Black Diamond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Diamond clear sky chart from 2005-11-05 to 2017-09-17.

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
40%
15172
14%
46796
9%
15139
46%
15139
22%
30967

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
31%
900
13%
2685
6%
895
37%
895
17%
1915
January16th to endNight
32%
801
19%
2721
12%
801
43%
801
20%
1760
February1st to 15thNight
38%
701
13%
2414
9%
697
46%
697
19%
1584
February16th to endNight
38%
632
15%
1967
10%
632
46%
632
20%
1380
March1st to 15thNight
33%
720
15%
2121
7%
720
42%
720
20%
1468
March16th to endNight
33%
768
11%
2084
4%
768
39%
768
18%
1534
April1st to 15thNight
33%
635
11%
1715
5%
635
36%
635
18%
1266
April16th to endNight
36%
540
12%
1620
9%
540
40%
540
20%
1145
May1st to 15thNight
43%
422
11%
1434
10%
422
48%
422
21%
940
May16th to endNight
43%
374
5%
1309
4%
374
45%
374
14%
946
June1st to 15thNight
41%
360
1%
1260
0%
360
41%
360
17%
862
June16th to endNight
54%
360
2%
1260
0%
360
54%
360
26%
757
July1st to 15thNight
61%
340
3%
1190
0%
340
62%
340
28%
697
July16th to endNight
62%
376
11%
1296
13%
354
67%
354
32%
700
August1st to 15thNight
64%
402
14%
1474
18%
400
68%
400
28%
818
August16th to endNight
61%
573
22%
1719
18%
573
64%
573
41%
920
September1st to 15thNight
56%
672
19%
1818
12%
672
59%
672
37%
1097
September16th to endNight
53%
664
22%
1837
14%
664
59%
664
37%
1099
October1st to 15thNight
42%
660
18%
1939
11%
660
48%
660
22%
1332
October16th to endNight
43%
704
21%
2288
12%
704
54%
704
25%
1428
November1st to 15thNight
31%
808
18%
2383
10%
808
41%
808
24%
1545
November16th to endNight
29%
900
15%
2682
6%
900
38%
900
21%
1810
December1st to 15thNight
35%
900
14%
2700
8%
900
40%
900
18%
1930
December16th to endNight
32%
960
16%
2880
7%
960
40%
960
18%
2034

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%8%36%5%35%5%6%8%36%
48011
Night
7%8%36%5%35%5%5%8%39%
46948
Cloud CoverDay
10%8%36%5%35%5%6%8%36%
48012
Night
7%8%37%5%35%5%5%8%39%
46951
TransparencyDay
43%9%14%21%9%1
47667
Night
41%8%15%22%10%1
46796
SeeingDay
15%11%29%26%12%3
5999
Night
11%8%30%33%13%2
15177

By Month

Percentage Cloud Cover NW (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
49%38%5%3446%10%38%
1253
16th to endDay
310%38%7%35%45%8%37%
1512
February1st to 15thDay
38%49%5%26%5%7%10%35%
1448
16th to endDay
211%5%9%7%46%7%6%8%30%
1506
March1st to 15thDay
27%49%6%5%7%6%5%8%35%
1839
16th to endDay
7%12%6%9%6%46%6%6%6%27%
2138
April1st to 15thDay
11%13%5%7%7%35%5%5%8%27%
2233
16th to endDay
14%12%35%435%5%6%7%30%
2340
May1st to 15thDay
12%9%46%5%35%5%6%8%34%
2514
16th to endDay
23%7%36%6%36%45%7%25%
2802
June1st to 15thDay
20%8%36%5%36%5%6%7%25%
2700
16th to endDay
14%5%36%5%35%6%6%8%34%
2700
July1st to 15thDay
10%5%245%35%6%7%7%41%
2700
16th to endDay
6%323425%6%7%8%48%
2781
August1st to 15thDay
11%5%25%425%6%6%8%41%
2478
16th to endDay
10%31342445%9%50%
2483
September1st to 15thDay
13%5%14423345%51%
2139
16th to endDay
9%425%33446%8%47%
1828
October1st to 15thDay
11%10%37%6%33448%34%
1688
16th to endDay
6%9%36%5%35%5%8%9%37%
1584
November1st to 15thDay
5%10%46%5%35%5%5%9%37%
1463
16th to endDay
411%5%6%5%2345%10%39%
1278
December1st to 15thDay
310%410%7%47%6%6%8%30%
1260
16th to endDay
310%48%5%25%6%7%10%34%
1344
January1st to 15thNight
311%49%7%46%6%5%8%32%
2685
16th to endNight
38%5%8%7%345%6%8%39%
2721
February1st to 15thNight
310%5%7%5%36%46%8%38%
2403
16th to endNight
39%6%9%7%45%5%6%5%37%
1967
March1st to 15thNight
210%47%8%46%5%6%9%34%
2121
16th to endNight
412%5%9%6%45%5%7%8%30%
2081
April1st to 15thNight
11%13%5%7%5%245%5%6%32%
1715
16th to endNight
10%12%47%5%3445%7%34%
1620
May1st to 15thNight
10%8%45%5%35%448%38%
1433
16th to endNight
20%6%25%5%45%5%47%31%
1309
June1st to 15thNight
16%8%36%5%35%447%34%
1260
16th to endNight
12%3144245%5%11%42%
1260
July1st to 15thNight
8%325%4335%5%8%48%
1260
16th to endNight
7%3233245%5%8%53%
1385
August1st to 15thNight
10%41342446%9%47%
1482
16th to endNight
9%3231335%8%57%
1719
September1st to 15thNight
13%5%13312336%53%
1818
16th to endNight
10%41332335%8%52%
1837
October1st to 15thNight
11%9%36%5%245%5%6%38%
1939
16th to endNight
7%8%344345%6%8%43%
2288
November1st to 15thNight
5%9%345%25%5%5%8%43%
2383
16th to endNight
410%5%8%6%245%6%8%37%
2682
December1st to 15thNight
39%5%8%7%47%5%6%9%32%
2700
16th to endNight
210%5%9%8%46%6%6%7%33%
2880

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
49%48%5%335%7%9%37%
1253
16th to endDay
310%39%6%35%5%6%8%37%
1512
February1st to 15thDay
48%5%9%5%27%5%7%9%34%
1448
16th to endDay
211%5%10%6%46%7%6%8%29%
1506
March1st to 15thDay
28%49%7%46%6%6%8%34%
1839
16th to endDay
7%12%6%10%6%5%5%6%6%7%26%
2139
April1st to 15thDay
11%12%5%8%5%45%5%5%8%27%
2233
16th to endDay
14%11%45%5%36%5%7%7%29%
2340
May1st to 15thDay
11%9%46%5%25%5%7%7%33%
2514
16th to endDay
22%7%36%6%35%5%6%7%24%
2802
June1st to 15thDay
19%8%35%5%45%6%6%8%25%
2700
16th to endDay
14%5%35%6%36%5%6%9%33%
2700
July1st to 15thDay
10%425%5%35%5%7%8%41%
2700
16th to endDay
5%4134346%7%8%47%
2781
August1st to 15thDay
11%5%244246%7%8%41%
2478
16th to endDay
10%31432446%9%49%
2483
September1st to 15thDay
13%5%13424345%50%
2139
16th to endDay
9%5%2443446%8%46%
1828
October1st to 15thDay
11%11%37%6%2345%8%34%
1688
16th to endDay
6%9%36%5%35%6%7%9%36%
1584
November1st to 15thDay
6%9%45%5%45%46%8%37%
1463
16th to endDay
5%11%5%6%43345%10%39%
1278
December1st to 15thDay
310%410%8%48%6%6%7%29%
1260
16th to endDay
210%49%5%25%6%9%9%33%
1344
January1st to 15thNight
311%49%7%46%5%6%9%31%
2685
16th to endNight
39%48%6%35%46%8%38%
2721
February1st to 15thNight
410%5%7%5%35%5%7%8%37%
2403
16th to endNight
39%6%10%7%45%5%5%6%35%
1967
March1st to 15thNight
210%47%7%45%7%5%10%33%
2121
16th to endNight
5%11%6%9%6%45%47%8%29%
2084
April1st to 15thNight
11%12%48%5%345%5%6%31%
1715
16th to endNight
10%12%37%6%34447%34%
1620
May1st to 15thNight
10%8%36%5%345%5%7%37%
1433
16th to endNight
20%6%25%6%36%5%5%6%30%
1309
June1st to 15thNight
15%9%46%435%45%7%33%
1260
16th to endNight
12%4234245%6%10%42%
1260
July1st to 15thNight
7%425%43445%9%48%
1260
16th to endNight
6%423325%45%7%53%
1385
August1st to 15thNight
10%4145%2445%10%47%
1482
16th to endNight
9%21131245%8%57%
1719
September1st to 15thNight
12%6%13313336%53%
1818
16th to endNight
10%41441246%8%51%
1837
October1st to 15thNight
11%9%36%5%235%6%6%38%
1939
16th to endNight
7%8%25%4345%6%8%43%
2288
November1st to 15thNight
5%9%35%5%35%5%6%8%42%
2383
16th to endNight
5%9%5%9%5%3445%8%37%
2682
December1st to 15thNight
39%49%8%47%5%5%8%31%
2700
16th to endNight
210%5%9%8%46%6%6%7%32%
2880

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
42%7%14%25%6%2
1253
16th to endDay
43%8%14%18%10%4
1512
February1st to 15thDay
43%9%15%21%7%2
1448
16th to endDay
49%10%14%17%8%
1506
March1st to 15thDay
43%10%17%21%6%
1839
16th to endDay
56%7%13%16%6%
2139
April1st to 15thDay
55%6%14%15%6%1
2233
16th to endDay
51%8%13%17%7%1
2340
May1st to 15thDay
45%8%14%21%9%
2514
16th to endDay
56%9%13%15%5%
2807
June1st to 15thDay
53%10%13%15%6%1
2700
16th to endDay
44%10%15%19%7%1
2700
July1st to 15thDay
37%10%16%24%9%1
2541
16th to endDay
29%11%15%26%13%2
2607
August1st to 15thDay
36%12%18%23%7%1
2461
16th to endDay
29%9%16%30%12%2
2483
September1st to 15thDay
34%7%12%23%18%3
2139
16th to endDay
34%7%12%30%11%3
1828
October1st to 15thDay
47%9%13%19%9%1
1688
16th to endDay
39%9%16%23%7%1
1584
November1st to 15thDay
43%9%15%20%9%1
1463
16th to endDay
40%7%17%21%9%2
1278
December1st to 15thDay
51%9%13%17%8%
1260
16th to endDay
41%10%14%20%10%2
1344
January1st to 15thNight
47%9%15%18%7%2
2685
16th to endNight
41%8%13%20%12%3
2721
February1st to 15thNight
42%8%14%21%11%1
2414
16th to endNight
47%7%12%19%12%
1967
March1st to 15thNight
43%9%17%22%6%
2121
16th to endNight
49%8%14%17%8%
2084
April1st to 15thNight
52%6%12%18%9%
1715
16th to endNight
47%8%13%22%6%1
1620
May1st to 15thNight
43%7%12%24%10%
1434
16th to endNight
52%8%12%19%5%1
1309
June1st to 15thNight
48%6%13%20%9%
1260
16th to endNight
35%8%18%25%11%1
1260
July1st to 15thNight
33%7%18%27%12%
1190
16th to endNight
28%7%16%31%12%2
1296
August1st to 15thNight
31%7%18%29%10%1
1474
16th to endNight
23%6%15%32%18%2
1719
September1st to 15thNight
31%5%13%25%19%4
1818
16th to endNight
30%6%16%27%14%5%
1837
October1st to 15thNight
44%8%13%21%11%1
1939
16th to endNight
36%8%15%26%11%
2288
November1st to 15thNight
37%9%15%22%14%
2383
16th to endNight
42%8%17%17%10%3
2682
December1st to 15thNight
47%9%15%19%7%
2700
16th to endNight
47%8%13%21%8%
2880

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
8%331%20%20%16%
60
16th to endDay
18%6%17%37%9%10%
64
February1st to 15thDay
10%15%36%27%7%2
69
16th to endDay
10%6%32%36%14%
165
March1st to 15thDay
5%22%47%19%4
270
16th to endDay
13%20%37%20%6%1
288
April1st to 15thDay
22%20%31%18%6%
269
16th to endDay
26%13%28%21%9%1
270
May1st to 15thDay
16%13%29%22%15%3
357
16th to endDay
23%9%17%26%17%4
517
June1st to 15thDay
20%10%27%25%11%3
495
16th to endDay
14%10%26%29%14%3
495
July1st to 15thDay
12%6%27%29%20%3
475
16th to endDay
9%9%32%29%16%2
450
August1st to 15thDay
14%8%30%29%12%4
315
16th to endDay
11%9%35%28%9%6%
332
September1st to 15thDay
20%12%26%26%11%2
315
16th to endDay
13%18%25%31%10%1
260
October1st to 15thDay
18%16%28%25%11%
160
16th to endDay
12%425%32%19%6%
96
November1st to 15thDay
17%13%30%28%5%4
90
16th to endDay
11%11%22%26%12%15%
63
December1st to 15thDay
6%8%31%36%15%1
60
16th to endDay
47%26%32%21%6%
64
January1st to 15thNight
10%11%36%31%8%1
900
16th to endNight
9%11%36%32%8%1
801
February1st to 15thNight
7%10%32%30%13%4
704
16th to endNight
8%5%34%33%15%2
632
March1st to 15thNight
7%9%41%30%8%2
720
16th to endNight
10%7%34%36%9%1
768
April1st to 15thNight
17%8%31%29%12%1
635
16th to endNight
18%6%28%32%13%
540
May1st to 15thNight
14%6%26%32%18%1
423
16th to endNight
22%423%29%18%1
375
June1st to 15thNight
19%6%24%30%17%1
360
16th to endNight
12%321%39%21%1
360
July1st to 15thNight
9%316%41%26%2
340
16th to endNight
9%318%43%22%2
376
August1st to 15thNight
12%113%36%31%3
402
16th to endNight
9%321%40%23%1
573
September1st to 15thNight
15%419%31%22%5%
672
16th to endNight
13%325%37%14%5%
664
October1st to 15thNight
17%5%27%32%14%3
660
16th to endNight
12%7%29%35%12%2
704
November1st to 15thNight
10%13%39%27%6%1
808
16th to endNight
9%12%39%29%6%2
900
December1st to 15thNight
8%10%36%31%10%2
900
16th to endNight
8%9%37%31%10%2
960
Page generated at 2017-09-18 06:38:28. Version ac04

Copyright 2017 A. Danko


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