Pattern The Great December Dump

[Webberweather53]

One thing I've noticed right away in the short range w/ recent runs of the GEFS/GFS is the tendency for our shortwave over the North Pacific to trend weaker as verification nears and it is also losing latitude in the process.

This gives an edge to the weaker, less enthused, & more suppressed ECMWF/EPS camp in the longer term. I think some of this also has to do w/ the GFS being underdone on the Great Basin/Rockies ridge in the short range, effectively causing our trailing s/w over the Pacific to weaken as it has to lift and lose some relative vorticity passing thru stronger s/w ridge axis out in front of it over the western US.

However, beyond this point, there's still a ton of confounding variables & moving pieces left to resolve and we're still 3 days away from said wave actually being adequately sampled by North America RAOBs which may or may not have a significant impact on the eventual forecast of this system late next week.

 

[Ollie Williams]

One thing I've noticed right away in the short range w/ recent runs of the GEFS/GFS is the tendency for our shortwave over the North Pacific to trend weaker as verification nears and it is also losing latitude in the process.

This gives an edge to the weaker, less enthused, & more suppressed ECMWF/EPS camp in the longer term. I think some of this also has to do w/ the GFS being underdone on the Great Basin/Rockies ridge in the short range, effectively causing our trailing s/w over the Pacific to weaken as it has to lift and lose some relative vorticity passing thru stronger s/w ridge axis out in front of it over the western US.

However, beyond this point, there's still a ton of confounding variables & moving pieces left to resolve and we're still 3 days away from said wave actually being adequately sampled by North America RAOBs which may or may not have a significant impact on the eventual forecast of this system late next week.

View attachment 28148

Webb, what do we need to look out for in the short-term for more favorable system.

 

[Blue_Ridge_Escarpment]

Suppressed at this lead time is not a bad thing, at all.

 

[Webberweather53]

Webb, what do we need to look out for in the short-term for more favorable system.

A stronger initial wave will help, the wave timing right now is pretty close to ideal on the GEFS to maximize what little cold air we'll have available when this system emerges from the southern Rockies. Less northern stream interference won't necessarily hurt us either in the longer term. A slightly stronger/sharper wave pattern over North America also would help because this increases the ageostrophic geopotential fluxes between the waves (effectively making the entire packet of waves "stronger") and the stronger upper low obviously affords us a better opportunity to see a storm in general

 

[packfan98]

Definite improvements from my untrained eye on the Euro.

 

[whatalife]

Definite improvements from my untrained eye on the Euro.
View attachment 28155

What a great track and its to warm...


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[Webberweather53]

Definite improvements from my untrained eye on the Euro.
View attachment 28155

If we can get that upper low to track roughly another 100-125 miles ish to the north at a similar intensity w/ just a bit more cold air we might be sitting pretty in NC. Pretty ideal track though for the I-20 corridor except its just too warm. ;/

 

[Jessy89]

What a great track and its to warm...


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Of course it’s to warm we are working with marginal cold air. Really that’s always been the case with this system.

 

[packfan98]

With a 5-contour closed upper level low that is completely cutoff....all bets are off. The surface low just sits and spins for days on the Euro. Maybe it wait until the cold air returns before it moves out???

 

[ForsythSnow]

If we can get that upper low to track roughly another 100-125 miles ish to the north at a similar intensity w/ just a bit more cold air we might be sitting pretty in NC. Pretty ideal track though for the I-20 corridor except its just too warm. ;/

We need that cold air press to really get something going. That's a ton of moisture regardless on this run but it's 10 to 15 too warm. Is there any chance that cold air could come further south and we get a big storm for the mid to upper SE?

 

[GaWx]

Of course it’s to warm we are working with marginal cold air. Really that’s always been the case with this system.

But if one looks at this just from a potential big rain event perspective, this is a nice trend. Of course, I know many consider plain rain in DJF to be absolutely horrifying despite it being by far the main form of precip.

This Euro gives 2-4" of rain to much of the SE, especially GA, SC, and N FL. And good news is that it is not really that cold a rain either, especially for late Dec.

 

[Webberweather53]

This 12z ECMWF run is a great example of why you don't necessarily need phasing w/ the northern stream to get a big storm.







As noted earlier this is basically the ideal upper low track for the I-20 corridor (Birmingham - Atlanta - Columbia), except cold air is lacking.

NC folks want to see this 500mb low track from roughly about Montgomery, AL - Macon, GA - Savannah, GA to maximize their chances of cashing in.

Wrt @ForsythSnow 's question, the evolution of individual northern stream waves will be one major factor in determining the amount of cold air we have to work with, which will be limited by the +EPO that'll be ongoing next week as it attempts to flush arctic air out of the North American continent.

A few ways we can increase the amount of cold air we have to work with in this setup include (but aren't limited to):

1) A deeper, more equatorward trough off of New England that increases cold air advection/confluence into the parent surface high over SE Canada and the Great Lakes

2) Timing the ULL "just right" wrt other large-scale features such that the low-level airmass is already well entrenched but also hasn't had time to leave stage right into the Atlantic (& vis versa). The 12z ECMWF's timing is delayed ever-so-slightly if anything in this regard.

3) Having a stronger upper low to work with & one that's thus characterized by steeper height falls, colder air aloft, and more intense precipitation/dynamic lifting that effectively "creates more cold air "in-situ"/in place underneath it.

 

[Brick Tamland]

What a great track and its to warm...


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Good thing we still have a week to go and this is just one more model run and not the final solution.

 

[KyloG]

But if one looks at this just from a potential big rain event perspective, this is a nice trend. Of course, I know many consider plain rain in DJF to be absolutely horrifying despite it being by far the main form of precip.

This Euro gives 2-4" of rain to much of the SE, especially GA, SC, and N FL. And good news is that it is not really that cold a rain either, especially for late Dec.

Yeah, a big soaker for the SE.

 

[Webberweather53]

This 12z ECMWF run is a great example of why you don't necessarily need phasing w/ the northern stream to get a big storm.


View attachment 28157




As noted earlier this is basically the ideal upper low track for the I-20 corridor (Birmingham - Atlanta - Columbia), except cold air is lacking.

NC folks want to see this 500mb low track from roughly about Montgomery, AL - Macon, GA - Savannah, GA to maximize their chances of cashing in.

Wrt @ForsythSnow 's question, the evolution of individual northern stream waves will be one major factor in determining the amount of cold air we have to work with, which will be limited by the +EPO that'll be ongoing next week as it attempts to flush arctic air out of the North American continent.

A few ways we can increase the amount of cold air we have to work with in this setup include (but aren't limited to):

1) A deeper, more equatorward trough off of New England that increases cold air advection/confluence into the parent surface high over SE Canada and the Great Lakes

2) Timing the ULL "just right" wrt other large-scale features such that the low-level airmass is already well entrenched but also hasn't had time to leave stage right into the Atlantic (& vis versa). The 12z ECMWF's timing is delayed ever-so-slightly if anything in this regard.

3) Having a stronger upper low to work with & one that's thus characterized by steeper height falls, colder air aloft, and more intense precipitation/dynamic lifting that effectively "creates more cold air "in-situ"/in place underneath it.

Unfortunately, I'm personally pretty doubtful even at this early stage that there's enough room for error to potentially get a legit winter storm down to the I-20 corridor even if all of the above points are met to a significant degree. TN, NC, upstate SC, northern GA (well north-NE of Atlanta) & extreme northern AL probably still have enough wiggle room left where something could materialize here, but we shall see.

Imho, if a threat were to emerge, this would probably be confined to roughly the I-40 corridor & points north into the mid-Atlantic

 

[Mitch West]

Unfortunately, I'm personally pretty doubtful even at this early stage that there's enough room for error to potentially get a legit winter storm down to the I-20 corridor even if all of the above points are met to a significant degree. TN, NC, upstate SC, northern GA (well north-NE of Atlanta) & extreme northern AL probably still have enough wiggle room left where something could materialize here, but we shall see.

Imho, if a threat were to emerge, this would probably be confined to roughly the I-40 corridor & points north into the mid-Atlantic

Awesome breakdown, hopefully this is a good sign for us in the Midlands for the future as far as storms track. Seemed like we could never get the right storm track last year, hopefully we have another shot down the road with a similar storm track.

 

[BIG FROSTY]

From Joe D'Aleo-

The pattern will be wacky as the stratosphere is going through contortions with the very low solar and some factors favoring warming. The warming will return and tank the AO, NAO and EPO. The timing is our challenge and we will be working on that.

Maybe some good signs down the road a bit!

 

[Webberweather53]

From Joe D'Aleo-

The pattern will be wacky as the stratosphere is going through contortions with the very low solar and some factors favoring warming. The warming will return and tank the AO, NAO and EPO. The timing is our challenge and we will be working on that.

Maybe some good signs down the road a bit!

There's definitely signs of increasing wave - 1 forcing from the troposphere in the extended as our big Scandinavian high tries to make a comeback along w/ the deep Bering Sea/AK vortex. The good thing is in a pattern like this the warm ups are going to be transient/short-lived in the grand scheme of things. Our next legit round of -NAO after this upcoming week is probably coming sometime in early January based on the SCAND progression.

 

[BIG FROSTY]

There's definitely signs of increasing wave - 1 forcing from the troposphere in the extended as our big Scandinavian high tries to make a comeback along w/ the deep Bering Sea/AK vortex. The good thing is in a pattern like this the warm ups are going to be transient/short-lived in the grand scheme of things. Our next legit round of -NAO after this upcoming week is probably coming sometime in early January based on the SCAND progression.

Sounds good to me! Maybe we can really score this January!

 

[Webberweather53]

I'm very thankful to see the continued cyclonic wave breaks over Atlantic Canada in the extended attempting reinforce this -NAO that's putting a damper on the longevity and intensity of the warm-ups being induced by the crappy Pacific pattern we've been contending with lately. I'm curious to see how the mid-latitudes will respond to this temporary hiatus in Indian Ocean forcing at the end of the month into early January.