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Met Winter 20-21: Pattern Drivers & Evolution


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10 hours ago, Thundersnow3765 said:

A quick reminder of how incredibly snowless last winter was, and another reminder not to make a kneejerk reaction forecast to it. Odds are very favorable that this winter ends up better than last :) 

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I know I'm in the minority here, but yes please to that green blob over MO haha. I'll try to share it. 

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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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Tomorrow will be partly sunny and continued warm. However, Tuesday through Thursday could be a wet period. The potential exists for a coastal storm to develop that could bring 1.00" or more rain to parts of the region. Temperatures will likely remain at generally above normal levels for the remainder of September.

 

Phoenix reached 102° today. That was Phoenix's 130th 100° day. Only 1989 with 143 such days had more. Phoenix has an implied 99% probability of recording just its 13th September on record with a mean temperature of 90° or above. The most recent such occurrence was 2018 with a mean temperature of 91.8°. Phoenix will very likely record its hottest June-September period on record with a four-month mean temperature of near 95.4°. That would exceed the previous June-August record of 95.1°, which was set in 2013 and tied in 2015. The existing record is 93.9°, which was set in 2011.

 

A cool shot is likely during the opening week of October, but warmer readings could return during the following week.

 

October could be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.  

 

The ENSO Region 1+2 anomaly was -0.4°C and the Region 3.4 anomaly was -0.8°C for the week centered around September 16. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.93°C and the ENSO Region 3.4 anomaly has averaged -0.68°C. La Niña conditions have developed and will likely prevail through the remainder of autumn.

 

The SOI was +11.41.

 

Today, the preliminary Arctic Oscillation (AO) figure was +0.162.

 

On September 26, the MJO was in Phase 5 at an amplitude of 1.388 (RMM). The September 25-adjusted amplitude was 1.350.

 

Since 1990, there have been 11 La Niña events, 6 of which followed an El Niño winter. 10/11 (91%) case saw warmer than normal September. All 6 following an El Niño winter were warmer than normal. September mean temperatures for New York City for those cases were: 11 cases: 69.9°; Subset of 6 cases: 70.8°; Entire 1990-2019 period: 69.0°. The September mean temperature for all La Niña and neutral-cool cases following an El Niño winter (1950-2019: n=13) was 69.9°.

 

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.   

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 85% probability that New York City will have a warmer than normal September. September will likely finish with a mean temperature near 68.7°.

 

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6 hours ago, Analog96 said:

I think those darker reds should extend further northward into the NY Metro.

I actually think the east coast cold do ok. If only he NAO could just go negative during the winter and stay there. Out here Ninas are truly feast or famine. The strong ones are disasters and the weak ones tend to be great. Its the moderate ones like that one that tend to go either way. I feel like back east the Nnos tend to be more like that vs the Ninas but I could be wrong. 

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9 hours ago, MI Storm said:

I actually think the east coast cold do ok. If only he NAO could just go negative during the winter and stay there. Out here Ninas are truly feast or famine. The strong ones are disasters and the weak ones tend to be great. Its the moderate ones like that one that tend to go either way. I feel like back east the Nnos tend to be more like that vs the Ninas but I could be wrong. 

That was last year's snowfall.

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Clouds broke for sunshine this afternoon. In response, the temperature rose into the upper 70s and lower 80s. A frontal boundary will approach the region later tomorrow and a storm will develop along the front and move northward. Late Tuesday into Wednesday, the region will likely see a general 0.50"-1.50" of rain with some locally higher amounts. Temperatures will likely remain at generally above normal levels for the remainder of September.

 

Phoenix has an implied near 100% probability of recording just its 13th September on record with a mean temperature of 90° or above. The most recent such occurrence was 2018 with a mean temperature of 91.8°. Phoenix will very likely record its hottest June-September period on record with a four-month mean temperature of near 95.4°. That would exceed the previous June-August record of 95.1°, which was set in 2013 and tied in 2015. The existing record is 93.9°, which was set in 2011.

 

A cool shot is likely during the opening week of October, but warmer readings could return during the following week. The latest EPS weeklies favor the development of a sustained warmer than normal pattern for the second half of October.  

 

October could be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.  

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +8.62.

 

Today, the preliminary Arctic Oscillation (AO) figure was +0.139.

 

On September 27 the MJO was in Phase 5 at an amplitude of 1.275 (RMM). The September 26-adjusted amplitude was 1.392.

 

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.   

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 98% probability that New York City will have a warmer than normal September. September will likely finish with a mean temperature near 68.7°.

 

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A frontal boundary will cross the region tonight into tomorrow with a storm moving northward along that front. The region will likely see a general 1.00"-2.00" rainfall by the time the storm departs tomorrow. Eastern New England will likely see lesser amounts. Some pockets of amounts in excess of 2.50" are likely. The month will end on a mild note.

 

Phoenix has an implied near 100% probability of recording just its 13th September on record with a mean temperature of 90° or above. The most recent such occurrence was 2018 with a mean temperature of 91.8°. Phoenix will record its hottest June-September period on record with a four-month mean temperature of near 95.4°. That would exceed the previous June-August record of 95.1°, which was set in 2013 and tied in 2015. The existing record is 93.9°, which was set in 2011.

 

A cool shot is likely during the opening week of October, but warmer readings could return during the following week. The latest EPS weeklies favor the development of a sustained warmer than normal pattern for the second half of October. Overall, October will likely be somewhat warmer than normal in much of the region.  

 

October could be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.  

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +7.01.

 

Today, the preliminary Arctic Oscillation (AO) figure was +0.139.

 

On September 28 the MJO was in Phase 5 at an amplitude of 1.495 (RMM). The September 27-adjusted amplitude was 1.277.

 

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.   

 

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 September. September will likely finish with a mean temperature near 68.8°.

 

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New York City is concluding September with a monthly mean temperature of 68.8° (0.8° above normal). A somewhat warmer than normal October lies ahead, with the second half of the month likely to be warmer relative to normal than the first half.

 

Phoenix recorded just its 13th September on record with a mean temperature of 90° or above with a monthly mean temperature of 91.5°. That made September 2020 the 3rd warmest September on record. Phoenix also registered its hottest June-September period on record with a four-month mean temperature of 95.4°. The previous record was 93.9°, which was set in 2011. The June-September 2020 figure also exceeded the previous summer (June-August) record of 95.1°, which was set in 2013 and tied in 2015.

 

Climate change contributed to this most recent heat event. Climate change has increased the frequency, magnitude, and duration of extreme heat events in the United States and worldwide. Further increases are likely in coming decades as the world's climate continues to warm (for more information, refer to the links in the note below this discussion).

 

The opening week of October will see generally cooler than normal conditions. No exceptional cold is likely. Warmer readings could return during the following week, though a renewed push of cool air remains possible. The latest EPS weeklies favor the development of a sustained warmer than normal pattern for the second half of October. The development of this warmth also shows up on the 63-ensemble MME subseasonal guidance and latest weekly CFSv2 guidance. Overall, October will likely be somewhat warmer than normal in much of the region with temperatures generally 0.5° - 1.5° above normal.

 

October could also be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.  

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +16.11.

 

Today, the preliminary Arctic Oscillation (AO) figure was -1.039.

 

On September 29 the MJO was in Phase 5 at an amplitude of 1.555 (RMM). The September 28-adjusted amplitude was 1.498.

 

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.   

 

Note:

 

1. https://www.globalchange.gov/browse/indicator-details/3983
2. https://advances.sciencemag.org/content/6/12/eaay2368
3. https://www.researchgate.net/publication/234114398_Global_increase_in_record-breaking_monthly-mean_temperatures

 

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19 minutes ago, Analog96 said:

Eartha will come on Christmas singing "Santa Baby"

I cant stand when a storm is quoted from the past with a weather channel name...I dont remember those stupid names...just the dates...

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14 minutes ago, uncle w said:

I cant stand when a storm is quoted from the past with a weather channel name...I dont remember those stupid names...just the dates...

Jan 2016 is one. I hate when it’s called “Jonas”

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Under partly to mostly sunny skies, the temperature rose into the lower 70s across much of the region today. Tomorrow will start off cloudy with a few showers. The sun could return later in the day. Temperatures will be likely rise only to the lower and middle 60s.

 

Meanwhile, fresh off of its 3rd hottest September and hottest June-September period on record, Phoenix saw the high temperature reach an October record-tying 107° earlier today. Parts of Argentina, Brazil, and Paraguay saw temperatures topple monthly and even all-time high temperature records.

 

Overall, the opening week of October will see generally cooler than normal conditions. No exceptional cold is likely. Warmer readings could return during the following week ahead of a renewed push of cool air. Afterward, a pronounced and sustained warmup is possible. The latest EPS weeklies favor the development of a sustained warmer than normal pattern for the second half of October. The development of this warmth also shows up on the 63-ensemble MME subseasonal guidance and latest weekly CFSv2 guidance. Overall, October will likely be somewhat warmer than normal in much of the region with temperatures generally 0.5° - 1.5° above normal.

 

October could also be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.  

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +20.43.

 

Today, the preliminary Arctic Oscillation (AO) figure was -1.900.

 

On September 30 the MJO was in Phase 5 at an amplitude of 1.490 (RMM). The September 29-adjusted amplitude was 1.564.

 

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.   

 

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Tomorrow will be mainly sunny and cool. Highs will generally reach the middle 60s.

 

Overall, the opening week of October will see generally cooler than normal conditions. No exceptional cold is likely. Warmer readings could return during the following week ahead of a renewed push of cool air. Afterward, a pronounced and sustained warmup is possible.

 

October could also be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +18.11.

 

Today, the preliminary Arctic Oscillation (AO) figure was -1.989.

 

On October 1 the MJO was in Phase 5 at an amplitude of 1.534 (RMM). The September 30-adjusted amplitude was 1.498.

 

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.   

 

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3 hours ago, donsutherland1 said:

Tomorrow will be mainly sunny and cool. Highs will generally reach the middle 60s.

 

Overall, the opening week of October will see generally cooler than normal conditions. No exceptional cold is likely. Warmer readings could return during the following week ahead of a renewed push of cool air. Afterward, a pronounced and sustained warmup is possible.

 

October could also be wetter than September in and around the New York City area. Since 1950, 10 of the 12 (83%) of the La Niña cases that followed an El Niño winter saw October receive more precipitation than September, including 7 of the 8 (88%) cases since 1980. October 1954 and October 1998 were the exceptions. The largest increase in precipitation occurred in 2005. September 2005 saw just 0.48" precipitation in New York City. October 2005 received 16.73" precipitation.

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 23. 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 -0.87°C. La Niña conditions will likely prevail into at least the start of winter.

 

The SOI was +18.11.

 

Today, the preliminary Arctic Oscillation (AO) figure was -1.989.

 

On October 1 the MJO was in Phase 5 at an amplitude of 1.534 (RMM). The September 30-adjusted amplitude was 1.498.

 

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.   

 

2016-17 or 1983-84 would be decent winters.  1988-89 and 1998-99 were total clunkers.

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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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