Black Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Creek Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
55%
15875
21%
46971
16%
15836
61%
15836
29%
29440

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
38%
718
21%
2327
13%
716
50%
716
24%
1422
January16th to endNight
39%
768
22%
2475
15%
768
50%
768
25%
1540
February1st to 15thNight
41%
701
23%
2108
14%
700
51%
700
30%
1277
February16th to endNight
37%
631
24%
1854
14%
631
48%
631
29%
1162
March1st to 15thNight
42%
720
28%
1980
15%
720
53%
720
35%
1176
March16th to endNight
48%
768
25%
2112
16%
768
56%
768
37%
1229
April1st to 15thNight
49%
718
24%
1976
17%
718
55%
718
37%
1162
April16th to endNight
53%
695
27%
1805
15%
695
59%
695
41%
1066
May1st to 15thNight
65%
539
25%
1619
18%
539
71%
539
41%
887
May16th to endNight
72%
561
23%
1682
18%
561
73%
561
36%
984
June1st to 15thNight
68%
540
14%
1620
11%
540
68%
540
26%
1062
June16th to endNight
73%
540
10%
1620
8%
540
74%
540
25%
1103
July1st to 15thNight
73%
510
11%
1530
11%
510
73%
510
24%
1048
July16th to endNight
76%
564
9%
1595
10%
531
77%
531
24%
1101
August1st to 15thNight
77%
539
9%
1609
8%
536
77%
536
23%
1121
August16th to endNight
64%
690
12%
1986
11%
690
65%
690
21%
1410
September1st to 15thNight
65%
720
11%
1980
11%
720
65%
720
21%
1440
September16th to endNight
59%
681
17%
1881
15%
681
61%
681
23%
1330
October1st to 15thNight
65%
660
27%
1880
25%
660
68%
660
33%
1153
October16th to endNight
59%
704
30%
2112
27%
704
66%
704
33%
1244
November1st to 15thNight
55%
700
28%
2101
23%
700
63%
700
36%
1214
November16th to endNight
49%
720
27%
2283
19%
720
62%
720
30%
1337
December1st to 15thNight
45%
720
25%
2340
21%
720
52%
720
27%
1428
December16th to endNight
49%
768
23%
2496
20%
768
57%
768
26%
1544

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
10%5%36%6%46%5%6%7%37%
47874
Night
8%425%5%345%6%8%44%
47175
TransparencyDay
44%7%12%16%13%6%
47575
Night
35%7%14%19%14%7%
46978
SeeingDay
12%314%21%24%23%
5730
Night
11%5%19%32%26%5%
15883

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
11%6%37%5%34346%42%
1611
16th to endDay
12%6%36%424345%45%
1746
February1st to 15thDay
15%5%2442433447%
1750
16th to endDay
12%5%345%2335%5%48%
1617
March1st to 15thDay
9%424423348%52%
1980
16th to endDay
8%6%35%434446%49%
2111
April1st to 15thDay
8%425%5%35%5%5%6%46%
1972
16th to endDay
7%325%5%35%5%6%7%46%
2161
May1st to 15thDay
7%3245%36%6%6%7%46%
2331
16th to endDay
8%326%6%47%5%6%9%38%
2431
June1st to 15thDay
11%428%9%6%8%6%6%8%26%
2340
16th to endDay
9%5%37%8%5%8%7%7%9%26%
2340
July1st to 15thDay
8%6%39%9%49%7%8%10%23%
2340
16th to endDay
9%6%49%9%6%8%7%7%9%22%
2465
August1st to 15thDay
9%7%48%8%5%7%8%8%10%19%
2340
16th to endDay
13%6%38%9%6%8%6%6%8%21%
2198
September1st to 15thDay
12%6%38%9%5%8%7%8%7%22%
1980
16th to endDay
15%8%49%7%5%5%5%6%6%23%
1872
October1st to 15thDay
10%6%37%7%35%45%7%38%
1749
16th to endDay
10%5%36%323446%48%
1760
November1st to 15thDay
8%5%25%5%2445%7%47%
1757
16th to endDay
10%5%245%345%46%47%
1675
December1st to 15thDay
12%6%25%6%235%6%7%41%
1620
16th to endDay
10%5%26%5%35%46%9%40%
1728
January1st to 15thNight
12%6%35%42445%7%43%
2327
16th to endNight
13%5%345%23447%44%
2475
February1st to 15thNight
11%5%35%5%2334451%
2103
16th to endNight
11%5%25%5%33345%47%
1854
March1st to 15thNight
8%425%424448%51%
1980
16th to endNight
7%315%42335%6%55%
2112
April1st to 15thNight
7%5%23324448%53%
1976
16th to endNight
6%42432445%8%54%
1805
May1st to 15thNight
4113325%36%11%55%
1619
16th to endNight
6%4245%2446%10%50%
1682
June1st to 15thNight
10%4245%36%6%9%12%33%
1620
16th to endNight
6%415%7%46%7%7%12%35%
1620
July1st to 15thNight
6%325%6%35%7%8%11%37%
1620
16th to endNight
3436%7%48%8%8%11%33%
1703
August1st to 15thNight
5%426%5%47%8%9%13%32%
1620
16th to endNight
8%5%36%6%35%6%8%11%33%
1986
September1st to 15thNight
9%6%26%6%47%7%7%10%31%
1980
16th to endNight
12%7%36%6%4447%11%31%
1881
October1st to 15thNight
7%425%5%3345%8%48%
1880
16th to endNight
8%425%5%24447%50%
2112
November1st to 15thNight
7%42433445%7%51%
2101
16th to endNight
8%415%5%3445%6%49%
2283
December1st to 15thNight
11%5%25%5%23447%46%
2340
16th to endNight
9%6%25%5%34447%44%
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
43%38%16%17%10%
1612
16th to endDay
40%37%17%19%11%
1746
February1st to 15thDay
41%46%12%20%15%
1752
16th to endDay
37%410%13%22%11%
1617
March1st to 15thDay
31%49%22%22%10%
1980
16th to endDay
37%410%18%19%10%
2112
April1st to 15thDay
37%48%18%20%9%
1972
16th to endDay
34%5%11%19%19%9%
2161
May1st to 15thDay
35%5%10%20%19%8%
2331
16th to endDay
40%7%13%19%15%4
2435
June1st to 15thDay
51%8%16%15%7%
2340
16th to endDay
50%11%18%14%5%
2340
July1st to 15thDay
51%12%21%12%1
2201
16th to endDay
55%10%18%12%2
2310
August1st to 15thDay
55%13%20%9%1
2327
16th to endDay
58%11%16%11%2
2198
September1st to 15thDay
54%12%15%11%5%
1980
16th to endDay
58%7%10%13%7%2
1872
October1st to 15thDay
45%5%8%14%15%10%
1749
16th to endDay
37%5%5%14%23%13%
1760
November1st to 15thDay
35%39%20%19%10%
1757
16th to endDay
37%47%16%21%12%
1675
December1st to 15thDay
43%410%20%14%6%
1620
16th to endDay
39%5%11%22%12%8%
1728
January1st to 15thNight
40%39%18%18%8%
2327
16th to endNight
39%48%14%20%11%
2475
February1st to 15thNight
36%48%15%19%16%
2112
16th to endNight
38%48%18%19%10%
1854
March1st to 15thNight
31%412%23%18%9%
1980
16th to endNight
30%411%21%20%11%
2112
April1st to 15thNight
29%5%11%20%22%9%
1976
16th to endNight
28%5%13%23%21%7%
1805
May1st to 15thNight
24%7%15%25%19%7%
1620
16th to endNight
29%6%17%27%15%3
1684
June1st to 15thNight
37%10%22%23%5%
1620
16th to endNight
37%12%23%19%6%
1620
July1st to 15thNight
37%14%27%18%2
1530
16th to endNight
36%15%27%16%3
1595
August1st to 15thNight
36%16%31%13%2
1609
16th to endNight
42%13%23%17%3
1986
September1st to 15thNight
44%12%21%14%5%1
1980
16th to endNight
44%9%15%20%8%2
1881
October1st to 15thNight
34%6%12%18%19%9%
1880
16th to endNight
33%5%7%18%22%13%
2112
November1st to 15thNight
31%410%21%20%10%
2101
16th to endNight
33%5%8%18%18%14%
2283
December1st to 15thNight
38%411%23%14%6%
2340
16th to endNight
39%412%20%13%9%
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
18%12%33%22%7%5%
90
16th to endDay
15%13%37%20%11%1
96
February1st to 15thDay
10%16%35%21%16%
90
16th to endDay
16%436%32%10%
118
March1st to 15thDay
12%7%29%30%19%1
270
16th to endDay
11%326%27%25%4
288
April1st to 15thDay
13%8%23%25%20%8%
270
16th to endDay
5%418%27%24%20%
270
May1st to 15thDay
6%5%17%27%23%18%
288
16th to endDay
9%28%19%32%28%
331
June1st to 15thDay
15%16%12%31%31%
315
16th to endDay
9%1317%26%42%
315
July1st to 15thDay
6%110%30%49%
305
16th to endDay
12%310%27%45%
326
August1st to 15thDay
13%15%14%26%38%
313
16th to endDay
15%26%9%22%43%
332
September1st to 15thDay
16%1317%26%34%
315
16th to endDay
18%16%16%29%27%
275
October1st to 15thDay
18%113%27%27%10%
255
16th to endDay
12%413%33%27%8%
272
November1st to 15thDay
11%319%33%23%8%
265
16th to endDay
11%5%31%24%22%4
145
December1st to 15thDay
12%6%33%30%13%4
90
16th to endDay
14%5%18%42%11%7%
96
January1st to 15thNight
16%11%27%31%11%1
720
16th to endNight
17%10%27%33%10%
768
February1st to 15thNight
13%8%30%35%9%1
704
16th to endNight
13%9%33%35%7%
631
March1st to 15thNight
11%10%30%35%11%
720
16th to endNight
9%7%29%36%16%
768
April1st to 15thNight
10%7%28%37%16%
718
16th to endNight
9%5%26%38%19%1
695
May1st to 15thNight
5%222%42%25%2
540
16th to endNight
7%28%34%38%7%
563
June1st to 15thNight
12%27%30%38%9%
540
16th to endNight
9%5%20%44%19%
540
July1st to 15thNight
8%1318%44%23%
510
16th to endNight
4322%52%16%
564
August1st to 15thNight
6%317%53%18%
539
16th to endNight
11%16%20%42%18%
690
September1st to 15thNight
14%5%25%43%11%
720
16th to endNight
16%17%27%37%9%
681
October1st to 15thNight
11%113%35%33%4
660
16th to endNight
9%318%39%27%2
704
November1st to 15thNight
10%423%36%24%1
700
16th to endNight
10%6%27%34%19%1
720
December1st to 15thNight
14%8%24%32%18%
720
16th to endNight
12%7%23%37%17%1
768
Page generated at 2017-09-22 07:35:29. Version ac04

Copyright 2017 A. Danko


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