December 2017 Discussions & Observations Thread

[CIK62]

Next 8 days creeping up to average 37degs , NORMAL or slightly AN.

We are now -0.20degs for the month and should still be there 8 days from now.

[donsutherland1]

AO Update:

During the 12/1-15 period, the preliminary average for the Arctic Oscillation is -0.873. 93% of the first 15 days of meteorological winter have experienced a negative AO and 40% saw the AO at or below -1.000. No days have seen the AO at or above +1.000. In contrast, the same period in 2016 saw 67% of days with a positive AO, 47% days with an AO at or above +1.000 and no days with an AO of -1.000 or below.

With a negative AO having a higher correlation with snowfall events than a positive one, the first 14 days of December 2017 have been much snowier across the region than the corresponding period last year. Islip, New York City, and Newark have already seen more snowfall than they had in all of December 2016.

Bridgeport: 5.4” (12/1-15/2016: 0.7”; December 2016 total: 6.0”)
Islip: 3.1” (12/1-15/2016: 0.1”; December 2016 total: 3.2”)
New York City: 5.8” (12/1-15/2016: 0.4”; December 2016 total: 3.2”)
Newark: 6.0” (12/1-15/2016: 0.3”; December 2016 total: 3.4”)

With the AO-/PNA+ still in place, it is not too much of a surprise that the trough in the East has turned out to be a little sharper than modeled a few days ago. The result is that a system that will develop offshore will come close enough to bring a light snowfall to much of the region and potentially a moderate snowfall to a portion of New Jersey and Long Island.

Going forward, the AO is likely to go positive. The result will be a 7 to, at most, 14 day relaxation in the pattern. My best guess is that the development of a strong ridge in the EPO region (EPO-) will evolve with that ridge expanding across much of the Arctic. The end result will be a return of an AO- in the closing week of December. As a result, December 25 +/- 2 days will probably see a trough in the East with renewed threats of at least some accumulating snow.

All said, NYC and EWR remain well on course for a winter that will bring more than 30” snow. 40” or more snow remains a possibility.

[CIK62]

With just a 0.10" liquid equivalent!

https://www.msn.com/en-us/weather/topstories/quick-hitting-snow-may-trigger-slippery-friday-evening-commute-from-dc-to-new-york-city/ar-BBGLM71?li=BBnb7Kz&ocid=SK2EDHP

[Paragon]

28 minutes ago, donsutherland1 said:

AO Update:

During the 12/1-15 period, the preliminary average for the Arctic Oscillation is -0.873. 93% of the first 15 days of meteorological winter have experienced a negative AO and 40% saw the AO at or below -1.000. No days have seen the AO at or above +1.000. In contrast, the same period in 2016 saw 67% of days with a positive AO, 47% days with an AO at or above +1.000 and no days with an AO of -1.000 or below.

With a negative AO having a higher correlation with snowfall events than a positive one, the first 14 days of December 2017 have been much snowier across the region than the corresponding period last year. Islip, New York City, and Newark have already seen more snowfall than they had in all of December 2016.

Bridgeport: 5.4” (12/1-15/2016: 0.7”; December 2016 total: 6.0”)
Islip: 3.1” (12/1-15/2016: 0.1”; December 2016 total: 3.2”)
New York City: 5.8” (12/1-15/2016: 0.4”; December 2016 total: 3.2”)
Newark: 6.0” (12/1-15/2016: 0.3”; December 2016 total: 3.4”)

With the AO-/PNA+ still in place, it is not too much of a surprise that the trough in the East has turned out to be a little sharper than modeled a few days ago. The result is that a system that will develop offshore will come close enough to bring a light snowfall to much of the region and potentially a moderate snowfall to a portion of New Jersey and Long Island.

Going forward, the AO is likely to go positive. The result will be a 7 to, at most, 14 day relaxation in the pattern. My best guess is that the development of a strong ridge in the EPO region (EPO-) will evolve with that ridge expanding across much of the Arctic. The end result will be a return of an AO- in the closing week of December. As a result, December 25 +/- 2 days will probably see a trough in the East with renewed threats of at least some accumulating snow.

All said, NYC and EWR remain well on course for a winter that will bring more than 30” snow. 40” or more snow remains a possibility.

Don, based on what I am reading, it looks like a gradient pattern will set up.  The gradient cold will be just north of us through Christmas and then gradually move to our south, getting to ACY by New Years and even further south for the first half of January.  Some of these mild/snowless Jan forecasts might need to be revised.

[Paragon]

1 minute ago, CIK62 said:

With just a 0.10" liquid equivalent!

https://www.msn.com/en-us/weather/topstories/quick-hitting-snow-may-trigger-slippery-friday-evening-commute-from-dc-to-new-york-city/ar-BBGLM71?li=BBnb7Kz&ocid=SK2EDHP

Well those are the worst for travel, most accidents happen with 1-3" of snow

[MJO812]

CMC has some more snow Sunday night into Monday especially for areas just to the north of NYC.

[Paragon]

10 minutes ago, bluewave said:

You can really see the the EPS dropping the gradient south faster than the GEFS since it gets to phase 8 earlier. The weeklies looked great right through January 8th.

 

 

Chris, what is the ideal location of the gradient for us?  ACY?  Might RDU be a bit too far south and result in suppression?

 

 

[SnoSki14]

22 minutes ago, bluewave said:

The 12z Euro jumped right to overrunning here for for the 24 and 25th. Have to wait and seen how the ensembles come in. But the GFS was hinting at this also.

I wonder where the gradient will set up, it could easily be north of the area.

[MJO812]

14 minutes ago, SnoSki14 said:

I wonder where the gradient will set up, it could easily be north of the area.

Eps is south of the area

Imo the gradient will be south of our area with the big epo ridge.

 

[donsutherland1]

6 hours ago, Paragon said:

Don, based on what I am reading, it looks like a gradient pattern will set up.  The gradient cold will be just north of us through Christmas and then gradually move to our south, getting to ACY by New Years and even further south for the first half of January.  Some of these mild/snowless Jan forecasts might need to be revised.

Yes. The trough will be sinking southward. There could be waves running along it with opportunities for at least some frozen precipitation. The ECMWF looks nice.

[doncat]

Nice 26 degree high today! My station midmonth is averaging 36.7 ( -1.3 ) departure, 1.37" precip and 7.6" of snow, plus today of course

[PB GFI]

5 hours ago, SnoSki14 said:

I wonder where the gradient will set up, it could easily be north of the area.

Why / how ? Can you please be specific as to the mechanism that is going to cause that.

Don't say the SE ridge / that idea is dead 

[PB GFI]

5 hours ago, bluewave said:

Yeah, the -EPO Arctic high pressure is pressing hard to the SE around Christmas.

 

 

Agree -EPO HP confluence has been under modeled each of the last 3 years

Whatever is left of that SE ridge will only help in bringing LP to the Mason Dixon line.

Day 8 - 15 on the GEFS entering phase 8 is brutal 

[MJO812]

CFS ha a cold January

[AfewUniversesBelowNormal]

The most difficult thing in the long range is for a -EPO to verify. 

[NorthShoreWx]

I went for a walk on a local trail just before (and after) dark this evening:

 

 

[CIK62]

Next 8 days back down to average 34degs., or 2 to3 degs. BN.

GFS is 50degs. and rain on Christmas, while CMC is 30degs. and snow.   I like Dallas' chances better than ours---before anomalous trough leaves them and heads east.

[MJO812]

21 minutes ago, bluewave said:

Yeah, it should set up a natural overrunning zone along the coast as the Arctic high pushes against a flattening out SE Ridge near the tail end of MJO 7 influence. Euro is already going for a repeat of the strong jet of last weekend with a 200KT jet streak just or north. I agree with you that the coldest temperatures will arrive once the MJO 8 phase has a chance to deepen the trough near the East Coast.  Ideal forcing pattern just west of DL for -EPO maintenance.

Euro unleashes the arctic hounds in the long range with multiple chances of snow.

[Paragon]

17 hours ago, SnoSki14 said:

I wonder where the gradient will set up, it could easily be north of the area.

Based on modeling, I'd be more worried about suppression than anything else.

 

But for now it looks really good for us.

[Paragon]

15 hours ago, donsutherland1 said:

Yes. The trough will be sinking southward. There could be waves running along it with opportunities for at least some frozen precipitation. The ECMWF looks nice.

Wow it looks like the frozen fun might begin in time for Christmas, even along the coast!

[Paragon]

11 hours ago, PB GFI said:

Agree -EPO HP confluence has been under modeled each of the last 3 years

Whatever is left of that SE ridge will only help in bringing LP to the Mason Dixon line.

Day 8 - 15 on the GEFS entering phase 8 is brutal 

You need that SE ridge to avoid suppression.

[Paragon]

15 minutes ago, Snow88 said:

Euro unleashes the arctic hounds in the long range with multiple chances of snow.

Early Jan might be even better than Late Dec.

 

[Paragon]

17 hours ago, bluewave said:

The 12z Euro jumped right to overrunning here for for the 24 and 25th. Have to wait and seen how the ensembles come in. But the GFS was hinting at this also.

Temps look good even along the coast.

[MJO812]

PB GFI

Quote

 

Why I really like the Christmas period 

 

Taking a look at this mornings day 10 EPS you can see the start of softening SE of the BM

All the operational have seen this to some degree or another and with various precip types from run to run.

 

So models aside , I am going to favor the pattern here and what these Arctic waves typically likes to do , and that's find its way to the BM.

That should allow us to remain on the favorable side of the barroclinic zone.

 

With a -4 SD EPO it will dominate the pattern. -EPO confluence / HP systems press through the lakes and are usually under modeled in the L/R.

We have a dominate well sourced vortex over Hudson Bay as the 0 line will be at the US / Canada border. ( that's 0 Fahrenheit) ,so this press should actually dominate the flow and suppression should be more of a worry to me than rain.

 

So that SE ridge albeit weak will be a necessity and help guide one or more of these positively tilted SWs out of TX off the Delmarva and ending up near the BM

 

I am going to trust the pattern over the models. 

 

 

[Paragon]

17 hours ago, donsutherland1 said:

Yes. The trough will be sinking southward. There could be waves running along it with opportunities for at least some frozen precipitation. The ECMWF looks nice.

Wow it looks like the frozen fun might begin in time for Christmas, even along the coast!

 

27 minutes ago, Snow88 said:

PB GFI

 

I am sort of excited about this pattern because it has occurred in the past and it usually produces, even if you don't get a big event you get frequent smaller events that happen over a longer period of time.  That's a lot better than Feb 2006 type of deals.

[SnoSki14]

06z gfs does show how that gradient ends up north of us, I don't think anything is set in stone yet. 

[Paragon]

2 minutes ago, bluewave said:

The best case scenario is that we get into a really productive phase 12/25-1/7 like we saw in Feb 94. The 500 mb EPS forecast is not too far off from that. Even a bit less productive that that would make people very happy.

 

 

Do you think this is a climatologically favorable time for that though, Chris?  I figured February is best for that kind of pattern because of colder SST.

[Paragon]

10 minutes ago, SnoSki14 said:

06z gfs does show how that gradient ends up north of us, I don't think anything is set in stone yet. 

Doesn't it drop south with time, and end up south of us by New Years?

[Animal]

Mt Holly NWS is already hitting the war drums.

Longer term:

A quick look into Christmas week does still provide the chance of a
white Christmas with an active weather pattern that looks to turn
colder thanks to a EPO which is falling several standard deviations
below normal. The - EPO will discharge cold from AK southeast into
the United States just before Christmas. However, the colder air can
dive into the western United States first leading to warmer
conditions and a typical ridge in La-Ninas over the Southeastern
United States. Exactly how this plays out is still outside the
forecast window and a lot of possibilities are in play. Be mindful
of any weather information you see about Christmas can still change
quite a bit over the next few days

 

[MJO812]

17 minutes ago, Paragon said:

Doesn't it drop south with time, and end up south of us by New Years?

I have no clue why people look at the pp runs this far out . 

Ensembles are the way to go at this range