December 2017 Discussions & Observations Thread

[NJwx85]

There was actually an improvement in the overnight EPS run with the Western ridge axis further East, resulting in a slightly more amplified pattern over the East between the ridging over Greenland. 

[Isotherm]

The overall progression of the near to medium term appears to be congruous with thoughts hitherto. There have been some red flags in various data that reaffirm my thinking regarding the super long-term (post December), but will eschew discussing that right now. The ostensible positive trend in the NAO proggs isn't too surprising given the stratospheric circulation structure which preferentially favors higher than normal geopotential heights from the Arctic through the NW Territories, and along the West Coast, an orientation not dissimilar from recent previous winters. The predilection for lower heights in the NATL will act to increase the probability of non-frozen events for the East Coast, if an upstream short wave were to rapidly intensify. However, the poleward extent of the NPAC ridge is such that it partially countervails the effects of a more positive (relatively) NAO, in that it suppresses the zone of greatest baroclinicity. Weak to moderate short waves which do not significantly pump geopotential heights immediately downstream are our most probable snowfall opportunities through the first half of December. I expect the NAO domain to gradually improve from the middle part of December onward, which is still the time frame I like best for something significant to major+. It's indubitably a colder than normal pattern for December, and very likely snowier than normal as well. But there are some risks still present which certainly deserve recognition as well. One of the highest confidence features, which has been explicated innumerable times in this thread, is the poleward EPAC ridging, due to the fact that multifarious forcing mechanisms support its maintenance, including CHI 200hpa progression, internal wave breaking, and downwelling. It's the best looking December pattern we've seen since 2013 and possibly since 2010.

 

PS - official SSW likely won't occur.

[donsutherland1]

55 minutes ago, nrgjeff said:

Interesting break-down between 4" and 10" events for NYC. I figure the -AO gives good 4" stats due to cold. The +PNA can bring the 10" goods due to a strong trough in the Mississippi Valley, leading to a true Miller A, so long as the track is right and NYC avoids coastal front heart break. Good stuff as always Don!

 

Thanks and great explanation, Nrgjeff.

[uncle W]

6" storms during December in NYC...1959 and 1990 had no indices you want to see...1959 had it's coldest temperature of the winter after the storm...1990 torched just after the storm causing rapid melting...

date...........amount...AO.........NAO.........PNA.....NDJ ONI...

12/3-4/1957.....8.0"...+0.561....-0.197.....+0.534...+1.6.....ao was rising from nega2009 tive...

12/21-22/59...13.7"...+1.032...+1.291......-0.812....-0.1.....6-9" in most places...

12/11-12/60...15.2"....-0.316....-0.916.....+1.527.....0.0

12/23-24/61.....6.2"....-0.862....-2.530......-0.436....-0.2

12/23-24/63.....6.6"...+0.129....-0.103.....+1.218...+1.1.....ao was rising from negative...

12/24-25/66.....7.1"....-2.324...+0.411.....+0.686....-0.3

12/25-27/69.....6.8"....-0.971....-0.148.....+0.547...+0.7

12/27/1990......7.2"...+2.601...+1.950......-0.936...+0.4

12/19-20/95.....7.7"....-4.353....-0.774.....+0.926....-0.9

12/30/2000....12.0"....-4.115....-0.537.....+1.075....-0.8

12/5/2002.......6.0"....-1.938.....-0.479.....+0.672...+1.1

12/5-6/2003...14.0"...+0.481.....-0.197.....+0.784...+0.3

12/19-20/09...10.9"....-4.651.....-1.833.....+0.549...+1.3

12/26-27/10...20.0"....-2.886.....-1.144......-0.284....-1.4

 

[uncle W]

11 hours ago, Paragon said:

One of my favorite seasons that I have read about   A rare Christmas eve snowstorm too  followed by a truly epic February and March tandem in 1967.  Came after a historically hot summer too.

 

 

66-67 had some very warm days between periods of cold waves and snowstorms...66 the first week in Dec...68 the last week in January...60 in mid February...72 the second week in March...all these warm spells were followed by much colder weather with snow...

[swamplover56]

Gfs has a snowstorm next Thursday night Friday. More south 

[MJO812]

Gfs for next Friday has a coastal storm which gives the whole area several inches of snow.

 

[UlsterCountySnowZ]

500 looks prime on GFS

[UlsterCountySnowZ]

I’d love to see our trof with more of a Neg tilt, getting that moisture to pull back into the coastline/interior...

[frd]

9 hours ago, Isotherm said:

The overall progression of the near to medium term appears to be congruous with thoughts hitherto. There have been some red flags in various data that reaffirm my thinking regarding the super long-term (post December), but will eschew discussing that right now. The ostensible positive trend in the NAO proggs isn't too surprising given the stratospheric circulation structure which preferentially favors higher than normal geopotential heights from the Arctic through the NW Territories, and along the West Coast, an orientation not dissimilar from recent previous winters. The predilection for lower heights in the NATL will act to increase the probability of non-frozen events for the East Coast, if an upstream short wave were to rapidly intensify. However, the poleward extent of the NPAC ridge is such that it partially countervails the effects of a more positive (relatively) NAO, in that it suppresses the zone of greatest baroclinicity. Weak to moderate short waves which do not significantly pump geopotential heights immediately downstream are our most probable snowfall opportunities through the first half of December. I expect the NAO domain to gradually improve from the middle part of December onward, which is still the time frame I like best for something significant to major+. It's indubitably a colder than normal pattern for December, and very likely snowier than normal as well. But there are some risks still present which certainly deserve recognition as well. One of the highest confidence features, which has been explicated innumerable times in this thread, is the poleward EPAC ridging, due to the fact that multifarious forcing mechanisms support its maintenance, including CHI 200hpa progression, internal wave breaking, and downwelling. It's the best looking December pattern we've seen since 2013 and possibly since 2010.

 

PS - official SSW likely won't occur.

I very much enjoyed your summary here and your thoughts about the upcoming pattern. This fits perfectly so far with your seasonal forceast.

I had a question, as we enter the period you favor for the potential of a significant to major event do you see similarities  to December 2013 ? 

Also , Judah Cohen pointed out the PV disruption may be short lived, I know you did not focus beyond the end of Dec but what we are seeing now with the PV is that in your opinion sometihng that does not continue in Jan or Feb.?

Also, does the Easterly QBO favor additional PV disruptions in the months ahead, or does the Nina background state discourage that ? 

Thanks very much. I look forward to future updates.  

[NJwx85]

The Euro has nothing meaningful for the end of next week. Cold and dry behind the mid-week front.

[NJwx85]

If we don't cash in towards the end of next week with the coastal, we're probably going to be shutout at least till mid-month as the PV drops the hammer. We could get lucky with an amplifying shortwave around day 9, similar to what the 12z Euro shows, however it looks like the baroclinic zone is too far offshore in a suppression, depression setup as the trough digs all the way to Florida.

[markyk]

Euro may be dry for the 9th, but likes the 12th timeframe.....long ways out

[UlsterCountySnowZ]

3 pieces of energy at play on that gfs, 3 separate waves..models won’t lock into to anything anytime soon imo

[UlsterCountySnowZ]

Although euro doesn’t depict a storm on the precip map, 500 is still encouraging... gfs and euro both have energy riding the southern portion of the trof, albeit gfs is more consolidated allowing trof to rotate neg, giving us a quicker phase. The euro has an elongated energy profile rotating on our trof, it forms a bit late..we really need the frontal boundry to pass and see how much it stalls

[MJO812]

Euro weeklies have the cold lasting in the east through January 15.

[Paragon]

6 hours ago, Snow88 said:

Gfs for next Friday has a coastal storm which gives the whole area several inches of snow.

 

Goldberg is already honking it on ABC lol.  And mentioned another chance a week after that.

[bluewave]

The tropical forcing pattern in December is very similar to what we experienced during the 13-14 winter. Notice how the models maintain the convection just to the west of the Date Line  in the Pacific. This pattern produces a very cold -EPO/+PNA /-AO blocking ridge. It's an east based La Nina with unusually warm SST's just west of the Date Line. 

 

 

[Isotherm]

7 hours ago, frd said:

I very much enjoyed your summary here and your thoughts about the upcoming pattern. This fits perfectly so far with your seasonal forceast.

I had a question, as we enter the period you favor for the potential of a significant to major event do you see similarities  to December 2013 ? 

Also , Judah Cohen pointed out the PV disruption may be short lived, I know you did not focus beyond the end of Dec but what we are seeing now with the PV is that in your opinion sometihng that does not continue in Jan or Feb.?

Also, does the Easterly QBO favor additional PV disruptions in the months ahead, or does the Nina background state discourage that ? 

Thanks very much. I look forward to future updates.  

 

Thanks frd, appreciate it. The December pattern won't be dissimilar from 2013, but there will be higher geopotential heights over the Arctic and the NATL than we had in 2013. Thus, the Eastern trough will be more amplified / meridional w/ less SE-ridge as a consequence. I think the best opportunity for something significant will come in the second half of December, at which time, heights will be more conducive over the NATL. Prior to mid month, threats will be a function of good timing; any short wave that becomes overly amplified could be wet rather than white for the coast.

The stratospheric PV will intensify after mid month, though it should remain weaker than normal for December w/ renewed wave-1 forcing by week 2, and wave-2 vertical driving by week 3. So I expect the pressure on the vortex to continue such that the stratosphere will be favorable for a blocky troposphere. I expect the SPV to wind-up/strengthen (not to the levels of the past two winters) in January, coupled w/ a pattern retrogression to more classic Aleutian ridging / RNA.

The EQBO typically features disturbed stratosphere early winter and again late winter. In my winter outlook, I liked Dec 15-30 and Feb 1-15 the best for sig/major storm opportunities. Still believe perturbation will increase again by February, but in a pattern that's overall quite a bit warmer relative to the December one.

 

 

[snowman19]

19 minutes ago, Isotherm said:

 

Thanks frd, appreciate it. The December pattern won't be dissimilar from 2013, but there will be higher geopotential heights over the Arctic and the NATL than we had in 2013. Thus, the Eastern trough will be more amplified / meridional w/ less SE-ridge as a consequence. I think the best opportunity for something significant will come in the second half of December, at which time, heights will be more conducive over the NATL. Prior to mid month, threats will be a function of good timing; any short wave that becomes overly amplified could be wet rather than white for the coast.

The stratospheric PV will intensify after mid month, though it should remain weaker than normal for December w/ renewed wave-1 forcing by week 2, and wave-2 vertical driving by week 3. So I expect the pressure on the vortex to continue such that the stratosphere will be favorable for a blocky troposphere. I expect the SPV to wind-up/strengthen (not to the levels of the past two winters) in January, coupled w/ a pattern retrogression to more classic Aleutian ridging / RNA.

The EQBO typically features disturbed stratosphere early winter and again late winter. In my winter outlook, I liked Dec 15-30 and Feb 1-15 the best for sig/major storm opportunities. Still believe perturbation will increase again by February, but in a pattern that's overall quite a bit warmer relative to the December one.

 

 

Isotherm, how are you expecting the ongoing Mount Agung volcano eruption to possibly affect the AO once into Jan, Feb, Mar? I read that very high levels of SO2 from the eruption are being detected right now. The experts seem to be expecting a rather profound climate effect from it, with dropping global temps over the next several years as a result of this, seems to be a very significant, impressive event

[gravitylover]

I've been on the volcanic eruption cooling thing for a couple of years now. A significant event in the tropics like this is what cooled things off several times over the course of history, whether this is big enough to have a profound effect remains to be seen but a second reinforcing event in a relatively short period of time could happen and be enough to tilt things back to a cool period. 

[LongBeachSurfFreak]

24 minutes ago, gravitylover said:

I've been on the volcanic eruption cooling thing for a couple of years now. A significant event in the tropics like this is what cooled things off several times over the course of history, whether this is big enough to have a profound effect remains to be seen but a second reinforcing event in a relatively short period of time could happen and be enough to tilt things back to a cool period. 

That could be very intersecting, with all the latent heat currently stored in the oceans from recent warmth. Pair that with cooling and we could be in for enhanced winter storms. Obviously the effect will be slight based on the current eruption, but notable. 

[CIK62]

Next 8 days (the first 8 of Dec.) averaging 46degs., or  a solid 6degs. AN.

Dec. 09---31 period will have to be -2degs. just to get back to normal due to this warm start.

[PB GFI]

39 minutes ago, CIK62 said:

Next 8 days (the first 8 of Dec.) averaging 46degs., or  a solid 6degs. AN.

Dec. 09---31 period will have to be -2degs. just to get back to normal due to this warm start.

Dec I  - 8 will end up close to Normal 

You erase most of the positive departures on the 7th and 8th  ( which are found on the 4th 5th 6th ).

Then the following 15 days are solidy BN and not the -2 kind 

[bluewave]

4 minutes ago, PB GFI said:

Dec I  - 8 will end up close to Normal 

You erase most of the positive departures on the 7th and 8th  ( which are found on the 4th 5th 6th ).

Then the following 15 days are solidy BN and not the -2 kind 

Yeah, the EPS continues to play catch up on how cold the Eastern US will get after December 5th. Check out how the -EPO/+PNA portion of the block keeps trending stronger over time.

New run stronger and colder

 

Old run

 

 

 

 

 

[PB GFI]

20 minutes ago, bluewave said:

Yeah, the EPS continues to play catch up on how cold the Eastern US will get after December 5th. Check out how the -EPO/+PNA portion of the block keeps trending stronger over time.

New run stronger and colder

 

Old run

 

 

 

 

 

I agree that is just cold by January standards .

I always hate to forecast  those back 10 days because on the 1st even though the guidance is really BN for now , so I am just focusing on the 5th - 20th.

I will look at those last 10 days in a week to get a real handle.

I don't think people realize that we trap the vortex under a hotshoe and pin the neg in HB for 2 weeks.

There are going to several - 10 days and a 15 day period of -5 with  " chances of snow " .

Only because the pattern will support it , nothing more.

This December for some in the GL and could be their Feb 15

 

Thats what's coming.

[CIK62]

GFS flirting with reaching record low 850mb. T's for the first 15 days of Dec. of -18C.   It does this for a few days and tosses in 2 snowstorms for good measure too.  Those -18C 850mb. T's should be good for 7 to 14 degrees @2M.

[Paragon]

3 minutes ago, CIK62 said:

GFS flirting with reaching record low 850mb. T's for the first 15 days of Dec. of -18C.   It does this for a few days and tosses in 2 snowstorms for good measure too.  Those -18C 850mb. T's should be good for 7 to 14 degrees @2M.

What are the two dates for those projected snowstorms?  And what does it predict for the weather for the week between Christmas and New Years (let's say going from Dec 23 to Jan 1).

 

[bluewave]

59 minutes ago, PB GFI said:

I agree that is just cold by January standards .

I always hate to forecast  those back 10 days because on the 1st even though the guidance is really BN for now , so I am just focusing on the 5th - 20th.

I will look at those last 10 days in a week to get a real handle.

I don't think people realize that we trap the vortex under a hotshoe and pin the neg in HB for 2 weeks.

There are going to several - 10 days and a 15 day period of -5 with  " chances of snow " .

Only because the pattern will support it , nothing more.

This December for some in the GL and could be their Feb 15

 

Thats what's coming.

The forcing pattern just west of the DL is close to what we experienced during the January 2014 -EPO/+PNA/-AO block.

 

 

 

 

 

 

 

 

[MJO812]

8 minutes ago, bluewave said:

The forcing pattern just west of the DL is close to what we experienced during the January 2014 -EPO/+PNA/-AO block.

 

 

 

 

 

 

 

 

That was a very cold month with alot of fluffy snow.

There was one  morning where I had a low temperature of 1.