Black Cliff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Cliff clear sky chart from 2005-11-05 to 2017-12-02.

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
65%
15744
31%
47586
25%
15706
71%
15706
47%
23639

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
62%
716
27%
2425
24%
716
70%
716
44%
1177
January16th to endNight
63%
768
28%
2496
26%
768
70%
768
38%
1325
February1st to 15thNight
61%
698
29%
2128
24%
698
69%
698
43%
1110
February16th to endNight
53%
632
27%
1895
25%
632
61%
632
37%
1063
March1st to 15thNight
57%
720
31%
2107
22%
720
69%
720
45%
1075
March16th to endNight
54%
768
29%
2112
18%
768
63%
768
45%
1144
April1st to 15thNight
49%
719
27%
1808
12%
719
57%
719
42%
1035
April16th to endNight
51%
600
32%
1680
16%
600
60%
600
45%
868
May1st to 15thNight
53%
540
28%
1619
18%
539
59%
539
44%
809
May16th to endNight
56%
562
25%
1685
19%
561
61%
561
39%
885
June1st to 15thNight
60%
499
29%
1579
25%
499
67%
499
51%
709
June16th to endNight
81%
360
36%
1440
44%
360
87%
360
67%
471
July1st to 15thNight
74%
349
24%
1369
29%
349
77%
349
38%
638
July16th to endNight
72%
564
23%
1593
21%
531
72%
531
39%
878
August1st to 15thNight
75%
539
33%
1611
27%
536
77%
536
54%
762
August16th to endNight
82%
750
38%
1896
26%
750
83%
750
63%
960
September1st to 15thNight
80%
720
36%
1910
25%
720
84%
720
61%
945
September16th to endNight
78%
716
45%
1980
36%
716
85%
716
70%
869
October1st to 15thNight
69%
720
37%
1980
29%
720
75%
720
57%
980
October16th to endNight
74%
768
40%
2406
36%
768
81%
768
57%
1047
November1st to 15thNight
71%
760
34%
2470
32%
760
79%
760
54%
1097
November16th to endNight
68%
780
38%
2535
36%
780
76%
780
51%
1145
December1st to 15thNight
64%
728
27%
2366
24%
728
71%
728
40%
1239
December16th to endNight
55%
768
26%
2496
21%
768
64%
768
32%
1408

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
3313323346%64%
48840
Night
3313323346%63%
47771
TransparencyDay
20%38%18%25%23%
48525
Night
21%38%21%26%18%
47587
SeeingDay
5%11%24%29%20%7%
5825
Night
5%5%18%38%28%3
15755

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
3323323346%60%
1496
16th to endDay
5%6%14423346%58%
1728
February1st to 15thDay
44144245%5%8%53%
1733
16th to endDay
5%6%24313246%59%
1579
March1st to 15thDay
231341345%7%61%
1851
16th to endDay
45%24323346%57%
2112
April1st to 15thDay
342442345%5%57%
2137
16th to endDay
4212312346%66%
2280
May1st to 15thDay
2212323447%62%
2331
16th to endDay
231443445%6%59%
2429
June1st to 15thDay
1212323336%69%
2376
16th to endDay
1111222481%
2520
July1st to 15thDay
3214434447%59%
2507
16th to endDay
3213425%46%7%56%
2467
August1st to 15thDay
2112212345%71%
2340
16th to endDay
112313346%70%
2304
September1st to 15thDay
211232333471%
2049
16th to endDay
11121123478%
1980
October1st to 15thDay
321222335%5%66%
1980
16th to endDay
221221343472%
1815
November1st to 15thDay
3212213246%68%
1719
16th to endDay
3213323345%65%
1755
December1st to 15thDay
35%25%322436%59%
1630
16th to endDay
7%6%1432345%7%51%
1722
January1st to 15thNight
35%23323346%62%
2425
16th to endNight
45%1343435%8%53%
2496
February1st to 15thNight
3424324347%58%
2117
16th to endNight
5%7%34433247%54%
1895
March1st to 15thNight
34233235%5%6%59%
2107
16th to endNight
35%25%323346%60%
2112
April1st to 15thNight
4424423446%59%
1808
16th to endNight
3313323446%63%
1680
May1st to 15thNight
3323423446%60%
1619
16th to endNight
5%424424447%56%
1684
June1st to 15thNight
2313322336%68%
1579
16th to endNight
1211213480%
1440
July1st to 15thNight
4324433345%60%
1449
16th to endNight
33245%35%47%7%51%
1701
August1st to 15thNight
1213324345%66%
1620
16th to endNight
112323445%69%
1896
September1st to 15thNight
21221235%5%70%
1910
16th to endNight
111211235%78%
1980
October1st to 15thNight
4213212346%67%
1980
16th to endNight
222213335%72%
2406
November1st to 15thNight
3212313246%68%
2470
16th to endNight
3212213447%66%
2535
December1st to 15thNight
5%414323447%58%
2366
16th to endNight
7%5%2433445%8%50%
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
23%416%31%20%3
1496
16th to endDay
26%314%27%20%7%
1728
February1st to 15thDay
27%5%13%26%19%7%
1733
16th to endDay
26%210%28%25%6%
1579
March1st to 15thDay
21%38%32%27%6%
1851
16th to endDay
26%310%27%22%8%
2112
April1st to 15thDay
26%39%20%27%12%
2137
16th to endDay
18%37%20%35%15%
2280
May1st to 15thDay
20%26%16%34%18%
2331
16th to endDay
22%46%15%31%19%
2432
June1st to 15thDay
16%25%9%27%38%
2376
16th to endDay
8%12420%62%
2520
July1st to 15thDay
23%25%8%14%44%
2359
16th to endDay
23%38%12%17%34%
2312
August1st to 15thDay
13%25%10%20%47%
2325
16th to endDay
13%25%11%21%44%
2304
September1st to 15thDay
16%26%9%17%46%
2049
16th to endDay
10%1411%38%33%
1980
October1st to 15thDay
18%35%15%35%21%
1980
16th to endDay
14%36%21%36%17%
1815
November1st to 15thDay
17%210%30%29%9%
1719
16th to endDay
20%29%28%29%8%
1755
December1st to 15thDay
26%5%12%31%22%2
1630
16th to endDay
30%5%19%23%18%3
1722
January1st to 15thNight
22%414%30%23%3
2425
16th to endNight
27%414%22%23%6%
2496
February1st to 15thNight
24%412%28%23%7%
2128
16th to endNight
31%310%26%24%3
1895
March1st to 15thNight
21%410%30%25%7%
2107
16th to endNight
25%211%30%21%8%
2112
April1st to 15thNight
24%49%25%26%8%
1808
16th to endNight
21%37%20%32%13%
1680
May1st to 15thNight
22%37%17%32%16%
1620
16th to endNight
26%37%15%30%16%
1685
June1st to 15thNight
17%2410%26%37%
1579
16th to endNight
9%125%19%61%
1440
July1st to 15thNight
25%25%9%12%44%
1369
16th to endNight
28%5%6%10%13%34%
1593
August1st to 15thNight
17%36%9%19%43%
1611
16th to endNight
15%26%10%24%40%
1896
September1st to 15thNight
15%36%11%19%44%
1910
16th to endNight
9%2412%33%37%
1980
October1st to 15thNight
17%2419%34%21%
1980
16th to endNight
14%25%19%39%18%
2406
November1st to 15thNight
16%27%28%33%11%
2470
16th to endNight
17%37%26%35%9%
2535
December1st to 15thNight
25%5%13%31%21%2
2366
16th to endNight
31%5%15%25%18%3
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
19%11%23%30%11%2
71
16th to endDay
9%6%15%31%25%12%
96
February1st to 15thDay
5%11%22%31%21%7%
248
16th to endDay
12%16%31%23%10%5%
238
March1st to 15thDay
7%15%28%25%18%3
270
16th to endDay
8%21%31%23%12%1
288
April1st to 15thDay
11%25%25%20%13%4
269
16th to endDay
9%29%25%22%10%2
270
May1st to 15thDay
417%32%27%13%4
288
16th to endDay
6%13%24%28%20%6%
330
June1st to 15thDay
315%24%29%21%4
315
16th to endDay
26%24%29%27%9%
315
July1st to 15thDay
2223%39%21%9%
305
16th to endDay
4219%42%23%7%
327
August1st to 15thDay
45%28%34%18%7%
315
16th to endDay
3419%31%26%13%
332
September1st to 15thDay
25%22%32%26%10%
315
16th to endDay
211%20%23%33%8%
315
October1st to 15thDay
212%32%30%14%8%
315
16th to endDay
6%321%27%28%11%
144
November1st to 15thDay
4216%33%27%15%
135
16th to endDay
7%11%16%25%35%3
135
December1st to 15thDay
25%25%43%19%4
94
16th to endDay
13%5%20%36%18%5%
95
January1st to 15thNight
7%320%36%26%6%
720
16th to endNight
8%319%41%24%3
768
February1st to 15thNight
5%420%42%22%4
704
16th to endNight
10%6%22%38%18%2
632
March1st to 15thNight
48%24%37%23%1
720
16th to endNight
5%10%24%36%20%1
768
April1st to 15thNight
5%13%25%31%21%2
719
16th to endNight
5%11%27%35%17%2
600
May1st to 15thNight
48%26%37%21%1
540
16th to endNight
6%8%21%32%28%2
563
June1st to 15thNight
47%21%41%24%1
499
16th to endNight
1113%49%32%2
360
July1st to 15thNight
47%43%41%2
349
16th to endNight
49%42%40%2
564
August1st to 15thNight
313%48%32%1
539
16th to endNight
28%34%47%6%
750
September1st to 15thNight
310%32%46%6%
720
16th to endNight
1313%34%38%9%
716
October1st to 15thNight
5%317%37%31%4
720
16th to endNight
3414%35%36%6%
768
November1st to 15thNight
2217%39%31%5%
760
16th to endNight
35%17%39%28%5%
780
December1st to 15thNight
8%220%43%21%4
728
16th to endNight
8%5%23%37%22%1
768
Page generated at 2017-12-03 08:16:42. Version ac04

Copyright 2017 A. Danko


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