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Met Winter 20-21: Pattern Drivers & Evolution


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Tomorrow will be mostly sunny and warmer as the clouds associated with the remnants of Delta move out of the area.

 

Generally above normal temperatures will prevail through mid-month. By mid-month, New York City will likely have an October 1-15 mean temperature above 60° and the region will likely see temperatures running an overall 1°-3° above normal. Afterward, a brief period of cooler than normal to near normal temperatures could develop. The potential exists for a fairly sharp shot of cold just after mid-month. However, milder conditions will return shortly afterward.

 

The ENSO Region 1+2 anomaly was -1.2°C and the Region 3.4 anomaly was -1.2°C for the week centered around October 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.92°C and the ENSO Region 3.4 anomaly has averaged -1.00°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +10.31.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.137.

 

On October 12 the MJO was in Phase 4 at an amplitude of 1.911 (RMM). The October 11-adjusted amplitude was 1.780.

 

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.

 

In addition, from the larger pool of La Niña winters following El Niño winters, there were four cases where October saw the MJO in Phases 4-6 for 20 days or more: 1983-84, 1988-89, 1998-99, and 2016-17. All four cases featured an EPO+/AO+ winter. Three cases saw the MJO in Phases 4-6 for less than 20 days: 1995-96: 12 days, 2007-08: 6 days, and 2010-11: 6 days. Both 1995-96 and 2010-11 featured a predominantly negative AO. The latest ensemble guidance favors October 2020 falling into the former pool.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 67% probability that New York City will have a warmer than normal October. October will likely finish with a mean temperature near 58.3°.   

 

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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

I think that we are going to see a pretty impeccable 500mb pattern after January 10th.    The -NAO originally forced by wave breaking (which is occurring in the very near future) will become

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3 hours ago, CentralOHwx said:

I've never made one. I feel like generalizing 4 whole months of the weather is completely useless. Same reason most people don't make them for summer. Does saying it'll be hot and humid with storms do anything for anyone? 

When I do make one, I try to go month by month, but I get your idea.

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2 hours ago, OHweather said:

I think any sort of SSW event would be more of a late-winter save than a game changer for the whole season. I'm still on the relatively cold/blocky train for December (with an up and down November that could yield some snow, especially in the interior), but I think it will be hard for the PV to not get strong during the mid-winter for a period of time and yield a more canonical La Nina pattern with a +NAO/EPO and -PNA.  A February SSW ala 2018 that results in a late rally wouldn't be a complete shock.

 

Obviously, if we completely whiff on an early good pattern (ie it's cold / blocky but just doesn't work out along I-95 because it's still early) that puts an average or better snow season in peril...a late rally starting in early March like in 2018 can also do quite a bit for us, but if we don't turn until the end of March like last year then it's too late. If we do have a decent pattern early, how quickly it turns milder for Jan-Feb and the subtleties in that pattern (can cold seap into New England for a while even as a SE ridge tries to flex and slow the onset of any sustained mild pattern?).

 

Enough analogs are interesting early and / or late that I definitely think we'll have our chances this year, but so many are mild right in the middle of winter that that's the elephant in the room that we likely will have to work around. With a moderate-strong La Nina and +QBO, a strong PV is favored...but how strong and then how quickly it weakens later in winter can influence the exact timing of various pattern changes and significantly alter how much snow a given area sees. 

 

Actually 2010 had a split PV mid-DEC. Had another later but...yea. PV disruption during La Nina is often associated with MJO. 

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1 hour ago, Grace said:

 

Actually 2010 had a split PV mid-DEC. Had another later but...yea. PV disruption during La Nina is often associated with MJO. 

That would help the mid-winter prospects. But that's such an extreme example that while 2010-11 may be a decent analog, it's hard to put faith in that sort of outcome at this point. If we're sitting here a month from now and the PV is still relatively weak I'll be a little more intrigued. I do like that the AAM will likely be relatively high for a La Nina over the next few weeks and the pattern will be amped enough that the PV may not strengthen out of control in that time...but if I had to go with the "most likely" outcome I'd still go towards the PV getting stronger towards the middle of winter and hope that it goes the other way. 

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11 hours ago, OHweather said:

That would help the mid-winter prospects. But that's such an extreme example that while 2010-11 may be a decent analog, it's hard to put faith in that sort of outcome at this point. If we're sitting here a month from now and the PV is still relatively weak I'll be a little more intrigued. I do like that the AAM will likely be relatively high for a La Nina over the next few weeks and the pattern will be amped enough that the PV may not strengthen out of control in that time...but if I had to go with the "most likely" outcome I'd still go towards the PV getting stronger towards the middle of winter and hope that it goes the other way. 

 

PV or no PV split, as long as it takes hits & weakens at times you can have good winter periods in a moderate to strong La Nina:

1970-71

1973-74

1974-75

1988-89 

1995-96 

1999-2000

2007-08

2010-11

 

All of those had some decent periods of winter. 1970-71, 1995-96, 2010-11 are 3 stronger La Nina's that stick out as the best for winter lovers in Eastern half. 

 

But because the PV has been so strong in several La Nina's, 3 month long-range seasonal guidance will always slant that way for the most part. 

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its hard to get a snowstorm that's 4" or more in December during a la nina year...only seven years had one since 1950...mostly recent years...

2017......4.6"

2010....20.0"

2008......4.0"

2005......5.8"

2000....12.0"

1995......7.7"

1984......4.8"

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Temperatures rose into the middle and upper 60s and even lower 70s in parts of the region today under bright sunshine. Tomorrow will be a little warmer with temperatures rising into the lower 70s across a large part of the region.

 

Out west, Phoenix recorded its 144th day on which the temperature rose to 100° or above. That surpassed the previous annual record of 143 days, which was set in 1989.

 

Generally above normal temperatures will prevail through mid-month. By mid-month, New York City will likely have an October 1-15 mean temperature above 60° and the region will likely see temperatures running an overall 1°-3° above normal. Afterward, a brief period of cooler than normal to near normal temperatures could develop. The potential exists for a fairly sharp shot of cold just after mid-month. However, milder conditions will return shortly afterward.

 

The ENSO Region 1+2 anomaly was -1.2°C and the Region 3.4 anomaly was -1.2°C for the week centered around October 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.92°C and the ENSO Region 3.4 anomaly has averaged -1.00°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was -2.26.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.301.

 

On October 13 the MJO was in Phase 4 at an amplitude of 1.987 (RMM). The October 12-adjusted amplitude was 1.911.

 

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.

 

In addition, from the larger pool of La Niña winters following El Niño winters, there were four cases where October saw the MJO in Phases 4-6 for 20 days or more: 1983-84, 1988-89, 1998-99, and 2016-17. All four cases featured an EPO+/AO+ winter. Three cases saw the MJO in Phases 4-6 for less than 20 days: 1995-96: 12 days, 2007-08: 6 days, and 2010-11: 6 days. Both 1995-96 and 2010-11 featured a predominantly negative AO. The latest ensemble guidance favors October 2020 falling into the former pool.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 70% probability that New York City will have a warmer than normal October. October will likely finish with a mean temperature near 58.3°.   

 

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8 hours ago, Grace said:

 

PV or no PV split, as long as it takes hits & weakens at times you can have good winter periods in a moderate to strong La Nina:

1970-71

1973-74

1974-75

1988-89 

1995-96 

1999-2000

2007-08

2010-11

 

All of those had some decent periods of winter. 1970-71, 1995-96, 2010-11 are 3 stronger La Nina's that stick out as the best for winter lovers in Eastern half. 

 

But because the PV has been so strong in several La Nina's, 3 month long-range seasonal guidance will always slant that way for the most part. 

I certainly agree with you that if the PV takes hits at times we can have a better outcome. Even though most of those winters all had periods that got cold in the east, some of those I really wouldn't want to roll the dice on outside of the Midwest/Great Lakes, Upstate NY and New England. 10-11 and 95-96 had a negative AO/NAO, and 88-89 did it with a better Pacific pattern...I can see how both happen at times (especially early, and perhaps again late). Given most of the analogs and the seasonal guidance, I feel that I don't have much of a choice but to assume a period of strong PV with a +AO/NAO (and probably +EPO) in mid-winter for my forecast though until I have reason not to. I'll be watching the evolution of the PV and for things like the MJO to be active (and occasionally push past phase 6) and see if anything happens to break our way. 

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19 minutes ago, OHweather said:

I certainly agree with you that if the PV takes hits at times we can have a better outcome. Even though most of those winters all had periods that got cold in the east, some of those I really wouldn't want to roll the dice on outside of the Midwest/Great Lakes, Upstate NY and New England. 10-11 and 95-96 had a negative AO/NAO, and 88-89 did it with a better Pacific pattern...I can see how both happen at times (especially early, and perhaps again late). Given most of the analogs and the seasonal guidance, I feel that I don't have much of a choice but to assume a period of strong PV with a +AO/NAO (and probably +EPO) in mid-winter for my forecast though until I have reason not to. I'll be watching the evolution of the PV and for things like the MJO to be active (and occasionally push past phase 6) and see if anything happens to break our way. 

2005-06 evolved something like that.. even 1995-96 had a very warm period in late January.

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2 hours ago, uncle w said:

its hard to get a snowstorm that's 4" or more in December during a la nina year...only seven years had one since 1950...mostly recent years...

2017......4.6"

2010....20.0"

2008......4.0"

2005......5.8"

2000....12.0"

1995......7.7"

1984......4.8"

The 4.8 inches in Dec 1984 was with the passage of a very strong warm front.  The temperature than soared to 70 degrees the next day and that snow vanished almost instantly.  I was almost 12 years old and remember it very clearly.  Do you remember it happening that way?

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16 minutes ago, MR FREEZE said:

The 4.8 inches in Dec 1984 was with the passage of a very strong warm front.  The temperature than soared to 70 degrees the next day and that snow vanished almost instantly.  I was almost 12 years old and remember it very clearly.  Do you remember it happening that way?

I always like to refresh my memory by looking at the data for that storm...the temp hit 70 two days later...that winter had one good month...

https://www.ncei.noaa.gov/pub/orders/IPS/IPS-027C835F-1FDA-4951-820B-F8C74173BD97.pdf

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8 minutes ago, uncle w said:

I always like to refresh my memory by looking at the data for that storm...the temp hit 70 two days later...that winter had one good month...

https://www.ncei.noaa.gov/pub/orders/IPS/IPS-027C835F-1FDA-4951-820B-F8C74173BD97.pdf

Ok, I do remember the 70 degree day being a Saturday as my parents took me to Jahn's restaurant in Gerritsen Beach Brooklyn and then down to the Sheepshead Bay boardwalk.  People were in shorts and the last few piles of snow were rapidly disappearing.  I am sure you must have this warm air advection snowfall in your video vault.  We definitely need some good snow events this winter.  I simply can't stomach another dud.  

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NYC 12" snowfalls and the monthly QBO.....

dates..........QBO...

3/56..............-2.01

3/58...............4.27

3/60..............-0.04

12/60...........-11.36

1/61...............-0.62

2/61...............-5.47

1/64................3.94

2/67...............10.94

2/69..............-4.43

1/78.................3.21

2/78.................6.07

2/79.................4.12

2/83...............11.40

2/94...............-9.84

1/96................-5.79

12/00............-14.56

2/03................-1.43

12/03.............-11.38

1/05.................-0.69

2/06...............-11.24

2/10...............-16.98

12/10................10.97

1/11.....................9.18

1/16....................9.34

3/18................-19.77

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13 hours ago, NotSparta said:

Going to be time to look at this again soon... just staying the course for now. We'll have to see if the SPV gets disrupted or stays stout like last year

pv graph.png

 

Members all over the place. 

20201015_125729.jpg.8043dbaa5c1a40a448c0ab183ffd91b5.jpg

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A slow-moving cold front will move across the region tomorrow and tomorrow night. At the same time, low pressure will develop and move northward along that front. As a result, tomorrow will be breezy, with periods of rain, and noticeably cooler temperatures. A general 0.50"-1.50" rain, with lighter amounts from New York City and westward and higher amounts over eastern New England is likely. A few parts of northern New England and southern Quebec could pick up 2" or more precipitation.

 

In the wake of the cold front, a chilly weekend is in store. However, temperatures will likely return to normal and above normal conditions early next week. This warmth will likely persist through the remainder of next week.

 

The ENSO Region 1+2 anomaly was -1.2°C and the Region 3.4 anomaly was -1.2°C for the week centered around October 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.92°C and the ENSO Region 3.4 anomaly has averaged -1.00°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was -7.29.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.946.

 

On October 14 the MJO was in Phase 4 at an amplitude of 2.346 (RMM). The October 13-adjusted amplitude was 1.986.

 

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.

 

In addition, from the larger pool of La Niña winters following El Niño winters, there were four cases where October saw the MJO in Phases 4-6 for 20 days or more: 1983-84, 1988-89, 1998-99, and 2016-17. All four cases featured an EPO+/AO+ winter. Three cases saw the MJO in Phases 4-6 for less than 20 days: 1995-96: 12 days, 2007-08: 6 days, and 2010-11: 6 days. Both 1995-96 and 2010-11 featured a predominantly negative AO. The latest ensemble guidance favors October 2020 falling into the former pool.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 72% probability that New York City will have a warmer than normal October. October will likely finish with a mean temperature near 58.5°.   

 

Finally, the NOAA released its annual winter outlook, which can be found here: https://www.noaa.gov/media-release/us-winter-outlook-cooler-north-warmer-south-with-ongoing-la-nina

 

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