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Met Winter 20-21: Pattern Drivers & Evolution


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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

Hey all!   I apologize for my absence as i'm currently in the "heat" of finishing up my undergrad, working on some side projects, and working with my advisor regarding, well grad school; tha

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3 hours ago, Event Horizon said:

 

Another thing to add is the sea ice. I think above average sea ice promotes a stronger PV and we don't have that yet. 

 

1420941425_SeaIce10-11-20.png.dd87c85a2cefc6585ed579808fe541c5.png

 

How good is the correlation? It was low last year too but there wasn't much -AO

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7 minutes ago, NotSparta said:

How good is the correlation? It was low last year too but there wasn't much -AO

 

That I'm not entirely sure of. It seems that other factors like the MJO and QBO need to be considered in determining the strength of the PV. 

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For the most part, rainfall from Hurricane Delta's remnants was below what had previously been modeled. Through 8 pm, storm total rainfall amounts included:

 

Atlantic City: 2.11"
Baltimore: 1.32"
Bridgeport:0.18"
Islip: 0.94"
New York City: 0.80"
Newark: 0.71"
Philadelphia: 0.80"
Poughkeepsie: 0.25"
Washington, DC: 1.50"

 

Additional light rain and showers will depart tomorrow. In response to a return of sunshine, temperatures will rebound well into the 60s.

 

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 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.

 

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 +11.28.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.107.

 

On October 11 the MJO was in Phase 5 at an amplitude of 1.781 (RMM). The October 10-adjusted amplitude was 1.685.

 

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 66% 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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47 minutes ago, NotSparta said:

How good is the correlation? It was low last year too but there wasn't much -AO

"We find that decreased sea-ice cover during early winter months (November–December), especially over the Barents–Kara seas, enhances the upward propagation of planetary-scale waves with wavenumbers of 1 and 2, subsequently weakening the stratospheric polar vortex in mid-winter (January–February)."

 

Kim, B., Son, S., Min, S. et al. Weakening of the stratospheric polar vortex by Arctic sea-ice loss. Nat Commun 5, 4646 (2014). https://doi.org/10.1038/ncomms5646

 

Lower sea ice levels over the Barents-Kara sea are linked to wave 1 and 2 disruptions of the PV which in turn causes weakening and potential SSW events. I linked the paper for anyone interested in the research.

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Still seeing signs here that give me pause in jumping on the warmer/drier train that a lot were pushing earlier this season. 
 

AAM, and ONI particular are showing odd realities  compared to forecast, and how past trends show favoriability to average snowfall and temperature years. Add this to ENSO wavering more to East Based....idk, feels like things just may luck out this year in much better fortune than a lot of people are prediciting. 

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44 minutes ago, RAllen964 said:

Still seeing signs here that give me pause in jumping on the warmer/drier train that a lot were pushing earlier this season. 
 

AAM, and ONI particular are showing odd realities  compared to forecast, and how past trends show favoriability to average snowfall and temperature years. Add this to ENSO wavering more to East Based....idk, feels like things just may luck out this year in much better fortune than a lot of people are prediciting. 

I'm not even doing a winter forecast this year.  I know it's a cop out, but after last year's bust, I'm in a "damned if you do and damned if you don't" situation.

If I forecast cold and snowy, they'll say that's all I do every year.
If I forecast warm and snowless, they'll say that's because last year I busted.

If I forecast normal, then it's a cop out.  So this year I am an independent observer.  And I have ZERO expectations after last year, but I do like a few things I am seeing.

So I am cautiously optimistic,

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2 hours ago, Analog96 said:

I'm not even doing a winter forecast this year.  I know it's a cop out, but after last year's bust, I'm in a "damned if you do and damned if you don't" situation.

If I forecast cold and snowy, they'll say that's all I do every year.
If I forecast warm and snowless, they'll say that's because last year I busted.

If I forecast normal, then it's a cop out.  So this year I am an independent observer.  And I have ZERO expectations after last year, but I do like a few things I am seeing.

So I am cautiously optimistic,

The wide world of weather. The thrill of victory and the agony of defeat. 

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1 minute ago, Analog96 said:

Yeah, I just don't see any personal benefit to me making a winter forecast this year.

I am in the same boat. I have zero expectations for this winter but secretly hoping for a good one (which I think we all are). We'll see.

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Not really a surprise to be seeing the forecasts above, not uncommon for the winter to start with some blocking/-NAO then for it to erode and eventually become more +NAO through the winter. Probably best case for more of it is that this is the solar minimum, so perhaps the high end is something like 2010/11 where La Niña came on strong but other factors pushed it in the other direction. Just now starting to remember the winter factors I've forgotten over the past year or two

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3 minutes ago, NotSparta said:

Not really a surprise to be seeing the forecasts above, not uncommon for the winter to start with some blocking/-NAO then for it to erode and eventually become more +NAO through the winter. Probably best case for more of it is that this is the solar minimum, so perhaps the high end is something like 2010/11 where La Niña came on strong but other factors pushed it in the other direction. Just now starting to remember the winter factors I've forgotten over the past year or two

Good to see you posting here, Cyclonic ;)

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19 minutes ago, Grace said:

JMA UPDATED...I'll post the DJF means then DEC & JAN months individually. The individual FEB is not available yet:

 

DJF

20201013_061237.jpg.e27b111ad7f7476388530e5185308875.jpg

 

 

DEC

20201013_061038.jpg.f00ba5aa158239b3018d65c783702b43.jpg

 

 

JAN

20201013_061119.jpg.ed0e5c0835c9dfed8ba32ab2330207a1.jpg

 

Seems like the ridging in this scenario is too progressive for any real blocking. A legitimate scenario. 

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1 hour ago, Event Horizon said:

 

Seems like the ridging in this scenario is too progressive for any real blocking. A legitimate scenario. 

 

Stratosphere expert from NOAA,  Amy Butler tweeted the other day:

20201013_120436.jpg.2545c9cd528865268bfdccb830c8e4cd.jpg

 

And went on to say.

 

"So if you're a SSW fan, don't give up hope yet; if we get the right weather conditions, we could still see a SSW this winter. Note that split events in particular are hard to predict > a week ahead; seasonal forecasts are going to see La Nina and predict a strong vortex."

 

 

In other words, seasonal models are going to see strong Nina & automatically forecast strong Stratosphere PV which means +AO/+NAO...but her research says not so fast. So, have to remember seasonal guidance is not always accurate. In fact mostly not. There are exceptions for sure. 

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11 hours ago, Analog96 said:

Yeah, I just don't see any personal benefit to me making a winter forecast this year.

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? 

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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. 

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  • 33andrain changed the title to Met Winter 20-21: Pattern Drivers & Evolution
  • NJwxguy78 changed the title to Mid/Long Range:Met Winter 20-21: Pattern Drivers & Evolution

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