Aspen Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aspen Science Center clear sky chart from 2005-11-06 to 2024-03-01.

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
47%
24686
22%
80011
16%
24590
54%
24590
29%
47604

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
37%
941
16%
4361
13%
926
43%
926
16%
2801
January11th to 20thNight
37%
769
18%
4092
19%
750
46%
750
14%
2637
January21st to endNight
39%
826
14%
4333
16%
814
44%
814
14%
2743
February1st to 10thNight
32%
760
17%
2470
12%
760
40%
760
21%
1631
February11th to 20thNight
29%
741
17%
2330
10%
740
37%
740
22%
1529
February21st to endNight
25%
628
21%
1884
9%
628
37%
628
22%
1243
March1st to 10thNight
36%
722
21%
2064
11%
722
45%
722
27%
1308
March11th to 20thNight
44%
720
24%
1980
14%
720
51%
720
34%
1208
March21st to endNight
33%
738
17%
2124
8%
738
40%
738
23%
1425
April1st to 10thNight
32%
540
19%
1800
13%
540
43%
540
22%
1106
April11th to 20thNight
35%
533
20%
1777
14%
533
44%
533
23%
1098
April21st to endNight
38%
540
21%
1800
14%
540
48%
540
26%
1071
May1st to 10thNight
38%
540
20%
1696
15%
540
45%
540
27%
1031
May11th to 20thNight
52%
531
19%
1445
15%
531
56%
531
34%
897
May21st to endNight
50%
584
22%
1552
13%
582
59%
582
37%
903
June1st to 10thNight
60%
540
27%
1440
18%
540
67%
540
50%
748
June11th to 20thNight
56%
540
27%
1440
19%
540
62%
540
48%
757
June21st to endNight
67%
540
30%
1440
23%
540
72%
540
54%
730
July1st to 10thNight
73%
525
19%
1400
17%
525
74%
525
39%
828
July11th to 20thNight
78%
522
22%
1415
19%
522
80%
522
45%
779
July21st to endNight
74%
591
14%
1674
13%
558
76%
558
32%
991
August1st to 10thNight
72%
537
16%
1602
15%
534
73%
534
32%
940
August11th to 20thNight
73%
534
26%
1694
24%
534
76%
534
39%
896
August21st to endNight
73%
594
26%
1980
27%
594
75%
594
35%
1100
September1st to 10thNight
73%
540
30%
1800
28%
540
80%
540
41%
924
September11th to 20thNight
69%
540
32%
1800
31%
540
74%
540
41%
912
September21st to endNight
65%
652
32%
2034
24%
652
72%
652
46%
1005
October1st to 10thNight
51%
720
27%
2160
17%
720
59%
720
37%
1205
October11th to 20thNight
50%
720
32%
2160
16%
720
62%
720
43%
1110
October21st to endNight
49%
792
30%
2376
18%
792
58%
792
36%
1344
November1st to 10thNight
47%
851
30%
2331
17%
851
55%
851
41%
1301
November11th to 20thNight
42%
950
28%
2470
15%
950
50%
950
40%
1438
November21st to endNight
46%
950
24%
2660
16%
950
52%
950
34%
1591
December1st to 10thNight
37%
950
18%
2660
10%
950
43%
950
28%
1698
December11th to 20thNight
35%
949
22%
3085
12%
948
41%
948
21%
1884
December21st to endNight
27%
1036
11%
4682
8%
1026
34%
1026
14%
2792

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
39%5%9%7%3445%7%44%
78602
Night
27%49%6%3445%7%49%
80867
TransparencyDay
41%6%10%20%17%5%
78317
Night
35%5%13%23%19%5%
80674
SeeingDay
16%21%30%22%10%2
14451
Night
9%12%27%34%17%2
24719

By Month

Percentage Cloud Cover SW (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
7%5%16%15%3335%6%37%
2543
11th to 20thDay
11%9%14%11%5%3435%34%
2860
21st to endDay
19%8%15%6%23346%44%
3146
February1st to 10thDay
112%8%16%9%43345%35%
1710
11th to 20thDay
110%7%14%7%44446%39%
1736
21st to endDay
17%9%16%10%33346%38%
1570
March1st to 10thDay
211%7%10%8%34446%41%
1898
11th to 20thDay
112%6%11%6%35%45%7%41%
1980
21st to endDay
114%9%12%7%435%5%6%35%
2232
April1st to 10thDay
312%6%9%5%345%6%6%40%
2160
11th to 20thDay
215%7%10%7%36%45%6%33%
2131
21st to endDay
214%7%8%7%36%5%6%8%34%
2160
May1st to 10thDay
5%13%5%8%6%46%5%7%8%35%
2261
11th to 20thDay
5%12%47%6%46%5%7%7%37%
2450
21st to endDay
5%8%36%7%35%6%6%9%40%
2724
June1st to 10thDay
3425%5%36%6%6%9%50%
2520
11th to 20thDay
44245%3446%7%57%
2520
21st to endDay
3425%5%35%5%6%8%54%
2520
July1st to 10thDay
6%5%36%6%46%5%5%6%47%
2520
11th to 20thDay
46%47%7%47%6%8%8%39%
2493
21st to endDay
8%7%48%9%5%8%6%6%8%31%
2545
August1st to 10thDay
9%7%47%8%47%6%7%9%33%
2328
11th to 20thDay
5%6%37%6%45%6%6%8%44%
2206
21st to endDay
5%5%37%8%45%6%7%7%42%
2376
September1st to 10thDay
5%5%36%6%35%5%5%6%51%
2160
11th to 20thDay
6%6%36%5%345%5%6%51%
2160
21st to endDay
7%6%25%424445%58%
1920
October1st to 10thDay
5%8%37%5%45%35%6%50%
1800
11th to 20thDay
39%24323347%60%
1800
21st to endDay
39%48%323245%56%
1980
November1st to 10thDay
27%45%32345%6%58%
1727
11th to 20thDay
211%46%42335%6%56%
1706
21st to endDay
17%5%10%6%23226%55%
1520
December1st to 10thDay
112%7%13%7%34335%44%
1520
11th to 20thDay
11%5%12%7%34446%44%
1926
21st to endDay
18%6%14%8%44446%40%
2794
January1st to 10thNight
6%6%18%13%33346%37%
4417
11th to 20thNight
11%8%15%8%7%3345%35%
4133
21st to endNight
11%7%14%8%33445%41%
4521
February1st to 10thNight
18%6%13%8%45%35%7%40%
2470
11th to 20thNight
19%6%13%7%445%6%8%38%
2329
21st to endNight
111%7%13%9%3335%7%39%
1884
March1st to 10thNight
18%7%9%7%345%48%45%
2064
11th to 20thNight
18%5%9%5%23347%53%
1980
21st to endNight
110%7%10%7%3445%6%41%
2124
April1st to 10thNight
29%49%5%35%5%6%8%45%
1800
11th to 20thNight
211%5%9%5%345%5%7%44%
1777
21st to endNight
412%47%43335%7%48%
1800
May1st to 10thNight
49%36%5%35%5%6%8%47%
1696
11th to 20thNight
47%245%35%6%8%9%47%
1444
21st to endNight
35%234335%7%10%54%
1552
June1st to 10thNight
131432345%9%65%
1440
11th to 20thNight
332231445%8%63%
1440
21st to endNight
11123245%6%9%65%
1440
July1st to 10thNight
33235%36%7%6%9%53%
1440
11th to 20thNight
1224425%6%6%9%58%
1463
21st to endNight
33245%37%7%8%11%47%
1773
August1st to 10thNight
5%424435%6%8%10%49%
1611
11th to 20thNight
3315%43447%10%56%
1694
21st to endNight
33145%35%5%7%10%53%
1980
September1st to 10thNight
43244245%6%9%59%
1800
11th to 20thNight
3425%4235%47%62%
1800
21st to endNight
341332245%6%67%
2034
October1st to 10thNight
36%2432445%7%59%
2160
11th to 20thNight
36%23323347%65%
2160
21st to endNight
310%47%312335%59%
2376
November1st to 10thNight
18%35%323347%62%
2331
11th to 20thNight
110%5%6%423345%57%
2470
21st to endNight
17%5%9%5%33346%54%
2660
December1st to 10thNight
10%5%10%6%44445%48%
2660
11th to 20thNight
19%6%9%7%3447%9%43%
3271
21st to endNight
8%6%13%10%44447%40%
4873

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
50%5%10%16%17%3
2544
11th to 20thDay
54%315%16%10%2
2860
21st to endDay
44%410%24%14%5%
3146
February1st to 10thDay
53%5%13%13%12%4
1710
11th to 20thDay
48%48%19%16%5%
1745
21st to endDay
49%5%9%17%15%5%
1570
March1st to 10thDay
46%48%23%17%2
1898
11th to 20thDay
45%415%22%12%3
1980
21st to endDay
52%5%10%20%11%2
2232
April1st to 10thDay
44%7%11%19%14%5%
2160
11th to 20thDay
52%411%16%15%1
2134
21st to endDay
49%5%9%24%11%1
2160
May1st to 10thDay
48%5%10%22%13%1
2261
11th to 20thDay
47%6%14%24%8%1
2454
21st to endDay
40%7%10%23%16%4
2724
June1st to 10thDay
29%6%13%24%21%7%
2520
11th to 20thDay
27%47%19%28%14%
2520
21st to endDay
29%6%7%19%25%14%
2520
July1st to 10thDay
37%9%6%14%21%13%
2451
11th to 20thDay
40%10%13%16%13%8%
2418
21st to endDay
50%9%15%13%10%3
2404
August1st to 10thDay
48%9%10%14%15%5%
2313
11th to 20thDay
39%8%10%16%21%7%
2206
21st to endDay
40%10%10%18%17%5%
2376
September1st to 10thDay
35%6%8%14%25%12%
2160
11th to 20thDay
35%7%8%18%24%9%
2160
21st to endDay
32%5%5%23%29%6%
1920
October1st to 10thDay
37%7%6%22%22%7%
1800
11th to 20thDay
27%5%6%29%25%8%
1800
21st to endDay
33%411%29%18%5%
1980
November1st to 10thDay
27%5%11%24%29%3
1727
11th to 20thDay
30%316%26%19%5%
1706
21st to endDay
35%39%30%14%9%
1520
December1st to 10thDay
46%5%13%19%13%3
1520
11th to 20thDay
42%49%26%17%1
1924
21st to endDay
46%5%7%14%22%6%
2794
January1st to 10thNight
48%412%19%14%3
4417
11th to 20thNight
51%314%19%11%2
4133
21st to endNight
48%310%21%12%5%
4521
February1st to 10thNight
45%6%14%18%14%4
2470
11th to 20thNight
44%5%11%21%15%3
2330
21st to endNight
46%39%22%16%5%
1884
March1st to 10thNight
39%5%11%26%17%3
2064
11th to 20thNight
34%5%14%29%14%4
1980
21st to endNight
43%6%13%24%11%2
2124
April1st to 10thNight
37%8%11%22%18%4
1800
11th to 20thNight
40%5%12%24%17%2
1777
21st to endNight
37%5%13%29%16%1
1800
May1st to 10thNight
36%7%13%28%16%1
1696
11th to 20thNight
32%8%19%28%12%1
1445
21st to endNight
26%8%12%29%20%5%
1552
June1st to 10thNight
19%5%14%29%27%6%
1440
11th to 20thNight
20%5%11%19%30%16%
1440
21st to endNight
17%6%10%25%24%18%
1440
July1st to 10thNight
26%10%15%15%23%11%
1400
11th to 20thNight
22%8%21%22%18%9%
1415
21st to endNight
28%12%28%17%12%3
1674
August1st to 10thNight
28%11%19%21%15%6%
1602
11th to 20thNight
25%7%17%18%24%8%
1694
21st to endNight
27%9%14%24%20%6%
1980
September1st to 10thNight
23%7%14%17%28%11%
1800
11th to 20thNight
24%5%14%21%27%9%
1800
21st to endNight
20%5%10%32%29%4
2034
October1st to 10thNight
27%6%11%26%22%8%
2160
11th to 20thNight
22%5%9%31%25%7%
2160
21st to endNight
31%312%29%20%6%
2376
November1st to 10thNight
25%5%11%27%28%4
2331
11th to 20thNight
29%314%28%20%5%
2470
21st to endNight
33%410%25%20%8%
2660
December1st to 10thNight
39%5%16%20%16%4
2660
11th to 20thNight
38%5%10%23%20%4
3272
21st to endNight
45%310%15%20%7%
4873

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%19%27%23%10%1
270
11th to 20thDay
18%30%25%21%6%1
270
21st to endDay
12%22%36%22%7%1
297
February1st to 10thDay
28%33%24%13%11
270
11th to 20thDay
26%31%26%13%41
270
21st to endDay
30%33%20%14%3
225
March1st to 10thDay
27%30%24%15%4
338
11th to 20thDay
22%27%32%15%4
420
21st to endDay
23%36%32%8%2
462
April1st to 10thDay
21%32%29%13%41
420
11th to 20thDay
30%31%27%10%1
412
21st to endDay
19%34%30%13%31
420
May1st to 10thDay
24%32%26%13%4
423
11th to 20thDay
13%20%30%25%10%2
597
21st to endDay
16%19%30%22%11%2
679
June1st to 10thDay
7%16%30%28%17%3
630
11th to 20thDay
9%18%35%24%12%1
630
21st to endDay
6%16%33%26%16%3
630
July1st to 10thDay
8%8%28%32%20%5%
621
11th to 20thDay
7%6%27%32%22%6%
591
21st to endDay
15%9%28%31%15%3
487
August1st to 10thDay
15%10%31%28%14%2
447
11th to 20thDay
8%9%38%27%14%4
437
21st to endDay
7%12%34%32%11%3
495
September1st to 10thDay
9%18%32%26%10%4
450
11th to 20thDay
12%17%38%22%7%4
450
21st to endDay
14%21%30%21%12%3
326
October1st to 10thDay
18%22%20%22%15%3
270
11th to 20thDay
16%27%27%18%10%3
270
21st to endDay
16%28%29%18%8%1
297
November1st to 10thDay
21%29%24%17%9%1
270
11th to 20thDay
14%30%27%19%7%2
270
21st to endDay
15%26%28%23%7%1
270
December1st to 10thDay
19%27%27%19%6%2
270
11th to 20thDay
18%26%32%17%6%2
270
21st to endDay
20%28%33%15%31
297
January1st to 10thNight
11%16%28%30%12%2
950
11th to 20thNight
12%14%31%28%12%2
770
21st to endNight
5%16%31%35%10%3
836
February1st to 10thNight
10%17%36%29%7%
760
11th to 20thNight
10%17%39%26%9%
744
21st to endNight
13%16%39%29%3
628
March1st to 10thNight
13%14%32%31%9%1
722
11th to 20thNight
7%14%31%34%14%1
720
21st to endNight
9%17%35%30%8%
738
April1st to 10thNight
10%19%36%29%7%
540
11th to 20thNight
10%20%30%28%10%1
533
21st to endNight
11%16%31%30%10%2
540
May1st to 10thNight
9%11%36%33%11%1
540
11th to 20thNight
9%8%26%35%19%2
531
21st to endNight
9%11%26%35%17%2
584
June1st to 10thNight
46%24%43%21%2
540
11th to 20thNight
6%10%24%42%17%1
540
21st to endNight
1325%43%26%1
540
July1st to 10thNight
4213%42%35%3
525
11th to 20thNight
229%44%39%3
522
21st to endNight
5%39%39%41%5%
591
August1st to 10thNight
7%211%42%36%2
537
11th to 20thNight
4412%44%33%3
534
21st to endNight
5%214%38%38%4
594
September1st to 10thNight
5%412%46%31%2
540
11th to 20thNight
5%5%16%41%28%4
540
21st to endNight
6%9%17%37%24%7%
652
October1st to 10thNight
7%12%27%31%20%3
720
11th to 20thNight
9%11%26%35%15%4
720
21st to endNight
11%14%24%32%17%3
792
November1st to 10thNight
9%14%27%33%15%2
851
11th to 20thNight
11%13%31%31%11%3
950
21st to endNight
10%15%26%34%15%1
950
December1st to 10thNight
11%15%35%30%9%1
950
11th to 20thNight
11%18%30%28%11%1
950
21st to endNight
12%15%38%29%5%1
1045
Page generated at 2024-02-27 04:30:14. Version ac07

Copyright © 2024 Attilla Danko.


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