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Pattern The Great December Dump

CADEffect said:
Really beginning to get nervous for the end of the month into January. Just looking at the GEFS and the separation from the PV to the stretch of the SSW into our side of the world makes me think January will be warm. However, the GEFS has done this before in November and completely flopped days later.

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Stratospheric warming over out part of the world definitely doesn't mean it's going to be warm at the surface.
 
112Z Euro gives a whopping 2-4" of rain over most of SC, GA, AL, and N FL. Other aspect of this storm on 12Z Euro is winds up to 40 knots parts of N GOM and just off SE US coast! Lowest SLP gets to below 1,000 mb at times. This is shaping up to be a big dog per this run even if no wintry.
 
GaWx said:
112Z Euro gives a whopping 2-4" of rain over most of SC, GA, AL, and N FL. Other aspect of this storm on 12Z Euro is winds up to 40 knots parts of N GOM and just off SE US coast! Lowest SLP gets to below 1,000 mb at times. This is shaping up to be a big dog per this run even if no wintry.
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Crucial December rainstorm BF5ED4E2-337A-4D64-80ED-F29DD4F0F600.jpeg
 
GaWx said:
112Z Euro gives a whopping 2-4" of rain over most of SC, GA, AL, and N FL. Other aspect of this storm on 12Z Euro is winds up to 40 knots parts of N GOM and just off SE US coast! Lowest SLP gets to below 1,000 mb at times. This is shaping up to be a big dog per this run even if no wintry.
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If we only had some cold air to put all that moisture to use with then we could get a good snowstorm the SE hasn't seen in a long time. Just gotta get that high further west and we may be in business.
 
Jimmy Hypocracy said:
Cool zonal flow? yeah that lakes low has me chomping at the bit! No, it’s not that bad. As long as we can keep some of the colder air on our side of the globe we might have a shot
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True....It's a couple of tweaks away from being cold, as opposed to a monumental, herculean effort to situate the PV on our side of the globe.
 
Jimmy Hypocracy said:
I feel like this is what it looked like during the blizzard of 73’ except it wasn’t hot like 2019
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I've found only 3 Gulf lows since late 1800s with pressure under 1,000 mb giving KATL a major winter sorm:

1. 976 mb: Storm of Century 3/13/1993 ~4" snow
2. 997 mb: 2/12/2010 ~4" snow
3. 998 mb: 1/22/1987 ~4" snow

So, of the 32 major KATL snow or sleetstorms since the 1870s, only ~10% had sub 1,000 mb. The median was way up at 1,008 mb. So, fairly weak Gulf lows tend to be more conducive to giving ATL big winter events.

Edit: note that all 3 have been since 1993, perhaps due to a warmer Gulf due to GW but may just be random since only 3.
 
GaWx said:
I've found only 3 Gulf lows since late 1800s with pressure under 1,000 mb giving KATL a major winter sorm:

1. 976 mb: Storm of Century 3/13/1993 ~4" snow
2. 997 mb: 2/12/2010 ~4" snow
3. 998 mb: 1/22/1987 ~4" snow

So, of the 32 major KATL snow or sleetstorms since the 1870s, only ~10% had sub 1,000 mb. The median was way up at 1,008 mb. So, fairly weak Gulf lows tend to be more conducive to giving ATL big winter events.
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What about 93? Thought that was a low mb.


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The turn of the new year might be one of those rare instances where we get a simultaneous -EPO/-NAO where +SCAND is trying to assert itself in concert w/ a deeper Sea of Okhotsk/eastern Russia vortex that's enforcing a -EPO.

This Alaskan + Scandinavian ridging creates a wavenumber 2 "squeeze play" that ultimately could split the polar vortex. It's nice to have the primary TPV lobe on our side of the pond and this sort of pattern will typically force it to descend southward into North America. We may have to contend w/ at least some transient southeast US ridging on the front end of this, but this particular planetary-scale pattern is certainly capable of unloading absurdly cold air masses into the CONUS in early January. Whether or not those actually impact us in the SE US (& if so when) are questions that will remain unanswered for the immediate foreseeable future

gfs-ens_z500a_nhem_51.png
 
NoSnowATL said:
What about 93? Thought that was a low mb.


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You’re correct that that was low (lowest by far), but I already do have that in my list as #1 strongest. That’s why it was named “Storm of Century”. You just missed it.
 
GaWx said:
You’re correct that that was low (lowest by far), but I already do have that in my list as #1 strongest. That’s why it was named “Storm of Century”. You just missed it.
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Haha my bad, shouldn’t be on my phone and drive at the same time.


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Pretty obvious why the CMC is colder. CMC does have a cold bias though

You can see the CMC low is actually aiding our CAD regions here. Verses the euro where the low is working against the CAD. You can see the CAD fighting back in NC on euro.

for anyone to see frozen we have to get help from the Low pressure. Whether that’s created cold or wind funneling cold into the CAD.1753B8DC-FEF8-44E5-8CA2-E59A186CA62F.jpegFFF83112-6073-44C6-BDAE-2689F55677D0.jpeg
 
WxBlue said:
There's nothing more frustrating having a nice cyclone with the moisture... only to lack the d*** cold.
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True! That's why my number one rule is always COLD FIRST. I know others have different preferences, but getting cold in place is always THE priority for me.
 
CMC I noticed actually brings accumulating snow down to I85 in upstate SC not likely. But I’m curious as to how the trends will go this week.


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68/51 and clouds starting to come in soon. It is a nice day, but we're +14 from the normal high. Bleh
 
Webberweather53 said:
These 2 trends are intrinsically linked to one another.

Deeper trough off of Newfoundland = more CAA & confluence over New England = stronger CAD high at day 5. It also helps when our s/w isn't getting squashed into oblivion as it was on earlier runs.

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Fountainguy97 said:
Pretty obvious why the CMC is colder. CMC does have a cold bias though

You can see the CMC low is actually aiding our CAD regions here. Verses the euro where the low is working against the CAD. You can see the CAD fighting back in NC on euro.

for anyone to see frozen we have to get help from the Low pressure. Whether that’s created cold or wind funneling cold into the CAD.View attachment 28297View attachment 28298
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this is why we need this storm to be faster, no? CMC has snow and the low is already off of the coast of SC, but Euro has it near Mobile at the same time. I know we want the high to anchor in place, but seems like the s/w speed is even more important
 
ecmwf-ens_mslpaNorm_us_fh144_trend.gif



It's easy to see why we're going in a direction that's depositing more low-level cold air into our parent surface high over NE US & SE Canada as time progresses. Notice the amplifying trough east of Newfoundland on the 2nd animation below. The wave pattern is definitely favorable for a winter storm in the planetary-scale sense.

I'm seeing quite a few people here already jumping to conclusions about how much cold air we're going to have to work with in this setup based on the current status of NWP operational models & their ensemble suites. The general amount of low-level cold is actually yet to be determined as evidenced by the pair of z500 & MSLPa "trend" animations in this post. Outside of the mountains, if you're well north of I-20 in the Carolinas or VA, tread carefully & cautiously when making hasty assumptions about how much cold air there's going to generally be in this setup because it's still within the realm of error this far out that enough could be present to generate wintry precipitation & vis versa if you're in the mountains of NC/TN.

ecmwf-ens_z500a_namer_fh144_trend (3).gif
 
Stormdoc said:
this is why we need this storm to be faster, no? CMC has snow and the low is already off of the coast of SC, but Euro has it near Mobile at the same time. I know we want the high to anchor in place, but seems like the s/w speed is even more important
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The speed and amplitude of the s/w are equally important here, a stronger & faster s/w would certainly be to our benefit. An unfortunate reality that emerges in this situation however is that the phase speed of rossby waves and their intensity are inversely proportional to one another because more intense & meridionally extensive waves move slower in the mean stream flow due to planetary vorticity advection & vis versa. Basically, we won't be able to have our cake and eat it too, thus we'll likely have to rely on the northern stream to give us a configuration we want.


We need a stronger parent mid-upper level trough to reinforce the CAD dome over the Carolinas & NE GA plus generate enough dynamical cooling thru sensible + latent heat fluxes that cool the column to a marginal (enough) level in order to produce snow/ice. The s/w timing is also key because we want both enough time for the air mass to become well entrenched while also not affording so much time that it leaves stage right into the Atlantic. The problem we're currently having is diametrically opposed to the general sentiment here in that we need the cold air to arrive first. In reality, the air mass is actually leaving too quickly on the models before the s/w reaches the SE US. Additional northern stream waves will also reinforce this Newfoundland vortex/50-50 low late this week into the following week & may play a significant role in the evolution of this event.
 
I would love to just see some snow falling right before Christmas, even if we don't have any accumulations. It could just be an appetizer for more to come in January and February, which is really the heart of winter for us. I think anyone seeing snow in December should consider it a big win and a bonus.
 
Brick Tamland said:
I would love to just see some snow falling right before Christmas, even if we don't have any accumulations. It could just be an appetizer for more to come in January and February, which is really the heart of winter for us. I think anyone seeing snow in December should consider it a big win and a bonus.
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That's what we said about the December 9th snow last year. We saw nothing the rest of the year. I'll take my rain this go round and wait for hopefully better situations later on in the winter.
 
Shaggy said:
That's what we said about the December 9th snow last year. We saw nothing the rest of the year. I'll take my rain this go round and wait for hopefully better situations later on in the winter.
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That's why I said it would be a bonus.
 
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