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Pattern Failbruary Thread

NickyBGuarantee said:
Things that will work .. this! .. also +PNA is the real deal and is the only reason we were able to have a streak of good storm potential like we just had .. I will root for that more than anything else at this point. -NAO is great and all but it didn’t help with any storm potential of our past 3 so we don’t need it really View attachment 112060View attachment 112059
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False
 
Rain Cold said:
False
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SD said:
Yeah if you overlap the recent pattern with a -nao we'd probably have 2x snow or more
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While I agree a -NAO coupled with +PNA would have us score quite easily.. I would take a plain +PNA over a plain -NAO .. last year is a good example of having the amazing -NAO but no +PNA and just getting cold rain all the time.. no good .. straight up +PNA has given us 3 weeks of winter weather every weekend.. so it is not “false” to say we don’t need the
-NAO as that’s been proven by the last 3 weeks (see below we’ve had a +NAO all month with a good ole +PNA doing all the work) but I agree that having BOTH mechanisms to work with would give us a fat thanksgiving big dog feast A24FED16-48D5-4872-AAD9-7429451ACDA8.jpeg767CB3C6-23C4-4897-8148-71E9E972639F.jpeg
 
NickyBGuarantee said:
While I agree a -NAO coupled with +PNA would have us score quite easily.. I would take a plain +PNA over a plain -NAO .. last year is a good example of having the amazing -NAO but no +PNA and just getting cold rain all the time.. no good .. straight up +PNA has given us 3 weeks of winter weather every weekend.. so it is not “false” to say we don’t need the
-NAO as that’s been proven by the last 3 weeks (see below we’ve had a +NAO all month with a good ole +PNA doing all the work) but I agree that having BOTH mechanisms to work with would give us a fat thanksgiving big dog feast View attachment 112078View attachment 112079
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I'm not a believer in you have to have a -nao for us to get a big dog here. That said in this fast northern stream dominant regime a -nao would have given us a shot at much larger events the last 2 weekends imo
 
SD said:
I'm not a believer in you have to have a -nao for us to get a big dog here. That said in this fast northern stream dominant regime a -nao would have given us a shot at much larger events the last 2 weekends imo
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100% agree I would even go to say it probably would have given us a big dog or at least a much larger portion of the SE a big dog. I was simply talking to the point that if we had to pick having one being dominant over the other I would take +PNA all day over a
-NAO
 
NickyBGuarantee said:
The next weekends threat is already being primed and set on the 00z GFS .. obviously fantasy stuff but the every weekend winter threat is quite comical to keep up with View attachment 112097
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What's interesting is that it's trying to develop a -NAO in the long range.
gfs_z500a_namer_48.png

Also that +PNA block!
 
Rain Cold said:
NAO is not just nice. It's extremely helpful when it comes to SE snowstorms. You can absolutely get cold without a -NAO. You can absolutely get winter storms without a -NAO. But we need to remember that it helps slow the pattern down and keep the storm track suppressed. A PNA is nice, but it doesn't suppress the storm track. The downstream effect is a trough in the east. But the flow still remains pretty fast and you need great timing for big winter storms. You still need great timing with a -NAO, but adding that in (and I'm not saying it's the only piece) gives you a bigger (and maybe much) bigger eye of the needle.
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I don’t disagree with any of what you’re saying. It all makes sense. Regardless, I looked in my files and actually found an analysis I did of RDU 6"+ SN/IP and posted here back in 2017. I just added 1/17-18/2018 and 12/9-10/2018 to complete the list.

(2/24-26/2015 and 1/13/14/1982 were both not included since both of those periods' snow were actually from two different storms with the heaviest at 5". 2015 would have counted as +NAO and 1982 neutral)

Here's the NAO for the 21 Raleigh 6"+ SN/IP storms since 1950. (I'm calling neutral NAO to be from +0.25 to -0.25):

-1/19/1955: -NAO

- 12/11/1958: neutral NAO

- 3/2-3/1960: neutral NAO

- 3/9/1960: neutral NAO

- 2/26/1963: neutral NAO

- 1/25-7/1966: -NAO

- 2/9/1967: +NAO

- 3/1/1969: -NAO

- 1/7-8/1973: -NAO

- 2/18-9/1979: neutral NAO

- 3/1-2/1980: +NAO

- 3/24/1983: neutral NAO

- 2/6/1984: +NAO

- 1/7-8/1988: +NAO

- 2/17-8/1989: +NAO

- 1/24-5/2000 (“Crusher”): -NAO

- 1/2-3/2002: -NAO

- 2/26-7/2004: -NAO

- 12/25-6/2010: -NAO

- 1/17-8/2018: +NAO

- 12/9-10/2018 +NAO



Tally:

-NAO: 8

Neutral NAO: 6

+NAO: 7

Though 2000-2010’s four big storms including the Crusher were all during -NAO, this shows a pretty even split through the entire period and the sample size isn’t small. Note that the last two were during +NAO as well as very notable storms like 3/1980 and 1/1988.

I don’t know. I’m admittedly a bit surprised the numbers are this balanced. Perhaps some of this is due to how the NCEP based NAO is defined/calculated. I mean I think you can still have good blocking near Greenland and it not officially be calculated as -NAO. What do you think?

By the way, I also did a similar analysis for the NAO five days before each storm and the result didn’t change much with any -NAO advantage still small.
 
Good news is that we still have a +PNA that will continue for awhile per GEFS. But the bad news is that there’s currently no -NAO or -AO (other than next few days) in sight (per GEFS forecast):

PNA:
870035DD-D40A-42F8-BE64-0360E8036C67.gif

NAO:
265B9D0E-AC95-4AB0-92DA-7FC371C37B80.gif

AO:
4BFCDC4F-A78E-4B6C-8427-C2F5514543A7.gif

Edit: About two weeks ago I made a prediction of 3 BN or colder 2/1-14 at ATL and RDU. With the early Feb warmth now through 2/4 instead of just 2/3 and with models suggesting a warmup next week after the cooldown, it is not looking so good right now. Going to need a cooling trend on the models to get the -3, especially for ATL.
 
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NickyBGuarantee said:
Yes this is fantasy and wont happen but this is why I say Ill take a naked +PNA over a naked -NAO although both would be nice but the GFS gives the entire SE a significant winter storm with about as positive as an NAO could be View attachment 112183
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This isn't really telling the whole story. There is actually an insanely strong TPV that is basically acting as a temporary, pseudo -NAO that sets the whole thing up and then gets out of the way. There's plenty of research to suggest that most of the big dog storms come as the NAO is receding - the NAO sets the table and aligns the wave pattern in a favorable way, the NAO does not in and of itself produce any winter storms.
 
NickyBGuarantee said:
Yes this is fantasy and wont happen but this is why I say Ill take a naked +PNA over a naked -NAO although both would be nice but the GFS gives the entire SE a significant winter storm with about as positive as an NAO could be View attachment 112183
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Yes the western ridge is great here but you are leaving out the fact that the cold vortex in SE Canada is acting as a pseudo -nao here and suppressing the height field. You lose the cold vortex and you can still cut not to mention it's accelerating the flow and there's not much room for amplification so the likely end solution may not be as juicy as the gfs suggests
 
SD said:
Yes the western ridge is great here but you are leaving out the fact that the cold vortex in SE Canada is acting as a pseudo -nao here and suppressing the height field. You lose the cold vortex and you can still cut not to mention it's accelerating the flow and there's not much room for amplification so the likely end solution may not be as juicy as the gfs suggests
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Yes, these scenarios can create a "block" of sorts. I am simply saying the NAO is positive the entire run and we get a great winter set up regardless. The PNA is positive most of the run and if we did not have the +PNA here it wouldn't matter if there's a "pseudo" set up or not we would be flooded with pacific air and get warm air or maybe a cold rain. +PNA is more key for us than a -NAO is my only point
 
Tarheel1 said:
I think it’s safe to say at this point, February will end up below normal for the whole month for most of the SE! Debunking the dreaded February torch in a Nina pattern!
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Way to early to call that. Things are gonna be mild the first few days of the month.
 
SD said:
Yes the western ridge is great here but you are leaving out the fact that the cold vortex in SE Canada is acting as a pseudo -nao here and suppressing the height field. You lose the cold vortex and you can still cut not to mention it's accelerating the flow and there's not much room for amplification so the likely end solution may not be as juicy as the gfs suggests
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And therein beats the heart of the issue. The GFS is excellent, and I mean excellent at showing these unreal solutions at the outer edges of its range. I can hardly name a time when we get up to the event and the height field looks anything like this. I don't know why it does this, and if it were showing this at 24 hours, I'd totally agree that a +NAO is just fine. But I can almost guarantee you that the PV will be well north when we get to Day 15. It's just not reality, usually. Maybe 1 out of 50 times it works out that way, but it usually does not.
 
NickyBGuarantee said:
Yes, these scenarios can create a "block" of sorts. I am simply saying the NAO is positive the entire run and we get a great winter set up regardless. The PNA is positive most of the run and if we did not have the +PNA here it wouldn't matter if there's a "pseudo" set up or not we would be flooded with pacific air and get warm air or maybe a cold rain. +PNA is more key for us than a -NAO is my only point
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If you want a true pna driven winter storm in central nc this is what you wantgfs_z500_vort_us_41 (5).png

The ridge/trough couplet suppress the pattern naturally but allows for amplification along the coast

Here:gfs_z500_vort_us_65 (3).png
It opens up amplification concerns and warm noses if there's phasing or it shears the flow leading to SE/E trends and relies on extra factors. What the gfs has late in its run is probably a once in a decade plus perfect setup
 
Rain Cold said:
And therein beats the heart of the issue. The GFS is excellent, and I mean excellent at showing these unreal solutions at the outer edges of its range. I can hardly name a time when we get up to the event and the height field looks anything like this. I don't know why it does this, and if it were showing this at 24 hours, I'd totally agree that a +NAO is just fine. But I can almost guarantee you that the PV will be well north when we get to Day 15. It's just not reality, usually. Maybe 1 out of 50 times it works out that way, but it usually does not.
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This is a fantastic post. It has to be down to the GFS post-truncation resolution because if reality rountinely matched the end-of-the-run GFS, I'm pretty sure RDU would mirror Boston for average annual snowfall. There are clearly some kind of cascading errors that result in late run (+300 hr) evolutions that always favor these physics-defying PV intrusions that never happen, and usually trend further and further north almost until verification. Come to think of it, it is probably some minor bias in the GFS (strong vortexes too far south) that gets exponentially magnified beyond truncation...
 
Chazwin said:
Way to early to call that. Things are gonna be mild the first few days of the month.
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But the month is shorter, so when the hammer drops, there will be less day to formulate! I’m going -2 below avg for the month at GSP
 
The GFS dangles the carrot yet again. Why even run the model past hour 200?


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Hypsometric said:
This is a fantastic post. It has to be down to the GFS post-truncation resolution because if reality rountinely matched the end-of-the-run GFS, I'm pretty sure RDU would mirror Boston for average annual snowfall. There are clearly some kind of cascading errors that result in late run (+300 hr) evolutions that always favor these physics-defying PV intrusions that never happen, and usually trend further and further north almost until verification. Come to think of it, it is probably some minor bias in the GFS (strong vortexes too far south) that gets exponentially magnified beyond truncation...
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Yep, you're probably right. The thing I take away is that the model still thinks that through the next couple of weeks we will still have the potential for wintry weather. Disregarding the magnitude of any threat or cold outbreak seems wise. But suffice it to say, according to the GFS, winter is not done, not by a long shot. That's what I take away just from the Ops run. If other ensemble suites concur, that obviously increases confidence.

I'm just thrilled that we're not being sent to unending SER purgatory for the rest of the winter like we were promised way back in December ?
 
Rain Cold said:
Yep, you're probably right. The thing I take away is that the model still thinks that through the next couple of weeks we will still have the potential for wintry weather. Disregarding the magnitude of any threat or cold outbreak seems wise. But suffice it to say, according to the GFS, winter is not done, not by a long shot. That's what I take away just from the Ops run. If other ensemble suites concur, that obviously increases confidence.

I'm just thrilled that we're not being sent to unending SER purgatory for the rest of the winter like we were promised way back in December ?
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Agreed, and I think this (below) is why the GFS is delaying a return trip to SER purgatory. If we can avoid 4/5 through most of the month, we still are alive. If we don't, you can pack away your winter coats (at least until spring, when the inevitable perfect +PNA/-west based NAO sets up).

diagram_40days_forecast_GEFSBC_member.gif
 
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