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 2017-10-16.

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%
16008
28%
47215
13%
15964
56%
15964
41%
24429

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%
876
32%
2485
10%
874
49%
874
48%
1141
January16th to endNight
27%
768
34%
2496
13%
768
53%
768
47%
1083
February1st to 15thNight
24%
700
28%
2273
7%
696
48%
696
38%
1088
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%
708
35%
2124
16%
708
61%
708
49%
1029
November1st to 15thNight
39%
858
34%
2258
13%
858
53%
858
53%
1123
November16th to endNight
36%
900
36%
2424
13%
900
53%
900
51%
1167
December1st to 15thNight
23%
900
25%
2520
5%
900
41%
900
41%
1256
December16th to endNight
27%
960
26%
2688
7%
960
44%
960
37%
1439

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%49%
48213
Night
231332335%8%61%
47395
TransparencyDay
29%8%12%23%19%5%
47896
Night
20%6%16%29%21%5%
47215
SeeingDay
8%17%29%25%14%3
5892
Night
412%35%29%16%1
16016

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
1132245%6%9%61%
1462
16th to endDay
22433345%9%60%
1728
February1st to 15thDay
325%435%46%8%56%
1588
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
332432435%6%62%
1768
November1st to 15thDay
23212348%67%
1587
16th to endDay
213213247%69%
1533
December1st to 15thDay
215%42235%8%61%
1440
16th to endDay
131342447%13%54%
1536
January1st to 15thNight
111113348%70%
2485
16th to endNight
213212246%72%
2496
February1st to 15thNight
224223346%66%
2262
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
131331235%5%66%
2124
November1st to 15thNight
211212348%71%
2258
16th to endNight
21221325%8%70%
2424
December1st to 15thNight
212422347%67%
2520
16th to endNight
31431335%9%62%
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
16%7%24%32%16%3
1463
16th to endDay
19%7%16%31%19%5%
1728
February1st to 15thDay
21%9%19%30%14%4
1588
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
20%6%8%29%29%5%
1768
November1st to 15thDay
13%6%14%27%26%11%
1587
16th to endDay
14%411%33%27%8%
1533
December1st to 15thDay
20%6%19%33%17%2
1440
16th to endDay
19%10%21%26%16%4
1536
January1st to 15thNight
11%423%35%19%4
2485
16th to endNight
12%417%32%24%6%
2496
February1st to 15thNight
19%5%17%37%17%3
2273
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%30%5%
2124
November1st to 15thNight
12%6%13%28%28%10%
2258
16th to endNight
13%412%36%26%7%
2424
December1st to 15thNight
16%5%24%31%20%2
2520
16th to endNight
19%8%20%29%18%3
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
426%28%23%14%2
90
16th to endDay
221%40%31%4
96
February1st to 15thDay
8%35%35%15%4
90
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
10%15%22%28%23%1
99
November1st to 15thDay
220%22%27%24%3
90
16th to endDay
428%44%17%4
90
December1st to 15thDay
6%34%44%12%2
90
16th to endDay
119%53%20%32
96
January1st to 15thNight
122%44%22%8%1
879
16th to endNight
118%48%23%6%1
768
February1st to 15thNight
118%51%22%6%
704
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%13%2
708
November1st to 15thNight
113%41%31%10%1
858
16th to endNight
218%40%30%6%1
900
December1st to 15thNight
123%46%22%5%
900
16th to endNight
120%45%24%7%
960
Page generated at 2017-10-17 14:35:24. Version ac04

Copyright 2017 A. Danko


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