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 2018-02-13.

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
42%
16557
28%
48797
13%
16513
56%
16513
41%
25070

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
28%
949
32%
2693
10%
947
50%
947
49%
1225
January16th to endNight
29%
832
35%
2704
14%
832
54%
832
48%
1158
February1st to 15thNight
23%
748
27%
2429
7%
744
47%
744
39%
1144
February16th to endNight
26%
632
34%
1894
9%
632
53%
632
45%
924
March1st to 15thNight
32%
720
30%
2067
10%
720
49%
720
44%
1052
March16th to endNight
30%
708
28%
2052
9%
708
48%
708
40%
1072
April1st to 15thNight
35%
539
26%
1798
10%
539
54%
539
38%
869
April16th to endNight
31%
540
24%
1800
11%
540
49%
540
30%
984
May1st to 15thNight
39%
539
20%
1633
10%
539
51%
539
29%
966
May16th to endNight
48%
563
20%
1498
10%
561
58%
561
37%
880
June1st to 15thNight
56%
540
25%
1440
15%
540
63%
540
53%
729
June16th to endNight
67%
540
27%
1440
21%
540
72%
540
54%
733
July1st to 15thNight
71%
510
16%
1360
14%
510
72%
510
32%
858
July16th to endNight
71%
564
16%
1512
16%
531
72%
531
30%
941
August1st to 15thNight
70%
539
16%
1644
15%
536
72%
536
32%
963
August16th to endNight
69%
573
23%
1910
24%
573
72%
573
30%
1117
September1st to 15thNight
65%
540
25%
1800
22%
540
72%
540
33%
994
September16th to endNight
60%
571
33%
1939
23%
571
72%
571
43%
949
October1st to 15thNight
44%
720
32%
2160
15%
720
58%
720
48%
1072
October16th to endNight
46%
768
37%
2304
17%
768
62%
768
50%
1104
November1st to 15thNight
38%
932
34%
2452
13%
932
52%
932
54%
1205
November16th to endNight
36%
975
37%
2626
13%
975
54%
975
51%
1255
December1st to 15thNight
24%
975
26%
2730
5%
975
42%
975
42%
1343
December16th to endNight
27%
1040
28%
2912
8%
1040
45%
1040
37%
1533

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
45%25%5%35%5%5%8%50%
49251
Night
231332335%8%62%
48977
TransparencyDay
28%8%12%24%19%5%
48934
Night
19%6%16%29%21%5%
48797
SeeingDay
8%18%29%25%14%3
6249
Night
412%35%29%15%1
16565

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
1132145%6%9%62%
1585
16th to endDay
22433335%9%61%
1872
February1st to 15thDay
324435%46%8%58%
1696
16th to endDay
215%6%36%5%48%55%
1580
March1st to 15thDay
425%5%25%45%7%55%
1890
16th to endDay
26%24425%5%6%9%50%
2172
April1st to 15thDay
25%25%5%25%5%6%9%48%
2150
16th to endDay
39%37%6%35%5%5%7%41%
2160
May1st to 15thDay
6%9%36%6%36%5%6%7%37%
2316
16th to endDay
6%7%25%5%36%6%6%8%40%
2616
June1st to 15thDay
44245%35%5%6%8%49%
2520
16th to endDay
23245%35%5%6%7%52%
2520
July1st to 15thDay
9%6%27%7%46%5%5%6%37%
2520
16th to endDay
9%6%37%6%5%7%7%6%7%32%
2549
August1st to 15thDay
11%7%27%8%5%6%5%5%7%32%
2307
16th to endDay
8%5%26%7%46%6%6%8%37%
2292
September1st to 15thDay
8%5%26%6%3445%6%47%
2160
16th to endDay
45%245%23446%56%
2019
October1st to 15thDay
432342436%7%57%
1800
16th to endDay
2313324346%63%
1920
November1st to 15thDay
23212348%69%
1722
16th to endDay
212213247%70%
1661
December1st to 15thDay
215%422348%63%
1560
16th to endDay
131342437%12%56%
1664
January1st to 15thNight
111113348%71%
2693
16th to endNight
213112236%74%
2704
February1st to 15thNight
214223346%67%
2418
16th to endNight
22331345%9%64%
1894
March1st to 15thNight
312223348%66%
2067
16th to endNight
25%24223347%62%
2052
April1st to 15thNight
141232435%8%62%
1798
16th to endNight
47%23323335%57%
1800
May1st to 15thNight
7%7%343135%6%8%48%
1632
16th to endNight
5%5%1332446%9%51%
1497
June1st to 15thNight
221221235%10%64%
1440
16th to endNight
211232347%7%63%
1440
July1st to 15thNight
5%424425%7%6%10%45%
1440
16th to endNight
6%424436%6%7%9%44%
1616
August1st to 15thNight
6%5%24325%47%10%47%
1653
16th to endNight
5%4145%345%6%8%48%
1910
September1st to 15thNight
6%32442446%7%53%
1800
16th to endNight
4313323346%63%
1939
October1st to 15thNight
332213347%66%
2160
16th to endNight
131231235%5%67%
2304
November1st to 15thNight
211212347%72%
2452
16th to endNight
21211325%8%70%
2626
December1st to 15thNight
212312347%69%
2730
16th to endNight
314313349%64%
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
16%7%24%31%17%3
1586
16th to endDay
18%7%16%31%20%4
1872
February1st to 15thDay
20%9%20%31%13%4
1696
16th to endDay
22%9%13%28%21%4
1580
March1st to 15thDay
24%7%13%29%21%3
1890
16th to endDay
27%8%12%30%16%4
2172
April1st to 15thDay
28%9%13%26%17%4
2150
16th to endDay
36%8%12%23%17%2
2160
May1st to 15thDay
40%9%11%21%15%
2316
16th to endDay
36%10%13%21%14%3
2620
June1st to 15thDay
28%8%11%18%22%11%
2520
16th to endDay
25%7%7%21%26%11%
2520
July1st to 15thDay
41%11%10%14%12%8%
2371
16th to endDay
43%12%14%16%9%4
2391
August1st to 15thDay
45%11%11%11%12%6%
2292
16th to endDay
37%11%10%20%16%3
2292
September1st to 15thDay
33%8%11%16%20%9%
2160
16th to endDay
26%6%8%25%28%4
2019
October1st to 15thDay
23%6%8%25%29%7%
1800
16th to endDay
19%6%8%30%28%6%
1920
November1st to 15thDay
12%6%13%27%28%10%
1722
16th to endDay
13%411%33%27%8%
1661
December1st to 15thDay
18%6%19%33%18%4
1560
16th to endDay
18%9%20%27%19%4
1664
January1st to 15thNight
11%422%36%20%4
2693
16th to endNight
12%417%32%26%6%
2704
February1st to 15thNight
18%419%37%16%3
2429
16th to endNight
15%5%14%35%24%4
1894
March1st to 15thNight
17%6%13%34%23%3
2067
16th to endNight
21%5%14%35%19%2
2052
April1st to 15thNight
19%6%16%31%22%4
1798
16th to endNight
29%5%14%31%16%2
1800
May1st to 15thNight
32%7%15%28%15%1
1633
16th to endNight
27%7%17%28%16%3
1498
June1st to 15thNight
15%6%16%25%23%12%
1440
16th to endNight
16%6%12%24%27%13%
1440
July1st to 15thNight
30%11%17%18%14%7%
1360
16th to endNight
30%12%22%20%10%3
1512
August1st to 15thNight
28%11%20%18%14%6%
1644
16th to endNight
29%11%16%21%17%3
1910
September1st to 15thNight
28%7%16%20%17%8%
1800
16th to endNight
21%5%12%30%26%3
1939
October1st to 15thNight
17%5%11%28%27%9%
2160
16th to endNight
16%411%30%31%5%
2304
November1st to 15thNight
12%5%12%28%30%9%
2452
16th to endNight
12%412%36%26%6%
2626
December1st to 15thNight
15%5%23%30%22%3
2730
16th to endNight
18%7%19%29%20%4
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
231%28%25%10%1
135
16th to endDay
121%39%31%41
144
February1st to 15thDay
7%40%30%18%3
126
16th to endDay
38%32%14%14%
81
March1st to 15thDay
5%30%36%23%3
180
16th to endDay
8%36%38%13%2
288
April1st to 15thDay
6%33%33%18%6%1
269
16th to endDay
14%35%31%13%4
270
May1st to 15thDay
8%22%35%21%9%1
366
16th to endDay
10%14%29%27%13%4
517
June1st to 15thDay
5%15%27%27%20%4
495
16th to endDay
38%25%32%24%6%
495
July1st to 15thDay
9%421%28%25%9%
475
16th to endDay
12%21%32%24%8%
408
August1st to 15thDay
15%5%28%30%15%4
315
16th to endDay
14%6%23%31%19%3
332
September1st to 15thDay
13%10%31%26%13%4
315
16th to endDay
8%17%35%25%8%5%
210
October1st to 15thDay
222%25%22%21%4
135
16th to endDay
7%20%22%26%20%2
144
November1st to 15thDay
224%24%28%17%2
135
16th to endDay
5%32%38%20%2
135
December1st to 15thDay
435%40%14%5%
135
16th to endDay
129%42%20%41
144
January1st to 15thNight
122%44%22%7%1
952
16th to endNight
218%46%25%6%
832
February1st to 15thNight
119%51%22%5%
752
16th to endNight
17%51%26%4
632
March1st to 15thNight
214%45%28%7%
720
16th to endNight
414%46%28%5%
708
April1st to 15thNight
313%44%30%6%
539
16th to endNight
8%15%40%26%8%
540
May1st to 15thNight
10%8%35%30%12%1
540
16th to endNight
9%6%29%31%18%2
563
June1st to 15thNight
35%29%38%21%1
540
16th to endNight
2221%40%30%2
540
July1st to 15thNight
7%8%32%44%5%
510
16th to endNight
7%17%27%50%5%
564
August1st to 15thNight
8%110%34%42%3
539
16th to endNight
7%10%34%40%5%
573
September1st to 15thNight
8%115%39%28%6%
540
16th to endNight
5%424%37%25%2
571
October1st to 15thNight
5%7%39%30%15%2
720
16th to endNight
49%35%33%14%2
768
November1st to 15thNight
114%41%31%10%
932
16th to endNight
218%39%31%6%1
975
December1st to 15thNight
123%46%23%5%
975
16th to endNight
122%43%24%6%
1040
Page generated at 2018-02-13 18:46:09. Version ac04

Copyright 2018 A. Danko


Black Mountain Observatory Clear Sky Chart |Charts Home