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Met Winter 20-21: Pattern Drivers & Evolution


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20 hours ago, Grace said:

 

No. They doubled down that DEC would flip very cold after Christmas. After they missed they got bitter & canceled rest of winter. 

 

I like them...but just being honest about what occurred. 

100% correct.  Stopped following after that.  

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While there's reasonable agreement on a -AO and -NAO persisting into early January, there is some uncertainty WRT whether or not the Pacific side offers any help or not. The EPS develops a +EPO into e

I'm starting to get a little more excited for early-mid December. It looks like the Pacific jet will retract significantly, which is the real reason for the retrograding Alaskan LP. Upper level diverg

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22 minutes ago, Webberweather said:

Boy, talk about an uncertain pattern. Wouldn't take much for this to go from being blowtorch warm to absurdly cold

 

image.png.8c227b72fa045c5ab84b3c4528a19a58.png

 

 

The EURO & GEM 12z OP runs totally changed out west. Of course reflected in the means as well as you posted. Strange. 

 

ecmwf_z500a_nhem_fh120-240.gif.94eeeba471b6863b23d663b62564a755.gif

 

gem_z500a_nhem_fh108-240.gif.7fb9038c37522bf8cb4466cf463472ae.gif

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20 hours ago, MJOP8 said:

Per Toms forecast...16”-24” of snow in NYC would be fantastic after the crapshoot of last winter. 

That was his forecast for NYC last year as well.  Hopefully this year that part is more accurate.   I know forecasting snow is the hardest part.  

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7 hours ago, CCB! said:

Much of this paper actually details errors in the short to medium range... But naturally, the errors can snowball downstream. Not to mention, this is the hot thread right now, so yeah. :) 

I haven’t read this paper yet, but I do know organizations that house atmospheric data (via aircraft/satellites) are now sharing it amongst one another to alleviate some of that. More radiosondes are being deployed and more information is now being pulled from satellite imagery to fill gaps. Even with all that, I don’t think it matches the data we normally have with aircraft but I read that it’s pretty close. Aircraft data accounts for <15% of model data, where the rest is satellite and surface derived.

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20 minutes ago, Above The Storm said:

I haven’t read this paper yet, but I do know organizations that house atmospheric data (via aircraft/satellites) are now sharing it amongst one another to alleviate some of that. More radiosondes are being deployed and more information is now being pulled from satellite imagery to fill gaps. Even with all that, I don’t think it matches the data we normally have with aircraft but I read that it’s pretty close. Aircraft data accounts for <15% of model data, where the rest is satellite and surface derived.

That was my understanding as well. My initial take on it back in April was that the the upcoming, significant loss of commercial ABO data would be negligible with that <15% figure in mind. But the paper seems to imply that the notable abatement in these flights may have had a significant impact on NWP after all. So therefore I figured it was worth a share.

 

From the abstract:

 

A special additional experiment excluding approximately 80% of aircraft observations reveals a reduction in forecast skill for both summer and winter amounting to 30%–60% of the degradation seen when all aircraft observations are excluded. These results represent an approximate quantification of the NWP impact of COVID-19-related commercial flight reductions, demonstrating that regional NWP guidance is degraded as a result of the decreased number of aircraft observations.

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snowiest NYC Decembers since 1950 and indices...

year....snowfall....big snow......ave temp....oni…...AO.......NAO....PNA....QBO...

2010.....20.1"...…….20.0"...…….32.8......-1.6....-2.631....-1.85....-1.78....10.97

2003.....19.8"...…….14.0"...…….37.6...….0.4.....0.265.....0.64.....0.86...-11.38

1960.....18.6"...…….15.2"...…….30.9...….0.1....-0.343.....0.06.....1.46...-11.36

1959.....15.8"...…….13.7"...…….38.4...….0.0....-0.042.....0.44.....0.66......8.30

2000.....13.4"...…….12.0"...…….31.1...…-0.7....-2.354....-0.58.....1.23...-14.56

2009.....12.4"...…….10.7"...…….35.9...….1.6....-3.413....-1.93.....0.34...-15.57

1995.....11.5"...……...7.9"...…….32.4...…-1.0....-2.127....-1.67.....0.92.....-4.57

1963.....11.3"...……...6.3"...…….31.2...….1.3....-1.178....-1.92....-0.08......5.48

2002.....11.0"...……...6.0"...…….36.0...….1.1....-1.592....-0.94.....1.59.....-0.50

2005...….9.7"...…......5.8"...…….35.3...…-0.8....-2.104....-0.44.....1.38...-25.04

1966...….9.1"...……..7.1"...…….35.7...….-0.3....-1.401.....0.72.....0.09....13.26

1957...….8.7"...……..8.0"...…….40.2...…..1.7.....0.828.....0.12....-0.43...…7.35

2013...….8.6"...……..5.0"...…….38.5...….-0.3.....1.475.....0.95....-0.86....12.52

1961...….7.7"...……..6.2"...…….35.5...….-0.2....-1.668....-1.48....-1.24......6.25

2017...….7.7"...……..4.5"...…….35.0...….-1.0....-0.059.....0.88.....0.89...-18.12

1952...….7.5"...……..4.5"...…….38.4...…..0.1....-1.827....-0.43.....0.93.....-1.65

1990...….7.2"...……..7.2"...…….42.6...…..0.4.....1.277.....0.22....-1.32....10.68

1968...….7.0"...……..5.2"...…….34.3...…..1.0....-0.783....-1.40....-1.44...-11.36

1993...….6.9"...……..4.0"...…….37.3...…..0.1....-0.104.....1.56.....0.72.....-6.00

1969...….6.8"...……..6.8"...…….33.4...…..0.6....-1.856....-0.28.....1.84......5.00

..................................................................................................................................

6" or greater snowfalls

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 negative...

12/21-22/59...13.7"...+1.032...+1.291......-0.812....-0.1.....

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

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4 hours ago, Webberweather said:

Boy, talk about an uncertain pattern. Wouldn't take much for this to go from being blowtorch warm to absurdly cold

 

image.png.8c227b72fa045c5ab84b3c4528a19a58.png

That’s still an ugly looking map, IMHO. That northwestern North American ridging is both too far west and oriented in a direction which would favor cold dumping out west into a positively tilted trough (which is hinted at by the weakness of the anomaly structure between the two maxima). Similarly, troughing would likely extend southeastward from northeastern New England/southeastern Canada into the northwestern Atlantic based on the same anomaly structure argument. Thus, the eastern North American ridging would likely verify more robust during this period as it splits the mean trough structure depicted here verbatim, which would fit the overall pattern/hemispheric forcing.

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1 hour ago, uncle w said:

snowiest NYC Decembers since 1950 and indices...

year....snowfall....big snow......ave temp....oni…...AO.......NAO....PNA....QBO...

2010.....20.1"...…….20.0"...…….32.8......-1.6....-2.631....-1.85....-1.78....10.97

2003.....19.8"...…….14.0"...…….37.6...….0.4.....0.265.....0.64.....0.86...-11.38

1960.....18.6"...…….15.2"...…….30.9...….0.1....-0.343.....0.06.....1.46...-11.36

1959.....15.8"...…….13.7"...…….38.4...….0.0....-0.042.....0.44.....0.66......8.30

2000.....13.4"...…….12.0"...…….31.1...…-0.7....-2.354....-0.58.....1.23...-14.56

2009.....12.4"...…….10.7"...…….35.9...….1.6....-3.413....-1.93.....0.34...-15.57

1995.....11.5"...……...7.9"...…….32.4...…-1.0....-2.127....-1.67.....0.92.....-4.57

1963.....11.3"...……...6.3"...…….31.2...….1.3....-1.178....-1.92....-0.08......5.48

2002.....11.0"...……...6.0"...…….36.0...….1.1....-1.592....-0.94.....1.59.....-0.50

2005...….9.7"...…......5.8"...…….35.3...…-0.8....-2.104....-0.44.....1.38...-25.04

1966...….9.1"...……..7.1"...…….35.7...….-0.3....-1.401.....0.72.....0.09....13.26

1957...….8.7"...……..8.0"...…….40.2...…..1.7.....0.828.....0.12....-0.43...…7.35

2013...….8.6"...……..5.0"...…….38.5...….-0.3.....1.475.....0.95....-0.86....12.52

1961...….7.7"...……..6.2"...…….35.5...….-0.2....-1.668....-1.48....-1.24......6.25

2017...….7.7"...……..4.5"...…….35.0...….-1.0....-0.059.....0.88.....0.89...-18.12

1952...….7.5"...……..4.5"...…….38.4...…..0.1....-1.827....-0.43.....0.93.....-1.65

1990...….7.2"...……..7.2"...…….42.6...…..0.4.....1.277.....0.22....-1.32....10.68

1968...….7.0"...……..5.2"...…….34.3...…..1.0....-0.783....-1.40....-1.44...-11.36

1993...….6.9"...……..4.0"...…….37.3...…..0.1....-0.104.....1.56.....0.72.....-6.00

1969...….6.8"...……..6.8"...…….33.4...…..0.6....-1.856....-0.28.....1.84......5.00

..................................................................................................................................

6" or greater snowfalls

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 negative...

12/21-22/59...13.7"...+1.032...+1.291......-0.812....-0.1.....

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

How about the coldest December's relative to average since 1950 in the park.  Dec. 1989 comes to mind.  I am fairly sure that 26 out of the 31 days or thereabouts failed to crack the freezing mark by day or by night.  Very little snow though.  As much as I love snow, I wouldn't mind a repeat of that Dec.  By the way, that winter was downright dreadful once beyond the New Year which rang in under a mini ice storm.  We ended with a cold bang in march.

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12 minutes ago, MR FREEZE said:

How about the coldest December's relative to average since 1950 in the park.  Dec. 1989 comes to mind.  I am fairly sure that 26 out of the 31 days or thereabouts failed to crack the freezing mark by day or by night.  Very little snow though.  As much as I love snow, I wouldn't mind a repeat of that Dec.  By the way, that winter was downright dreadful once beyond the New Year which rang in under a mini ice storm.  We ended with a cold bang in march.

all 31 days had a temp below freezing in Dec 1989...

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Just now, MR FREEZE said:

Yes, but I believe the opening days of Dec had daytime highs above freezing?

It was epic.....I remember watching Frank Field keep showing those 5 day forecasts on channel 2 and every time it might appear to be creeping up towards 30 degrees or so, all of a sudden, you would see the 5th day back down to 22 or 23.  It was endless.  I was a junior in high school and remember it like it was yesterday.  I lived in Brooklyn like you did.  I could never get tired of all of your classic videos during the 80s and 90s.

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49 minutes ago, rb924119 said:

Edit to my above: I’m discussing the time-mean, not explicitly saying that we couldn’t have a brief cold shot or two.

To be honest with you I don’t think anybody is expecting extend cold either 

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The historic November warm period is now coming to an end. Ahead of an approaching cold front, temperatures again rose to unseasonable levels. High temperatures included:

 

Bangor: 68° (old record: 65°, 2002)
Boston: 73° (old record: 69°, 1966 and 2002)
Caribou: 67° (old record: 66°, 2002)
Chibougamau, Quebec: 62° (old record: 48°, 1940)
Concord: 73° (old record: 70°, 2002)
Fredericton, New Brunswick: 66° (old record: 64°, 2002)
Hartford: 71° (old record: 69°, 1977)
Islip: 68° (old record: 66°, 1970)
Manchester, NH: 74° (old record: 70°, 2002)
Montreal: 67° (old record: 65°, 2002)
New York City: 72° ***November Record 6th Consecutive 70° Day***
Newark: 73° ***November Record 7th Consecutive 70° Day***
Ottawa: 66° (old record: 62°, 1995 and 2002)
Philadelphia: 71°
Portland: 69° (old record: 65°, 2002)
Providence: 74° (old record: 68°, 1966)
Quebec City: 65° (old record: 60°, 1966)
Worcester: 68° (old record: 66°, 1935)

 

In the wake of the frontal passage, readings will become cooler, but remain somewhat warmer than normal. Overall, the above normal temperatures will likely continue until at least near mid-November. The probability of a fairly sharp cold shot just after mid-month has increased in recent days.

 

The ENSO Region 1+2 anomaly was -1.0°C and the Region 3.4 anomaly was -1.5°C for the week centered around November 4. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.02°C and the ENSO Region 3.4 anomaly has averaged -1.38°C. La Niña conditions will likely prevail at through the winter.

 

The SOI was +6.31.

 

Today, the preliminary Arctic Oscillation (AO) figure was +2.096.

 

On November 10 the MJO was in Phase 8 at an amplitude of 1.255 (RMM). The November 9-adjusted amplitude was 1.015.

 

Since 1950, there have been five cases where a La Niña developed during June-July-August or afterward following an El Niño winter. 4/5 (80%) of those cases saw a predominant EPO+/AO+ winter pattern. The most recent such case was 2016-17. 9/10 (90%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO. A predominant EPO+/AO+ pattern is likely for winter 2020-21. It is likely that the Middle Atlantic and southern New England areas will see a warmer than normal winter with potentially below normal snowfall. The November run of the seasonal European guidance suggests that winter 2020-21 will likely be warmer to much warmer than normal in the region.

 

The potential also exists for below to much below normal seasonal snowfall in the Middle Atlantic and southern New England areas. Since 1970, there were 9 winters that saw the AO and EPO average +0.25 or above. Mean snowfall for Boston, Harrisburg, New York City, Philadelphia, and Washington, DC averaged 50% of the most recent 30-season mean. The largest snowfall deficits relative to the most recent 30-season mean figure were located in the Philadelphia to New York City corridor. In addition, 33% of cases saw less than 10" seasonal snowfall in New York City and 44% saw less than 10" seasonal snowfall in Philadelphia.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 83% probability that New York City will have a warmer than normal November. November will likely finish with a mean temperature near 51.0°.

 

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1 hour ago, rb924119 said:

That’s still an ugly looking map, IMHO. That northwestern North American ridging is both too far west and oriented in a direction which would favor cold dumping out west into a positively tilted trough (which is hinted at by the weakness of the anomaly structure between the two maxima). Similarly, troughing would likely extend southeastward from northeastern New England/southeastern Canada into the northwestern Atlantic based on the same anomaly structure argument. Thus, the eastern North American ridging would likely verify more robust during this period as it splits the mean trough structure depicted here verbatim, which would fit the overall pattern/hemispheric forcing.

But its a work in progress just needs some adjustment. At least its showing a -EPO and +PNA. The CMC is also showing the same thing. 

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2 hours ago, rb924119 said:

Edit to my above: I’m discussing the time-mean, not explicitly saying that we couldn’t have a brief cold shot or two.

 

Read his post carefully. He did not say its a good pattern. He said it would "not take much" for that to go from blowtorch to really cold. He is correct...would not take much. Sorry, taking steroids right now & in a correcting mode. 🤒🤐

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7 hours ago, Webberweather said:

Boy, talk about an uncertain pattern. Wouldn't take much for this to go from being blowtorch warm to absurdly cold

 

image.png.8c227b72fa045c5ab84b3c4528a19a58.png

Yeah, despite the overall hate for the current pattern I spewed on Twitter earlier today, there is some support for an EPO dip in a week or so...maybe a brief uptick in western Pacific convection along with an increase in EAMT. It'd take a lucky wavebreak in the northern Pacific and I think if we pull it off, we'd at least temporarily go back to a +EPO pretty quickly, but I'm open to the idea of a brief but potent cold shot around or just before Thanksgiving. 

 

----------------------

 

Otherwise, I've been meaning to put together a longer post for this thread for about two weeks now that my employer has put out our final outlook. I may get to it this weekend or next week. My overall thoughts from Sept-Oct haven't changed much (still not 100% against a pattern change in December if we can get the MJO into the western Pacific in the next few weeks, but still think mid-late winter trends canonical Nina with a strong strat PV, +EPO/-PNA and SE ridge in the means unless we get something like a January SSW to shake that up earlier).

 

It'll be an uphill battle to get above-average snow or below normal temperatures for the season from the Ohio Valley and Mid-Atl points south (the Great Lakes, interior Northeast and New England should do somewhat better), but with an east-based (or at worst, basin-wide) La Nina and +QBO to go with that there is some hope for occasional EPO-induced cold (especially December-January) when or if we get convection to wander into the Pacific. 

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  • 33andrain changed the title to Met Winter 20-21: Pattern Drivers & Evolution
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