Black Range Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Range Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
59%
15244
33%
46905
23%
15201
70%
15201
45%
23187

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%
717
32%
2327
26%
716
68%
716
43%
1126
January16th to endNight
51%
768
37%
2496
26%
768
69%
768
42%
1217
February1st to 15thNight
52%
700
35%
2248
23%
696
70%
696
49%
1019
February16th to endNight
40%
632
41%
1822
20%
632
62%
632
45%
894
March1st to 15thNight
46%
720
39%
1980
19%
720
63%
720
49%
977
March16th to endNight
48%
768
38%
2112
16%
768
65%
768
54%
1000
April1st to 15thNight
39%
566
36%
1825
14%
566
65%
566
46%
801
April16th to endNight
38%
540
42%
1800
19%
540
69%
540
54%
704
May1st to 15thNight
44%
539
31%
1790
19%
539
62%
539
51%
763
May16th to endNight
48%
563
35%
1684
18%
561
65%
561
53%
787
June1st to 15thNight
60%
540
28%
1620
20%
540
68%
540
53%
758
June16th to endNight
68%
540
22%
1620
18%
540
71%
540
44%
837
July1st to 15thNight
73%
510
18%
1530
15%
510
75%
510
33%
906
July16th to endNight
74%
564
16%
1593
15%
531
74%
531
29%
1017
August1st to 15thNight
78%
539
18%
1679
20%
536
78%
536
30%
1040
August16th to endNight
76%
573
21%
1910
24%
573
77%
573
27%
1182
September1st to 15thNight
74%
540
23%
1800
25%
540
75%
540
31%
1058
September16th to endNight
74%
653
36%
1898
28%
653
80%
653
52%
955
October1st to 15thNight
68%
660
36%
1980
26%
660
75%
660
54%
927
October16th to endNight
74%
704
42%
2112
30%
704
83%
704
65%
899
November1st to 15thNight
68%
700
43%
2100
29%
700
78%
700
64%
891
November16th to endNight
60%
720
42%
2160
30%
720
71%
720
48%
1049
December1st to 15thNight
57%
720
37%
2323
27%
720
70%
720
45%
1111
December16th to endNight
49%
768
34%
2496
26%
768
60%
768
40%
1269

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
431342445%7%58%
47965
Night
321332345%7%62%
47112
TransparencyDay
23%47%15%26%22%
47661
Night
20%47%17%28%21%
46917
SeeingDay
9%12%26%29%17%4
5159
Night
5%7%22%32%26%5%
15252

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
35%2331343463%
1611
16th to endDay
7%433212246%60%
1728
February1st to 15thDay
3212413245%67%
1603
16th to endDay
2412213445%66%
1650
March1st to 15thDay
3313322346%63%
1980
16th to endDay
2212212346%69%
2112
April1st to 15thDay
2213323336%68%
2123
16th to endDay
1111213345%74%
2160
May1st to 15thDay
11231335%6%68%
2157
16th to endDay
3112223345%70%
2429
June1st to 15thDay
2212313447%66%
2340
16th to endDay
22134245%6%7%57%
2340
July1st to 15thDay
6%426%7%47%6%9%10%34%
2340
16th to endDay
8%6%36%9%48%8%8%10%26%
2467
August1st to 15thDay
6%325%7%48%7%9%9%33%
2271
16th to endDay
6%5%27%6%46%7%7%8%37%
2292
September1st to 15thDay
8%5%36%5%35%6%6%8%39%
2160
16th to endDay
5%21233446%6%58%
1870
October1st to 15thDay
4112324445%65%
1650
16th to endDay
222222235%73%
1760
November1st to 15thDay
2212222236%72%
1759
16th to endDay
3314322245%65%
1800
December1st to 15thDay
5%312212446%63%
1635
16th to endDay
45%13313347%58%
1728
January1st to 15thNight
4312323345%64%
2327
16th to endNight
6%413313346%62%
2496
February1st to 15thNight
2213213446%67%
2248
16th to endNight
2312413335%68%
1822
March1st to 15thNight
221331335%5%67%
1980
16th to endNight
221221323374%
2112
April1st to 15thNight
3212213345%69%
1825
16th to endNight
11111224477%
1800
May1st to 15thNight
312213435%70%
1790
16th to endNight
3212212336%70%
1684
June1st to 15thNight
2212313346%67%
1620
16th to endNight
2222435%6%6%9%55%
1620
July1st to 15thNight
5%2245%47%7%9%13%37%
1620
16th to endNight
35%25%5%47%7%8%14%34%
1701
August1st to 15thNight
3425%6%36%8%9%13%36%
1688
16th to endNight
43246%48%8%8%11%37%
1910
September1st to 15thNight
6%325%435%6%7%10%43%
1800
16th to endNight
42232235%5%66%
1898
October1st to 15thNight
311231335%5%68%
1980
16th to endNight
111212235%77%
2112
November1st to 15thNight
112212226%75%
2100
16th to endNight
4213212335%67%
2160
December1st to 15thNight
5%31221245%7%62%
2323
16th to endNight
45%13323446%59%
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%25%15%34%20%
1612
16th to endDay
23%2318%32%19%
1728
February1st to 15thDay
18%26%16%28%27%
1604
16th to endDay
18%2316%35%23%
1650
March1st to 15thDay
21%2413%32%25%
1980
16th to endDay
16%1413%36%27%
2112
April1st to 15thDay
17%2313%36%26%
2123
16th to endDay
11%2211%33%38%
2160
May1st to 15thDay
15%25%14%29%32%
2157
16th to endDay
15%35%11%28%35%
2432
June1st to 15thDay
16%3311%23%41%
2340
16th to endDay
22%47%14%18%32%
2340
July1st to 15thDay
36%8%13%16%12%11%
2201
16th to endDay
44%11%18%18%6%1
2312
August1st to 15thDay
38%9%16%19%13%2
2256
16th to endDay
37%9%14%16%15%6%
2292
September1st to 15thDay
36%5%12%19%17%8%
2160
16th to endDay
21%45%18%34%16%
1870
October1st to 15thDay
19%37%14%30%24%
1650
16th to endDay
15%2315%33%29%
1760
November1st to 15thDay
14%2418%32%27%
1759
16th to endDay
21%2315%34%22%
1800
December1st to 15thDay
20%36%20%31%16%
1635
16th to endDay
24%38%22%30%10%
1728
January1st to 15thNight
22%36%15%35%17%
2327
16th to endNight
22%2318%35%17%
2496
February1st to 15thNight
17%25%19%29%25%
2258
16th to endNight
18%2318%34%22%
1822
March1st to 15thNight
17%35%16%33%24%
1980
16th to endNight
15%1314%37%27%
2112
April1st to 15thNight
16%2415%38%22%
1825
16th to endNight
11%1313%34%35%
1800
May1st to 15thNight
14%35%10%32%33%
1791
16th to endNight
16%3413%25%36%
1685
June1st to 15thNight
17%25%10%23%39%
1620
16th to endNight
22%49%12%18%31%
1620
July1st to 15thNight
30%9%16%20%13%10%
1530
16th to endNight
34%10%23%23%6%1
1593
August1st to 15thNight
33%10%18%21%12%4
1679
16th to endNight
33%11%16%18%14%5%
1910
September1st to 15thNight
31%8%15%19%14%10%
1800
16th to endNight
19%46%19%34%16%
1898
October1st to 15thNight
17%39%15%31%23%
1980
16th to endNight
11%2319%30%33%
2112
November1st to 15thNight
12%1419%36%26%
2100
16th to endNight
20%2316%29%28%
2160
December1st to 15thNight
21%26%21%30%18%
2323
16th to endNight
25%39%20%28%12%
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
20%16%30%20%11%2
90
16th to endDay
14%16%30%20%11%6%
96
February1st to 15thDay
10%8%20%34%22%4
90
16th to endDay
15%31%21%19%10%1
151
March1st to 15thDay
11%21%38%19%7%2
270
16th to endDay
9%28%35%18%7%1
288
April1st to 15thDay
10%26%36%19%41
269
16th to endDay
12%30%37%16%12
270
May1st to 15thDay
5%30%36%23%31
288
16th to endDay
5%16%44%24%7%
330
June1st to 15thDay
6%7%36%33%13%2
315
16th to endDay
4322%40%26%3
315
July1st to 15thDay
8%10%42%31%6%
305
16th to endDay
11%7%30%37%13%
327
August1st to 15thDay
6%19%33%37%12%
315
16th to endDay
8%110%35%32%11%
332
September1st to 15thDay
13%215%41%21%5%
315
16th to endDay
5%432%40%14%3
241
October1st to 15thDay
11%6%24%31%18%7%
90
16th to endDay
12%122%35%22%5%
96
November1st to 15thDay
13%13%28%24%17%2
90
16th to endDay
16%13%31%30%8%
90
December1st to 15thDay
6%10%34%24%20%4
90
16th to endDay
25%15%22%30%42
96
January1st to 15thNight
6%9%23%33%21%6%
720
16th to endNight
10%9%24%32%19%3
768
February1st to 15thNight
311%28%31%20%4
704
16th to endNight
419%34%30%11%
632
March1st to 15thNight
315%30%30%17%3
720
16th to endNight
413%31%34%14%1
768
April1st to 15thNight
416%36%30%10%1
566
16th to endNight
217%39%28%10%1
540
May1st to 15thNight
311%38%35%11%
540
16th to endNight
45%36%36%15%1
563
June1st to 15thNight
3327%43%20%1
540
16th to endNight
3217%37%35%2
540
July1st to 15thNight
6%6%28%47%11%
510
16th to endNight
5%15%19%52%16%
564
August1st to 15thNight
4221%54%16%
539
16th to endNight
5%5%22%52%13%
573
September1st to 15thNight
7%6%28%49%7%
540
16th to endNight
6%111%36%35%7%
653
October1st to 15thNight
3419%40%25%6%
660
16th to endNight
3316%39%28%8%
704
November1st to 15thNight
26%20%34%29%8%
700
16th to endNight
7%8%19%30%25%9%
720
December1st to 15thNight
6%10%20%32%23%5%
720
16th to endNight
8%9%28%33%16%4
768
Page generated at 2017-09-23 04:43:47. Version ac04

Copyright 2017 A. Danko


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