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Observations & Discussion: Autumn 2021


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Howdy Everyone - been a while since I posted some weather pictures, but I couldn't help but share this wonderful moment.  Here is a cloud inversion in the Delaware Water Gap National Recreation Area f

8:42 a.m. in Vernon, 41*      

It begins. 🤣

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In the wake of the frontal passage that brought a widespread 1"-2" rainfall into today, clouds and rain shifted eastward and the sun returned. Abundant sunshine occurred near New York City and westward. There, readings soared into the 70s.

 

Tomorrow, the entire region will benefit from abundant sunshine. It will be a warm day with temperatures rising into the middle and upper 70s. A few locations could reach or exceed 80°. Sunday will be a similar but perhaps slightly cooler day.

 

The MJO had recently been locked in Phase 3 at a high amplitude, frequently in excess of 1.500. Only 2006 and 2009 saw the MJO in Phase 3 at an amplitude of 1.500 or above for 2 or more days during September 10-20. Both years saw September end with a cold shot that continued into the first days of October. Both days saw Central Park's temperature fall to 49° on September 30. A fairly sharp rebound in temperatures followed. October wound up wetter than normal with 7.07" rainfall in 2006 and 5.58" of rainfall in 2009. Normal rainfall (1991-2020) is 4.38".

 

Despite the guidance of a few days ago and a likely cold shot to end the month, 2021 is still on course to become the 6th out of the last 7 years during which September has had a mean temperature of 70° or above in New York City. Prior to 2000, New York City saw such warmth on average once every five years. In short, September has become more an extension of summer than a gateway to autumn in the New York City area.

 

There is increasing consensus on the long-range guidance that October will be an unseasonably warm month. The first half could feature much above normal readings in the Northern Plains into Central Canada.

 

Fall 2021 will likely be wetter to much wetter than normal in the northern Middle Atlantic region. Since 1869, there have been 9 August cases where New York City picked up 20.00" or more rainfall during the summer. Two thirds of those cases (and 4/5 of those with summer mean temperatures of 73.0° or above) had 17.00" or more fall precipitation in New York City. 2011 is probably the closest match in terms of precipitation and a nearly identical summer mean temperature. Mean fall precipitation for those 9 cases was 14.86". The median was 17.35". The 1991-2020 normal value is 12.27".

 

The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.4°C for the week centered around September 15. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.03°C and the ENSO Region 3.4 anomaly has averaged -0.45°C. Neutral ENSO conditions will likely prevail through September. Afterward, La Niña conditions could begin to develop.

 

The SOI was -18.18 today.

 

The preliminary Arctic Oscillation (AO) figure was +0.787 today.

 

On September 22 the MJO was in Phase 4 at an amplitude of 1.305 (RMM). The September 21-adjusted amplitude was 1.553 (RMM).

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 86% probability that New York City will have a warmer than normal September (1991-2020 normal). September will likely finish with a mean temperature near 70.5° (1.3° above normal).

 

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Morning thoughts…

 

Today will be mostly sunny and pleasantly warm. High temperatures will likely reach the middle and upper 70s in most of the region. A few locations could reach or exceed 80°.  Likely high temperatures around the region include:

 

New York City (Central Park): 75°

Newark: 79°

Philadelphia: 77°

 

Normals:

New York City: 30-Year: 72.7°; 15-Year: 73.9°

Newark: 30-Year: 74.3°; 15-Year: 75.6°

Philadelphia: 30-Year: 75.5°; 15-Year: 76.6°

 

Tomorrow will be another sun-filled day.

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Tomorrow and Monday will be fair and pleasantly warm days. Afterward, a cold front could bring some showers or thundershowers to the region on Tuesday.

 

The MJO had recently been locked in Phase 3 at a high amplitude, frequently in excess of 1.500. Only 2006 and 2009 saw the MJO in Phase 3 at an amplitude of 1.500 or above for 2 or more days during September 10-20. Both years saw September end with a cold shot that continued into the first days of October. Both days saw Central Park's temperature fall to 49° on September 30. The guidance has now come into better agreement concerning a cool shot to end the month. Afterward, in the MJO cases, a fairly sharp rebound in temperatures followed. October wound up wetter than normal with 7.07" rainfall in 2006 and 5.58" of rainfall in 2009. Normal rainfall (1991-2020) is 4.38".

 

2021 remains on course to become the 6th out of the last 7 years during which September has had a mean temperature of 70° or above in New York City. Prior to 2000, New York City saw such warmth on average once every five years. In short, September has become more an extension of summer than a gateway to autumn in the New York City area.

There is increasing consensus on the long-range guidance that October will be an unseasonably warm month. The first half could feature much above normal readings in the Northern Plains into Central Canada.

 

Fall 2021 will likely be wetter to much wetter than normal in the northern Middle Atlantic region. Since 1869, there have been 9 August cases where New York City picked up 20.00" or more rainfall during the summer. Two thirds of those cases (and 4/5 of those with summer mean temperatures of 73.0° or above) had 17.00" or more fall precipitation in New York City. 2011 is probably the closest match in terms of precipitation and a nearly identical summer mean temperature. Mean fall precipitation for those 9 cases was 14.86". The median was 17.35". The 1991-2020 normal value is 12.27".

 

The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.4°C for the week centered around September 15. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.03°C and the ENSO Region 3.4 anomaly has averaged -0.45°C. Neutral ENSO conditions will likely prevail through September. Afterward, La Niña conditions could begin to develop.

 

The SOI was -15.92 today.

 

The preliminary Arctic Oscillation (AO) figure was +0.142 today.

 

On September 23 the MJO was in Phase 4 at an amplitude of 0.946 (RMM). The September 22-adjusted amplitude was 1.305 (RMM).

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 89% probability that New York City will have a warmer than normal September (1991-2020 normal). September will likely finish with a mean temperature near 70.4° (1.2° above normal).

 

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Absolutely beautiful weather for the for seeable future as the Pacific Jet roars. 
 

While it won't get cold, it eint get hot either and the dewpoints will be nice and comfortable. Next 10 days are going to be the nicest we have had in a long time. 

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1 hour ago, Andrew Maddis said:

Absolutely beautiful weather for the for seeable future as the Pacific Jet roars. 
 

While it won't get cold, it eint get hot either and the dewpoints will be nice and comfortable. Next 10 days are going to be the nicest we have had in a long time. 


Sometimes normal is extreme.

 

It is wild to me that we could go from a 1-in-1,000 year flood event to driest two week period we’ve had in 6 months.

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18 minutes ago, NJwxguy78 said:


Sometimes normal is extreme.

 

It is wild to me that we could go from a 1-in-1,000 year flood event to driest two week period we’ve had in 6 months.

Yeah since the remnants of Ida we have had basically quiet weather overall with the exception of a couple of events. The next 7-10 days may continue that theme until maybe the first full week of October. We'll see. 

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1 hour ago, Andrew Maddis said:

Absolutely beautiful weather for the for seeable future as the Pacific Jet roars. 
 

While it won't get cold, it eint get hot either and the dewpoints will be nice and comfortable. Next 10 days are going to be the nicest we have had in a long time. 

Let the pacific jet roar now! Nice 60s/40s splits coming for a lot around here through what we can see. Don’t want to “waste” good blocking patterns yet, so I’m perfectly fine with this pattern. True autumn weather!

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Tomorrow will be mostly sunny and unseasonably warm. Temperatures will likely reach the upper 70s and lower 80s. Tuesday will also be warm, but a cold front will push across the region overnight bringing some showers and perhaps thundershowers to parts of the region. Afterward, the coolest air so far this fall will close out the month.

 

The MJO had recently been locked in Phase 3 at a high amplitude, frequently in excess of 1.500. Only 2006 and 2009 saw the MJO in Phase 3 at an amplitude of 1.500 or above for 2 or more days during September 10-20. Both years saw September end with a cold shot that continued into the first days of October. Both days saw Central Park's temperature fall to 49° on September 30. The guidance has now come into better agreement concerning a cool shot to end the month. Afterward, in the MJO cases, a fairly sharp rebound in temperatures followed. October wound up wetter than normal with 7.07" rainfall in 2006 and 5.58" of rainfall in 2009. Normal rainfall (1991-2020) is 4.38".

 

2021 remains on course to become the 6th out of the last 7 years during which September has had a mean temperature of 70° or above in New York City. Prior to 2000, New York City saw such warmth on average once every five years. In short, September has become more an extension of summer than a gateway to autumn in the New York City area.

 

There is increasing consensus on the long-range guidance that October will be an unseasonably warm month. The first half could feature much above normal readings in the Northern Plains into Central Canada.

 

Fall 2021 will likely be wetter to much wetter than normal in the northern Middle Atlantic region. Since 1869, there have been 9 August cases where New York City picked up 20.00" or more rainfall during the summer. Two thirds of those cases (and 4/5 of those with summer mean temperatures of 73.0° or above) had 17.00" or more fall precipitation in New York City. 2011 is probably the closest match in terms of precipitation and a nearly identical summer mean temperature. Mean fall precipitation for those 9 cases was 14.86". The median was 17.35". The 1991-2020 normal value is 12.27".

 

The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.4°C for the week centered around September 15. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.03°C and the ENSO Region 3.4 anomaly has averaged -0.45°C. Neutral ENSO conditions will likely prevail through September. Afterward, La Niña conditions could begin to develop.

 

The SOI was -0.24 today.

 

The preliminary Arctic Oscillation (AO) figure was -0.455 today.

 

On September 24 the MJO was in Phase 4 at an amplitude of 0.714 (RMM). The September 23-adjusted amplitude was 0.945 (RMM).

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 94% probability that New York City will have a warmer than normal September (1991-2020 normal). September will likely finish with a mean temperature near 70.4° (1.2° above normal).

 

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  • NJwxguy78 changed the title to Observations & Discussion: Autumn 2021

Tomorrow will be another warm day, but a cold front will push across the region overnight bringing some showers and perhaps thundershowers to parts of the region. It is almost a coin toss as to whether Central Park will pick up the 0.24" of rain that it needs to reach 10" for September. The 12z EPS had 30/51 (59%) of members with sufficient rainfall. Afterward, the coolest air so far this fall will close out the month.

 

The MJO had recently been locked in Phase 3 at a high amplitude, frequently in excess of 1.500. Only 2006 and 2009 saw the MJO in Phase 3 at an amplitude of 1.500 or above for 2 or more days during September 10-20. Both years saw September end with a cold shot that continued into the first days of October. Both days saw Central Park's temperature fall to 49° on September 30. The guidance has now come into better agreement concerning a cool shot to end the month. Afterward, in the MJO cases, a fairly sharp rebound in temperatures followed. October wound up wetter than normal with 7.07" rainfall in 2006 and 5.58" of rainfall in 2009. Normal rainfall (1991-2020) is 4.38".

 

2021 remains on course to become the 6th out of the last 7 years during which September has had a mean temperature of 70° or above in New York City. Prior to 2000, New York City saw such warmth on average once every five years. In short, September has become more an extension of summer than a gateway to autumn in the New York City area.

 

There is increasing consensus on the long-range guidance that October will be an unseasonably warm month. The first half could feature much above normal readings in the Northern Plains into Central Canada.

 

Fall 2021 will likely be wetter to much wetter than normal in the northern Middle Atlantic region. Since 1869, there have been 9 August cases where New York City picked up 20.00" or more rainfall during the summer. Two thirds of those cases (and 4/5 of those with summer mean temperatures of 73.0° or above) had 17.00" or more fall precipitation in New York City. 2011 is probably the closest match in terms of precipitation and a nearly identical summer mean temperature. Mean fall precipitation for those 9 cases was 14.86". The median was 17.35". The 1991-2020 normal value is 12.27".

 

The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.3°C for the week centered around September 22. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.05°C and the ENSO Region 3.4 anomaly has averaged -0.43°C. Neutral ENSO conditions will likely prevail through September. Afterward, La Niña conditions could begin to develop during October.

 

The SOI was +24.25 today.

 

The preliminary Arctic Oscillation (AO) figure was -1.185 today.

 

On September 25 the MJO was in Phase 5 at an amplitude of 0.815 (RMM). The September 24-adjusted amplitude was 0.715 (RMM).

 

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 (1991-2020 normal). September will likely finish with a mean temperature near 70.4° (1.2° above normal).

 

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Morning thoughts…

 

Today will be partly sunny and warm. A strong cold front could trigger some showers and thunderstorms from late afternoon into the night. High temperatures will likely reach the upper 70s and lower 80s in most of the region. Likely high temperatures around the region include:

 

New York City (Central Park): 75°

Newark: 79°

Philadelphia: 80°

 

Normals:

New York City: 30-Year: 71.5°; 15-Year: 72.8°

Newark: 30-Year: 73.0°; 15-Year: 74.5°

Philadelphia: 30-Year: 74.3°; 15-Year: 75.5°

 

The remainder of the month will be fair but unseasonably cool.

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An area of showers and thundershowers moved through the region late this morning and early this afternoon. A total of 0.27" of rain fell in New York City's Central Park pushing the monthly rainfall total to 10.03". As a result, New York City has seen a record 3 consecutive months with 10" or more of rain. Records go back to 1869.

 

In addition, 10" or more of rain each month from July-September is unprecedented this far north. In 1894 and again in 1945, Downtown Charleston, SC (32.78°N) saw 10" or more of rain during this period. In 1946, Wilmington, NC (34.21°N) saw 10" or more of rain during this period. Then, in 2018, Dunn (4 NW), NC (35.31°N) recorded 10" or more during July, August, and September.

 

Year-to-date rainfall in New York City is now 51.96". That ranks 2021 as New York City's 33rd wettest year on record.

 

In the Northern Plains, today witnessed searing heat. The thermometer topped out at 98° at Bismarck, which surpassed the daily mark of 97° from 1905. This is also the latest 98° or above reading on record.

 

This evening, a few isolated showers and thundershowers are possible in parts of the region, but skies will clear. Tomorrow through Friday will feature plentiful sunshine and cool temperatures.

 

2021 remains on course to become the 6th out of the last 7 years during which September has had a mean temperature of 70° or above in New York City. Prior to 2000, New York City saw such warmth on average once every five years. In short, September has become more an extension of summer than a gateway to autumn in the New York City area.

 

There is strong consensus on the long-range guidance that October will be an unseasonably warm month. The first half could feature much above normal readings in the Northern Plains into Central Canada. Overall, the Middle Atlantic and southern New England areas appear to be in line with a warmer to much warmer than normal October.

 

Fall 2021 will likely be wetter to much wetter than normal in the northern Middle Atlantic region. Since 1869, there have been 9 August cases where New York City picked up 20.00" or more rainfall during the summer. Two thirds of those cases (and 4/5 of those with summer mean temperatures of 73.0° or above) had 17.00" or more fall precipitation in New York City. 2011 is probably the closest match in terms of precipitation and a nearly identical summer mean temperature. Mean fall precipitation for those 9 cases was 14.86". The median was 17.35". The 1991-2020 normal value is 12.27".

 

The ENSO Region 1+2 anomaly was +0.2°C and the Region 3.4 anomaly was -0.3°C for the week centered around September 22. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.05°C and the ENSO Region 3.4 anomaly has averaged -0.43°C. Neutral ENSO conditions will likely prevail through September. Afterward, La Niña conditions could begin to develop during October.

 

The SOI was +36.90 today.

 

The preliminary Arctic Oscillation (AO) figure was -1.474 today.

 

On September 26 the MJO was in Phase 4 at an amplitude of 1.081 (RMM). The September 25-adjusted amplitude was 0.823 (RMM).

 

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 (1991-2020 normal). September will likely finish with a mean temperature near 70.3° (1.1° above normal).

 

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Models are all over the place regarding next week and beyond because of #Typhoon Nindull and what happens when it recurves and merges with the jetstream. This typhoon should bring us closer to a Positive AMM(relative that is) so one possibility I see is for a trough to dig then cut-off off the SE coast/around the Carolina's and cause a prolonged low-level easterly fetch over the Mid Atlantic/Northeast while the Southeast/Florida get cooler then average temps in an El Nino-esque setup! As Don alluded to, the high Plains/South Central Canada would get the ridge which should eventually retrograde to the West as is typical in a lag phase 4/phase 5 MJO this time of year!!

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