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September 2021


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At this point watching these Temp/Dewpoint deviations is like watching a rain/snow line for a cutter. We know what is going to happen before it starts


It took a couple of decades to say this, but this is your new September weather: a slightly cooler August

We are no longer transitioning to a new climate…We are in a new climate in the NYC area

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SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 503
NWS STORM PREDICTION CENTER NORMAN OK
340 PM EDT WED SEP 15 2021

SEVERE THUNDERSTORM WATCH 503 IS IN EFFECT UNTIL 1000 PM EDT
FOR THE FOLLOWING LOCATIONS

NYC027-071-079-160200-
/O.NEW.KWNS.SV.A.0503.210915T1940Z-210916T0200Z/

NY
.    NEW YORK COUNTIES INCLUDED ARE

DUTCHESS             ORANGE              PUTNAM
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With regard to that listing of 80 degree seasons at NYC, here's a breakdown of the 30-year averages. This shows both 1871-1900 and 1869-1900 which have the same averages within 0.1 (A), then 1901-30 (B), 1931-60 (C), 1961-90 (D) and 1991-2020 (E). The overall average of 152 seasons is also shown in bold type (F). 

The calendar dates shown are for non leap years, go one day earlier to apply to leap years. I derived an actual average duration (of 80 and + seasons) for all leap years and found that it was almost five days shorter (duration) than the overall data, so one would expect the actual leap year data set to have narrower extremes. However the sample size may account for that kind of internal variation in the data. 

80 and + seasons ________________________________________ >80 seasons ____________________

_____________ A ______ B ____ C ____ D ____ E ____ F ________ A _____ B _____ C _____ D _____ E _____ F

start date _ May 3 _ Apr 30 _ Apr 30 _ Apr 21 _ Apr 20 _ Apr 27 <<>>May 6 _ May 4 __ Apr 30 _ Apr 22 _ Apr 23 _ Apr 29

end date __ Sep 24 _Sep 30 _Oct 10 _ Oct 5 _ Sep 30 _ Oct 2 <<..>>Sep 19 _ Sep 28 _ Oct 7 __ Oct 3 __ Sep 26 _ Sep 28

duration ___ 143 __ 153 ___ 162 ___ 166 __ 162 __ 157 <<....>> _135 __ 146 ___ 159 ___ 163 __ 154 __ 151

__________________

Some interesting trends emerge from this. The season was getting longer until around the 1960s, but while the onset continued to advance or at least remain static, the end of these seasons began to pull back towards the earlier termination dates seen around the second interval 1901-30. My guess is that it won't continue to do that for 2021-50, but the phenomenon of record warmth in late autumn seems to have peaked around the 1960s while that of early spring warmth has shown a tendency to be more evenly distributed since about 1930. The differential between 80 and + and the >80 seasons was smaller when they lasted longer, and I noticed while compiling the table a tendency for quite a few years to end with a much higher reading than 80, a few actually ended their 80+ or >80 seasons with a 90 degree reading. 

By the way, the longest 90 deg season was way back in 1927 (first date Apr 20, 90F and last Oct 2, 90F). That was a season of 164 days. The second longest was 1939 (first May 7, 92F and last Oct 10, 91F). That season was 155 days. 2010 went from Apr 7 to Sep 9 but had an 89 deg reading on Sep 26. 

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1 hour ago, jfklganyc said:

At this point watching these Temp/Dewpoint deviations is like watching a rain/snow line for a cutter. We know what is going to happen before it starts


It took a couple of decades to say this, but this is your new September weather: a slightly cooler August

We are no longer transitioning to a new climate…We are in a new climate in the NYC area

Hard to argue, but it's also hard to believe a global increase of 2 degrees since the 1880's can have such a profound effect.  I certainly am ignorant of the "accumulated heat" topic.  I guess that may explain why such a seemingly small increase would result in extreme warmer temperatures in our area?

 

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A cold front will cross the region tonight with some showers and thundershowers. Its progression will slow resulting in a partly to mostly cloudy and cooler day tomorrow. Additional showers are possible in parts of the region.

A warm September outcome remains on track. Despite a cooler than normal first 7-10 days (for example, the 9/1-7 anomaly was -2.5° in New York City and the 9/1-10 anomaly was -1.6° in New York City), September will likely feature near normal to somewhat warmer than normal temperatures in much of the region. The second half of the month could feature above to perhaps much above normal temperatures. As a result, 2021 is increasingly likely 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.

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 8. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.22°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.

The SOI was +10.34 today.

The preliminary Arctic Oscillation (AO) figure was +0.141 today.

On September 13 the MJO was in Phase 3 at an amplitude of 1.898 (RMM). The September 12-adjusted amplitude was 1.603 (RMM).

Based on sensitivity analysis applied to the latest guidance, there is an implied 76% probability that New York City will have a warmer than normal September (1991-2020 normal). September will likely finish with a mean temperature near 71.0° (1.8° above normal).

 

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89 max today and yesterday...if these high dew points continue into winter we'll get our share of snow...another foot or more storm?...the last four winters with 30" or more were not cold winters on average...2014-15 was the last cold-snowy winter and it was a late starter...

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1 hour ago, uncle W said:

89 max today and yesterday...if these high dew points continue into winter we'll get our share of snow...another foot or more storm?...the last four winters with 30" or more were not cold winters on average...2014-15 was the last cold-snowy winter and it was a late starter...

some 40" winters in there too like 2015-16 here.  50" seems to be the demarcation for when you actually need a cold winter to get that kind of snow.

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Morning thoughts…

Today will be mostly cloudy and cooler. Showers and perhaps thundershowers are possible in some areas. High temperatures will likely reach the middle and upper 70s 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: 76.3°; 15-Year: 77.1°

Newark: 30-Year: 77.8°; 15-Year: 78.6°

Philadelphia: 30-Year: 79.0°; 15-Year: 79.7°

Tomorrow will be partly to mostly cloudy.

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The next 8 days are averaging 75degs.(68/73), or +6.

Month to date is  71.9[Normal] at its midpoint.     Convienient.

Could be  73.0[+2.1] by the 23rd.     More likely 72.0[+1.1].

74-78 today, e. wind, rain? late.

EURO drops off by the 24th., but the GFS goes to the 29th, it seems.

Reached 80 here yesterday.

72*(78%RH) here at 6am, some overcast.       77*  by Noon.      77* at 3pm.      78* at 4pm.        76* at 6pm.

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This was only the 2nd 40-40 year for Newark. 41 days reaching 90°after 45.7” of snow. The  other 3 years with at least 30” of snow were strong to super El Niño’s. I guess it fits since winter was more El Niño-like.

Year /snowfall/ #90°days/peak ENSO ONI

2021…..45.7”…41...-1.3

2010….47.9”….54…+1.6…strong  El Niño

2016….32.8”….40.+2.6…super El Niño

1983….31.0”….40.+2.2….super El Nino

https://www.climate.gov/news-features/blogs/enso/did-northern-hemisphere-get-memo-years-la-niña
 

That means you can argue that the Northern Hemisphere atmosphere looked a little more like El Niño than La Niña!

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2 hours ago, bluewave said:

This was only the 2nd 40-40 year for Newark. 41 days reaching 90°after 45.7” of snow. The  other 3 years with at least 30” of snow were strong to super El Niño’s. I guess it fits since winter was more El Niño-like.

Year /snowfall/ #90°days/peak ENSO ONI

2021…..45.7”…41...-1.3

2010….47.9”….54…+1.6…strong  El Niño

2016….32.8”….40.+2.6…super El Niño

1983….31.0”….40.+2.2….super El Nino

https://www.climate.gov/news-features/blogs/enso/did-northern-hemisphere-get-memo-years-la-niña
 

That means you can argue that the Northern Hemisphere atmosphere looked a little more like El Niño than La Niña!

I don't have Newark's monthly and annual snowfall on hand so I'll use NYC snowfall after Newark having 40 days 90 or higher and above average snowfall...

1959-60..above average

1983-84...average

1993-94...way above average...

2002-03...way above average...

2010-11...way above average...

2016-17...above average...

2021-22...???

......................................

two other 40 days 90 or above years were 1988-89, 1991-92...they had below average snowfall ...

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