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Pattern The Great December Dump

Darklordsuperstorm said:
Meanwhile something to watch from DOC
DISCUSSION...
Medium-range guidance remains in relatively good agreement that a
shortwave trough will move from the Great Basin into the
southern/central Plains on D4/Sunday, continuing through the mid MS
Valley and into the Upper Great Lakes on D5/Monday. Guidance differs
on the location of the surface low associated with this shortwave
trough, with current forecasts of its position at 12Z D5/Monday
ranging from the KS/OK/MO border intersection to central TX. Even
with these differences, consensus is good for a moist and moderately
unstable environment from the Lower MS Valley through the TN Valley
on D5/Monday ahead of the approaching shortwave. Strong vertical
shear will extend across this region, supporting long hodographs and
supercell wind profiles. Consequently, there is a threat for severe
thunderstorms D5/Monday afternoon and evening from the Mid-South
into the Lower OH Valley as the shortwave trough and associated cold
front move through. Forecast confidence is high enough to introduce
severe probabilities. Refinements to this area are likely in
subsequent forecast as mesoscale details become more apparent.View attachment 27844
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yeah, GEFS has mean SCPs of 2-4, which is pretty high for a ensemble mean, right now things are looking a little unidirectional, but that wind shear is gonna be pretty strong, and cape is gonna be there 1576155858981.png
 
The EPS don’t have a clue and are caving slowly to a more colder solution...
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Webberweather53 said:
Our pattern in week 2 is trending in a direction that resembles the GEFS cold temperature bias & thus will temporarily mask the underlying issues w/ the model of late around here.

View attachment 27838


The EPS in the 11-15 has obviously been too warm across nearly the entire CONUS.

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Where did you find these great maps?

Folks, note that in the area from DC SW to N GA, the GEFS cold bias has been the strongest in the entire US while there’s been a pretty strong WARM bias over the Rockies/inter mountain west. This is consistent with the idea that the model itself doesn’t have a consistent cold bias everywhere because much of the bias is instead a pattern bias consistent with a +PNA bias in the means.

OTOH, note that the EPS warm bias is more of a classic warm bias vs the GEFS cold pattern type of bias since this EPS warm bias covers nearly the entire country. But also note that the EPS warm bias doesn’t include most of the SE with even a small cold EPS bias in the far SE consistent with the idea of the tendency of a not strong enough forecasted SER in the means.
 
Curious to see how this Dec pattern evolves...kind of extrapolating it looks like it could be one of our better Dec patterns since 2010. Can't recall the last Dec or winter month for that matter that had low heights off the east coast.

compday.t8XDOYkd3e.gifecmwf-ensemble-avg-nhemi-z500_anom_10day-7404800.pngecmwf-ensemble-avg-nhemi-z500_anom_10day-6972800.png
 
“Models continue to struggle beyond 5-6 days lead, with the operational models seeing the largest change from yesterday’s 12z run to this morning’s 0z in the 6-10 Day period. The GFS OP gained ~20 GWHDDs, while the Euro OP gained ~14 GWHDDs. The Maxar forecast gained +7.1 GWHDDs over the course of the next 15 days, and +6.1 GWHDDs of the cold change occurred in the 6-10 Day period. There is still room for additional model volatility, and this is echoed by the widening spread of solutions among members of the Euro EN in the Midwest. In St. Louis, the spread among members increases to more than 20° for the average temperatures on Day 7 and is 35° (range from 9°-44°) on Day 8. Similar spreads are in Chicago...”

“The spread is not only wide within the Euro EN, but sizable differences between models also exists. About 12 GWHDDs separate the colder GFS EN from its Euro counterpart. The upper air maps below show where the difference between models originates. The Alaska region will be the area to watch in future model runs, as the colder GFS EN has more ridging here and downstream south displacement of the polar vortex. Alternatively, the Euro EN has more troughing near Alaska and a faster shift warmer from west to central North America under a stronger Pacific influence.” from Maxar
 
Don’t look now but the GFS might try and pop a system Tuesday /Wednesday that ARCC has been mentioning


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Storm5 said:
Don’t look now but the GFS might try and pop a system Tuesday /Wednesday that ARCC has been mentioning


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Up until the energy gets strung out and the western ridge goes to hell


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Here comes the solstice system....let's see what we get looks like it shouldn't be able to NW but temps might be an issue

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GFS continues to be active across the SE. Very good for continuing to beat back the remaining drought conditions. Hopefully, the active pattern will continue as we transition deeper into winter and evolve to better high latitude support.

gfs_apcpn_seus_64.png

The storm around the 21st takes a great track, but we're not getting help farther north. While winter weather is possible, we're still in a period where super timing is needed. We need that PV lobe to scoot east and remain suppressed ahead of the storm. Coming in with or behind the storm effectively blocks our cold air feed, as shown on the 12z run.
 
Storm5 said:
Don’t look now but the GFS might try and pop a system Tuesday /Wednesday that ARCC has been mentioning


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Definitely trending the right way. Biggest problem I see right now is that is some very dry air being pumped in from the northwest.
 

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Rain Cold said:
The old rule of Nino thumb, where it exits at the same latitude it enters, will hopefully hold serve here.
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True and probably will just not as a bowling ball but a jacked up strung out good for nothing mess....
 
I will say that I think the 12/21-12/22 period is a legitimate threat. Almost every run of the GEFS and EPS has shown the potential with a decent setup for the past several days. Almost every member of the GEFS has the system. A couple of days ago some of the members were leaning towards a warmer aps runner. However, the blocking has been improving as well as the PNA. Now some of the ensembles and operational runs are suppressing and squashing the system! Experience tells me its just about everything we look for with a potential system. Cold air will always be an issue in the south, but it feels right to me. Let's see how it trends the next few days.
 
Ollie Williams said:
The Euro doesn't look bad. It has a system, Its just way too suppressed. extremely deep 50/50 low
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The timing of that 50/50 low and a S/W would need to be just right. If a deep 50/50 low comes into places first, a storm system would likely not form. Perhaps one would form after the 50/50 low kicks out, but then it would probably warm ahead of a S/W. A 50/50 can mean a significant east coast snow storm (SECS) but there's no guarantee. If an SECS occurs, bombogenesis can occur far south as the Mid-Atlanic.
packfan98 said:
I will say that I think the 12/21-12/22 period is a legitimate threat. Almost every run of the GEFS and EPS has shown the potential with a decent setup for the past several days. Almost every member of the GEFS has the system. A couple of days ago some of the members were leaning towards a warmer aps runner. However, the blocking has been improving as well as the PNA. Now some of the ensembles and operational runs are suppressing and squashing the system! Experience tells me its just about everything we look for with a potential system. Cold air will always be an issue in the south, but it feels right to me. Let's see how it trends the next few days.
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I have a feeling that time frame is right for something to possibly occur as well. I haven't seen enough consistency for my liking - consistency is your friend. The pattern does though look like something good could happen for that time though.

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