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 2017-09-22.

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
46%
15526
22%
46989
14%
15484
54%
15484
25%
29432

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
27%
720
22%
2327
9%
716
43%
716
17%
1483
January16th to endNight
23%
768
23%
2473
9%
768
40%
768
20%
1560
February1st to 15thNight
28%
703
25%
2111
9%
701
44%
701
23%
1281
February16th to endNight
22%
631
23%
1893
8%
631
36%
631
20%
1204
March1st to 15thNight
28%
720
23%
2058
10%
720
40%
720
23%
1327
March16th to endNight
35%
768
19%
2112
10%
768
42%
768
27%
1354
April1st to 15thNight
39%
644
24%
1902
14%
644
50%
644
31%
1101
April16th to endNight
49%
540
24%
1683
16%
540
57%
540
28%
1004
May1st to 15thNight
49%
540
18%
1620
10%
540
55%
540
26%
1026
May16th to endNight
61%
561
19%
1683
13%
561
64%
561
29%
1041
June1st to 15thNight
64%
540
13%
1620
11%
540
67%
540
27%
1049
June16th to endNight
74%
540
16%
1620
12%
540
76%
540
32%
1000
July1st to 15thNight
68%
510
12%
1530
10%
510
68%
510
26%
1026
July16th to endNight
74%
564
15%
1595
13%
531
76%
531
27%
1045
August1st to 15thNight
67%
539
16%
1609
15%
536
68%
536
26%
1069
August16th to endNight
66%
573
18%
1909
19%
573
68%
573
22%
1270
September1st to 15thNight
60%
708
17%
1968
16%
708
62%
708
26%
1332
September16th to endNight
58%
685
24%
1892
18%
685
63%
685
30%
1215
October1st to 15thNight
50%
660
33%
1834
24%
660
59%
660
35%
1084
October16th to endNight
49%
704
32%
2112
23%
704
62%
704
34%
1189
November1st to 15thNight
48%
700
30%
2262
25%
700
59%
700
33%
1221
November16th to endNight
35%
720
25%
2340
15%
720
49%
720
24%
1398
December1st to 15thNight
34%
720
22%
2340
14%
720
45%
720
20%
1477
December16th to endNight
27%
768
19%
2496
11%
768
39%
768
16%
1676

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
14%5%245%35%5%6%7%39%
47885
Night
13%42442445%7%45%
47188
TransparencyDay
42%7%11%18%16%4
47586
Night
37%6%12%19%18%5%
46991
SeeingDay
18%7%18%22%19%13%
5399
Night
17%10%20%26%20%4
15529

By Month

Percentage Cloud Cover SE (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
20%6%24423345%43%
1611
16th to endDay
18%42442344446%
1749
February1st to 15thDay
18%5%2332345%7%43%
1750
16th to endDay
19%42333435%7%42%
1580
March1st to 15thDay
18%425%424447%41%
1902
16th to endDay
17%424424447%41%
2111
April1st to 15thDay
13%4145%345%7%6%43%
2055
16th to endDay
13%4145%2445%6%45%
2274
May1st to 15thDay
12%425%436%5%5%7%41%
2331
16th to endDay
12%425%7%35%6%6%9%37%
2431
June1st to 15thDay
9%5%16%7%5%6%7%7%10%31%
2340
16th to endDay
5%3146%5%7%7%8%11%38%
2340
July1st to 15thDay
11%426%9%48%7%8%10%25%
2340
16th to endDay
7%5%25%8%6%8%8%9%9%27%
2465
August1st to 15thDay
11%425%6%48%8%8%10%29%
2338
16th to endDay
14%6%36%6%47%6%7%9%26%
2290
September1st to 15thDay
13%5%26%5%36%5%6%7%34%
1980
16th to endDay
17%424425%5%5%7%40%
1881
October1st to 15thDay
13%42332334455%
1796
16th to endDay
13%31332133359%
1760
November1st to 15thDay
14%322222246%55%
1593
16th to endDay
17%5%24323345%47%
1620
December1st to 15thDay
20%6%2432335%6%40%
1620
16th to endDay
26%6%2332344338%
1728
January1st to 15thNight
20%42431435%5%43%
2327
16th to endNight
17%6%24424345%44%
2473
February1st to 15thNight
15%323424445%49%
2103
16th to endNight
16%425%43445%5%44%
1893
March1st to 15thNight
15%6%14324445%46%
2058
16th to endNight
13%425%5%23445%47%
2112
April1st to 15thNight
14%21332345%6%52%
1902
16th to endNight
11%415%32345%7%49%
1683
May1st to 15thNight
12%5%145%245%5%8%43%
1619
16th to endNight
10%4135%3446%9%46%
1682
June1st to 15thNight
8%4246%35%7%8%10%39%
1620
16th to endNight
5%2135%36%6%8%11%44%
1620
July1st to 15thNight
8%425%6%37%6%8%11%36%
1620
16th to endNight
5%424437%8%8%11%39%
1703
August1st to 15thNight
11%5%25%5%26%46%10%39%
1620
16th to endNight
12%6%25%5%25%6%7%10%35%
1909
September1st to 15thNight
11%5%25%6%345%6%9%39%
1968
16th to endNight
14%4144235%47%46%
1892
October1st to 15thNight
14%313312235%55%
1834
16th to endNight
11%314423335%58%
2112
November1st to 15thNight
12%422312236%57%
2262
16th to endNight
17%413313445%49%
2340
December1st to 15thNight
17%5%25%42445%5%42%
2340
16th to endNight
23%6%25%323346%36%
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
44%37%16%21%5%
1612
16th to endDay
40%47%20%19%7%
1749
February1st to 15thDay
40%310%18%22%3
1752
16th to endDay
42%38%21%18%5%
1580
March1st to 15thDay
43%5%8%17%19%6%
1902
16th to endDay
42%6%12%19%15%3
2112
April1st to 15thDay
38%5%11%21%17%4
2055
16th to endDay
38%6%10%19%20%5%
2274
May1st to 15thDay
41%7%12%19%15%2
2331
16th to endDay
42%9%14%18%12%2
2435
June1st to 15thDay
45%10%18%19%5%1
2340
16th to endDay
36%11%17%20%12%2
2340
July1st to 15thDay
47%12%17%15%5%1
2201
16th to endDay
46%12%16%15%7%1
2310
August1st to 15thDay
43%12%15%18%7%1
2325
16th to endDay
50%11%14%15%6%
2290
September1st to 15thDay
46%9%13%15%12%3
1980
16th to endDay
41%6%11%17%20%3
1881
October1st to 15thDay
33%410%16%26%8%
1796
16th to endDay
30%35%20%29%11%
1760
November1st to 15thDay
31%36%16%31%11%
1593
16th to endDay
38%46%16%25%7%
1620
December1st to 15thDay
45%49%16%17%7%
1620
16th to endDay
49%48%16%15%6%
1728
January1st to 15thNight
42%48%17%21%6%
2327
16th to endNight
42%38%17%21%6%
2473
February1st to 15thNight
36%49%19%22%7%
2112
16th to endNight
41%49%21%20%4
1893
March1st to 15thNight
39%5%9%18%18%7%
2058
16th to endNight
38%413%24%16%2
2112
April1st to 15thNight
31%412%24%21%5%
1902
16th to endNight
33%6%10%22%20%6%
1683
May1st to 15thNight
36%8%14%21%17%1
1620
16th to endNight
33%8%16%26%11%2
1684
June1st to 15thNight
34%12%22%21%8%1
1620
16th to endNight
29%11%19%22%14%2
1620
July1st to 15thNight
37%11%22%18%8%1
1530
16th to endNight
31%15%21%20%9%1
1595
August1st to 15thNight
37%11%18%20%11%1
1609
16th to endNight
40%10%17%18%11%
1909
September1st to 15thNight
39%9%16%17%14%3
1968
16th to endNight
36%7%11%22%16%4
1892
October1st to 15thNight
32%310%18%26%7%
1834
16th to endNight
30%46%18%28%11%
2112
November1st to 15thNight
30%35%19%28%12%
2262
16th to endNight
37%46%18%23%8%
2340
December1st to 15thNight
42%410%16%18%8%
2340
16th to endNight
49%39%16%15%5%
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
30%18%31%16%3
90
16th to endDay
23%35%30%9%1
96
February1st to 15thDay
23%30%35%11%
90
16th to endDay
30%20%37%9%1
81
March1st to 15thDay
27%17%25%20%8%1
192
16th to endDay
23%13%28%22%10%1
288
April1st to 15thDay
17%15%26%22%15%3
270
16th to endDay
17%6%25%25%16%8%
270
May1st to 15thDay
16%9%28%16%14%13%
288
16th to endDay
18%6%15%25%16%17%
331
June1st to 15thDay
13%112%26%23%21%
315
16th to endDay
9%117%23%22%24%
315
July1st to 15thDay
11%11%24%26%24%
305
16th to endDay
7%17%16%33%33%
326
August1st to 15thDay
20%29%20%21%25%
313
16th to endDay
17%28%21%30%19%
332
September1st to 15thDay
17%312%21%29%15%
315
16th to endDay
18%311%27%29%10%
278
October1st to 15thDay
17%6%21%25%21%7%
255
16th to endDay
15%7%18%28%23%5%
272
November1st to 15thDay
28%11%25%18%11%2
101
16th to endDay
18%14%32%22%10%2
90
December1st to 15thDay
28%25%24%17%21
90
16th to endDay
42%11%30%14%1
96
January1st to 15thNight
26%20%21%24%6%
720
16th to endNight
21%18%32%23%3
768
February1st to 15thNight
20%18%28%27%4
704
16th to endNight
20%22%32%21%3
631
March1st to 15thNight
21%16%31%25%5%
720
16th to endNight
18%12%27%28%11%
768
April1st to 15thNight
16%15%26%26%13%1
644
16th to endNight
13%9%23%32%18%2
540
May1st to 15thNight
15%7%21%32%19%4
540
16th to endNight
14%214%28%33%6%
563
June1st to 15thNight
10%113%29%35%10%
540
16th to endNight
6%10%30%40%12%
540
July1st to 15thNight
10%6%22%48%10%
510
16th to endNight
5%7%22%49%13%
564
August1st to 15thNight
14%17%22%39%13%
539
16th to endNight
16%6%23%42%9%
573
September1st to 15thNight
15%312%23%36%9%
708
16th to endNight
16%213%36%26%3
685
October1st to 15thNight
17%8%19%28%21%5%
660
16th to endNight
13%10%20%29%21%3
704
November1st to 15thNight
15%11%20%29%19%3
700
16th to endNight
20%14%26%24%13%
720
December1st to 15thNight
19%15%25%27%9%1
720
16th to endNight
29%13%25%24%6%
768
Page generated at 2017-09-23 06:43:43. Version ac04

Copyright 2017 A. Danko


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