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Pattern December, Make analogs relevant again

I’m not a fan of the 18z gfs..warmest cycle compared to the last six for Atlanta. How do ensembles look?
 
EastAtlwx said:
I’m not a fan of the 18z gfs..warmest cycle compared to the last six for Atlanta. How do ensembles look?
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This is tricky for the SE. Indeed, the 18Z GFS 6-15 is the warmest GFS of the last 6. However, the 18Z GEFS is just about as cold as any run in the 6-10 and is either the coldest or about tied for the coldest in the 11-15. Moreover, the 12Z EPS and CMC ensembles in the 6-15 are about the coldest yet.
 
GaWx said:
This is tricky for the SE. Indeed, the 18Z GFS 6-15 is the warmest GFS of the last 6. However, the 18Z GEFS is just about as cold as any run in the 6-10 and is either the coldest or about tied for the coldest in the 11-15. Moreover, the 12Z EPS and CMC ensembles in the 6-15 are about the coldest yet.
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Thanks Larry for pointing this out! Just another great example of why we use ensembles not deterministic forecasts esp beyond the medium range and/or when the operational looks nothing like its ensemble mean at the synoptic-planetary scale
 
GaWx said:
No, the models for the most part aren't plunging the cold deep down into the SE (at least not yet). Rather, the SE is near the bottom of intense cold to the north, which could pay off at some point with a winter storm traveling along the boundary if it can tap into the lower level cold air via CAD assuming WSW upper flow/upper trough axis near the MS River or a little further west..
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Lol, that's where it gets so twisted down here. We need the cold, good strong cold that won't erode, but it can't be too cold, or get in here too quick :) It's got to get into just the right position, with just the right winds at different levels, to allow the over running, while being reinforced. Meanwhile, we want a gulf low that's weakish, but not too weak, lol. And most of all, for me, the whole set up has to remain ignorant of the I 20 mystery line, lol. We just need a good little ice age to come along for a few years so we don't have to work for it so hard :) T
 
SD said:
That's cold

Sent from my SM-G955U using Tapatalk
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Yep, below-well below average by day 4 and thru at least mid month, not bad.
Of course right as I post this, Maue just finished the EPS city charts page on his free wx.graphics site
http://wx.graphics/models/city/eps_charts.php

Really like how he gives us spread & uncertainty in the members in addition to the mean. Once he gets these done and snowfall accumulation maps for the EPS suite, I'd consider weatherbell completely obsolete and not worth paying for anymore.

KRAH_2017120312_forecast_EPS_360.png
 
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pcbjr said:
No, but 43 and 45 have possibilities for a like - in January ... :p
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Yeah, 43 would "nail" us both with 0.5". "Nail", of course is a relative term as that would be huge for either of us, especially you.

I do find the 50 members overall to be rather interesting for my area as I count 7 of the 50 (14%) with measurable SN/IP and 5 of the 50 with 0.5-2", any of which would be a pretty rare hit. Now that SN is supposedly really SN (that glitch has been fixed, correct?) I would only rarely expect to see any run as good as that of this 12Z EPS absent the rare impending storm. In the city, itself, since 12/1989, the few measurable hits (3) were under 0.5". So, this is saying there is a 10% chance for the heaviest SN/IP here in 28 years! That's more than enough for me to be hopeful, especially considering the EPS' warm bias and the expected averaged out solidly -AO for the rest of Dec.
 
To show how potentially long this upcoming cold period is to our north, the 12Z EPS mean has Chicago (O'Hare) staying at 28 or colder for at least 12 straight days to the end of the run. I believe I have to go all of the way back to Jan-Feb 2007 for the last time that was exceeded. There may not be any extreme lows showing up (at least not yet... maybe that would require much more snowcover there and to their north), but the longevity is quite impressive. Very long cold like this (and it could go even longer though short breaks would be normal) will hopefully pay off with a SE winter storm underneath at some point this month or in the first half of Jan, the most likely period per my analogs.
 
GaWx said:
Analogs for similar 12/1-15 AO's going back to 1950 with similar ENSO (centered on weak La Nina) suggest that 12/16-31's AO will likely be at least down to -1.5 and quite possibly down to -2.0 or lower as the 3 best ENSO/AO analogs of 1995 (-2.8), 2000 (-3.7), and 2005 (-2.3) suggest. The #1 analog when considering QBO, ENSO, and -AO of late Nov and early Dec. is 2000 and it had AO of -3.7 during 12/16-31, 3rd most negative AO to the -4.9 of 2009 and the -3.9 of 2010. That would favor a continuation of solid cold dominating the E US through the end of the month.
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These 3 best AO/ENSO analogs favor a solidly cold month in the SE US. KATL and KRDU, for example, averaged 5 below normal for the average of the 3 months while KSAV averaged 4 below. Considering the mild start, that would make for quite the cold last 3 weeks or so.
Moreover, a month potentially as cold (8 colder than normal) and snowy (ATL, GSP, and Chattanooga 3"; Asheville 6") as Dec of 2000 is on the table as that is my number one analog.
 
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Webberweather53 said:
12z EPS. I think just about everyone here would need a new pair of pants if member 12 magically verified...
View attachment 1749
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I counted 31 that give me at least some snow. That's 60%. Not too shabby at this point. Most of the misses showed snow to my east. If the NW trend is real, then the foothills and mountains would certainly have a pretty good shot at some type of winter event.
 
Lol, a 200 kt jet streak off the east coast in fantasy land on the EPS control... Been seeing it spit out these monstrous jet streaks periodically for the past few days and it makes some sense given there's a really steep height gradient between the huge vortex over SE Canada and the WAR off the SE US coast plus confluent flow between the northern stream and subtropical jet. Of course the exact intensity is really questionable
eps_uv200_c_conus_51.png
 
Massive cold coming into the N Plains 252+. Let's see how far SE it gets.
 
^Some of those look delish for the Tennessee Valley... meanwhile, this is about par for the course for clippers in the Chattanooga area... The Cumberland Plateau loves to rob us of scant moisture associated with clipper systems:
sn10_acc.us_ov.png
 
Euro trying to develop something in the Western Pacific. Luckily the waveguide (i.e. the jet stream) is so strong and bgd conditions are less favorable s.t. it's hard to get a big typhoon that recurves into the Pacific jet and sends a huge rossby wave train downstream across the Pacific - North American sector, but it does happen from time to time. See Archambult's thesis on "The Downstream Extratropical Flow Response to Recurving North Pacific Tropical Cyclones" for more detailed, technical information regarding the climatology, behavior, evolution, and sensible impacts on our weather from these storms...
http://www.atmos.albany.edu/student/heathera/dissertation/archambault_dissertation.pdf

ecmwf_mslpa_wpac_26.png
 
Euro in general is looking interesting by day 8-9... Huge snow cover in the eastern US with renewed shots of powder from clippers riding on the southern periphery of this SE Canada gyre and here comes a disturbance out of the southern stream in the southwestern US
ecmwf_z500_vort_noram_35.png
 
Interesting stuff, Webb. Meanwhile, big cold coming into the SE US 12/12-13 on the 0Z Euro!

Teen lows 12/13 most of NC into far NW SC, far N GA, far NE AL, E half of TN!

And if that isn't enough, still another W. Canadian Arctic high is poised to come down into the US shortly after the end of this run. What a pattern!
 
So if a Pac typhoon recurves and sends a Rossby wave downstream, would that break up the Eastern Pacific pattern?
 
I've seen this pattern play out so many times in analyzing historic winter storms for NC using ECMWF's 20th Century Reanalysis (ERA-20C) esp for cold air damming and/or overrunning events...
ecmwf_z500_vort_conus_39.png

Really awesome airmass comes out in front of it as well. This airmass and SE Canada vortex begin to retreat after this on the latest EPS/GEFS suites so that definitely opens the door for this shortwave over northern Mexico and south Texas to come out and start inducing moist, southwesterly flow aloft over top of this residual low level arctic airmass. Overall, sticking with what I said last week, I still like the December 13-21 period for us to score a storm for a majority on the board...
ecmwf_t850a_conus_38.png
 
very odd little discussed storm, late Nov 1952... not much info out there. A lot of people know about the Nov. 1950 storm, but this one happened 2 years later. Chattanooga got completely robbed in this one, with only a Trace recorded while Knoxville scored 18 inches. Those are some borderline/boundary layer temps that hurt your very soul...Very bizarre: http://tennesseewx.com/index.php?topic=3071.0
and: ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/mwr/080/mwr-080-11-0227.pdf
 
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6z GFS looks meh. It's just one run, but verbatim, looks like cold shots, warm up, frontal passage, cool down, repeat
 
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