Adolphson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adolphson Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
36%
24761
18%
80450
11%
24658
44%
24658
22%
53582

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
19%
941
11%
4397
5%
926
30%
926
11%
3178
January11th to 20thNight
18%
950
13%
4304
5%
930
25%
930
10%
3229
January21st to endNight
20%
1037
8%
4499
3%
1023
28%
1023
10%
3531
February1st to 10thNight
22%
950
14%
2470
3%
950
28%
950
19%
1804
February11th to 20thNight
25%
824
18%
2302
7%
823
32%
823
22%
1568
February21st to endNight
19%
611
20%
1831
6%
611
32%
611
20%
1229
March1st to 10thNight
23%
716
17%
2156
7%
716
32%
716
20%
1465
March11th to 20thNight
30%
540
19%
1980
13%
540
41%
540
19%
1274
March21st to endNight
22%
594
12%
2066
6%
594
30%
594
13%
1524
April1st to 10thNight
27%
540
17%
1800
10%
540
38%
540
22%
1162
April11th to 20thNight
30%
533
19%
1775
14%
533
41%
533
22%
1141
April21st to endNight
31%
540
16%
1800
9%
540
42%
540
21%
1198
May1st to 10thNight
32%
540
15%
1604
8%
540
39%
540
23%
1097
May11th to 20thNight
41%
531
19%
1417
12%
531
47%
531
26%
975
May21st to endNight
45%
584
17%
1551
9%
582
50%
582
28%
1038
June1st to 10thNight
58%
540
18%
1440
10%
540
62%
540
38%
876
June11th to 20thNight
55%
540
21%
1440
13%
540
59%
540
37%
883
June21st to endNight
50%
540
18%
1440
9%
540
55%
540
34%
912
July1st to 10thNight
70%
525
18%
1400
14%
525
71%
525
39%
841
July11th to 20thNight
68%
522
25%
1392
16%
522
72%
522
46%
779
July21st to endNight
70%
591
24%
1515
19%
558
72%
558
42%
864
August1st to 10thNight
71%
537
22%
1601
21%
534
73%
534
38%
891
August11th to 20thNight
68%
534
24%
1713
27%
534
71%
534
35%
973
August21st to endNight
70%
594
24%
1980
26%
594
75%
594
41%
1021
September1st to 10thNight
60%
540
25%
1800
24%
540
65%
540
36%
963
September11th to 20thNight
61%
540
32%
1800
31%
540
67%
540
35%
994
September21st to endNight
55%
711
26%
1998
16%
711
62%
711
37%
1162
October1st to 10thNight
46%
720
24%
2160
17%
720
51%
720
33%
1270
October11th to 20thNight
36%
720
24%
2160
14%
720
45%
720
28%
1306
October21st to endNight
28%
792
18%
2436
9%
792
37%
792
21%
1609
November1st to 10thNight
32%
740
26%
2406
16%
740
47%
740
31%
1356
November11th to 20thNight
25%
760
23%
2470
10%
760
42%
760
22%
1553
November21st to endNight
26%
945
19%
2655
8%
945
36%
945
23%
1829
December1st to 10thNight
23%
950
14%
2660
6%
950
31%
950
21%
1870
December11th to 20thNight
25%
949
16%
3162
7%
948
32%
948
17%
2199
December21st to endNight
18%
1040
8%
4870
4%
1026
27%
1026
7%
4018

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
13%8%47%6%35%45%7%38%
78431
Night
13%9%47%5%3445%6%39%
80905
TransparencyDay
45%7%12%22%12%2
78133
Night
44%6%12%22%14%2
80723
SeeingDay
15%10%28%26%16%5%
14738
Night
16%10%31%30%12%1
24786

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
11%12%7%12%8%45%446%26%
2527
11th to 20thDay
12%11%5%10%11%5%8%5%5%5%23%
2576
21st to endDay
15%18%9%12%8%34335%18%
3135
February1st to 10thDay
15%11%6%9%7%5%6%446%28%
1710
11th to 20thDay
14%9%47%6%45%5%47%35%
1765
21st to endDay
14%12%410%7%3335%6%33%
1520
March1st to 10thDay
15%11%5%7%5%3445%6%35%
1819
11th to 20thDay
13%10%37%6%35%46%8%33%
1980
21st to endDay
20%12%48%6%3446%6%26%
2290
April1st to 10thDay
15%10%46%6%44447%36%
2160
11th to 20thDay
16%9%46%5%3445%5%38%
2134
21st to endDay
21%7%38%6%34446%34%
2160
May1st to 10thDay
18%7%36%6%35%5%6%8%32%
2351
11th to 20thDay
19%8%36%5%345%5%7%35%
2479
21st to endDay
14%7%36%6%46%6%7%9%33%
2725
June1st to 10thDay
8%5%35%5%35%5%6%9%46%
2520
11th to 20thDay
8%5%25%6%35%45%7%49%
2520
21st to endDay
10%5%25%6%45%5%6%10%41%
2520
July1st to 10thDay
7%4245%35%6%7%9%47%
2520
11th to 20thDay
7%4246%35%6%6%10%46%
2520
21st to endDay
6%4246%46%5%7%11%45%
2710
August1st to 10thDay
7%425%6%47%6%8%11%39%
2328
11th to 20thDay
9%435%6%35%46%9%47%
2186
21st to endDay
7%42443446%9%50%
2376
September1st to 10thDay
12%5%25%5%3346%7%48%
2160
11th to 20thDay
11%42343445%8%53%
2149
21st to endDay
8%5%25%435%5%6%8%49%
1949
October1st to 10thDay
13%6%35%5%33446%49%
1800
11th to 20thDay
16%8%36%5%24346%43%
1800
21st to endDay
20%9%25%424446%40%
1918
November1st to 10thDay
10%7%246%235%5%7%47%
1672
11th to 20thDay
15%9%47%5%34448%38%
1710
21st to endDay
16%11%46%5%33345%39%
1521
December1st to 10thDay
14%12%5%8%6%45%445%33%
1520
11th to 20thDay
14%11%47%7%3445%6%34%
1918
21st to endDay
21%18%9%12%7%23345%17%
2783
January1st to 10thNight
13%12%6%12%7%34445%30%
4428
11th to 20thNight
12%16%8%10%7%35%5%8%423%
4379
21st to endNight
18%16%6%12%6%24345%24%
4532
February1st to 10thNight
15%10%5%8%6%35%446%33%
2470
11th to 20thNight
13%9%46%6%345%5%7%38%
2301
21st to endNight
15%11%47%5%33435%40%
1831
March1st to 10thNight
14%11%46%5%35%445%39%
2156
11th to 20thNight
15%9%36%5%3446%7%38%
1980
21st to endNight
21%10%5%8%6%35%45%6%28%
2066
April1st to 10thNight
13%9%36%5%4445%7%40%
1800
11th to 20thNight
15%10%26%43435%5%42%
1775
21st to endNight
18%6%36%6%35%35%7%38%
1800
May1st to 10thNight
16%7%36%6%45%46%8%36%
1604
11th to 20thNight
15%6%46%5%3445%8%41%
1416
21st to endNight
11%5%36%5%36%5%6%9%41%
1551
June1st to 10thNight
8%4245%336%5%9%50%
1440
11th to 20thNight
7%6%35%5%245%7%10%47%
1440
21st to endNight
9%5%25%435%5%6%9%47%
1440
July1st to 10thNight
7%3244345%7%10%49%
1440
11th to 20thNight
5%3234245%7%10%56%
1440
21st to endNight
5%325%5%25%5%6%8%53%
1604
August1st to 10thNight
5%4245%35%5%5%9%53%
1611
11th to 20thNight
6%4345%35%5%5%7%53%
1713
21st to endNight
6%31442445%7%59%
1980
September1st to 10thNight
11%5%1432335%7%56%
1800
11th to 20thNight
10%4235%335%6%7%53%
1800
21st to endNight
7%4245%345%6%9%51%
1998
October1st to 10thNight
11%5%245%23445%53%
2160
11th to 20thNight
14%7%25%42445%6%48%
2160
21st to endNight
17%8%35%5%345%5%6%40%
2436
November1st to 10thNight
11%6%2442335%7%53%
2406
11th to 20thNight
13%8%36%4335%5%7%42%
2470
21st to endNight
17%9%46%5%33446%39%
2655
December1st to 10thNight
13%11%47%6%35%45%7%35%
2660
11th to 20thNight
14%11%5%8%6%34445%36%
3279
21st to endNight
22%16%7%10%7%4443419%
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
58%7%11%18%6%
2528
11th to 20thDay
62%6%10%14%8%
2576
21st to endDay
69%5%9%11%6%
3135
February1st to 10thDay
57%5%13%17%6%2
1710
11th to 20thDay
49%6%12%21%11%1
1774
21st to endDay
53%5%11%21%9%1
1520
March1st to 10thDay
50%7%13%20%9%1
1819
11th to 20thDay
48%6%14%21%10%1
1980
21st to endDay
57%6%11%18%6%1
2290
April1st to 10thDay
47%6%12%23%11%
2160
11th to 20thDay
46%6%10%24%12%2
2134
21st to endDay
50%7%10%19%12%1
2160
May1st to 10thDay
49%8%12%21%10%1
2351
11th to 20thDay
47%7%11%22%12%
2483
21st to endDay
46%9%13%16%14%2
2725
June1st to 10thDay
33%8%15%26%15%2
2520
11th to 20thDay
35%7%11%23%22%3
2520
21st to endDay
37%9%15%22%15%2
2520
July1st to 10thDay
31%8%15%28%13%4
2451
11th to 20thDay
31%9%17%27%14%3
2445
21st to endDay
31%8%18%28%14%1
2559
August1st to 10thDay
33%11%17%27%11%1
2314
11th to 20thDay
33%8%14%28%15%1
2186
21st to endDay
30%8%13%27%19%4
2376
September1st to 10thDay
33%7%13%24%18%5%
2160
11th to 20thDay
30%5%12%27%22%4
2149
21st to endDay
31%7%12%28%20%2
1949
October1st to 10thDay
36%6%10%26%20%2
1800
11th to 20thDay
43%48%25%17%2
1800
21st to endDay
46%413%21%13%3
1918
November1st to 10thDay
35%6%16%24%15%4
1672
11th to 20thDay
46%5%11%24%12%1
1710
21st to endDay
49%5%13%23%9%1
1521
December1st to 10thDay
53%6%12%20%9%1
1520
11th to 20thDay
49%6%11%23%8%2
1915
21st to endDay
71%5%7%11%5%
2783
January1st to 10thNight
54%8%12%18%8%
4428
11th to 20thNight
61%5%11%15%8%1
4379
21st to endNight
64%5%10%16%5%1
4532
February1st to 10thNight
53%412%19%11%1
2470
11th to 20thNight
46%5%12%24%12%1
2302
21st to endNight
48%49%24%13%3
1831
March1st to 10thNight
46%6%11%24%12%1
2156
11th to 20thNight
44%7%12%21%12%3
1980
21st to endNight
57%6%11%18%7%1
2066
April1st to 10thNight
42%6%11%24%14%2
1800
11th to 20thNight
43%5%9%22%17%4
1775
21st to endNight
45%6%12%20%13%4
1800
May1st to 10thNight
45%7%14%21%12%1
1604
11th to 20thNight
43%6%11%22%17%1
1417
21st to endNight
39%8%13%20%17%2
1552
June1st to 10thNight
29%9%15%24%19%4
1440
11th to 20thNight
30%8%12%23%22%5%
1440
21st to endNight
34%8%16%18%21%3
1440
July1st to 10thNight
29%7%16%30%14%4
1400
11th to 20thNight
23%7%16%31%21%3
1392
21st to endNight
26%7%16%28%20%3
1515
August1st to 10thNight
26%8%18%32%14%2
1601
11th to 20thNight
30%7%11%30%19%2
1713
21st to endNight
24%6%15%28%20%7%
1980
September1st to 10thNight
29%5%13%26%22%6%
1800
11th to 20thNight
29%7%12%27%21%5%
1800
21st to endNight
29%6%12%25%24%3
1998
October1st to 10thNight
33%6%11%23%24%4
2160
11th to 20thNight
36%5%10%25%20%3
2160
21st to endNight
44%6%10%20%17%2
2436
November1st to 10thNight
32%5%13%26%20%4
2406
11th to 20thNight
41%6%12%24%16%2
2470
21st to endNight
46%5%11%24%13%1
2655
December1st to 10thNight
49%5%13%22%10%1
2660
11th to 20thNight
49%6%12%25%8%1
3281
21st to endNight
69%6%8%11%5%
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
21%18%33%20%7%1
270
11th to 20thDay
25%20%37%13%5%
270
21st to endDay
21%21%33%19%6%
297
February1st to 10thDay
23%17%40%17%4
270
11th to 20thDay
21%18%34%21%41
270
21st to endDay
24%17%41%17%1
210
March1st to 10thDay
19%19%41%18%4
240
11th to 20thDay
30%13%33%15%9%
240
21st to endDay
29%16%32%15%6%1
376
April1st to 10thDay
23%14%33%24%5%
420
11th to 20thDay
19%16%33%20%11%1
412
21st to endDay
25%12%32%20%8%2
420
May1st to 10thDay
21%10%33%25%9%2
502
11th to 20thDay
20%13%28%24%13%2
625
21st to endDay
15%7%30%26%15%8%
679
June1st to 10thDay
8%5%25%31%25%7%
630
11th to 20thDay
8%428%35%21%4
630
21st to endDay
10%8%29%32%15%5%
630
July1st to 10thDay
9%316%31%27%14%
621
11th to 20thDay
9%322%36%21%8%
618
21st to endDay
8%220%36%28%6%
684
August1st to 10thDay
6%320%35%27%8%
626
11th to 20thDay
9%5%17%29%29%12%
500
21st to endDay
7%416%33%30%11%
495
September1st to 10thDay
14%6%18%28%27%8%
450
11th to 20thDay
9%218%35%24%12%
450
21st to endDay
10%7%27%25%24%7%
419
October1st to 10thDay
14%8%31%28%15%4
270
11th to 20thDay
20%19%31%18%10%1
270
21st to endDay
32%14%30%18%5%1
297
November1st to 10thDay
11%11%39%26%10%3
270
11th to 20thDay
21%16%34%20%7%1
270
21st to endDay
26%13%32%25%4
270
December1st to 10thDay
14%17%38%21%6%3
270
11th to 20thDay
20%15%38%20%7%
270
21st to endDay
23%21%37%16%3
297
January1st to 10thNight
15%16%42%20%6%
950
11th to 20thNight
19%15%39%21%5%1
950
21st to endNight
19%13%37%28%3
1045
February1st to 10thNight
22%12%39%23%5%
950
11th to 20thNight
18%15%37%26%3
826
21st to endNight
21%15%41%20%3
611
March1st to 10thNight
21%14%39%22%5%
716
11th to 20thNight
20%11%34%28%7%
540
21st to endNight
25%12%34%25%41
594
April1st to 10thNight
18%13%39%26%4
540
11th to 20thNight
21%11%33%27%7%
533
21st to endNight
20%10%33%31%6%
540
May1st to 10thNight
16%9%36%31%6%1
540
11th to 20thNight
17%8%27%34%13%1
531
21st to endNight
12%6%30%32%20%1
584
June1st to 10thNight
9%423%45%18%1
540
11th to 20thNight
9%425%40%21%
540
21st to endNight
10%429%37%18%1
540
July1st to 10thNight
8%212%41%33%4
525
11th to 20thNight
6%120%46%25%2
522
21st to endNight
6%213%47%30%1
591
August1st to 10thNight
6%113%47%30%3
537
11th to 20thNight
6%216%40%31%5%
534
21st to endNight
8%114%44%31%2
594
September1st to 10thNight
13%418%37%25%3
540
11th to 20thNight
12%318%36%26%4
540
21st to endNight
10%6%24%36%22%3
711
October1st to 10thNight
12%7%30%31%18%2
720
11th to 20thNight
16%12%32%28%12%
720
21st to endNight
21%12%34%25%7%
792
November1st to 10thNight
16%9%40%27%8%1
740
11th to 20thNight
17%15%38%24%6%
760
21st to endNight
21%12%36%25%6%
945
December1st to 10thNight
18%13%39%24%41
950
11th to 20thNight
22%11%34%26%6%
950
21st to endNight
26%16%34%23%2
1045
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