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Dark Ranger Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dark Ranger Observatory clear sky chart from 2005-11-05 to 2020-06-03.

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
62%
19183
31%
57842
23%
19146
70%
19146
48%
28238

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
57%
896
30%
2912
25%
896
67%
896
47%
1399
January16th to endNight
58%
960
33%
3120
28%
960
68%
960
45%
1519
February1st to 15thNight
54%
880
28%
2817
22%
880
64%
880
43%
1390
February16th to endNight
51%
792
33%
2375
24%
792
63%
792
43%
1223
March1st to 15thNight
53%
900
29%
2513
20%
900
63%
900
47%
1324
March16th to endNight
52%
960
30%
2640
16%
960
63%
960
47%
1384
April1st to 15thNight
45%
854
27%
2409
12%
854
56%
854
46%
1210
April16th to endNight
47%
669
35%
2007
18%
669
61%
669
44%
958
May1st to 15thNight
57%
675
32%
2024
22%
674
65%
674
52%
947
May16th to endNight
57%
705
29%
2117
20%
705
65%
705
48%
1025
June1st to 15thNight
68%
637
30%
1911
26%
637
72%
637
61%
827
June16th to endNight
73%
630
29%
1890
27%
630
76%
630
66%
799
July1st to 15thNight
78%
600
22%
1800
20%
600
79%
600
43%
941
July16th to endNight
80%
660
20%
1881
19%
627
80%
627
36%
1051
August1st to 15thNight
79%
620
28%
1854
23%
617
79%
617
44%
956
August16th to endNight
81%
693
36%
2062
31%
693
83%
693
53%
986
September1st to 15thNight
77%
840
32%
2310
26%
840
80%
840
52%
1216
September16th to endNight
74%
836
41%
2310
29%
836
81%
836
66%
1046
October1st to 15thNight
64%
840
35%
2418
24%
840
72%
840
54%
1182
October16th to endNight
65%
896
40%
2688
28%
896
78%
896
57%
1212
November1st to 15thNight
65%
880
36%
2814
30%
880
75%
880
56%
1238
November16th to endNight
62%
900
37%
2925
31%
900
73%
900
51%
1306
December1st to 15thNight
57%
900
28%
2925
22%
900
66%
900
43%
1444
December16th to endNight
51%
960
28%
3120
20%
960
62%
960
36%
1655

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
342442445%7%56%
58569
Night
231332335%7%62%
58037
TransparencyDay
25%49%21%24%14%
58264
Night
19%411%24%27%13%
57843
SeeingDay
7%12%28%29%16%5%
8937
Night
46%21%35%25%6%
19193

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
14133235%6%7%59%
2016
16th to endDay
25%1332435%7%59%
2160
February1st to 15thDay
15%1432346%9%57%
2032
16th to endDay
26%3442346%6%54%
1979
March1st to 15thDay
25%2442445%8%55%
2436
16th to endDay
26%35%42446%8%51%
2640
April1st to 15thDay
25%1443445%8%53%
2525
16th to endDay
4425%5%34346%55%
2888
May1st to 15thDay
35%14425%5%5%7%52%
2916
16th to endDay
45%24425%46%8%50%
3053
June1st to 15thDay
1213323346%66%
2758
16th to endDay
211331223472%
2730
July1st to 15thDay
5%426%6%46%6%6%6%45%
2730
16th to endDay
8%5%36%7%47%7%6%6%35%
2883
August1st to 15thDay
5%426%6%36%6%5%6%45%
2680
16th to endDay
4325%5%45%5%6%7%49%
2840
September1st to 15thDay
7%5%25%5%345%5%450%
2310
16th to endDay
321332334468%
2310
October1st to 15thDay
5%31322234464%
2202
16th to endDay
3312322335%69%
2240
November1st to 15thDay
123213235%71%
2031
16th to endDay
2313313348%64%
2025
December1st to 15thDay
15%15%5%2345%8%56%
2025
16th to endDay
36%3441345%9%53%
2160
January1st to 15thNight
141332345%7%62%
2912
16th to endNight
241432345%8%58%
3120
February1st to 15thNight
1423323447%62%
2806
16th to endNight
1424425%45%8%56%
2375
March1st to 15thNight
25%2332347%9%55%
2513
16th to endNight
132432436%8%59%
2640
April1st to 15thNight
2313224449%61%
2409
16th to endNight
221242435%8%63%
2007
May1st to 15thNight
221331336%7%64%
2024
16th to endNight
221332335%7%62%
2116
June1st to 15thNight
1112213347%70%
1911
16th to endNight
11111323476%
1890
July1st to 15thNight
2324325%5%6%8%55%
1890
16th to endNight
23235%36%6%10%10%44%
1989
August1st to 15thNight
23145%3346%8%56%
1863
16th to endNight
22232446%8%60%
2062
September1st to 15thNight
5%213323447%61%
2310
16th to endNight
121121123477%
2310
October1st to 15thNight
432213345%68%
2418
16th to endNight
2212312235%71%
2688
November1st to 15thNight
1212213346%69%
2814
16th to endNight
2312212247%67%
2925
December1st to 15thNight
25%23313448%59%
2925
16th to endNight
36%2442435%9%53%
3120

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
20%7%15%32%22%2
2017
16th to endDay
22%415%30%21%6%
2160
February1st to 15thDay
22%416%27%21%6%
2032
16th to endDay
26%5%13%23%27%4
1979
March1st to 15thDay
24%411%30%24%4
2436
16th to endDay
27%412%27%23%4
2640
April1st to 15thDay
24%410%25%26%7%
2525
16th to endDay
27%38%25%26%8%
2888
May1st to 15thDay
27%48%21%28%8%
2916
16th to endDay
28%5%8%18%29%9%
3056
June1st to 15thDay
18%15%13%31%29%
2758
16th to endDay
15%128%25%46%
2730
July1st to 15thDay
33%6%7%12%14%25%
2591
16th to endDay
38%8%12%15%11%12%
2728
August1st to 15thDay
33%6%9%13%16%21%
2665
16th to endDay
28%5%8%16%22%19%
2840
September1st to 15thDay
33%5%6%11%18%26%
2310
16th to endDay
18%25%18%30%24%
2310
October1st to 15thDay
21%35%17%31%21%
2202
16th to endDay
17%27%21%34%15%
2240
November1st to 15thDay
14%29%25%32%14%
2031
16th to endDay
17%49%30%27%10%
2025
December1st to 15thDay
25%415%28%20%5%
2025
16th to endDay
26%6%18%25%19%3
2160
January1st to 15thNight
19%416%31%25%3
2912
16th to endNight
20%413%30%22%6%
3120
February1st to 15thNight
20%5%14%27%22%9%
2817
16th to endNight
22%411%25%29%6%
2375
March1st to 15thNight
21%412%30%25%5%
2513
16th to endNight
20%412%32%24%5%
2640
April1st to 15thNight
19%411%28%28%8%
2409
16th to endNight
18%38%32%31%5%
2007
May1st to 15thNight
17%310%26%33%8%
2025
16th to endNight
18%49%22%35%9%
2117
June1st to 15thNight
13%25%12%36%30%
1911
16th to endNight
11%147%25%48%
1890
July1st to 15thNight
21%7%10%13%18%27%
1800
16th to endNight
26%8%15%22%11%15%
1881
August1st to 15thNight
23%5%11%16%20%22%
1854
16th to endNight
17%49%18%26%23%
2062
September1st to 15thNight
21%39%16%21%27%
2310
16th to endNight
12%26%19%34%25%
2310
October1st to 15thNight
18%26%18%32%20%
2418
16th to endNight
14%27%22%38%14%
2688
November1st to 15thNight
15%310%27%31%12%
2814
16th to endNight
16%39%27%32%10%
2925
December1st to 15thNight
21%416%30%20%5%
2925
16th to endNight
27%417%25%20%3
3120

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
6%11%32%28%14%7%
225
16th to endDay
6%10%19%36%20%6%
240
February1st to 15thDay
7%14%29%26%15%6%
277
16th to endDay
5%20%34%28%11%1
398
March1st to 15thDay
7%17%34%26%11%2
450
16th to endDay
7%22%36%22%8%2
480
April1st to 15thDay
9%23%33%22%8%3
449
16th to endDay
8%24%31%22%10%2
438
May1st to 15thDay
6%19%31%27%11%4
468
16th to endDay
13%14%31%22%15%3
522
June1st to 15thDay
312%31%32%15%4
444
16th to endDay
35%31%36%16%5%
435
July1st to 15thDay
6%218%37%22%11%
425
16th to endDay
8%215%37%26%9%
455
August1st to 15thDay
6%121%39%22%8%
419
16th to endDay
8%222%32%26%9%
460
September1st to 15thDay
8%6%24%31%19%9%
435
16th to endDay
6%12%27%28%18%5%
435
October1st to 15thDay
10%16%33%24%10%5%
327
16th to endDay
9%13%28%26%17%4
240
November1st to 15thDay
29%25%29%24%8%
225
16th to endDay
6%18%22%27%19%6%
225
December1st to 15thDay
38%24%41%16%5%
225
16th to endDay
7%10%28%32%16%5%
240
January1st to 15thNight
46%28%32%20%8%
900
16th to endNight
5%6%24%37%21%5%
960
February1st to 15thNight
48%26%37%17%4
884
16th to endNight
5%8%30%39%14%2
792
March1st to 15thNight
5%7%29%38%18%2
900
16th to endNight
311%27%36%18%3
960
April1st to 15thNight
413%32%29%15%3
854
16th to endNight
415%28%30%17%2
669
May1st to 15thNight
46%26%38%21%2
675
16th to endNight
48%24%34%23%3
707
June1st to 15thNight
2420%42%27%2
637
16th to endNight
1218%41%32%3
630
July1st to 15thNight
46%36%43%8%
600
16th to endNight
5%328%53%8%
660
August1st to 15thNight
4435%49%5%
620
16th to endNight
36%34%42%11%
693
September1st to 15thNight
6%8%31%41%11%
840
16th to endNight
3215%33%32%12%
836
October1st to 15thNight
5%421%42%18%7%
840
16th to endNight
36%19%33%27%9%
896
November1st to 15thNight
2423%36%26%6%
880
16th to endNight
5%8%19%34%24%8%
900
December1st to 15thNight
6%6%24%38%18%4
900
16th to endNight
6%9%26%35%18%2
960
Page generated at 2020-06-04 01:18:52. Version ac04

Copyright 2020 A. Danko


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