Hines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hines Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
52%
24047
22%
74443
16%
23993
59%
23993
28%
46209

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
31%
759
23%
2459
10%
757
48%
757
24%
1510
January11th to 20thNight
39%
737
26%
2393
18%
737
52%
737
27%
1410
January21st to endNight
30%
792
24%
2470
11%
792
43%
792
24%
1557
February1st to 10thNight
36%
720
23%
2160
12%
720
46%
720
27%
1344
February11th to 20thNight
33%
702
23%
2098
10%
699
47%
699
27%
1320
February21st to endNight
37%
592
27%
1776
16%
592
48%
592
29%
1113
March1st to 10thNight
42%
720
29%
2044
18%
720
51%
720
34%
1225
March11th to 20thNight
40%
720
24%
1980
12%
720
50%
720
31%
1238
March21st to endNight
41%
792
24%
2178
11%
792
52%
792
34%
1306
April1st to 10thNight
45%
720
25%
1980
15%
720
52%
720
32%
1205
April11th to 20thNight
48%
628
24%
1870
17%
628
55%
628
33%
1098
April21st to endNight
58%
540
33%
1656
25%
540
67%
540
42%
876
May1st to 10thNight
58%
540
28%
1620
19%
540
66%
540
40%
890
May11th to 20thNight
61%
531
18%
1592
13%
531
66%
531
33%
977
May21st to endNight
68%
582
21%
1744
17%
582
71%
582
33%
1058
June1st to 10thNight
68%
540
14%
1620
13%
540
69%
540
26%
1077
June11th to 20thNight
76%
540
15%
1620
13%
540
77%
540
31%
1029
June21st to endNight
72%
540
12%
1620
11%
540
72%
540
23%
1125
July1st to 10thNight
70%
525
10%
1575
8%
525
70%
525
21%
1128
July11th to 20thNight
74%
522
11%
1566
11%
522
74%
522
25%
1082
July21st to endNight
81%
591
14%
1672
15%
558
81%
558
30%
1086
August1st to 10thNight
71%
537
11%
1600
11%
534
71%
534
23%
1118
August11th to 20thNight
70%
534
11%
1752
13%
534
70%
534
19%
1236
August21st to endNight
64%
643
13%
2029
14%
643
64%
643
19%
1442
September1st to 10thNight
64%
720
15%
1980
14%
720
64%
720
23%
1392
September11th to 20thNight
62%
720
16%
1980
14%
720
62%
720
25%
1371
September21st to endNight
61%
720
23%
1980
20%
720
64%
720
30%
1282
October1st to 10thNight
58%
720
28%
1980
23%
720
64%
720
37%
1189
October11th to 20thNight
59%
720
33%
2092
28%
720
67%
720
39%
1164
October21st to endNight
56%
792
30%
2376
27%
792
63%
792
37%
1355
November1st to 10thNight
54%
740
29%
2240
24%
740
62%
740
36%
1250
November11th to 20thNight
46%
760
27%
2470
22%
760
57%
760
32%
1382
November21st to endNight
44%
760
25%
2470
19%
760
55%
760
30%
1439
December1st to 10thNight
41%
760
25%
2470
16%
760
52%
760
28%
1466
December11th to 20thNight
37%
759
26%
2911
17%
758
48%
758
23%
1688
December21st to endNight
37%
829
16%
4420
17%
817
47%
817
13%
2781

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
10%6%35%6%45%5%6%8%42%
74886
Night
10%6%35%5%35%5%6%8%45%
74895
TransparencyDay
38%8%12%18%17%7%
74609
Night
36%7%12%17%19%8%
74691
SeeingDay
12%6%20%24%23%15%
13968
Night
12%6%22%32%24%4
24059

By Month

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 10thDay
12%7%36%6%3446%7%44%
1706
11th to 20thDay
11%5%25%5%2346%8%48%
1656
21st to endDay
16%7%35%5%2445%5%45%
1883
February1st to 10thDay
15%7%26%5%345%5%7%41%
1800
11th to 20thDay
14%7%25%43345%6%47%
1748
21st to endDay
15%6%35%43445%6%45%
1480
March1st to 10thDay
9%5%25%5%3345%7%51%
1914
11th to 20thDay
11%5%36%5%45%5%6%8%43%
1980
21st to endDay
11%6%25%4345%6%7%48%
2178
April1st to 10thDay
10%5%246%35%6%5%7%46%
1980
11th to 20thDay
12%5%245%34448%49%
2052
21st to endDay
7%424435%5%5%7%56%
2303
May1st to 10thDay
7%3234345%49%56%
2340
11th to 20thDay
7%5%36%6%45%6%6%9%41%
2301
21st to endDay
7%426%7%46%5%6%9%42%
2531
June1st to 10thDay
9%7%27%7%5%6%6%8%10%32%
2340
11th to 20thDay
4425%6%47%7%8%12%40%
2340
21st to endDay
6%5%37%6%5%7%9%9%12%31%
2340
July1st to 10thDay
6%6%36%8%5%8%10%10%11%28%
2340
11th to 20thDay
8%5%37%7%5%10%8%7%11%29%
2340
21st to endDay
7%5%37%6%5%7%9%8%11%32%
2547
August1st to 10thDay
8%7%37%8%5%8%7%9%13%27%
2327
11th to 20thDay
10%7%36%8%5%8%9%8%11%27%
2143
21st to endDay
11%7%38%8%5%7%7%8%9%27%
2309
September1st to 10thDay
8%7%37%8%47%6%7%10%32%
1980
11th to 20thDay
11%7%36%7%46%6%7%9%36%
1980
21st to endDay
12%435%5%346%6%8%44%
1980
October1st to 10thDay
11%5%245%345%5%5%51%
1980
11th to 20thDay
9%41433345%8%55%
1867
21st to endDay
8%425%42445%7%55%
1980
November1st to 10thDay
9%435%43435%6%54%
1834
11th to 20thDay
11%6%24423345%55%
1710
21st to endDay
12%6%35%5%335%6%8%46%
1710
December1st to 10thDay
14%5%35%5%4445%7%44%
1710
11th to 20thDay
16%7%25%5%2345%6%44%
2153
21st to endDay
17%11%37%424345%41%
3124
January1st to 10thNight
12%6%36%5%345%47%45%
2459
11th to 20thNight
11%5%35%5%35%35%6%48%
2393
21st to endNight
17%6%35%43445%6%44%
2470
February1st to 10thNight
14%7%25%4245%5%7%45%
2160
11th to 20thNight
14%7%35%5%34346%47%
2098
21st to endNight
13%6%345%345%5%7%46%
1776
March1st to 10thNight
11%5%245%34346%53%
2044
11th to 20thNight
11%6%244345%5%8%48%
1980
21st to endNight
8%6%25%43445%6%53%
2178
April1st to 10thNight
11%425%5%245%5%6%50%
1980
11th to 20thNight
9%425%5%25%46%8%50%
1870
21st to endNight
6%2134345%6%7%59%
1656
May1st to 10thNight
6%3245%35%46%8%56%
1620
11th to 20thNight
7%325%7%36%5%6%11%46%
1592
21st to endNight
6%436%5%35%5%7%9%47%
1744
June1st to 10thNight
8%5%26%7%47%6%8%12%35%
1620
11th to 20thNight
5%325%5%37%8%8%13%41%
1620
21st to endNight
5%6%35%7%5%8%8%8%11%35%
1620
July1st to 10thNight
6%6%36%7%46%8%9%13%30%
1620
11th to 20thNight
5%5%35%7%46%7%10%13%32%
1620
21st to endNight
4425%6%5%6%8%10%12%38%
1771
August1st to 10thNight
6%427%8%5%6%9%9%13%33%
1611
11th to 20thNight
8%6%36%7%46%7%9%14%32%
1752
21st to endNight
8%6%27%7%5%8%7%9%9%32%
2029
September1st to 10thNight
8%7%47%6%5%5%7%7%12%33%
1980
11th to 20thNight
10%7%26%6%46%6%6%8%38%
1980
21st to endNight
9%6%27%6%35%6%5%8%43%
1980
October1st to 10thNight
10%5%25%42445%7%52%
1980
11th to 20thNight
10%424323446%57%
2092
21st to endNight
9%5%245%35%446%55%
2376
November1st to 10thNight
10%5%2442345%5%56%
2240
11th to 20thNight
11%6%245%23346%53%
2470
21st to endNight
12%6%3442445%7%49%
2470
December1st to 10thNight
12%5%35%5%345%5%8%46%
2470
11th to 20thNight
14%6%35%5%23345%49%
3042
21st to endNight
16%10%37%6%3445%6%38%
4532

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
40%5%8%17%21%9%
1707
11th to 20thDay
34%5%9%20%23%10%
1656
21st to endDay
41%46%17%22%10%
1883
February1st to 10thDay
42%5%8%15%20%9%
1800
11th to 20thDay
39%46%16%26%9%
1758
21st to endDay
40%5%7%19%17%12%
1480
March1st to 10thDay
33%5%7%18%24%12%
1914
11th to 20thDay
38%6%14%15%18%9%
1980
21st to endDay
36%6%11%20%20%7%
2178
April1st to 10thDay
37%7%9%20%17%11%
1980
11th to 20thDay
35%5%7%19%24%9%
2052
21st to endDay
28%5%9%25%25%7%
2303
May1st to 10thDay
26%6%11%23%26%8%
2340
11th to 20thDay
37%8%15%21%15%4
2305
21st to endDay
36%8%13%22%18%3
2531
June1st to 10thDay
44%11%15%19%10%1
2340
11th to 20thDay
34%11%18%23%14%
2340
21st to endDay
40%14%21%16%9%1
2340
July1st to 10thDay
42%17%22%14%5%1
2275
11th to 20thDay
45%13%23%14%5%
2271
21st to endDay
39%14%22%19%41
2405
August1st to 10thDay
45%14%20%18%3
2314
11th to 20thDay
46%15%21%13%5%
2143
21st to endDay
50%13%15%13%7%1
2309
September1st to 10thDay
43%11%15%16%11%3
1980
11th to 20thDay
43%10%12%16%15%4
1980
21st to endDay
36%7%12%18%20%7%
1980
October1st to 10thDay
34%5%10%16%22%12%
1980
11th to 20thDay
28%5%9%20%28%10%
1867
21st to endDay
30%46%15%28%16%
1980
November1st to 10thDay
32%47%17%24%16%
1834
11th to 20thDay
32%36%17%26%15%
1710
21st to endDay
36%5%8%19%23%10%
1710
December1st to 10thDay
40%6%12%16%17%9%
1710
11th to 20thDay
41%47%16%25%8%
2150
21st to endDay
47%35%16%23%6%
3124
January1st to 10thNight
40%47%17%22%10%
2459
11th to 20thNight
38%47%15%27%9%
2393
21st to endNight
42%45%15%23%11%
2470
February1st to 10thNight
39%49%16%20%12%
2160
11th to 20thNight
40%36%14%21%15%
2099
21st to endNight
37%6%6%20%16%15%
1776
March1st to 10thNight
33%5%7%19%22%14%
2044
11th to 20thNight
36%6%12%18%18%11%
1980
21st to endNight
31%6%13%18%22%10%
2178
April1st to 10thNight
33%6%10%18%19%13%
1980
11th to 20thNight
32%6%9%19%24%10%
1870
21st to endNight
25%5%11%25%25%9%
1656
May1st to 10thNight
26%6%11%23%24%10%
1620
11th to 20thNight
32%9%19%17%18%6%
1593
21st to endNight
32%8%15%21%19%5%
1745
June1st to 10thNight
38%11%20%19%12%1
1620
11th to 20thNight
31%13%23%22%10%1
1620
21st to endNight
38%15%20%18%8%2
1620
July1st to 10thNight
41%16%22%15%6%1
1575
11th to 20thNight
36%16%27%15%6%1
1566
21st to endNight
31%14%27%23%41
1672
August1st to 10thNight
37%16%25%17%4
1600
11th to 20thNight
39%17%22%16%5%
1752
21st to endNight
43%14%19%16%5%3
2029
September1st to 10thNight
41%13%16%16%12%2
1980
11th to 20thNight
41%11%14%15%15%4
1980
21st to endNight
37%8%14%17%18%7%
1980
October1st to 10thNight
31%6%11%19%20%13%
1980
11th to 20thNight
29%47%21%28%11%
2092
21st to endNight
31%48%14%26%18%
2376
November1st to 10thNight
30%48%16%24%17%
2240
11th to 20thNight
33%47%14%26%16%
2470
21st to endNight
35%5%9%19%20%12%
2470
December1st to 10thNight
36%5%14%15%23%7%
2470
11th to 20thNight
39%36%16%26%11%
3044
21st to endNight
48%46%16%22%4
4532

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
13%20%39%21%5%1
270
11th to 20thDay
13%15%31%29%8%4
252
21st to endDay
22%17%44%13%41
264
February1st to 10thDay
19%18%35%20%9%
240
11th to 20thDay
23%13%38%20%6%
240
21st to endDay
14%19%37%26%5%1
198
March1st to 10thDay
13%9%34%31%12%1
354
11th to 20thDay
15%10%35%29%11%1
420
21st to endDay
15%11%32%29%13%1
462
April1st to 10thDay
16%12%27%26%17%2
420
11th to 20thDay
14%10%29%25%18%4
412
21st to endDay
9%7%21%34%22%7%
420
May1st to 10thDay
7%9%25%26%23%10%
423
11th to 20thDay
8%316%33%24%17%
447
21st to endDay
10%39%24%30%24%
485
June1st to 10thDay
10%112%24%31%21%
450
11th to 20thDay
8%212%19%30%30%
450
21st to endDay
8%28%21%33%29%
450
July1st to 10thDay
6%26%16%34%37%
445
11th to 20thDay
9%214%30%45%
444
21st to endDay
7%16%14%36%35%
488
August1st to 10thDay
10%17%19%30%34%
446
11th to 20thDay
9%1412%33%41%
439
21st to endDay
12%27%20%32%27%
495
September1st to 10thDay
12%38%22%30%26%
450
11th to 20thDay
12%29%31%33%13%
450
21st to endDay
13%19%24%32%20%
450
October1st to 10thDay
11%323%34%21%8%
450
11th to 20thDay
10%418%30%29%10%
450
21st to endDay
11%8%22%31%24%4
495
November1st to 10thDay
15%425%28%20%7%
432
11th to 20thDay
14%9%37%27%10%3
270
21st to endDay
10%13%30%29%15%3
270
December1st to 10thDay
17%12%30%27%11%3
270
11th to 20thDay
23%12%33%24%7%1
270
21st to endDay
18%12%31%27%11%1
297
January1st to 10thNight
16%11%36%31%41
760
11th to 20thNight
14%11%31%33%11%1
737
21st to endNight
20%10%36%29%5%
792
February1st to 10thNight
17%11%32%32%8%
720
11th to 20thNight
17%10%34%33%7%
703
21st to endNight
16%8%35%36%4
592
March1st to 10thNight
13%9%31%39%9%
720
11th to 20thNight
13%9%33%31%13%1
720
21st to endNight
10%11%32%34%11%1
792
April1st to 10thNight
13%9%29%35%14%1
720
11th to 20thNight
10%8%30%38%14%1
628
21st to endNight
6%5%26%39%22%1
540
May1st to 10thNight
6%5%24%40%22%2
540
11th to 20thNight
8%221%38%26%5%
531
21st to endNight
10%112%34%38%5%
584
June1st to 10thNight
9%19%38%35%7%
540
11th to 20thNight
6%18%32%41%12%
540
21st to endNight
7%1434%43%10%
540
July1st to 10thNight
9%16%24%45%15%
525
11th to 20thNight
8%318%51%19%
522
21st to endNight
5%1424%55%12%
591
August1st to 10thNight
8%6%23%50%12%
537
11th to 20thNight
9%1419%52%14%
534
21st to endNight
10%27%27%40%14%
643
September1st to 10thNight
10%19%27%41%11%
720
11th to 20thNight
12%210%35%37%5%
720
21st to endNight
12%213%31%39%4
720
October1st to 10thNight
13%219%35%27%3
720
11th to 20thNight
11%418%35%27%4
720
21st to endNight
11%5%23%34%26%1
792
November1st to 10thNight
13%6%20%37%21%2
740
11th to 20thNight
13%9%27%33%17%1
760
21st to endNight
13%7%31%33%15%1
760
December1st to 10thNight
14%8%31%31%14%1
760
11th to 20thNight
17%7%31%31%13%2
760
21st to endNight
22%10%24%32%12%
836
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