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Pattern Dazzling December

Recent trends on EPO Index from GEFS and EPS

ZlDNGHi.jpg
 
Is the PNA looking to go neutral/slight pos. for a decent period? Seems that long look is still erratic
 
Latest from WxSouth.

The weather is warm across the South today and next few days, from Texas across the heart of the south to the eastern Carolinas, but cold air damming in Virginia, western Carolinas continues to thwart the warm...but even there it will warm up next couple of days. Clouds and periods of rain dominate though, many more systems are slated over the next week.
So, the weather now is gloomy, rather boring across a big chunk of the region. Normal December weather, except this long cloudy stretch is a bit much to take :(
What is showing up though is, atleast in my estimation, going to be spectacular. All the signals continue to be there for a cascade of sequential Meteorological events that will thrust the central and eastern US into hard core Winter Weather over the next few weeks. A blocking ridge will build toward Alaska (this got us cold several times in October and November). A strong block around Greenland is developing as we speak and will maintain for several weeks--another cold signal for the Southeast. It's rare to get both simultaneously. I believe things are going to get very interesting down South in the next few weeks.
 
Things are pretty much evolving as expected overall & this is the best looking pattern we've had in late December since 2010 & it's not even close (of course that isn't saying a whole lot).


Fwiw, on average during Dec-Mar 1948-2021 in NC, we see at least a minor winter storm (accumulating snow or trace of ice) somewhere east of the mountains about once every 13-14 days or so.

When you also pair this with teleconnections, winter weather in NC is ~1.5x more likely than normal when -NAO/-EPO is present (< -0.5 sigma), or about one storm every 8-9 days in Dec-Mar. When -NAO/-EPO is coupled to a +PNA, this jumps to on average about one storm per week, or -NAO/-EPO/+PNA roughly doubles the climatological odds of winter weather in NC.

If -PNA/-EPO are coupled to -PNA, chances decrease slightly, but are still noticeably above normal w/ one storm occurring on average every 10 days (vs 13-14). Aside from the higher winter storm chances, what's also very noteworthy about -PNA/-EPO/-NAOs compared to +PNA/-EPO/-NAO is there are proportionally many more ice storms w/ -PNA/-EPO/-NAO compared to +PNA/-EPO/-NAO. A snowstorm is ~3x more likely compared to ice in +PNA/-EPO/-NAO, whereas ice is nearly 1.5x-2x more likely than snow during -PNA/-EPO/-NAO.


In summary:

NC (East of Mountains) Daily Winter Storm Chances wrt Climatology & Teleconnections (1948-2021, Dec-Mar)

Climatology: ~7.5% chance of a winter storm per day OR 1 winter storm every ~13-14 days

-NAO (<-0.5σ): ~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely than normal in NC during Dec-Mar w/ -NAO

-NAO (<-0.5σ)/-EPO (<-0.5σ): ~12% chance of a winter storm per day OR 1 winter storm every ~8 days
Winter storms are ~50% more likely in NC than normal during Dec-Mar w/ -NAO and -EPO

-NAO (<-0.5σ)/-EPO (<-0.5σ)/-PNA (<-0.5σ)
~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & -PNA
Ice storms are nearly 1.5x-2x more likely than snowstorms

-NAO (<-0.5σ)/-EPO (<-0.5σ)/+PNA (>+0.5σ)
~14% chance of a winter storm per day OR 1 winter storm every ~7 days.
Winter storms are ~2x more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & +PNA
Snowstorms are nearly 3x more likely than ice storms

Data source:

I need to update this at some point w/ 2022's data, as well as add on some additional winter storms.
Nov-Apr Daily Teleconnections and NC Winter Storms List (1948-2021)
 
Last edited:
Webberweather53 said:
Things are pretty much evolving as expected overall & this is the best looking pattern we've had in late December since 2010 & it's not even close (of course that isn't saying a whole lot).


Fwiw, on average during Dec-Mar 1948-2021 in NC, we see at least a minor winter storm (accumulating snow or trace of ice) somewhere east of the mountains about once every 13-14 days or so.

When you also pair this with teleconnections, winter weather in NC is ~1.5x more likely than normal when -NAO/-EPO is present (< -0.5 sigma), or about one storm every 8-9 days in Dec-Mar. When -PNA/-EPO is coupled to a +PNA, this jumps to on average about one storm per week, or -NAO/-EPO roughly doubles the climatological odds of winter weather in NC.

If -PNA/-EPO are coupled to -PNA, chances decrease slightly, but are still noticeably above normal w/ one storm occurring on average every 10 days (vs 13-14). Aside from the higher winter storm chances, what's also very noteworthy about -PNA/-EPO/-NAOs compared to +PNA/-EPO/-NAO is there are proportionally many more ice storms w/ -PNA/-EPO/-NAO compared to +PNA/-EPO/-NAO. A snowstorm is ~3x more likely compared to ice in +PNA/-EPO/-NAO, whereas ice is nearly 1.5x-2x more likely than snow during -PNA/-EPO/-NAO.


In summary:

NC (East of Mountains) Daily Winter Storm Chances wrt Climatology & Teleconnections (1948-2021, Dec-Mar)

Climatology: ~7.5% chance of a winter storm per day OR 1 winter storm every ~13-14 days

-NAO (<-0.5σ): ~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely than normal in NC during Dec-Mar w/ -NAO

-NAO (<-0.5σ)/-EPO (<-0.5σ): ~12% chance of a winter storm per day OR 1 winter storm every ~8 days
Winter storms are ~50% more likely in NC than normal during Dec-Mar w/ -NAO and -EPO

-NAO (<-0.5σ)/-EPO (<-0.5σ)/-PNA (<-0.5σ)
~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & -PNA
Ice storms are nearly 1.5x-2x more likely than snowstorms

-NAO (<-0.5σ)/-EPO (<-0.5σ)/+PNA (>+0.5σ)
~14% chance of a winter storm per day OR 1 winter storm every ~7 days.
Winter storms are ~2x more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & +PNA
Snowstorms are nearly 3x more likely than ice storms

Data source:

I need to update this at some point w/ 2022's data, as well as add on some additional winter storms.
Nov-Apr Daily Teleconnections and NC Winter Storms List (1948-2021)
Click to expand...
Wish we had someone in GA with data like the above.
 
Webberweather53 said:
It's a great feeling when every day 8-10 WPC 500mb anomaly cluster looks awesome

https://origin.wpc.ncep.noaa.gov/hmt/wk2/clusters/view.php?type=3daykmeans&uday=&field=cluster_hgt_500_forecasts&reg=_conus&regstr=CONUS

cluster_hgt_500_forecasts_k_means_conus.png
Click to expand...

I'll confess I was not familiar with this product. For my own and other's benefit, here is a brief/simple overview of these products:

These tools are incredibly useful for understanding the sources of ensemble uncertainty, identifying extremes, and evaluating potential forecast scenarios via ensemble clusters. The cluster analysis groups 90 ensemble members from the EPS (50), GEFS (30) and CMCE (20) into four clusters based on similarities and dissimilarities amongst these members (more information on this clustering process is provided later).
Click to expand...
Source: https://origin.wpc.ncep.noaa.gov/wpc_ensemble_clusters/cluster_analysis.pdf

That out of the way, this seems extremely encouraging!
 
Webberweather53 said:
Things are pretty much evolving as expected overall & this is the best looking pattern we've had in late December since 2010 & it's not even close (of course that isn't saying a whole lot).


Fwiw, on average during Dec-Mar 1948-2021 in NC, we see at least a minor winter storm (accumulating snow or trace of ice) somewhere east of the mountains about once every 13-14 days or so.

When you also pair this with teleconnections, winter weather in NC is ~1.5x more likely than normal when -NAO/-EPO is present (< -0.5 sigma), or about one storm every 8-9 days in Dec-Mar. When -PNA/-EPO is coupled to a +PNA, this jumps to on average about one storm per week, or -NAO/-EPO roughly doubles the climatological odds of winter weather in NC.

If -PNA/-EPO are coupled to -PNA, chances decrease slightly, but are still noticeably above normal w/ one storm occurring on average every 10 days (vs 13-14). Aside from the higher winter storm chances, what's also very noteworthy about -PNA/-EPO/-NAOs compared to +PNA/-EPO/-NAO is there are proportionally many more ice storms w/ -PNA/-EPO/-NAO compared to +PNA/-EPO/-NAO. A snowstorm is ~3x more likely compared to ice in +PNA/-EPO/-NAO, whereas ice is nearly 1.5x-2x more likely than snow during -PNA/-EPO/-NAO.


In summary:

NC (East of Mountains) Daily Winter Storm Chances wrt Climatology & Teleconnections (1948-2021, Dec-Mar)

Climatology: ~7.5% chance of a winter storm per day OR 1 winter storm every ~13-14 days

-NAO (<-0.5σ): ~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely than normal in NC during Dec-Mar w/ -NAO

-NAO (<-0.5σ)/-EPO (<-0.5σ): ~12% chance of a winter storm per day OR 1 winter storm every ~8 days
Winter storms are ~50% more likely in NC than normal during Dec-Mar w/ -NAO and -EPO

-NAO (<-0.5σ)/-EPO (<-0.5σ)/-PNA (<-0.5σ)
~10% chance of a winter storm per day OR 1 winter storm every ~10 days.
Winter storms are ~25% more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & -PNA
Ice storms are nearly 1.5x-2x more likely than snowstorms

-NAO (<-0.5σ)/-EPO (<-0.5σ)/+PNA (>+0.5σ)
~14% chance of a winter storm per day OR 1 winter storm every ~7 days.
Winter storms are ~2x more likely in NC than normal during Dec-Mar w/ -NAO, -EPO, & +PNA
Snowstorms are nearly 3x more likely than ice storms

Data source:

I need to update this at some point w/ 2022's data, as well as add on some additional winter storms.
Nov-Apr Daily Teleconnections and NC Winter Storms List (1948-2021)
Click to expand...
Very good Eric. Enjoyed the read. Informative

One thing, there are a couple places in the top section where it states "if -PNA/-EPO are coupled to -PNA" etc.....here I think you meant to say "if -NAO/-EPO are coupled to -PNA"
 
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