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UHI Effect on 90+ Days at KNYC


JBG

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At least at KNYC we exactly matched 1972 for first 90 degree day. I will point out that in those days KNYC had less vegetation and the high that day was 91. So in real world this first 90 day was probably a hotter day than 1972.

In terms of 90+ days this summer has been notably cool. Though probably not as cool as suggested by the statistics.

 

KNYC has been plagued by a reverse of the UHI effect. New York City's Central Park is actually man-made. Previously it was a mixture of slums, farms and slaughterhouses. It has been progressively getting more densely forested. New York City's weather station is also located there. Back in the 1970's the thirty-year moving average for summer temperatures included about a week where the mean was 78, implying a high of about 86 and a low of about 70. It could have been an 85/70 split since the practice is to round upwards. By the early 2000's the "78 degree" bulge was cut to two days and in the most recent thirty-year period eliminated. Now the average maximum high-low is rated as 84/69, for the period, roughly, July 10 through August 10. This works out to a 76.5 mean, or a full degree lower than the mean for most of the corresponding period historically.

The number of 90+ days has also dropped at Central Park (KNYC), so that in the recent summer we have only touched 90 for 7 or 8 days (today may be the 8th day). This summer was considered a cool one. Summers with similar weather patterns, i.e. relatively cool ones, such as 1969, 1972 and 1979 had more 90+ days. 1969 did have a few 96 or 97 days that clearly would have topped 90 even now but nowadays the same situations that created 90-92 degree Central Park readings now create 87-89 degree readings. All you have to do is look at statistics for LaGuardia Airport (KLGA) to see the difference.

I posted similar material separately as a comment on Sacrus' excellent 90 Degree days thread (link).

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the decade annual max temperature for KNYC...

1880-89...95.2

1890-99...96.7

1900-09...94.7

1910-19...97.3

1920-29...96.6

1930-39...99.3

1940-49...98.5

1950-59...98.1

1960-69...97.3

1970-79...96.5

1980-89...97.6

1990-99...97.9

2000-09...95.5

2010-14...99.2

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

decade total 90 degree days...

decade...90+days100+
1870's...101.....0.....
1880's.....81.....1.....
1890's...138.....1.....
1900's...101.....2.....
1910's...115.....3.....
1920's...128.....2.....
1930's...189.....8.....
1940's...202.....8.....
1950's...175...12.....
1960's...181.....4.....
1970's...183.....3.....
1980's...195.....2.....
1990's...197.....8.....
2000's...123.....1.....

2010's...100.....5.....as of 9/6...average 20 90's for the five years and one 100...
1870-
2009.....149.....4.....
1980-
2009.....172.....4.....

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