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Countdown to Winter 20-21: Pattern Drivers & Evolution


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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

Really big shift on the 00z GEFS in the 8-10 day range.      This doesn't look like a huge deal, but the more amplified +PNA allows for much more northern stream interaction. This

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Tomorrow a storm could bring moderate to perhaps heavy rainfall up the East Coast. Following the storm, the Southeast could see unseasonably cool temperatures. The core of this colder air will likely stay south of the region, but somewhat below normal to near normal readings are likely in parts of the Middle Atlantic area. Meanwhile, there are now early hints that an extended duration much warmer than normal regime will begin to develop in parts of western Canada starting during the first half of this week.

 

Overall, December could start off mild before that period of cooler than normal to near normal temperatures commences. This cooler period could still give way to warmer readings at some point during the second week of December, but there is is still uncertainty. The development of a AO-/PNA+ pattern has shifted the outlook toward colder temperatures during the first half of December (consistent with statistical guidance). Exceptional cold is unlikely. The duration of the AO-/PNA+ pattern could delay any warmup until near mid-month.

 

Statistical guidance based on the ENSO state and teleconnections would typically favor a colder regime for the first half of December. Both historic experience following exceptionally warm November cases and the latest weekly and monthly guidance suggest that a warmer than normal December remains the base case even if the first half of the month winds up colder than normal. Almost 90% of cases with a November mean temperature of 51.5° or above in Central Park went on to record a warmer than normal December and just over three-quarters of such cases saw December register a monthly mean temperature of 40.0° or above.  

 

The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -1.5°C for the week centered around November 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.90°C and the ENSO Region 3.4 anomaly has averaged -1.42°C. La Niña conditions will likely prevail at least through the winter.

 

The SOI was +19.40.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.026.

 

On November 28 the MJO was in Phase 4 at an amplitude of 0.882 (RMM). The November 27-adjusted amplitude was 1.004.

 

Based on the latest guidance, no significant stratospheric warming event is likely through the first week of December. Some warming above 2 mb is likely toward the end of that timeframe on account of Wave 1 activity.  

 

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. 10/11 (91%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO. A predominant EPO+/AO+ pattern is very 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 below normal snowfall.

 

Since 1950, there have been four La Niña winters that started with a warm December in the Northeast and warmth across much of Canada, as is the current forecast on the monthly EPS, latest weekly EPS and latest CFSv2 monthly guidance: 1974-75, 1998-99, 1999-00, and 2011-12. All featured a warmer than normal winter and among the winter months that followed December, only January 2000 was colder than normal in the East. Median seasonal snowfall figures were as follows: New York City: 12.9" and Philadelphia: 13.1".

 

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 near 100% probability that New York City will have a warmer than normal November. November will likely finish with a mean temperature near 52.9° (the warmest November on record).

 

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Holy smokes we are in warmest ever November territory? My goodness, we have truly forgotten what normal is, at least I have.

 

If anyone wants to truly get depressed at the state of the climate go on to climate reanalyzer and look up and monthly departure for the globe. 

 

The departures above normal over the last 15 years are insane and they just keep getting worse. 

 

 

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14 minutes ago, Sundog said:

Holy smokes we are in warmest ever November territory? My goodness, we have truly forgotten what normal is, at least I have.

 

If anyone wants to truly get depressed at the state of the climate go on to climate reanalyzer and look up and monthly departure for the globe. 

 

The departures above normal over the last 15 years are insane and they just keep getting worse. 

 

 

 

Nov 17 18 19 20.

 

Maybe a toasty November will lead to a surprise December.

 

As far as the climate goes, we are warming man. I was thinking about growing grapes on the property and becoming a winery.

 

Make some xtra cash. 

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21 minutes ago, Sundog said:

Holy smokes we are in warmest ever November territory? My goodness, we have truly forgotten what normal is, at least I have.

 

If anyone wants to truly get depressed at the state of the climate go on to climate reanalyzer and look up and monthly departure for the globe. 

 

The departures above normal over the last 15 years are insane and they just keep getting worse. 

 

 

I feel like looking back more than 10 years is just wrong these days, we have shifted, drastically

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13 minutes ago, PB GFI said:

 

Nov 17 18 19 20.

 

Maybe a toasty November will lead to a surprise December.

 

As far as the climate goes, we are warming man. I was thinking about growing grapes on the property and becoming a winery.

 

Make some xtra cash. 

20201129_201926.jpg

20201129_201942.jpg

20201129_201957.jpg

20201129_202007.jpg

Agree. Let’s see if a torched November works better for us. I think winter as we know it has changed. The ocean temps are on fire and the mjo has more control. 
 

13/14 and 14/15 are truly on a island all alone 

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11 minutes ago, NorEaster27 said:

I feel like looking back more than 10 years is just wrong these days, we have shifted, drastically

I domt mind this weather is great. I was out tanning today

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2 minutes ago, Allsnow said:

Agree. Let’s see if a torched November works better for us. I think winter as we know it has changed. The ocean temps are on fire and the mjo has more control. 
 

13/14 and 14/15 are truly on a island all alone 

Those two winters were not that far away. Ocean temps don't matter that much if the wind isn't blowing off the ocean. I worry more about canada being too warm, so that even when we get northerly winds, there isn't sufficient cold air to advect.

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