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The Great December Dump

Meteorologist1999

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Really nice to see the warm pattern continually being kicked down the road on successive EPS runs. Doesn't begin to turn legitimately mild until after mid month.
Wow, I notice warm air keeps getting pushed back.. it’s been pretty chilly the last month in the SE except for just a few above/near average days.
 
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EPS goes with the Dec 2009 look here in the US w/ widespread cold anomalies nearly from coast-coast. Obviously, there's no huge -NAO this time as there was then but as the old saying goes "there's more than one way to skin a cat".

Dare I ask, are we actually going to see a below normal December for once? Still not terribly likely but have to like our chances if we get a few big shots of arctic air the next few weeks and the vortex stays around in SE Canada.

I definitely thought we'd be warming relative to normal up by the 2nd week of the month. I'll be more than happy to be dead wrong because I've grown sick & tired of mild Decembers

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Myfrotho704_

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Geez, haven’t seen the gefs ensembles this lit for wintry precip in the SE in a long time, many have a icy signal and some have snow around that 180-300 hr timeframe, mostly Ice tho, most show a anafront or even some overrunning with the first system, then after shows another system with many solutions (miller B/CAD, overrunning, cutters with wintry precip that starts out with CAD) interesting signal for sure, makes sense tho if we have leftover strong high pressure and a SW decides to kick into that 6D8431D7-AB3A-44FC-97F9-425EF4A29BAA.jpeg
 

Jon

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Yeah, this isn’t a warm pattern. Awesome to see in December.

Models aren’t done with this one. And a forecaster asked me if I was “a fan of fiction” tweeting on this pattern on 11/28...having that attitude when both ensemble models had a strong signal at the same pattern is what’s wrong with folks...


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Verbatim there isn't a whole lot of support for the system at day 9 on the EPS, but certainly beyond ~ day 12 ish on the tail end of this big cold shot there's some snowier solutions.

Member 21 would be nice, 2-3 separate winter storms in 5 days.

In all seriousness though, it's hard not to get at least a little excited here given the active storm track we'll already have in place

eps_ptype_e21_conus_264 (1).png

eps_ptype_e21_conus_300.png

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Jon

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Verbatim there isn't a whole lot of support for the system at day 9 on the EPS, but certainly beyond ~ day 12 ish on the tail end of this big cold shot there's some snowier solutions.

Member 21 would be nice, 2-3 separate winter storms in 5 days.

In all seriousness though, it's hard not to get at least a little excited here given the active storm track we'll already have in place

View attachment 26879

View attachment 26878

View attachment 26877
Lol I just tweeted the same. The 13-17th period, if being modeled correctly, should deserve some excitement and hopefully we will grab one to track. I was thinking yesterday when graupel was falling...this winter feels different.


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Rain Cold

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Now, is this a woof or a womp or a oof or a gah? I can't keep track of all of the official terminology. :) Anyway, I'm glad to see warm patterns keep pushing back in time and the warm Euro starting to maybe cave in a bit. I am still not ready to go all in on a winter storm pattern yet, but getting deeper into the month, seeing the PV over on our side, seeing the WAR displaced north of where it usually is, and seeing a strong STJ continuing is encouraging. As some of you have said, this kind of pattern can pop a storm threat pretty quickly. But I'd feel a bit more confident in a specific period if I saw signs of a west-based -NAO developing. Maybe it will, at some point down the line.

gfs-ens_z500a_namer_51.png
 
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I'm wondering if the models are struggling with the mjo and the forcing there?
The evolution of these planetary-scale features is often driven by upscale growth from individual synoptic-scale events whose predictability is often limited to several days to a week or so. This basically seems like a case where a few minute details in the way the wave breaks were represented over the North Pacific have dramatically changed the outcome. The broader scale planetary waves didn't change much.

Errors in those synoptic-scale events are being amplified by the fact that we have the main lobe of the tropospheric polar vortex in our own backyard. Even minor modification to the North Pacific pattern evolution means massive alterations in sensible weather as we're now beginning to realize.

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download (12).png
 

GaWx

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Warning: As great as the models are trending (I especially like the EPS trend to less warmth in the SE near mid-month), don’t get your heart too set as the recent past tells us that the trend could continue too far to the point where the SER takes back over in future runs and the runs warm back up. Don’t get too complacent as the models have and will again break your heart. But hopefully not this time.
 
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Hard to dislike that configuration going into mid-December where the pattern was leaning mild for a while, perhaps for reasons I noted yesterday the GEFS will beat the EPS to the punch here in the extended. December NINOs that are BN around here usually find a way to produce a substantial winter storm in central NC in Dec, if we keep this up, eventually we may score one.
Yep, I noticed it this morning, the EPS is not warm, but seems to be coming around to the general idea of the GEFS, just a bit more muted: PV in SE Canada, westernish ridge, just not as tall, and the beginnings of an Aleutian low. Basically our pattern for the last 5 years, but this time in December too. I'm still a bit disappointed our -NAO evaporated (sigh), but having a cool/cold pattern persist this early is encouraging. Hopefully this is the beginning of a long cold winter.

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The bias of the EURO to push the trough into the West and build a ridge in the East is well known. The EURO will likely continue the correction and the trough will end up sliding East on future runs as we have seen it do so far. Nothing is guaranteed in the long term on the models but the pattern is looking much better than last December. If we can get that Western Canada ridge to build stronger and the NAO to go at least neutral, I like the chances for something happening before Christmas in the 40/85 corridor at least
 

Rain Cold

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The bias of the EURO to push the trough into the West and build a ridge in the East is well known. The EURO will likely continue the correction and the trough will end up sliding East on future runs as we have seen it do so far. Nothing is guaranteed in the long term on the models but the pattern is looking much better than last December. If we can get that Western Canada ridge to build stronger and the NAO to go at least neutral, I like the chances for something happening before Christmas in the 40/85 corridor at least
Agreed...the only thing I would say here is that the northern plains and east-central US is probably going to be favored for the coldest anomalies, until we get a favorable configuration up in the NAO domain. I would expect negative anomalies to be tempered in the SE with a bit of a gradient pattern through the region. Same with winter storm chances. I'd think northern and western zones are favored, as has been said, rather than threats to the deep SE. But you never know. Anyway, it's a much better boat to be in heading into mid-December than the last few.
 

GaWx

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Based on data today from Maxar, this Atlanta bias analysis is what really makes me wary about the recent trend toward colder in the models:

ATL Bias last 30 days (Negative Model Is Too Cold; Positive Model Is Too Warm)

1-5, 6-10, 11-15

T-AVG

GFS OP
GFS EN
Euro OP
Euro EN

1-5 Day
-2.6
-5.1
-3.6
-3.6

6-10 Day
-3.0
-6.6
-4.7
-4.3

11-15 Day
-1.1
-4.3
N/A
-2.3

This didn’t copy in the right format, but the gist of this is obvious: universal
model cold bias for ATL in 1-5, 6-10, and 11-15 the last 30 days with the GEFS being the worst in all 3 timeframes and even the Euro suite not a whole lot better.​
 
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Agreed...the only thing I would say here is that the northern plains and east-central US is probably going to be favored for the coldest anomalies, until we get a favorable configuration up in the NAO domain. I would expect negative anomalies to be tempered in the SE with a bit of a gradient pattern through the region. Same with winter storm chances. I'd think northern and western zones are favored, as has been said, rather than threats to the deep SE. But you never know. Anyway, it's a much better boat to be in heading into mid-December than the last few.
Yeah, the thing with these -EPO driven cold outbreaks when we do get good cold south, is they tend to be cold and dry for a bit, and by the time a storm comes through it's gone because of the progressive flow. It can be frustrating, but it can work. I'm not looking for storm chances this early anyway. I'll just call a cool December a win if we can get it and hope for a shake up in the NAO domain in January to slow everything down.
 
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Based on data today from Maxar, this Atlanta bias analysis is what really makes me wary about the recent trend toward colder in the models:

ATL Bias last 30 days (Negative Model Is Too Cold; Positive Model Is Too Warm)

1-5, 6-10, 11-15

T-AVG

GFS OP
GFS EN
Euro OP
Euro EN

1-5 Day
-2.6
-5.1
-3.6
-3.6

6-10 Day
-3.0
-6.6
-4.7
-4.3

11-15 Day
-1.1
-4.3
N/A
-2.3

This didn’t copy in the right format, but the gist of this is obvious: universal
model cold bias for ATL in 1-5, 6-10, and 11-15 the last 30 days with the GEFS being the worst in all 3 timeframes and even the Euro suite not a whole lot better.​
It appears that the GFS Op is not too bad after all. I can understand the GEFS being too cold because, and I may be wrong about this, the individual members are still the old GFS model.
 
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