December 2017 Discussions & Observations Thread

[doncat]

The Euro can tend to overdue the se ridge...let's hope thats the case this time so Christmas isn't as warm as its currently showing.

[donsutherland1]

I am increasingly leaning toward the idea that the pattern relaxation getting underway today won’t end until after Christmas, not on or just before it. It’s looking more like a 10-12 day period than a one-week period. The evolution of the EPS and 12z ECMWF have steadily delayed the return of the winter-like pattern. I still believe December has not seen its last snowfall or its coldest readings. As for the monthly anomaly, applying sensitivity analysis to the latest guidance now suggests it is nearly a toss-up as to whether NYC and EWR will have a cool or warm December anomaly. Despite the possible delay in the return of cold weather, things remain on track for a snowy, and possibly very snowy, winter overall.

[Stormlover74]

Can't imagine this will be worse than Friday afternoon's snow but I'm not the NWS

...WINTER WEATHER ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO
7 AM EST MONDAY...

* WHAT...Light freezing rain expected, including during the
  morning commute on Monday. Total accumulations of a trace to a
  hundredth of an inch are expected.

* WHERE...Portions of northeast New Jersey, southern Connecticut
  and southeast New York.

* WHEN...From 10 PM this evening to 7 AM EST Monday.

* ADDITIONAL DETAILS...The precipitation will likely start as snow tonight before transitioning to sleet and freezing rain late
  tonight and early Monday morning. A few tenths of an inch of
  snow and sleet are possible, especially from Connecticut to the
  Lower Hudson Valley.

[MJO812]

14 minutes ago, donsutherland1 said:

I am increasingly leaning toward the idea that the pattern relaxation getting underway today won’t end until after Christmas, not on or just before it. It’s looking more like a 10-12 day period than a one-week period. The evolution of the EPS and 12z ECMWF have steadily delayed the return of the winter-like pattern. I still believe December has not seen its last snowfall or its coldest readings. As for the monthly anomaly, applying sensitivity analysis to the latest guidance now suggests it is nearly a toss-up as to whether NYC and EWR will have a cool or warm December anomaly. Despite the possible delay in the return of cold weather, things remain on track for a snowy, and possibly very snowy, winter overall.

Negative epo crashing off the charts supports cold weather just before xmas

[uncle W]

12 minutes ago, donsutherland1 said:

I am increasingly leaning toward the idea that the pattern relaxation getting underway today won’t end until after Christmas, not on or just before it. It’s looking more like a 10-12 day period than a one-week period. The evolution of the EPS and 12z ECMWF have steadily delayed the return of the winter-like pattern. I still believe December has not seen its last snowfall or its coldest readings. As for the monthly anomaly, applying sensitivity analysis to the latest guidance now suggests it is nearly a toss-up as to whether NYC and EWR will have a cool or warm December anomaly. Despite the possible delay in the return of cold weather, things remain on track for a snowy, and possibly very snowy, winter overall.

the ao forecast continues to show more positives for a longer time...the nao is worse too...we would need a lot of help from the Pacific...

[EastonSN+]

3 minutes ago, uncle W said:

the ao forecast continues to show more positives for a longer time...the nao is worse too...we would need a lot of help from the Pacific...

How do we know that the ao forecast is correct? The forecast a few days ago was for it to stay negative and that was incorrect. Therefore the forecast now for it to stay positive may be incorrect.

[uncle W]

5 minutes ago, EastonSN+ said:

How do we know that the ao forecast is correct? The forecast a few days ago was for it to stay negative and that was incorrect. Therefore the forecast now for it to stay positive may be incorrect.

it could be wrong...it could be downplaying a very positive ao...

 

[LurkerBoy]

I almost can’t even believe that we’re gonna torch like that right in that timeframe. It seems designed. The odds seem impossible. 

[snowman19]

The GEFS, GEPS and EPS are unanimously the driest I can ever remember seeing during the winter, right through the very end of their runs. Are they correct? Who knows but it’s not often you see runs that dry in the middle of winter

[uncle W]

so far we have a dry December with above average snowfall...I'm not worried about it being dry...

[donsutherland1]

57 minutes ago, Snow88 said:

Negative epo crashing off the charts supports cold weather just before xmas

I think the cold is coming but will be delayed a few days.

[donsutherland1]

1 hour ago, uncle W said:

the ao forecast continues to show more positives for a longer time...the nao is worse too...we would need a lot of help from the Pacific...

Should the AO go strongly positive, it could blunt the effect of the EPO-. Right now, I think we're dealing with a transition issue where the expansion of the EPO- ridge will lead to the development of a negative AO.

Data for the 12/16-31/1950-2016 Period: NYC Mean Temperature

All dates: 35.5°

EPO of -1.000 or below: 34.8°

...With AO>0: 36.2°

...With AO <0: 33.5°

...With AO -1.000 or below: 33.1°

 

[snowman19]

15 minutes ago, bluewave said:

December has had the strongest +NAO tendency of the winter months since 2011.

2011  -0.88   0.70   0.61   2.48  -0.06  -1.28  -1.51  -1.35   0.54   0.39   1.36   2.52
2012   1.17   0.42   1.27   0.47  -0.91  -2.53  -1.32  -0.98  -0.59  -2.06  -0.58   0.17
2013   0.35  -0.45  -1.61   0.69   0.57   0.52   0.67   0.97   0.24  -1.28   0.90   0.95
2014   0.29   1.34   0.80   0.31  -0.92  -0.97   0.18  -1.68   1.62  -1.27   0.68   1.86
2015   1.79   1.32   1.45   0.73   0.15  -0.07  -3.18  -0.76  -0.65   0.44   1.74   2.24
2016   0.12   1.58   0.73   0.38  -0.77  -0.43  -1.76  -1.65   0.61   0.41  -0.16   0.48
2017   0.48   1.00   0.74   1.73  -1.91   0.05   1.26  -1.10  -0.61   0.19  -0.00

If you look back at all the other +NAO Decembers, going back to 1979, it strongly argues that the next 3 months (Jan, Feb, Mar) will also average positive, based on history

[CIK62]

CFS now likes Jan. 01/02 for a major snow event coming out of the GOM perhaps and hitting the deep South too.  This is after multiple misses to the west and north.  Of course, given enough time, the CFS will dance every step, with every girl on the floor and show whatever you want it to.  lol.   It was promising a White Christmas for a lot of people back in Nov.

[weathermedic]

Models pointing to extreme cold over the Rockies and in general a colder then normal Christmas Day and a day or two before west of the Mississippi. How much of that cold gets to the east coast after the 25th remains to be seen. Looks fairly dry here as well.

[AfewUniversesBelowNormal]

Warm/dry isn't the pattern. Major warming is happening in the arctic and the Polar Vortex is split and very far south. Imagine the whole latitude is dropped by 20* , that is this pattern. Although it could get warm out ahead of storms, that's because of a raging south wind. 

[MJO812]

Gefs has the gradient right near our area at 186 hours. Earlier than the op.

[snowman19]

1 hour ago, donsutherland1 said:

Should the AO go strongly positive, it could blunt the effect of the EPO-. Right now, I think we're dealing with a transition issue where the expansion of the EPO- ridge will lead to the development of a negative AO.

Data for the 12/16-31/1950-2016 Period: NYC Mean Temperature

All dates: 35.5°

EPO of -1.000 or below: 34.8°

...With AO>0: 36.2°

...With AO <0: 33.5°

...With AO -1.000 or below: 33.1°

 

As the last several winters have proved, we can get away with a +NAO/+AO combo and even along with a -PNA, as long as the EPO and WPO are solidly negative. That said, we would be playing with fire so to speak; if we loose the -EPO/-WPO. It would get real ugly in a hurry

[Paragon]

8 hours ago, Isotherm said:

 

But that isn't correct. The NAO variance on the positive side has not been statistically significant; the positive tendency over the past several years is well within averages. Keep in mind, NAO periodicity is such that there are usually protracted spells of negative or positive modality. For example, in the 1961-1971 period, only 2 winters featured a +NAO.

This recent period of +NAO, 2012-2018 is similar in length to the 1987-1994 +NAO period (every winter in this time frame was +NAO). We should be very thankful that the Pacific forcing has been sufficiently conducive to countervail the less auspicious Atlantic. 

I expect this NAO tendency to reverse soon, but not this current winter (although there will be more negative dips than the past couple of years).

It's interesting how the weather is radically different between those two periods.  When you statistically average out the NAO over a 30 year climate norm, what does it end up being? I'd be interested to see a trend from one norm to the previous one, etc.  I would argue that the 2012-18 +NAO period was better than an equal cross section from the 60s, -NAO or not.

One thing that has certainly increased between now and the 80s (and 60s) is that the precip averages are MUCH higher, that probably accounts for the increase in big snowfall events.  Warmer Pacific juicing up the STJ more and the record blocking in the Pacific.  Usually Pacific > Atlantic, as this most recent period has shown.

 

[Paragon]

8 hours ago, Isotherm said:

People myopically focusing on index forecasts such as the large error bar, long term AO guidance, will be completely missing this upcoming period of potentially severe Arctic chill for the nation as a whole. The higher geopotential heights will invariably expand into the AO domain as well as western NAO domain, as concerted MJO/strat forcing continue to manifest. The anomalous negative standard deviations in the EPO will produce significant dense, low level arctic air which will suppress the thermal boundary further south than heights and even 850mb temperatures indicate. It's the type of pattern in which 2m freezing lines could be south of 0c 850mb lines, introducing freezing rain threats as well for parts of the Central/East. Again, operational guidance has proven futile in terms of prognostication ability here. 

Very similar to 1993-94

[Paragon]

3 hours ago, donsutherland1 said:

I am increasingly leaning toward the idea that the pattern relaxation getting underway today won’t end until after Christmas, not on or just before it. It’s looking more like a 10-12 day period than a one-week period. The evolution of the EPS and 12z ECMWF have steadily delayed the return of the winter-like pattern. I still believe December has not seen its last snowfall or its coldest readings. As for the monthly anomaly, applying sensitivity analysis to the latest guidance now suggests it is nearly a toss-up as to whether NYC and EWR will have a cool or warm December anomaly. Despite the possible delay in the return of cold weather, things remain on track for a snowy, and possibly very snowy, winter overall.

Don, I think it will be delayed as is normally the case with these kinds of changes.  After all the delay to get warmer was delayed too- previously forecasts for the weekend were much milder than they turned out being.  Is there a possibility that the focus for more significant wintry threats might be held off until the first week of January?

 

 

[Paragon]

3 hours ago, uncle W said:

the ao forecast continues to show more positives for a longer time...the nao is worse too...we would need a lot of help from the Pacific...

I remember you said you were worried about those members staying positive in the long run, you may be right.

I wouldn't mind holding off more cold/snow until early January, just to break the 2005-06 analog lol.

We need to get off that train.

 

[Paragon]

1 hour ago, snowman19 said:

If you look back at all the other +NAO Decembers, going back to 1979, it strongly argues that the next 3 months (Jan, Feb, Mar) will also average positive, based on history

It didn't seem to matter for winters 2013-14 and 2014-15 though.  I think we emphasize the AO/NAO too much, especially with the weirdness going on in the Pacific for the last several years.

 

[Paragon]

48 minutes ago, snowman19 said:

As the last several winters have proved, we can get away with a +NAO/+AO combo and even along with a -PNA, as long as the EPO and WPO are solidly negative. That said, we would be playing with fire so to speak; if we loose the -EPO/-WPO. It would get real ugly in a hurry

Yep, that's exactly what I'm thinking, but I don't believe that will happen until the latter half of Jan.

[Paragon]

1 hour ago, CIK62 said:

CFS now likes Jan. 01/02 for a major snow event coming out of the GOM perhaps and hitting the deep South too.  This is after multiple misses to the west and north.  Of course, given enough time, the CFS will dance every step, with every girl on the floor and show whatever you want it to.  lol.   It was promising a White Christmas for a lot of people back in Nov.

Yes, I was thinking a delay into the first week of Jan might be in the cards....hey it would knock down the 2005-06 analog so that's a good thing.

 

[Paragon]

2 minutes ago, bluewave said:

Be interesting to see if we can actually get a near record 1060MB high over the West around Christmas.

 

 

 

Chris, what's causing that H to lurch to the SW like that?  The SE Ridge?  Or is it the other way around?

I wonder if this could mean a continuation of fire season in California.

[Paragon]

2 minutes ago, bluewave said:

It's a similar looking extreme -EPO block like we saw on Christmas 1983 but with a SE Ridge. That one set the US high pressure record in Miles City, Montana at 1064.

1983-84 had a couple of moderate events in, I think, January?  Back to back quick hitting 4-5 inch snowstorms.  Very cold too (some of which may have been due to the El Chichon eruption?)  With a SE Ridge we should get more precip than that- question is p-type lol.

[redbanknjandbigbasslakepa]

I thought this was going to be a couple day relaxation and those who were calling for the SE ridge we’re going to be wrong? Beuller? Beuller?

[dmillz25]

Just now, redbanknjandbigbasslakepa said:

I thought this was going to be a couple day relaxation and those who were calling for the SE ridge we’re going to be wrong? Beuller? Beuller?

It is lol. Everyone is freaking out over model runs that don’t know what’s happening 2 days in advance this winter. I would wait and see what happens honestly.

[snowman19]

36 minutes ago, Paragon said:

1983-84 had a couple of moderate events in, I think, January?  Back to back quick hitting 4-5 inch snowstorms.  Very cold too (some of which may have been due to the El Chichon eruption?)  With a SE Ridge we should get more precip than that- question is p-type lol.

83-84 was a volcanic winter