re often getting into the mature phase of the storm. By that point, the upper level trough and the surface low have gotten more vertically stacked, and the low begins to occlude and weaken.

Sorry if this got too technical, but your question covers several different meteorological concepts, and the evolution of a cyclone where conditions differ between the early stages of development and when it matures. 

[winter_warlock]

2 hours ago, CAPE said:

Very impressed with your posts lately. 

I'm definitely picking up ur sarcasm lol 

[Terpeast]

2 minutes ago, winter_warlock said:

I'm definitely picking up ur sarcasm lol 

I didn’t think he was being sarcastic. Snowenouthere has been dropping dimes lately, hopefully he keeps it up. 

[winter_warlock]

Just now, Terpeast said:

I didn’t think he was being sarcastic. Snowenouthere has been dropping dimes lately, hopefully he keeps it up. 

Ohh. It looked like sarcasm to me. Oops lol

[SnowenOutThere]

25 minutes ago, Terpeast said:

I was a little confused by your question, so I had to reread a few times. 

Correct me if I’m wrong, but I think what you are asking is why the low doesn’t develop right under the strongest winds of a jet stream. You’d be correct in your observation that it usually develops downstream of a trough where upper level winds diverge, air lifts, and surface pressure decreases.

When the vorticity “stretches”, we get an elongated region of positive vorticity advection as opposed to concentrated into a tight vort max over one area. That spreads upper level forcing for lifting over a large area, thereby “diluting” the tendency for a surface low to form.

So it’s not so much the sfc low doesn’t “prefer” to be away from the strongest winds, but more like it tends to deepen where that elongated band of vorticity overlaps the divergence (left exit/right entrance regions) and the baroclinic gradient. The displacement you’re noticing is really a reflection of where the total forcing (vorticity and upper level divergence) both line up, which often ends up a bit downstream and to the left of the jet streak, not directly under the strongest winds.

Now when the jet core “rounds the base” of the trough, you’re right that we’re often getting into the mature phase of the storm. By that point, the upper level trough and the surface low have gotten more vertically stacked, and the low begins to occlude and weaken.

Sorry if this got too technical, but your question covers several different meteorological concepts, and the evolution of a cyclone where conditions differ between the early stages of development and when it matures. 

Thank you so much for this post, and sorry for the confusing initial wording. This also helps clarify to me a how the arctic front theory of storm formation (while generally "wrong") can make some sense as I assume it comes from seeing the stretch between air masses as a line of vorticity that eventually spins up into a concentrated area to force surface low formation. Of course, it doesn't actually get into why that happens but it makes more sense regardless. If I read your post right in sensible terms we are in the best place for surface low development when we have a strong baroclinic boundary to our south (aids in convergence though my course didn't go too much in depth with it so I'll just accept a stronger temp gradient is better), a jet streak that is either positioned to the northwest (right entrance which I guess may be associated with a negatively tilted trough usually?) or a jet to our southeast (maybe more for broad bowl patterns?), and a condensed ball of vorticity (shortwave) to act as the initial perturbation in the system. I also know that 500mb low wise a sharper amplitude with shorter wavelength wave tends to increase vorticity though I don't actually know why (to be honest my ability to connect vorticity to low pressure is sketchy at best and I'd appreciate resources to find that connection). Additionally, If you have any websites to look at the upper air patterns for past storms I'd love to dive into that to see examples of this. 

[NorthArlington101]

I think I look the like of the NAM thus far thru 51 , but I’m no @SnowenOutThere

[stormtracker]

6 minutes ago, NorthArlington101 said:

I think I look the like of the NAM thus far thru 51 , but I’m no @SnowenOutThere

Meh....so far

[NorthArlington101]

1 minute ago, stormtracker said:

Meh....so far

Not as big a fan at 60 but thought things were headed north toggling back and forth the precip down in south. Mayhaps not 

Nope thru 69

[LP08]

Strung out mess.

[Terpeast]

9 minutes ago, SnowenOutThere said:

Thank you so much for this post, and sorry for the confusing initial wording. This also helps clarify to me a how the arctic front theory of storm formation (while generally "wrong") can make some sense as I assume it comes from seeing the stretch between air masses as a line of vorticity that eventually spins up into a concentrated area to force surface low formation. Of course, it doesn't actually get into why that happens but it makes more sense regardless. If I read your post right in sensible terms we are in the best place for surface low development when we have a strong baroclinic boundary to our south (aids in convergence though my course didn't go too much in depth with it so I'll just accept a stronger temp gradient is better), a jet streak that is either positioned to the northwest (right entrance which I guess may be associated with a negatively tilted trough usually?) or a jet to our southeast (maybe more for broad bowl patterns?), and a condensed ball of vorticity (shortwave) to act as the initial perturbation in the system. I also know that 500mb low wise a sharper amplitude with shorter wavelength wave tends to increase vorticity though I don't actually know why (to be honest my ability to connect vorticity to low pressure is sketchy at best and I'd appreciate resources to find that connection). Additionally, If you have any websites to look at the upper air patterns for past storms I'd love to dive into that to see examples of this. 

Here’s one I like (sadly it only goes up to 2013)

http://www.raymondcmartinjr.com/weather/1996/Weather.html

Gives me a nice trip down memory lane having lived through many of these storms. There are many maps at all levels of the atmosphere that shows the evolution of each storm. 

You’ll notice that the most powerful winter storms have a dual jet structure, where the low develops under the overlapping of both the left exit of one jet streak and the right rear entrance of another jet streak. Like double jeopardy. Rare, but truly amazing when it happens, and thats why they get so powerful. Look at the blizzard of 1996, perfect textbook example.  

 

[SnowenOutThere]

10 minutes ago, NorthArlington101 said:

I think I look the like of the NAM thus far thru 51 , but I’m no @SnowenOutThere

I'm actually not quite sure what goes wrong as I agree that on paper that what happens out west and to the north looks better with less push/suppression of the NS. My best guess is something happens either internally with the shortwave or the interaction between it and the low of Mexico causes its energy to become more stretched and further eastward based. Looking at it more the only real difference seems to be that the shortwave remains a bit more connected to the low of Mexico and there are slightly stronger H5 winds which as @CAPE pointed out hurts us by stretching out the vort. 

0z wind map

18z wind map

[Solution Man]

Looks like Icon will come north now, snow on doorstep at 60, strung out mess also

[SnowenOutThere]

Just now, Solution Man said:

Looks like Icon will come north now

So far it looks like it should at least hold from its 18z improvement I think. Still sorta does the Nam more connection with the low off western Mexico but seems like it should be fine for it. 

[Solution Man]

1 minute ago, SnowenOutThere said:

So far it looks like it should at least hold from its 18z improvement I think. Still sorta does the Nam more connection with the low off western Mexico but seems like it should be fine for it. 

Yeah, precip/snow shield expanded a little further north

[SnowenOutThere]

RDPS is significantly improved too (though not enough to help NOVA but Short Pump makes out like a bandit). It generally follows the positive aspect I've been highlighting which is the secondary bands of NS energy being modestly further west

[stormtracker]

1 minute ago, Ji said:

it keeps taking 2 steps south and 1 step north...so just always end up in the same place we started smh

It's substantially different than 18z so far.  but again, it's hard to tell what it's going to do

[WesternFringe]

Anyone have the GFS clown map?  
 

edit: I jumped the gun.  I will be patient.  Lol

[stormtracker]

Definitely wetter and more precip coverage out west

[stormtracker]

Assuming the shit out west doesn't collapse, the shield is heading for us...probably is, it's warmer so far vs 18z

[mitchnick]

I feel like we've gotten the band back together. 

[stormtracker]

1 minute ago, mitchnick said:

I feel like we've gotten the band back together. 

Assuming it doesn't get shunted south....next frame should tell the tale

[mitchnick]

Just now, stormtracker said:

Assuming it doesn't get shunted south....

The trough in se Canada looks crushing

[stormtracker]

Yep, lol.  South shunt.  Coulda been good.