Hamptons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hamptons Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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%
23118
18%
74569
10%
23077
45%
23077
21%
48826

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 10thNight
20%
760
19%
2649
7%
757
36%
757
17%
1669
January11th to 20thNight
19%
732
17%
2560
6%
732
33%
732
14%
1749
January21st to endNight
20%
792
20%
2744
8%
792
36%
792
18%
1724
February1st to 10thNight
17%
720
16%
2218
5%
720
32%
720
17%
1523
February11th to 20thNight
16%
703
19%
2100
5%
700
34%
700
18%
1420
February21st to endNight
19%
592
23%
1776
9%
592
39%
592
18%
1207
March1st to 10thNight
26%
719
20%
2160
10%
719
40%
719
22%
1408
March11th to 20thNight
29%
720
20%
2101
8%
720
41%
720
21%
1401
March21st to endNight
28%
792
23%
2003
7%
792
39%
792
27%
1358
April1st to 10thNight
32%
720
20%
1800
7%
720
39%
720
26%
1268
April11th to 20thNight
37%
711
18%
1775
6%
711
43%
711
29%
1212
April21st to endNight
35%
599
19%
1679
9%
599
42%
599
24%
1146
May1st to 10thNight
37%
540
14%
1620
8%
540
41%
540
18%
1169
May11th to 20thNight
35%
515
17%
1577
9%
515
43%
515
20%
1099
May21st to endNight
51%
388
11%
1551
15%
388
54%
388
16%
1028
June1st to 10thNight
47%
360
15%
1440
17%
360
53%
360
17%
939
June11th to 20thNight
54%
360
14%
1440
18%
360
58%
360
21%
876
June21st to endNight
60%
360
14%
1440
17%
360
64%
360
21%
881
July1st to 10thNight
59%
350
12%
1400
18%
350
60%
350
20%
859
July11th to 20thNight
62%
348
16%
1392
19%
348
64%
348
23%
816
July21st to endNight
58%
394
18%
1486
21%
372
62%
372
21%
888
August1st to 10thNight
68%
486
17%
1550
13%
484
70%
484
29%
948
August11th to 20thNight
61%
666
16%
1730
11%
666
62%
666
29%
1167
August21st to endNight
62%
792
21%
1980
11%
792
63%
792
34%
1295
September1st to 10thNight
52%
720
20%
1800
11%
720
55%
720
29%
1256
September11th to 20thNight
54%
720
25%
1952
16%
720
59%
720
35%
1199
September21st to endNight
44%
720
21%
1980
14%
720
51%
720
25%
1353
October1st to 10thNight
39%
720
18%
1980
12%
720
45%
720
22%
1377
October11th to 20thNight
38%
720
22%
2171
13%
720
50%
720
27%
1357
October21st to endNight
27%
792
17%
2574
8%
792
39%
792
20%
1723
November1st to 10thNight
38%
740
21%
2407
13%
740
50%
740
23%
1505
November11th to 20thNight
27%
760
22%
2470
11%
760
41%
760
19%
1592
November21st to endNight
28%
760
21%
2470
9%
760
43%
760
21%
1534
December1st to 10thNight
22%
760
16%
2608
5%
760
35%
760
14%
1782
December11th to 20thNight
20%
760
16%
3185
5%
759
32%
759
12%
2032
December21st to endNight
19%
827
12%
4801
6%
817
34%
817
9%
3066

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
16%6%25%43445%7%42%
74800
Night
17%7%35%5%3445%7%40%
74926
TransparencyDay
40%6%13%23%16%2
74505
Night
44%6%12%22%14%2
74755
SeeingDay
18%8%25%28%16%4
14006
Night
20%10%27%27%13%2
23129

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 10thDay
16%6%25%6%35%5%6%8%40%
1517
11th to 20thDay
17%10%25%5%3445%6%38%
1456
21st to endDay
15%8%35%5%35%46%7%40%
1611
February1st to 10thDay
19%7%36%6%35%5%7%7%34%
1739
11th to 20thDay
15%6%26%6%3445%6%43%
1748
21st to endDay
21%10%2442445%6%38%
1480
March1st to 10thDay
15%5%25%43345%8%44%
1797
11th to 20thDay
15%5%25%5%345%5%7%43%
1858
21st to endDay
18%8%36%43345%5%42%
2348
April1st to 10thDay
18%7%3443445%6%42%
2160
11th to 20thDay
18%6%2443345%7%45%
2134
21st to endDay
19%6%25%4345%6%7%40%
2280
May1st to 10thDay
23%8%44423447%38%
2340
11th to 20thDay
17%7%25%43345%8%42%
2331
21st to endDay
14%7%244345%5%9%44%
2725
June1st to 10thDay
17%5%25%5%35%46%8%41%
2520
11th to 20thDay
14%6%35%5%35%5%6%9%40%
2520
21st to endDay
12%6%25%4345%7%9%44%
2520
July1st to 10thDay
12%6%24425%5%8%9%44%
2520
11th to 20thDay
10%6%25%5%345%7%9%45%
2520
21st to endDay
12%5%25%435%5%6%9%44%
2744
August1st to 10thDay
10%5%25%4345%6%11%46%
2359
11th to 20thDay
12%5%245%345%6%8%45%
2167
21st to endDay
12%425%5%35%5%5%8%46%
2376
September1st to 10thDay
14%6%26%42445%8%46%
2160
11th to 20thDay
12%6%2432345%7%54%
2007
21st to endDay
19%6%245%345%5%6%42%
1980
October1st to 10thDay
21%6%2442345%6%43%
1980
11th to 20thDay
14%7%15%42345%7%45%
1784
21st to endDay
18%6%25%43445%7%41%
1782
November1st to 10thDay
16%6%24424446%48%
1671
11th to 20thDay
16%6%24434448%45%
1710
21st to endDay
16%7%344245%5%7%42%
1710
December1st to 10thDay
20%8%46%5%25%5%47%34%
1568
11th to 20thDay
21%7%25%323346%43%
1906
21st to endDay
19%11%47%6%34446%33%
2772
January1st to 10thNight
17%7%25%5%3445%9%40%
2649
11th to 20thNight
22%7%36%5%3345%6%36%
2560
21st to endNight
15%9%35%5%3445%8%40%
2744
February1st to 10thNight
18%9%37%5%345%47%36%
2218
11th to 20thNight
19%8%345%2445%8%37%
2098
21st to endNight
21%6%35%5%345%46%39%
1776
March1st to 10thNight
17%7%25%5%2445%6%43%
2150
11th to 20thNight
16%7%26%5%3446%7%39%
2100
21st to endNight
18%8%345%23446%43%
2003
April1st to 10thNight
19%8%25%43435%6%40%
1800
11th to 20thNight
17%7%35%42345%6%43%
1775
21st to endNight
21%7%36%424448%38%
1679
May1st to 10thNight
19%9%46%5%345%47%33%
1620
11th to 20thNight
20%8%35%5%345%5%9%33%
1576
21st to endNight
19%7%36%5%35%45%7%35%
1550
June1st to 10thNight
18%8%26%6%2445%8%37%
1440
11th to 20thNight
18%5%245%3445%10%39%
1440
21st to endNight
13%6%36%6%346%5%9%40%
1440
July1st to 10thNight
11%6%36%5%36%6%7%10%38%
1440
11th to 20thNight
13%5%346%35%6%7%10%39%
1440
21st to endNight
11%6%25%7%46%5%7%9%38%
1574
August1st to 10thNight
7%5%25%6%45%8%7%9%43%
1560
11th to 20thNight
11%5%25%6%35%5%7%9%40%
1730
21st to endNight
12%5%25%4345%5%9%46%
1980
September1st to 10thNight
15%7%25%5%35%5%6%6%41%
1800
11th to 20thNight
14%5%33423447%50%
1952
21st to endNight
17%7%36%6%3445%6%40%
1980
October1st to 10thNight
20%7%35%5%35%445%40%
1980
11th to 20thNight
17%6%25%42345%7%46%
2171
21st to endNight
20%7%35%5%3445%5%38%
2574
November1st to 10thNight
15%6%35%5%35%35%6%45%
2407
11th to 20thNight
19%6%35%43445%5%43%
2470
21st to endNight
15%6%35%5%25%46%7%44%
2470
December1st to 10thNight
21%8%35%5%3445%7%34%
2608
11th to 20thNight
19%7%36%5%33446%39%
3288
21st to endNight
20%10%35%5%34346%36%
4884

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 10thDay
42%5%13%25%13%1
1518
11th to 20thDay
47%7%14%21%11%1
1456
21st to endDay
43%5%11%23%15%1
1611
February1st to 10thDay
47%5%15%20%12%1
1739
11th to 20thDay
42%5%11%25%15%2
1757
21st to endDay
47%5%11%19%15%3
1480
March1st to 10thDay
38%5%15%23%16%4
1800
11th to 20thDay
39%5%12%25%16%2
1858
21st to endDay
45%410%19%17%5%
2348
April1st to 10thDay
41%6%12%20%18%4
2160
11th to 20thDay
39%411%22%21%3
2134
21st to endDay
43%5%10%22%17%4
2280
May1st to 10thDay
48%5%10%22%13%2
2340
11th to 20thDay
41%5%12%22%17%3
2335
21st to endDay
38%8%16%23%13%2
2725
June1st to 10thDay
42%6%13%24%14%1
2520
11th to 20thDay
40%7%14%24%14%1
2520
21st to endDay
36%8%15%26%15%1
2520
July1st to 10thDay
35%8%16%22%17%2
2450
11th to 20thDay
35%7%13%29%13%2
2445
21st to endDay
36%8%13%24%16%3
2591
August1st to 10thDay
33%7%18%26%16%1
2345
11th to 20thDay
36%9%14%26%13%2
2167
21st to endDay
35%7%14%23%20%2
2376
September1st to 10thDay
37%7%14%23%19%1
2160
11th to 20thDay
31%5%13%25%24%2
2007
21st to endDay
42%6%9%21%20%2
1980
October1st to 10thDay
42%6%10%22%17%3
1980
11th to 20thDay
37%5%14%25%18%1
1784
21st to endDay
43%5%12%22%14%3
1782
November1st to 10thDay
39%5%15%22%18%2
1671
11th to 20thDay
39%6%14%23%17%2
1710
21st to endDay
42%5%15%26%10%2
1710
December1st to 10thDay
49%5%15%17%13%1
1568
11th to 20thDay
44%416%16%18%2
1906
21st to endDay
52%5%11%22%9%
2772
January1st to 10thNight
43%6%13%23%13%2
2649
11th to 20thNight
50%5%13%22%9%1
2560
21st to endNight
42%6%12%22%17%2
2744
February1st to 10thNight
48%6%14%21%11%2
2218
11th to 20thNight
46%6%11%23%13%3
2100
21st to endNight
46%5%8%22%15%3
1776
March1st to 10thNight
42%5%12%22%15%3
2160
11th to 20thNight
43%7%10%21%15%4
2101
21st to endNight
43%5%9%19%19%6%
2003
April1st to 10thNight
46%5%10%19%16%4
1800
11th to 20thNight
42%5%11%20%20%2
1775
21st to endNight
46%410%20%15%5%
1679
May1st to 10thNight
52%5%9%18%13%3
1620
11th to 20thNight
47%7%10%19%14%3
1577
21st to endNight
47%8%14%18%11%1
1551
June1st to 10thNight
46%7%11%20%15%2
1440
11th to 20thNight
41%6%13%24%14%1
1440
21st to endNight
40%8%12%26%14%1
1440
July1st to 10thNight
40%9%16%19%15%1
1400
11th to 20thNight
37%8%15%27%12%1
1392
21st to endNight
39%8%14%24%13%2
1486
August1st to 10thNight
33%9%18%24%13%2
1550
11th to 20thNight
38%9%16%25%12%1
1730
21st to endNight
35%8%13%25%18%2
1980
September1st to 10thNight
44%6%9%24%16%2
1800
11th to 20thNight
34%6%11%23%24%2
1952
21st to endNight
44%6%8%19%19%3
1980
October1st to 10thNight
47%6%9%21%15%3
1980
11th to 20thNight
39%5%13%28%15%1
2171
21st to endNight
47%5%14%19%14%1
2574
November1st to 10thNight
41%5%12%22%18%3
2407
11th to 20thNight
43%5%11%21%15%3
2470
21st to endNight
39%6%14%28%12%2
2470
December1st to 10thNight
50%6%13%18%12%1
2608
11th to 20thNight
46%5%13%19%16%1
3288
21st to endNight
50%5%12%22%11%
4884

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 10thDay
22%18%33%21%6%1
180
11th to 20thDay
18%21%38%18%4
164
21st to endDay
21%12%40%16%9%2
188
February1st to 10thDay
26%14%35%21%4
359
11th to 20thDay
21%17%38%21%2
416
21st to endDay
24%15%35%20%5%
346
March1st to 10thDay
17%13%39%25%5%
420
11th to 20thDay
18%12%40%23%6%1
420
21st to endDay
22%12%35%22%8%1
462
April1st to 10thDay
22%12%34%23%9%1
420
11th to 20thDay
20%9%27%33%9%1
412
21st to endDay
25%9%27%31%7%2
420
May1st to 10thDay
25%8%29%26%10%1
423
11th to 20thDay
18%5%29%33%14%2
447
21st to endDay
18%216%31%24%7%
485
June1st to 10thDay
16%320%34%24%4
450
11th to 20thDay
15%320%36%22%5%
450
21st to endDay
16%215%37%25%6%
450
July1st to 10thDay
15%210%36%29%8%
445
11th to 20thDay
9%211%35%32%11%
444
21st to endDay
13%217%39%26%3
488
August1st to 10thDay
12%412%34%30%9%
446
11th to 20thDay
15%212%32%30%8%
439
21st to endDay
11%217%33%25%11%
495
September1st to 10thDay
18%317%29%23%11%
450
11th to 20thDay
15%422%27%21%11%
450
21st to endDay
22%422%30%17%4
450
October1st to 10thDay
27%7%18%23%18%7%
450
11th to 20thDay
15%8%27%29%17%3
430
21st to endDay
24%11%29%24%11%2
396
November1st to 10thDay
16%10%28%28%16%3
365
11th to 20thDay
21%16%32%22%9%
370
21st to endDay
18%16%30%24%11%1
370
December1st to 10thDay
20%17%37%16%9%
228
11th to 20thDay
23%24%27%23%3
180
21st to endDay
24%15%33%20%7%1
198
January1st to 10thNight
21%19%36%20%4
760
11th to 20thNight
27%16%33%20%4
732
21st to endNight
20%18%37%22%3
792
February1st to 10thNight
23%13%40%21%3
720
11th to 20thNight
24%17%40%16%3
703
21st to endNight
23%17%35%20%4
592
March1st to 10thNight
21%14%33%26%6%
720
11th to 20thNight
21%10%34%27%6%1
720
21st to endNight
22%8%36%24%9%1
792
April1st to 10thNight
23%8%32%29%7%1
720
11th to 20thNight
19%8%30%32%11%1
711
21st to endNight
23%6%27%30%12%2
599
May1st to 10thNight
23%6%25%30%13%3
540
11th to 20thNight
21%5%28%34%11%1
515
21st to endNight
22%115%32%25%4
389
June1st to 10thNight
21%218%31%26%2
360
11th to 20thNight
20%215%39%23%1
360
21st to endNight
16%114%42%26%2
360
July1st to 10thNight
13%214%39%29%3
350
11th to 20thNight
12%212%38%30%5%
348
21st to endNight
13%312%42%27%3
394
August1st to 10thNight
9%113%45%29%4
486
11th to 20thNight
13%210%37%32%6%
666
21st to endNight
13%313%33%30%8%
792
September1st to 10thNight
19%217%31%24%7%
720
11th to 20thNight
17%318%31%23%8%
720
21st to endNight
20%422%31%20%4
720
October1st to 10thNight
24%8%21%26%17%5%
720
11th to 20thNight
21%9%27%28%13%2
720
21st to endNight
24%10%33%21%11%1
792
November1st to 10thNight
17%10%30%27%14%2
740
11th to 20thNight
23%16%30%21%9%1
760
21st to endNight
18%18%31%23%8%1
760
December1st to 10thNight
25%16%31%21%6%1
760
11th to 20thNight
22%20%32%21%5%
760
21st to endNight
24%16%36%21%3
836
Page generated at 2024-01-10 10:16:13. Version ac07

Copyright 2024 Attilla Danko


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