January 24-26: Miracle or Mirage Thread 2

[MN Transplant]

Just now, yoda said:

 

~0.75" at that point.  Seems about right, 7-9" of snow and then an inch or two of sleet on top.

[Weather Will]

Flip occurs for most by 4pm Sunday.  Precipitation is less on latest run compared to  6Z.

[winter_warlock]

4 minutes ago, NorthArlington101 said:

That's only thru hr 83. Still going

[rjvanals]

Looking at the Euro soundings on Pivotal we don't get into the good snow growth zones this run around DC so even when we stay snow we're not going to get great ratios 

[StormyClearweather]

Just now, LP08 said:

Delaying the phase and flatter out front is causing some cut back on qpf for the thump.  

THIS. It's a fine line we're walking. You either clean up on the thump re: QPF with a better phase and change over faster, or vice versa. 

[Terpeast]

I think a blend gets us to 6-10" DC metro, 8-12" NW, 12"+ out up in WV panhandle through PA

SE of DC 4-8" with lots of sleet, and south of EZF start to see icing

(subject to change ofc)

[midatlanticweather]

I have to think that we get that last minute north jump.. and it is a scary point for me. Riding the line this far out is not a good recipe... except for disaster. Warm air seems to sneak north faster and not what you think.. sometimes it is wrong on models, but no cushion is the deal. Front thump looks like the win.. then sleety mess. Crazy we became the edge. We gotta drop that zero line in all levels!

 

 

[caviman2201]

1 minute ago, Eskimo Joe said:

Classic La Nina roulette. You play against the warm nose, primary low, late transfer to the coastal, or drier overall. 

I would personally take 6-8" of cold smoke, no mixing over 8-10" w/ sleet at the end... sleet sucks

[jayyy]

How’s the EPS look

[caviman2201]

1 minute ago, Terpeast said:

I think a blend gets us to 6-10" DC metro, 8-12" NW, 12"+ out up in WV panhandle through PA

SE of DC 4-8" with lots of sleet, and south of EZF start to see icing

Would you say its the same forecast for BWI/Baltimore?

[NorthArlington101]

4 minutes ago, wasnow215 said:

Thank you -does the European model continue to show freezing rain for central Virginia? Obviously we are hoping for sleet.

It does but I'm deferential to the NAMs not being totally wrong and feel like this should be more sleet. We'll see

[mitchnick]

1 minute ago, jayyy said:

How’s the EPS look

Not out yet, but maybe be getting past usefulness at this range.

[WxUSAF]

2 minutes ago, Eskimo Joe said:

Classic La Nina roulette. You play against the warm nose, primary low, late transfer to the coastal, or drier overall. 

 

2 minutes ago, LP08 said:

Delaying the phase and flatter out front is causing some cut back on qpf for the thump.  

Yeah I think we’re trading a slightly cooler column for a less intense WAA thump with most 12z runs? Think @SnowenOutThereMentioned this? All minor changes relatively. 

[psuhoffman]

19 minutes ago, NorthArlington101 said:

EURO def south with the initial WAA pus, at least

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... 

[wasnow215]

2 minutes ago, NorthArlington101 said:

It does but I'm deferential to the NAMs not being totally wrong and feel like this should be more sleet. We'll see

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

[jayyy]

00z tonight is going to be interesting around these parts

[SnowenOutThere]

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. 
 

[Scraff]

Just now, jayyy said:

00z tonight is going to be interesting around these parts

Every model run at this point will be interesting. 

[NorthArlington101]

Just now, psuhoffman said:

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... 

I agree - was hoping that would lead to a downstream outcome more like the GFS. I believe some of the nerds I listened to saw some positives at h5 in the Euro, but it ended up being drier and flipping us at essentially the same time. So kinda meh overall. Gonna be on repeat all the next 2 days mostly to convince myself but I think I'm fine with 5" then sleet storm. 

[stormtracker]

4 minutes ago, NorthArlington101 said:

It does but I'm deferential to the NAMs not being totally wrong and feel like this should be more sleet. We'll see

That would be a bit of a disaster for the public

[RevWarReenactor]

5 minutes ago, midatlanticweather said:

I have to think that we get that last minute north jump.. and it is a scary point for me. Riding the line this far out is not a good recipe... except for disaster. Warm air seems to sneak north faster and not what you think.. sometimes it is wrong on models, but no cushion is the deal. Front thump looks like the win.. then sleety mess. Crazy we became the edge. We gotta drop that zero line in all levels!

 

 

Meh- once you take 12+ off the table; additional shifts don't yield that much less snow. Its would take shifts of hundreds of miles to skunk on anything less than 6 inches.

So just set expectations accordingly. This is probably 6-9 for the metros followed by sleety. 

[IUsedToHateCold]

And so, as expected, the GFS is out enjoying a Pina Colada on its island. Uccinelli was right. 

Only thing we can really hope for is a turnaround as things get closer - a faster system that lets the confluence stick around or confluence that sticks around longer. 

 

[SomeguyfromTakomaPark]

Just now, stormtracker said:

That would be a bit of a disaster for the public

Yeah I wonder how accurate these ptype algos are? Tons of freezing rain on these things....

[SnowenOutThere]

4 minutes ago, WxUSAF said:

 

Yeah I think we’re trading a slightly cooler column for a less intense WAA thump with most 12z runs? Think @SnowenOutThereMentioned this? All minor changes relatively. 

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

[stormtracker]

Just now, SomeguyfromTakomaPark said:

Yeah I wonder how accurate these ptype algos are? Tons of freezing rain on these things....

Don't see it being talked up a long by LWX or mets here, so not sure if Ice storm is on the table

[clskinsfan]

8 minutes ago, caviman2201 said:

I would personally take 6-8" of cold smoke, no mixing over 8-10" w/ sleet at the end... sleet sucks

The sleet is going to make whatever falls stick around for while with the bitter cold to follow. 

[SomeguyfromTakomaPark]

2 minutes ago, RevWarReenactor said:

Meh- once you take 12+ off the table; additional shifts don't yield that much less snow. Its would take shifts of hundreds of miles to skunk on anything less than 6 inches.

So just set expectations accordingly. This is probably 6-9 for the metros followed by sleety. 

Yeah, agree.  We should be able to get a warning level snow even if the north creep continues.  Which is great!  We go years without warning level snows...

[Hokiehop]

13 minutes ago, JenkinsJinkies said:

A foot is solidly off the table for the metros then.

Says the guy who also chimed in with this nugget...

Welp I’m pulling out, I’ve been down this road before and I’m not going to hit that wall again. I’ll check again tomorrow morning but I’m not holding my breath. I am not saying it won’t snow, but I’m not holding my breath for a large event at this point.

[MillvilleWx]

My forecast for the metros, if I had to make one right now is 6-10” with a bunch of sleet to end it. Glacier incoming. I don’t think we’ll see much actual freezing rain, but some freezing drizzle at the end is plausible. Best chance for higher accumulations away from city centers. 
 

This reminds me of a cross between Valentine’s Day 2007 and February 2014

[rjvanals]

Anyone else concerned looking at the Euro soundings around DC? The snow growth zone temp is as follows:

9z: -8.6

12z: -7.6

15z: -5.4

18z: -4

This should be a big red flag if we're counting on ratios or even a shot at double digits around the metro imo.