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December 2017 Discussions & Observations Thread


Rtd208

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3 minutes ago, SnoSki14 said:

Really starting to wonder if an 89/90 pattern is possible. Just look at that massive wave of arctic air taking over most of the CONUS on the latest gfs. 

Timing looks very close to Christmas but most likely the 26th. 

I doubt we see it be that much of an extreme.  Maybe more like a 00-01 flip or even 03-04 flipping 2 weeks earlier than it did.  

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1 minute ago, bluewave said:

This is pretty much what the seasonal models have been showing since the beginning of November. The latest EPS weeklies support this as the tropical forcing shifts west from the WPAC to the Maritime Continent. 

Would this be considered a normal January thaw which seems to always center itself around the second or third week of the month? Curious to see where things would go after that.

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6 hours ago, bluewave said:

Probably some of the shortest wavelengths that we have seen with such a strong -EPO block  in late December. This allows the SE ridge to really flex its muscles right before Christmas. But the wavelengths expand after Christmas and the Arctic cold finally arrives. 

 

eps_z500a_noram_132.thumb.png.f94d13701b33515f94d6efe517ae8032.png

eps_z500a_noram_240.thumb.png.5b03802c7e585a10f60aebb7ec907699.png

 

 

 

The question is will the cold get here like in the 80s, just a little too late and the moisture will be gone and we'll just have cold and dry for a few days?

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4 hours ago, SnowGoose69 said:

I doubt we see it be that much of an extreme.  Maybe more like a 00-01 flip or even 03-04 flipping 2 weeks earlier than it did.  

Question is will it flip back (a la 1995-96)?  Also, if we do get snow will it occur in the final days of December or wait for early January like what we got in Jan 1996 before the flip to warmer weather?

 

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4 hours ago, bluewave said:

It seems like more  a result of the La Nina background state becoming dominant  as the anomalous WPAC forcing is forecast to wane. Forcing near the Maritime Continent during a La Nina is pretty normal. So a pattern favoring a strong SE ridge is what the latest EPS weeklies transition to after the first week of January.

Happened in 1995-96 too and then flipped back to colder in early February.

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13 hours ago, donsutherland1 said:

Following Christmas, the guidance suggests a fascinating battle of the teleconnections. The EPO remains forecast to dive to perhaps as low as -3.000. The Arctic Oscillation (AO), which now stands at a monthly high figure of a preliminary +2.047 is forecast by numerous ensemble members to be positive to possibly strongly positive before falling toward New Year’s Day. The PNA is forecast to be fairly neutral (somewhat negative to somewhat positive depending on which ensemble members one examines.

Yet, even as the AO+ can delay the onset of cold (and for that reason I continue to lean toward the ECMWF guidance that shows the cold moving into the East on or just after Christmas Day), the outcome does not always mean that the cold won’t arrive. Should the SOI remain negative, as is currently the case, the cold could be delayed further. However, the guidance currently suggests that the Pacific trade winds will begin to increase, leading to a positive SOI within the next 7-10 days.

Running a composite based on the teleconnections to avoid a possible skewed picture from a disproportionate reliance on the AO, which can have among the largest correlations to outcomes in the northeastern U.S., the following data from the 12/20-31/1981-2010 base period is available for NYC.

All dates:
Mean temperature: 36.0°

Expected pattern based on the AO, PNA, and EPO forecasts: 34.9°
…Expected pattern with an SOI-: 36.6°
…Expected pattern with an SOI+: 33.6° (presently the most likely outcome)

Based on this data, the GEFS, and a preference for the EPS for the Day 10-15 outlook, I remain confident that December has not yet seen its coldest readings in such cities as Bridgeport, New York, and Newark (lowest temperatures respectively 16°, 20°, and 17°). I also expect additional snowfall at all three locations before the month has ended. For the winter as a whole, the Middle Atlantic and southern New England regions still remain on course for above to possibly much above average snowfall.

Seasonal snowfall anomalies to date are as follows:

Baltimore: 3.8” (+2.0”)
Boston: 6.1” (+0.8”)
Bridgeport: 6.4” (+3.6”)
New York City: 7.0” (+4.7”)
Newark: 7.1” (+4.4”)
Philadelphia: 7.7” (+6.0”)
Portland: 8.9” (+1.0”)
Providence:  5.7” (No anomaly)
Washington, DC: 1.7” (+0.1”)

In terms of NYC’s monthly temperature, based on a sensitivity analysis using the latest modeled data, the City still has about a 50%-56% probability of having a cold anomaly.

Monthly Mean Temperature:
Through:
12/17 38.2°
12/20 38.4° - 39.0°
12/25 38.6° - 40.2°
12/31 35.9° - 38.4°

lol I didn't know Philly had more snow than NYC so far.  More than anyone in that list but Portland wow.

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14 hours ago, snowman19 said:

The GFS/GEFS is very likely too fast as is usual for that model. More likely the cold comes after Christmas Day like the EPS and GEPS are showing

That will also (I think anyway) delay any snow chances until New Years or just after.

 

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I'm not sure the gfs being too fast bias applies here, there's so much arctic air being ejected that it just overwhelms that SE ridge. 

There's also a boundary prior to Christmas that helps shift the ridge to the east. Tonight's gfs also builds the -EPO further north towards the pole, which dilutes the SE ridge further. 

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Just now, SnoSki14 said:

I'm not sure the gfs being too fast bias applies here, there's so much arctic air being ejected that it just overwhelms that SE ridge. 

There's also a boundary prior to Christmas that helps shift the ridge to the east. Tonight's gfs also builds the -EPO further north towards the pole, which dilutes the SE ridge further. 

? Tonight’s GFS just slowed the arrival of the cold front. It’s moving toward the other guidance 

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Next 8 days averaging 41degs., or 4 or 5 degrees AN.

Both the GFS/CMC still wasting 1.5" precipitation as rain.

GFS does keep temperature at 32 or less continuously starting Boxer Day, if that is any consolation.  Shows 9 STRAIGHT days and I think record is 16 in NYC.  Hardest type of record to set, one misstep and it is over, even it is only a degree above.

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1 hour ago, Snow88 said:

No

The other guidance are moving towards the gfs. Euro and eps just shifted east with the low and the speed of the frontal passage.

The Euro is rain and warm on Christmas, so is the Canadian. They're not caving to the gfs. If you want to believe the gfs because it’s showing snow, that’s your right

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