Black Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Mountain Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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%
15121
20%
47403
19%
15087
64%
15087
31%
28560

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
54%
716
12%
2506
12%
716
56%
716
18%
1737
January16th to endNight
53%
768
19%
2499
21%
768
55%
768
23%
1642
February1st to 15thNight
51%
698
12%
2288
13%
696
53%
696
19%
1600
February16th to endNight
53%
632
14%
1963
14%
632
55%
632
23%
1322
March1st to 15thNight
45%
720
10%
2025
9%
720
47%
720
19%
1488
March16th to endNight
46%
768
12%
2085
9%
768
47%
768
20%
1546
April1st to 15thNight
46%
719
11%
1799
6%
719
47%
719
23%
1315
April16th to endNight
57%
678
17%
1758
11%
678
58%
678
36%
1094
May1st to 15thNight
69%
453
17%
1533
15%
453
72%
453
38%
801
May16th to endNight
64%
375
15%
1496
18%
374
67%
374
26%
835
June1st to 15thNight
65%
360
16%
1440
23%
360
69%
360
28%
775
June16th to endNight
80%
360
26%
1440
39%
360
82%
360
53%
550
July1st to 15thNight
90%
340
28%
1360
41%
340
92%
340
56%
507
July16th to endNight
92%
457
36%
1491
41%
429
93%
429
67%
568
August1st to 15thNight
92%
538
35%
1611
32%
535
92%
535
69%
679
August16th to endNight
84%
707
42%
1853
30%
707
85%
707
74%
839
September1st to 15thNight
86%
720
42%
1800
28%
720
88%
720
83%
791
September16th to endNight
78%
716
33%
1974
29%
716
79%
716
55%
999
October1st to 15thNight
71%
720
24%
2160
24%
720
75%
720
47%
1113
October16th to endNight
69%
768
24%
2304
26%
768
71%
768
34%
1358
November1st to 15thNight
55%
700
13%
2290
15%
700
56%
700
19%
1598
November16th to endNight
51%
720
11%
2520
13%
720
53%
720
18%
1712
December1st to 15thNight
52%
720
14%
2520
14%
720
54%
720
19%
1704
December16th to endNight
42%
768
13%
2688
13%
768
44%
768
14%
1987

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
8%6%24424446%51%
48357
Night
10%6%24424446%49%
47582
TransparencyDay
32%6%12%20%18%8%
48036
Night
34%6%14%22%15%5%
47404
SeeingDay
12%11%22%25%18%8%
5967
Night
12%413%37%27%3
15132

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
14%8%26%5%36%5%7%11%28%
1432
16th to endDay
15%9%25%43345%8%36%
1725
February1st to 15thDay
11%7%36%5%36%6%8%9%29%
1576
16th to endDay
11%13%5%7%5%35%35%7%31%
1511
March1st to 15thDay
13%11%47%7%45%5%5%7%27%
1932
16th to endDay
15%9%37%5%36%5%6%8%29%
2138
April1st to 15thDay
11%9%48%8%45%5%5%7%30%
2149
16th to endDay
8%7%25%6%2445%7%45%
2200
May1st to 15thDay
7%5%2342345%7%53%
2415
16th to endDay
10%7%24424446%46%
2615
June1st to 15thDay
8%5%33323347%54%
2520
16th to endDay
4212212335%71%
2520
July1st to 15thDay
211111223477%
2520
16th to endDay
21121222280%
2574
August1st to 15thDay
11113435%76%
2340
16th to endDay
11111122483%
2348
September1st to 15thDay
1111235%80%
2160
16th to endDay
4213412345%64%
1984
October1st to 15thDay
6%42342445%6%55%
1800
16th to endDay
9%6%26%42445%7%44%
1918
November1st to 15thDay
13%7%46%5%35%4410%33%
1564
16th to endDay
13%10%36%6%36%6%5%8%29%
1440
December1st to 15thDay
16%9%345%45%6%7%7%30%
1440
16th to endDay
21%14%36%5%25%447%23%
1536
January1st to 15thNight
11%8%36%6%45%5%5%7%33%
2506
16th to endNight
14%9%35%42345%7%38%
2499
February1st to 15thNight
14%10%245%35%5%5%6%34%
2276
16th to endNight
10%10%45%5%35%5%47%36%
1963
March1st to 15thNight
14%10%45%5%45%46%7%31%
2025
16th to endNight
13%10%45%6%35%5%5%8%31%
2085
April1st to 15thNight
11%11%36%5%245%5%8%34%
1799
16th to endNight
11%6%1421335%8%50%
1758
May1st to 15thNight
6%31323446%6%56%
1533
16th to endNight
10%6%1331345%6%52%
1496
June1st to 15thNight
9%315%31445%5%54%
1440
16th to endNight
4211111135%75%
1440
July1st to 15thNight
111113345%75%
1440
16th to endNight
1111221383%
1593
August1st to 15thNight
111112235%78%
1620
16th to endNight
11111122382%
1853
September1st to 15thNight
111135%84%
1800
16th to endNight
4112323346%67%
1974
October1st to 15thNight
5%313312347%63%
2160
16th to endNight
8%5%144245%5%7%51%
2304
November1st to 15thNight
15%7%35%5%35%5%5%7%34%
2290
16th to endNight
16%8%35%5%35%45%7%36%
2520
December1st to 15thNight
15%8%36%434447%35%
2520
16th to endNight
19%12%36%5%3445%6%27%
2688

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
45%9%20%17%6%1
1432
16th to endDay
44%8%13%21%7%4
1725
February1st to 15thDay
44%11%17%19%6%
1576
16th to endDay
50%7%14%19%41
1511
March1st to 15thDay
53%8%14%15%7%
1932
16th to endDay
49%9%19%12%7%1
2138
April1st to 15thDay
53%7%13%17%7%
2149
16th to endDay
38%6%18%23%11%1
2200
May1st to 15thDay
30%5%15%26%17%3
2415
16th to endDay
37%7%15%25%11%2
2619
June1st to 15thDay
30%6%13%24%20%5%
2520
16th to endDay
16%38%32%27%10%
2520
July1st to 15thDay
12%36%24%31%22%
2371
16th to endDay
11%15%15%32%31%
2414
August1st to 15thDay
11%38%20%33%21%
2324
16th to endDay
7%25%21%40%22%
2348
September1st to 15thDay
7%35%19%34%29%
2160
16th to endDay
21%411%25%24%12%
1984
October1st to 15thDay
27%6%15%23%21%6%
1800
16th to endDay
36%8%13%18%18%3
1918
November1st to 15thDay
46%7%17%16%10%1
1564
16th to endDay
49%9%14%12%11%2
1440
December1st to 15thDay
48%8%15%17%9%
1440
16th to endDay
59%6%13%13%6%
1536
January1st to 15thNight
46%10%16%15%9%1
2506
16th to endNight
44%5%12%21%11%4
2499
February1st to 15thNight
47%8%14%18%9%1
2288
16th to endNight
44%6%19%19%7%1
1963
March1st to 15thNight
50%7%15%14%10%
2025
16th to endNight
48%9%18%16%6%
2085
April1st to 15thNight
47%7%20%17%5%1
1799
16th to endNight
32%6%23%26%8%2
1758
May1st to 15thNight
26%6%20%30%13%3
1534
16th to endNight
33%7%21%26%8%1
1496
June1st to 15thNight
30%7%15%32%12%2
1440
16th to endNight
14%312%44%21%3
1440
July1st to 15thNight
11%48%33%26%15%
1360
16th to endNight
10%2418%42%20%
1491
August1st to 15thNight
10%28%30%32%15%
1611
16th to endNight
9%27%27%37%17%
1853
September1st to 15thNight
5%15%23%37%25%
1800
16th to endNight
18%413%26%21%16%
1974
October1st to 15thNight
21%5%14%25%25%8%
2160
16th to endNight
30%7%16%21%17%6%
2304
November1st to 15thNight
48%8%17%15%8%2
2290
16th to endNight
47%7%14%15%12%2
2520
December1st to 15thNight
47%7%12%21%11%
2520
16th to endNight
55%7%11%17%6%
2688

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
25%8%15%46%31
60
16th to endDay
20%9%14%19%18%16%
253
February1st to 15thDay
20%12%15%25%20%5%
236
16th to endDay
21%13%22%22%14%4
227
March1st to 15thDay
28%15%17%21%11%5%
270
16th to endDay
23%21%23%18%12%
288
April1st to 15thDay
16%22%19%23%12%4
269
16th to endDay
17%19%27%20%11%3
270
May1st to 15thDay
14%20%26%21%12%4
288
16th to endDay
17%11%22%19%19%9%
330
June1st to 15thDay
11%15%26%26%14%4
315
16th to endDay
413%30%26%14%9%
315
July1st to 15thDay
6%7%27%31%17%10%
305
16th to endDay
26%33%28%22%7%
327
August1st to 15thDay
17%31%25%20%14%
315
16th to endDay
19%22%25%23%18%
332
September1st to 15thDay
25%20%26%28%15%
315
16th to endDay
6%9%20%26%30%7%
315
October1st to 15thDay
8%11%20%24%24%10%
315
16th to endDay
17%6%14%26%20%13%
336
November1st to 15thDay
12%411%33%32%4
102
16th to endDay
11%6%31%31%15%3
60
December1st to 15thDay
33%8%10%43%5%
60
16th to endDay
25%39%26%34%1
64
January1st to 15thNight
13%5%16%41%20%2
720
16th to endNight
18%313%34%24%5%
768
February1st to 15thNight
20%414%38%20%1
704
16th to endNight
14%6%16%43%16%1
632
March1st to 15thNight
17%9%18%33%18%2
720
16th to endNight
17%9%19%33%18%1
768
April1st to 15thNight
16%9%19%35%17%1
719
16th to endNight
14%418%35%22%3
678
May1st to 15thNight
7%114%46%27%1
454
16th to endNight
13%213%34%32%2
375
June1st to 15thNight
10%214%43%28%1
360
16th to endNight
5%111%45%36%
360
July1st to 15thNight
25%35%55%1
340
16th to endNight
338%52%4
457
August1st to 15thNight
2133%53%8%
538
16th to endNight
29%36%44%5%
707
September1st to 15thNight
119%33%45%7%
720
16th to endNight
4110%38%37%7%
716
October1st to 15thNight
6%114%43%30%3
720
16th to endNight
10%210%38%28%8%
768
November1st to 15thNight
16%214%43%19%4
700
16th to endNight
19%5%16%36%19%3
720
December1st to 15thNight
20%416%34%20%3
720
16th to endNight
24%7%17%34%14%1
768
Page generated at 2017-11-01 14:23:41. Version ac04

Copyright 2017 A. Danko


Black Mountain Observatory Clear Sky Chart |Charts Home