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 2005-11-05 to 2018-01-12.

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
50%
16427
22%
48392
16%
16384
55%
16384
31%
29515

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
41%
899
19%
2606
15%
895
46%
895
27%
1695
January16th to endNight
44%
768
22%
2496
20%
768
49%
768
24%
1600
February1st to 15thNight
38%
697
14%
2288
12%
696
43%
696
21%
1539
February16th to endNight
30%
632
21%
1908
12%
632
41%
632
23%
1257
March1st to 15thNight
44%
720
20%
2032
12%
720
51%
720
30%
1280
March16th to endNight
41%
732
20%
2076
13%
732
46%
732
28%
1332
April1st to 15thNight
37%
539
18%
1798
13%
539
46%
539
23%
1129
April16th to endNight
38%
540
20%
1800
14%
540
47%
540
24%
1100
May1st to 15thNight
40%
540
17%
1628
12%
540
46%
540
25%
1044
May16th to endNight
51%
563
19%
1498
13%
561
57%
561
34%
909
June1st to 15thNight
57%
540
26%
1440
16%
540
64%
540
52%
740
June16th to endNight
68%
540
29%
1440
23%
540
72%
540
53%
732
July1st to 15thNight
75%
510
16%
1360
13%
510
77%
510
35%
837
July16th to endNight
78%
564
15%
1550
14%
531
79%
531
34%
919
August1st to 15thNight
74%
539
17%
1614
16%
536
75%
536
33%
930
August16th to endNight
75%
573
25%
1910
27%
573
78%
573
33%
1091
September1st to 15thNight
70%
540
26%
1800
25%
540
76%
540
35%
985
September16th to endNight
69%
612
33%
1956
27%
612
76%
612
45%
975
October1st to 15thNight
50%
720
26%
2160
17%
720
56%
720
36%
1246
October16th to endNight
56%
768
31%
2304
20%
768
65%
768
40%
1250
November1st to 15thNight
48%
901
27%
2421
18%
901
54%
901
38%
1430
November16th to endNight
49%
975
26%
2665
18%
975
53%
975
37%
1570
December1st to 15thNight
37%
975
14%
2730
9%
975
42%
975
26%
1826
December16th to endNight
34%
1040
17%
2912
11%
1040
38%
1040
20%
2099

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
49%5%8%6%3445%6%42%
48951
Night
27%47%5%2445%7%49%
48575
TransparencyDay
43%5%11%20%14%4
48636
Night
34%6%14%24%16%3
48392
SeeingDay
15%19%30%21%10%2
6135
Night
8%10%26%33%19%2
16435

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 15thDay
8%6%14%5%34345%42%
1584
16th to endDay
110%8%11%6%12237%43%
1728
February1st to 15thDay
113%7%17%6%3423435%
1575
16th to endDay
8%10%15%7%33446%35%
1566
March1st to 15thDay
111%6%8%7%33346%43%
1926
16th to endDay
113%7%9%6%2335%6%39%
2148
April1st to 15thDay
214%7%8%5%2445%5%37%
2150
16th to endDay
217%7%8%6%25%46%7%29%
2160
May1st to 15thDay
6%14%48%6%35%46%6%32%
2321
16th to endDay
6%9%47%6%35%5%6%7%38%
2616
June1st to 15thDay
442343445%8%52%
2520
16th to endDay
231442445%6%59%
2520
July1st to 15thDay
7%5%47%7%46%5%5%6%39%
2520
16th to endDay
7%7%48%8%47%6%6%7%31%
2509
August1st to 15thDay
10%7%47%8%35%5%5%8%32%
2337
16th to endDay
5%6%37%8%445%7%6%38%
2292
September1st to 15thDay
7%7%26%5%345%5%5%46%
2160
16th to endDay
8%6%26%424345%51%
1999
October1st to 15thDay
5%9%35%434346%49%
1800
16th to endDay
410%35%213236%55%
1920
November1st to 15thDay
28%45%32335%5%54%
1754
16th to endDay
18%47%5%12236%57%
1622
December1st to 15thDay
12%7%12%7%2433440%
1560
16th to endDay
111%7%13%8%44445%33%
1664
January1st to 15thNight
8%7%11%5%34336%45%
2606
16th to endNight
110%6%11%6%3333445%
2496
February1st to 15thNight
19%5%11%7%4445%7%38%
2277
16th to endNight
11%7%12%6%2335%7%38%
1908
March1st to 15thNight
7%5%8%6%23337%48%
2032
16th to endNight
29%6%7%6%23345%47%
2076
April1st to 15thNight
19%47%42447%8%43%
1798
16th to endNight
312%5%6%42335%6%46%
1800
May1st to 15thNight
49%35%425%5%5%7%45%
1627
16th to endNight
35%234345%7%9%50%
1497
June1st to 15thNight
2212212348%66%
1440
16th to endNight
111121445%8%65%
1440
July1st to 15thNight
3323436%6%6%8%50%
1440
16th to endNight
2224427%6%7%10%48%
1657
August1st to 15thNight
3414425%5%7%10%49%
1623
16th to endNight
3314435%5%6%11%50%
1910
September1st to 15thNight
43244235%5%8%55%
1800
16th to endNight
3313312346%64%
1956
October1st to 15thNight
47%14323446%57%
2160
16th to endNight
38%24212235%61%
2304
November1st to 15thNight
18%35%423346%56%
2421
16th to endNight
18%5%7%422346%55%
2665
December1st to 15thNight
11%5%9%7%3435%5%43%
2730
16th to endNight
9%7%13%10%34346%35%
2912

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
44%5%18%19%9%2
1585
16th to endDay
43%5%15%20%13%2
1728
February1st to 15thDay
54%412%17%8%2
1575
16th to endDay
49%5%11%20%10%1
1566
March1st to 15thDay
44%313%23%13%
1926
16th to endDay
47%411%23%10%2
2148
April1st to 15thDay
48%5%11%19%12%2
2150
16th to endDay
54%412%19%8%1
2160
May1st to 15thDay
53%410%22%8%
2321
16th to endDay
44%6%11%24%10%2
2620
June1st to 15thDay
30%410%19%25%8%
2520
16th to endDay
27%45%20%28%13%
2520
July1st to 15thDay
44%9%8%11%15%10%
2371
16th to endDay
49%8%14%13%10%3
2353
August1st to 15thDay
51%8%8%12%13%5%
2322
16th to endDay
44%8%9%18%14%3
2292
September1st to 15thDay
40%5%8%15%21%7%
2160
16th to endDay
36%47%24%23%3
1999
October1st to 15thDay
37%47%26%19%4
1800
16th to endDay
32%410%31%17%3
1920
November1st to 15thDay
31%412%22%23%5%
1754
16th to endDay
30%315%32%14%4
1622
December1st to 15thDay
48%414%21%9%1
1560
16th to endDay
52%6%11%17%10%1
1664
January1st to 15thNight
41%5%16%21%13%2
2606
16th to endNight
43%412%21%13%4
2496
February1st to 15thNight
45%6%14%20%10%1
2288
16th to endNight
45%312%23%13%2
1908
March1st to 15thNight
36%5%14%28%12%2
2032
16th to endNight
39%414%28%10%2
2076
April1st to 15thNight
37%8%12%23%15%2
1798
16th to endNight
40%413%29%11%
1800
May1st to 15thNight
37%8%14%26%12%
1628
16th to endNight
29%8%14%31%13%2
1498
June1st to 15thNight
17%5%12%24%30%8%
1440
16th to endNight
17%5%8%22%29%17%
1440
July1st to 15thNight
29%9%16%12%19%10%
1360
16th to endNight
28%10%25%17%13%4
1550
August1st to 15thNight
28%9%19%19%15%7%
1614
16th to endNight
28%9%14%23%20%3
1910
September1st to 15thNight
27%7%15%18%23%7%
1800
16th to endNight
21%5%12%32%25%2
1956
October1st to 15thNight
29%6%10%27%21%5%
2160
16th to endNight
26%412%32%19%4
2304
November1st to 15thNight
29%5%11%26%23%4
2421
16th to endNight
31%313%27%19%3
2665
December1st to 15thNight
42%6%16%19%13%1
2730
16th to endNight
50%5%13%17%11%1
2912

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
17%19%26%23%13%
123
16th to endDay
8%21%32%30%6%1
96
February1st to 15thDay
23%24%28%21%2
90
16th to endDay
19%27%19%25%6%1
81
March1st to 15thDay
24%24%29%16%5%
216
16th to endDay
20%36%32%9%1
288
April1st to 15thDay
19%31%30%11%41
269
16th to endDay
26%34%28%9%
270
May1st to 15thDay
22%25%26%18%5%1
330
16th to endDay
15%19%29%20%11%3
517
June1st to 15thDay
8%15%30%26%15%2
495
16th to endDay
413%33%25%21%3
495
July1st to 15thDay
12%7%25%27%19%8%
475
16th to endDay
15%9%27%26%17%3
368
August1st to 15thDay
20%7%34%25%10%1
315
16th to endDay
9%10%35%32%9%2
332
September1st to 15thDay
11%20%34%20%8%3
315
16th to endDay
17%19%37%16%6%3
232
October1st to 15thDay
16%20%22%25%13%2
135
16th to endDay
17%21%28%20%9%2
144
November1st to 15thDay
17%21%22%21%15%2
135
16th to endDay
18%31%25%19%5%
135
December1st to 15thDay
18%23%31%20%41
135
16th to endDay
14%25%34%21%3
144
January1st to 15thNight
8%15%28%31%13%3
900
16th to endNight
7%12%29%33%13%3
768
February1st to 15thNight
8%10%34%36%9%
704
16th to endNight
9%15%37%30%7%
632
March1st to 15thNight
7%11%31%34%13%1
720
16th to endNight
8%14%31%32%13%
732
April1st to 15thNight
7%17%34%29%10%
539
16th to endNight
10%16%31%28%11%1
540
May1st to 15thNight
9%10%33%31%13%1
540
16th to endNight
9%9%26%32%19%2
563
June1st to 15thNight
5%6%26%39%19%2
540
16th to endNight
2422%41%28%1
540
July1st to 15thNight
5%110%39%39%3
510
16th to endNight
325%36%45%6%
564
August1st to 15thNight
5%110%37%42%2
539
16th to endNight
4211%32%43%5%
573
September1st to 15thNight
5%313%38%35%3
540
16th to endNight
6%6%16%33%28%9%
612
October1st to 15thNight
9%11%25%31%18%4
720
16th to endNight
9%8%22%33%20%5%
768
November1st to 15thNight
8%11%27%33%16%2
901
16th to endNight
9%12%25%33%15%2
975
December1st to 15thNight
10%13%33%30%9%1
975
16th to endNight
10%12%35%29%9%1
1040
Page generated at 2018-01-12 20:01:36. Version ac04

Copyright 2018 A. Danko


Aspen Science Center Clear Sky Chart |Charts Home