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New York City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New York City clear sky chart from 2005-11-05 to 2017-09-10.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
35%
15009
20%
46782
11%
14978
46%
14978
24%
29756

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
25%
720
21%
2506
10%
716
41%
716
19%
1576
January16th to endNight
20%
768
22%
2595
8%
768
39%
768
21%
1620
February1st to 15thNight
19%
704
18%
2220
5%
701
36%
701
20%
1455
February16th to endNight
22%
631
27%
1893
10%
631
43%
631
24%
1188
March1st to 15thNight
24%
720
19%
2157
8%
720
38%
720
23%
1405
March16th to endNight
27%
768
23%
1991
9%
768
39%
768
26%
1324
April1st to 15thNight
29%
718
17%
1796
6%
718
35%
718
27%
1235
April16th to endNight
32%
705
18%
1785
6%
705
38%
705
27%
1221
May1st to 15thNight
30%
509
18%
1589
8%
509
40%
509
21%
1061
May16th to endNight
47%
374
16%
1497
15%
374
54%
374
20%
917
June1st to 15thNight
45%
360
15%
1440
13%
360
54%
360
19%
906
June16th to endNight
59%
360
15%
1440
19%
360
64%
360
27%
805
July1st to 15thNight
54%
340
13%
1360
16%
340
57%
340
21%
810
July16th to endNight
59%
376
17%
1418
18%
354
65%
354
25%
814
August1st to 15thNight
58%
563
19%
1634
14%
561
61%
561
31%
1005
August16th to endNight
60%
764
19%
1910
11%
764
62%
764
33%
1274
September1st to 15thNight
49%
700
23%
1750
13%
700
52%
700
34%
1145
September16th to endNight
52%
657
25%
1809
19%
657
57%
657
33%
1128
October1st to 15thNight
42%
660
22%
1927
16%
660
50%
660
26%
1229
October16th to endNight
31%
704
22%
2200
11%
704
46%
704
26%
1364
November1st to 15thNight
33%
700
23%
2277
13%
700
48%
700
24%
1397
November16th to endNight
29%
720
20%
2380
11%
720
41%
720
21%
1502
December1st to 15thNight
25%
720
16%
2520
7%
720
38%
720
19%
1630
December16th to endNight
20%
768
20%
2688
6%
768
37%
768
18%
1745

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
15%5%2442445%7%41%
47855
Night
16%6%24424446%42%
46952
Cloud CoverDay
15%5%2442445%7%41%
47864
Night
16%5%24424446%42%
46958
TransparencyDay
41%5%12%23%16%2
47543
Night
41%411%22%16%2
46782
SeeingDay
18%7%28%26%14%3
5772
Night
19%8%30%29%11%1
15010

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%6%245%3446%6%41%
1432
16th to endDay
15%6%34424446%43%
1627
February1st to 15thDay
15%7%35%5%24345%41%
1639
16th to endDay
15%5%25%42435%7%41%
1580
March1st to 15thDay
17%6%25%5%2435%7%38%
1792
16th to endDay
17%6%34323445%43%
2232
April1st to 15thDay
19%5%34314347%42%
2152
16th to endDay
16%425%43435%7%43%
2175
May1st to 15thDay
21%5%25%424447%35%
2373
16th to endDay
17%5%2442445%8%38%
2618
June1st to 15thDay
18%6%344245%5%8%37%
2520
16th to endDay
11%5%25%435%5%6%8%40%
2520
July1st to 15thDay
10%425%5%36%5%7%10%37%
2520
16th to endDay
10%426%5%26%6%7%9%38%
2654
August1st to 15thDay
10%5%15%5%35%5%7%7%41%
2301
16th to endDay
12%5%245%3445%8%43%
2292
September1st to 15thDay
14%413425%446%47%
2098
16th to endDay
15%5%235%23446%45%
1821
October1st to 15thDay
16%5%25%5%33447%42%
1702
16th to endDay
18%414423347%44%
1672
November1st to 15thDay
19%5%24423335%46%
1581
16th to endDay
16%5%23424346%45%
1578
December1st to 15thDay
17%6%25%423436%42%
1440
16th to endDay
21%7%25%424346%38%
1536
January1st to 15thNight
18%5%23433446%42%
2506
16th to endNight
16%8%33424336%42%
2595
February1st to 15thNight
14%8%35%5%34445%41%
2219
16th to endNight
16%5%24333445%46%
1893
March1st to 15thNight
18%6%2432435%5%43%
2144
16th to endNight
17%7%24313445%44%
1991
April1st to 15thNight
18%5%2442445%7%39%
1796
16th to endNight
18%5%24425%346%42%
1785
May1st to 15thNight
18%7%25%6%23336%39%
1589
16th to endNight
18%5%24433448%40%
1495
June1st to 15thNight
18%5%34325%45%7%39%
1440
16th to endNight
8%424425%5%5%10%44%
1440
July1st to 15thNight
11%425%435%5%7%9%40%
1440
16th to endNight
8%5%235%36%6%6%9%41%
1514
August1st to 15thNight
10%3245%336%6%9%45%
1644
16th to endNight
12%425%5%345%5%8%42%
1910
September1st to 15thNight
15%414424447%46%
1750
16th to endNight
13%5%24413336%49%
1809
October1st to 15thNight
16%5%3442335%6%44%
1927
16th to endNight
17%5%24422345%47%
2200
November1st to 15thNight
16%6%24423335%48%
2277
16th to endNight
18%5%2442445%6%41%
2380
December1st to 15thNight
21%5%25%424445%38%
2520
16th to endNight
19%6%24424446%39%
2688

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%7%245%2435%6%41%
1432
16th to endDay
15%6%34423346%43%
1627
February1st to 15thDay
16%6%26%5%25%346%41%
1639
16th to endDay
15%5%35%424446%42%
1580
March1st to 15thDay
17%6%345%2435%8%39%
1802
16th to endDay
18%6%34424345%42%
2231
April1st to 15thDay
19%6%34313347%41%
2152
16th to endDay
16%42442445%7%43%
2175
May1st to 15thDay
21%5%25%43436%7%35%
2373
16th to endDay
18%42443445%9%38%
2618
June1st to 15thDay
19%6%235%135%6%9%36%
2520
16th to endDay
11%425%5%45%5%5%9%41%
2520
July1st to 15thDay
10%425%5%36%5%6%9%38%
2520
16th to endDay
10%5%25%5%35%6%7%8%39%
2654
August1st to 15thDay
11%4245%346%6%9%41%
2301
16th to endDay
12%5%245%345%5%8%44%
2292
September1st to 15thDay
14%324424446%47%
2098
16th to endDay
15%414434347%45%
1821
October1st to 15thDay
16%5%245%3435%6%42%
1702
16th to endDay
18%424324346%45%
1672
November1st to 15thDay
18%6%24323245%46%
1581
16th to endDay
16%5%24434437%45%
1578
December1st to 15thDay
16%7%25%323446%41%
1440
16th to endDay
22%7%23423346%38%
1536
January1st to 15thNight
19%5%24423346%42%
2506
16th to endNight
17%8%33414445%42%
2595
February1st to 15thNight
14%8%35%5%34336%41%
2212
16th to endNight
16%5%34324335%46%
1893
March1st to 15thNight
19%7%25%323346%42%
2157
16th to endNight
17%7%24323335%44%
1991
April1st to 15thNight
17%6%25%42345%7%39%
1796
16th to endNight
18%6%24424437%42%
1785
May1st to 15thNight
19%6%35%5%23446%39%
1589
16th to endNight
18%6%245%23448%40%
1495
June1st to 15thNight
19%5%24234447%39%
1440
16th to endNight
8%425%43447%10%44%
1440
July1st to 15thNight
11%425%5%35%46%10%39%
1440
16th to endNight
9%4145%45%6%6%10%40%
1514
August1st to 15thNight
10%423435%5%5%8%45%
1644
16th to endNight
13%424425%46%7%43%
1910
September1st to 15thNight
15%414434447%46%
1750
16th to endNight
13%5%25%413336%49%
1809
October1st to 15thNight
17%4245%23346%45%
1927
16th to endNight
18%5%24323246%46%
2200
November1st to 15thNight
16%6%24422335%48%
2277
16th to endNight
18%5%24424446%40%
2380
December1st to 15thNight
21%5%35%42345%6%38%
2520
16th to endNight
19%6%25%42445%5%39%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
42%414%24%12%3
1433
16th to endDay
41%212%26%13%3
1627
February1st to 15thDay
44%411%23%13%2
1642
16th to endDay
42%410%27%14%1
1580
March1st to 15thDay
44%315%23%10%2
1802
16th to endDay
43%410%20%18%3
2232
April1st to 15thDay
43%310%24%14%4
2152
16th to endDay
39%5%9%21%21%3
2175
May1st to 15thDay
47%49%20%15%1
2373
16th to endDay
42%6%14%21%13%1
2622
June1st to 15thDay
44%6%12%23%12%
2520
16th to endDay
38%7%12%25%14%1
2520
July1st to 15thDay
39%8%11%21%17%1
2371
16th to endDay
36%8%14%24%13%2
2487
August1st to 15thDay
37%7%14%21%17%
2287
16th to endDay
37%5%10%24%20%2
2292
September1st to 15thDay
36%6%11%22%22%1
2098
16th to endDay
39%38%21%24%2
1821
October1st to 15thDay
41%311%23%17%2
1702
16th to endDay
39%5%9%26%16%2
1672
November1st to 15thDay
40%312%20%20%2
1581
16th to endDay
40%211%27%14%2
1578
December1st to 15thDay
43%415%21%13%1
1440
16th to endDay
46%413%21%12%
1536
January1st to 15thNight
43%411%23%14%3
2506
16th to endNight
43%310%24%16%2
2595
February1st to 15thNight
45%411%22%14%2
2220
16th to endNight
40%38%25%19%3
1893
March1st to 15thNight
43%312%22%13%3
2157
16th to endNight
42%49%21%17%4
1991
April1st to 15thNight
43%410%21%16%3
1796
16th to endNight
43%48%18%22%2
1785
May1st to 15thNight
46%410%17%17%2
1589
16th to endNight
43%415%19%14%2
1497
June1st to 15thNight
44%5%12%19%17%
1440
16th to endNight
33%6%15%27%15%1
1440
July1st to 15thNight
39%7%13%23%14%2
1360
16th to endNight
34%8%15%25%13%3
1418
August1st to 15thNight
35%6%12%26%16%2
1634
16th to endNight
38%5%12%22%19%1
1910
September1st to 15thNight
38%411%25%19%1
1750
16th to endNight
36%47%23%26%1
1809
October1st to 15thNight
40%5%11%23%16%2
1927
16th to endNight
40%312%24%18%1
2200
November1st to 15thNight
40%38%21%20%4
2277
16th to endNight
43%310%26%13%2
2380
December1st to 15thNight
46%315%20%12%1
2520
16th to endNight
46%412%22%13%1
2688

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%21%35%25%1
60
16th to endDay
20%10%46%16%6%
79
February1st to 15thDay
20%19%35%21%3
155
16th to endDay
16%14%43%21%5%
239
March1st to 15thDay
19%15%34%25%5%
270
16th to endDay
21%11%38%19%7%1
288
April1st to 15thDay
22%8%36%18%11%2
270
16th to endDay
21%8%32%22%11%3
270
May1st to 15thDay
30%10%25%21%8%3
288
16th to endDay
23%325%25%19%2
331
June1st to 15thDay
18%8%27%26%14%4
315
16th to endDay
15%429%30%18%1
315
July1st to 15thDay
12%223%34%21%5%
305
16th to endDay
13%319%31%25%5%
326
August1st to 15thDay
15%218%32%23%7%
313
16th to endDay
13%115%36%24%9%
332
September1st to 15thDay
15%329%23%19%8%
294
16th to endDay
20%320%24%16%14%
254
October1st to 15thDay
21%320%31%17%5%
255
16th to endDay
16%11%34%26%10%
256
November1st to 15thDay
22%10%25%24%15%1
235
16th to endDay
16%11%37%24%9%1
198
December1st to 15thDay
16%18%40%16%6%1
60
16th to endDay
37%7%39%14%1
64
January1st to 15thNight
20%13%35%25%3
720
16th to endNight
22%14%38%22%2
768
February1st to 15thNight
18%13%41%24%1
704
16th to endNight
17%15%39%24%2
631
March1st to 15thNight
21%11%37%23%5%
720
16th to endNight
20%9%36%25%5%
768
April1st to 15thNight
21%8%36%28%5%
718
16th to endNight
20%8%34%28%7%
705
May1st to 15thNight
20%7%33%28%9%
509
16th to endNight
20%322%38%13%1
375
June1st to 15thNight
20%6%21%35%16%
360
16th to endNight
9%121%49%16%
360
July1st to 15thNight
12%220%42%20%1
340
16th to endNight
10%218%42%23%2
376
August1st to 15thNight
13%117%43%22%1
563
16th to endNight
14%113%37%29%3
764
September1st to 15thNight
17%323%33%18%2
700
16th to endNight
16%318%33%22%5%
657
October1st to 15thNight
19%8%22%29%17%2
660
16th to endNight
21%9%32%27%8%
704
November1st to 15thNight
19%9%31%24%14%1
700
16th to endNight
19%11%32%26%9%
720
December1st to 15thNight
24%10%34%23%6%1
720
16th to endNight
23%11%40%21%2
768
Page generated at 2017-09-11 19:35:23. Version ac04

Copyright 2017 A. Danko


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