Sundance Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sundance Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
72%
15671
35%
46865
29%
15633
78%
15633
52%
22633

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
65%
718
33%
2327
30%
716
73%
716
44%
1149
January16th to endNight
62%
768
35%
2496
32%
768
71%
768
41%
1272
February1st to 15thNight
67%
698
35%
2169
30%
698
77%
698
50%
1047
February16th to endNight
61%
632
34%
1895
31%
632
68%
632
43%
994
March1st to 15thNight
64%
720
36%
2007
28%
720
74%
720
52%
1010
March16th to endNight
68%
768
35%
2112
25%
768
75%
768
54%
1059
April1st to 15thNight
56%
719
29%
1978
15%
719
66%
719
51%
1026
April16th to endNight
63%
549
44%
1635
28%
549
75%
549
64%
684
May1st to 15thNight
70%
539
37%
1619
28%
539
76%
539
61%
707
May16th to endNight
70%
561
37%
1684
27%
561
77%
561
67%
701
June1st to 15thNight
77%
540
33%
1620
29%
540
79%
540
67%
684
June16th to endNight
86%
540
34%
1620
31%
540
88%
540
72%
663
July1st to 15thNight
86%
510
25%
1530
23%
510
86%
510
51%
760
July16th to endNight
82%
564
22%
1593
19%
531
84%
531
39%
902
August1st to 15thNight
87%
539
31%
1611
27%
536
88%
536
52%
780
August16th to endNight
83%
672
35%
1855
29%
672
83%
672
47%
1001
September1st to 15thNight
83%
706
29%
1942
25%
706
84%
706
48%
1045
September16th to endNight
81%
656
43%
1815
33%
656
87%
656
70%
809
October1st to 15thNight
74%
660
39%
1870
29%
660
80%
660
59%
878
October16th to endNight
77%
704
42%
2112
35%
704
84%
704
61%
945
November1st to 15thNight
75%
700
39%
2199
34%
700
82%
700
57%
983
November16th to endNight
69%
720
39%
2340
36%
720
77%
720
55%
1026
December1st to 15thNight
70%
720
35%
2340
31%
720
77%
720
43%
1162
December16th to endNight
60%
768
32%
2496
30%
768
66%
768
36%
1346

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
3313323346%64%
47792
Night
2212323346%67%
47061
TransparencyDay
21%45%15%27%25%
47487
Night
18%36%16%29%26%
46867
SeeingDay
411%24%31%19%7%
5472
Night
3415%34%35%6%
15682

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
2413323247%63%
1611
16th to endDay
5%42332335%6%60%
1728
February1st to 15thDay
342332335%7%61%
1694
16th to endDay
25%2442335%7%56%
1579
March1st to 15thDay
2313223446%65%
1951
16th to endDay
2222323345%67%
2112
April1st to 15thDay
2212324347%65%
1970
16th to endDay
1212212346%72%
2323
May1st to 15thDay
312212236%71%
2331
16th to endDay
221221323472%
2429
June1st to 15thDay
1111212482%
2340
16th to endDay
11121223380%
2340
July1st to 15thDay
3223435%46%6%56%
2340
16th to endDay
6%435%6%47%7%8%8%36%
2467
August1st to 15thDay
5%3145%36%5%6%7%49%
2340
16th to endDay
43235%245%7%6%54%
2342
September1st to 15thDay
5%314435%5%5%6%55%
1937
16th to endDay
22131233473%
1815
October1st to 15thDay
21221333472%
1758
16th to endDay
2112212236%73%
1760
November1st to 15thDay
22212345%72%
1657
16th to endDay
431211233471%
1620
December1st to 15thDay
36%13323347%58%
1620
16th to endDay
5%5%3441435%8%52%
1728
January1st to 15thNight
2213324345%64%
2327
16th to endNight
4324313445%61%
2496
February1st to 15thNight
1312412345%68%
2158
16th to endNight
231333445%6%60%
1895
March1st to 15thNight
221221345%6%67%
2007
16th to endNight
2112223346%68%
2112
April1st to 15thNight
221432334467%
1978
16th to endNight
11111236%78%
1635
May1st to 15thNight
21121232477%
1619
16th to endNight
11221122379%
1684
June1st to 15thNight
1111223380%
1620
16th to endNight
11123382%
1620
July1st to 15thNight
1133245%5%8%62%
1620
16th to endNight
22245%36%7%8%11%46%
1701
August1st to 15thNight
21242346%10%61%
1620
16th to endNight
22135%245%6%8%58%
1855
September1st to 15thNight
21134245%6%6%60%
1942
16th to endNight
1111123480%
1815
October1st to 15thNight
212212345%73%
1870
16th to endNight
121211335%74%
2112
November1st to 15thNight
121323335%72%
2199
16th to endNight
2212212236%72%
2340
December1st to 15thNight
23133245%46%63%
2340
16th to endNight
4425%42445%7%55%
2496

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
22%35%15%33%18%
1612
16th to endDay
25%37%17%29%15%
1728
February1st to 15thDay
24%46%19%24%21%
1694
16th to endDay
28%45%17%28%15%
1579
March1st to 15thDay
20%3416%35%19%
1951
16th to endDay
20%3418%34%17%
2112
April1st to 15thDay
20%3418%33%20%
1970
16th to endDay
13%2316%34%28%
2323
May1st to 15thDay
16%2316%32%27%
2331
16th to endDay
15%35%12%33%30%
2432
June1st to 15thDay
9%118%25%52%
2340
16th to endDay
10%12419%60%
2340
July1st to 15thDay
25%7%9%12%16%28%
2201
16th to endDay
37%9%15%15%14%7%
2312
August1st to 15thDay
30%5%8%17%19%19%
2325
16th to endDay
27%6%9%17%25%13%
2342
September1st to 15thDay
28%5%9%13%23%20%
1937
16th to endDay
14%4211%32%34%
1815
October1st to 15thDay
16%2415%29%31%
1758
16th to endDay
14%2412%34%31%
1760
November1st to 15thDay
15%3219%32%25%
1657
16th to endDay
17%3218%28%28%
1620
December1st to 15thDay
26%47%23%24%13%
1620
16th to endDay
29%47%21%26%9%
1728
January1st to 15thNight
22%4417%33%17%
2327
16th to endNight
25%35%16%30%18%
2496
February1st to 15thNight
19%36%19%27%23%
2169
16th to endNight
24%45%19%28%17%
1895
March1st to 15thNight
18%35%15%36%20%
2007
16th to endNight
17%36%18%32%19%
2112
April1st to 15thNight
21%25%13%35%21%
1978
16th to endNight
9%2315%35%32%
1635
May1st to 15thNight
13%2416%31%32%
1620
16th to endNight
11%1412%38%32%
1685
June1st to 15thNight
11%215%24%55%
1620
16th to endNight
9%11417%65%
1620
July1st to 15thNight
17%6%12%14%18%30%
1530
16th to endNight
24%9%18%18%20%8%
1593
August1st to 15thNight
17%5%10%20%24%21%
1611
16th to endNight
21%6%8%22%25%15%
1855
September1st to 15thNight
20%6%10%18%20%22%
1942
16th to endNight
9%3211%35%37%
1815
October1st to 15thNight
15%35%15%27%32%
1870
16th to endNight
13%35%11%28%38%
2112
November1st to 15thNight
16%2416%35%24%
2199
16th to endNight
15%2415%29%30%
2340
December1st to 15thNight
22%5%6%20%26%19%
2340
16th to endNight
28%48%20%27%9%
2496

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
12%11%27%36%8%3
90
16th to endDay
415%18%23%28%9%
96
February1st to 15thDay
5%10%27%29%20%6%
209
16th to endDay
10%27%28%20%9%3
238
March1st to 15thDay
419%30%25%14%6%
270
16th to endDay
424%30%23%12%4
288
April1st to 15thDay
8%22%31%21%9%6%
269
16th to endDay
231%33%18%10%2
270
May1st to 15thDay
417%36%28%9%4
288
16th to endDay
313%32%32%14%3
330
June1st to 15thDay
210%33%31%16%6%
315
16th to endDay
1220%45%22%8%
315
July1st to 15thDay
3120%42%23%8%
305
16th to endDay
7%110%39%26%15%
327
August1st to 15thDay
6%111%37%31%12%
315
16th to endDay
5%112%34%29%16%
332
September1st to 15thDay
4221%39%25%7%
300
16th to endDay
47%24%34%22%6%
255
October1st to 15thDay
311%29%28%22%6%
198
16th to endDay
45%18%29%35%7%
96
November1st to 15thDay
10%10%31%35%13%
90
16th to endDay
7%14%25%28%22%1
90
December1st to 15thDay
25%16%38%33%3
90
16th to endDay
7%12%21%35%20%2
96
January1st to 15thNight
46%17%37%25%8%
720
16th to endNight
5%6%19%38%26%4
768
February1st to 15thNight
35%17%42%27%3
704
16th to endNight
47%23%41%20%2
632
March1st to 15thNight
37%20%37%27%3
720
16th to endNight
26%19%39%28%3
768
April1st to 15thNight
36%27%37%22%2
719
16th to endNight
18%25%36%23%4
549
May1st to 15thNight
25%17%43%27%3
540
16th to endNight
2319%39%31%3
563
June1st to 15thNight
1116%43%33%3
540
16th to endNight
17%35%49%5%
540
July1st to 15thNight
1325%61%7%
510
16th to endNight
2217%61%14%
564
August1st to 15thNight
2220%60%12%
539
16th to endNight
3316%56%19%
672
September1st to 15thNight
3425%54%11%
706
16th to endNight
2113%30%43%8%
656
October1st to 15thNight
2316%37%35%4
660
16th to endNight
1312%33%37%10%
704
November1st to 15thNight
2117%39%32%6%
700
16th to endNight
25%18%34%31%7%
720
December1st to 15thNight
5%5%15%40%31%2
720
16th to endNight
6%7%18%40%22%4
768
Page generated at 2017-09-13 04:39:04. Version ac04

Copyright 2017 A. Danko


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