Black Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Lake Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
28%
14561
14%
46505
8%
14533
36%
14533
17%
32490

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
14%
720
8%
2506
3%
716
21%
716
7%
1986
January16th to endNight
20%
768
12%
2610
5%
768
28%
768
11%
1939
February1st to 15thNight
15%
701
10%
2287
4%
701
23%
701
11%
1744
February16th to endNight
19%
631
15%
1957
6%
631
30%
631
13%
1442
March1st to 15thNight
20%
720
15%
2079
7%
720
28%
720
16%
1511
March16th to endNight
30%
768
21%
2047
9%
768
38%
768
23%
1402
April1st to 15thNight
21%
718
17%
1796
5%
718
27%
718
19%
1294
April16th to endNight
28%
666
18%
1746
7%
666
34%
666
22%
1214
May1st to 15thNight
35%
360
18%
1440
16%
360
45%
360
18%
929
May16th to endNight
33%
374
15%
1497
12%
374
45%
374
20%
896
June1st to 15thNight
35%
360
11%
1440
9%
360
46%
360
16%
948
June16th to endNight
43%
360
10%
1440
13%
360
48%
360
19%
899
July1st to 15thNight
49%
340
15%
1360
21%
340
55%
340
28%
730
July16th to endNight
55%
376
15%
1418
17%
354
61%
354
29%
782
August1st to 15thNight
48%
465
16%
1514
11%
463
54%
463
28%
903
August16th to endNight
51%
645
21%
1695
11%
645
56%
645
39%
1017
September1st to 15thNight
45%
660
19%
1650
8%
660
49%
660
32%
1102
September16th to endNight
44%
657
23%
1801
14%
657
51%
657
32%
1136
October1st to 15thNight
32%
660
18%
1980
12%
660
42%
660
19%
1385
October16th to endNight
22%
704
11%
2180
4%
704
30%
704
13%
1637
November1st to 15thNight
25%
700
19%
2334
12%
700
35%
700
17%
1583
November16th to endNight
20%
720
13%
2520
7%
720
28%
720
10%
1902
December1st to 15thNight
14%
720
7%
2520
2%
720
20%
720
8%
1974
December16th to endNight
13%
768
9%
2688
4%
768
20%
768
8%
2135

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
17%9%36%5%34446%32%
47475
Night
17%9%36%5%34446%33%
46675
Cloud CoverDay
17%8%36%5%34446%33%
47484
Night
17%9%36%5%34446%33%
46680
TransparencyDay
51%311%21%10%1
47162
Night
52%311%20%10%1
46505
SeeingDay
23%11%28%21%10%4
5326
Night
23%12%28%24%9%
14565

By Month

Percentage Cloud Cover NE (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%15%5%7%5%35%34423%
1432
16th to endDay
14%14%5%11%9%4443423%
1612
February1st to 15thDay
14%13%5%11%8%45%445%22%
1575
16th to endDay
18%14%6%7%7%35%33326%
1515
March1st to 15thDay
17%11%49%8%5%5%33326%
1868
16th to endDay
16%10%35%423335%40%
2176
April1st to 15thDay
21%10%35%423335%33%
2152
16th to endDay
19%8%27%42345%5%37%
2225
May1st to 15thDay
19%6%46%5%34346%34%
2511
16th to endDay
13%6%36%5%445%5%8%36%
2618
June1st to 15thDay
22%7%35%4335%5%7%31%
2520
16th to endDay
17%5%26%5%36%5%5%7%33%
2520
July1st to 15thDay
11%5%35%5%35%5%5%9%38%
2520
16th to endDay
12%5%26%5%35%6%7%9%34%
2654
August1st to 15thDay
12%7%26%5%25%5%6%7%37%
2348
16th to endDay
12%5%25%5%3446%9%40%
2143
September1st to 15thDay
17%5%2443435%7%40%
1980
16th to endDay
17%5%34433336%44%
1828
October1st to 15thDay
21%7%36%433346%34%
1650
16th to endDay
27%9%47%6%245%35%24%
1691
November1st to 15thDay
14%8%46%5%45%446%34%
1521
16th to endDay
22%12%5%7%5%34435%25%
1440
December1st to 15thDay
23%13%5%8%5%35%345%20%
1440
16th to endDay
23%15%6%8%5%4443420%
1536
January1st to 15thNight
19%15%5%10%7%3434420%
2506
16th to endNight
14%14%5%10%6%35%445%25%
2610
February1st to 15thNight
14%14%6%8%7%35%45%5%23%
2285
16th to endNight
15%13%47%6%34346%29%
1957
March1st to 15thNight
19%11%37%5%33345%31%
2067
16th to endNight
15%7%46%423345%41%
2047
April1st to 15thNight
22%7%35%42334436%
1796
16th to endNight
18%8%35%423447%37%
1746
May1st to 15thNight
21%7%25%424346%37%
1440
16th to endNight
14%5%35%5%34448%40%
1495
June1st to 15thNight
17%7%45%5%245%5%7%34%
1440
16th to endNight
15%416%5%35%5%6%9%35%
1440
July1st to 15thNight
9%425%425%45%7%47%
1440
16th to endNight
9%414425%47%9%47%
1514
August1st to 15thNight
10%5%25%5%345%7%8%42%
1524
16th to endNight
9%42432336%7%50%
1695
September1st to 15thNight
15%5%2442445%6%44%
1650
16th to endNight
16%5%15%323346%48%
1801
October1st to 15thNight
21%6%35%43435%5%34%
1980
16th to endNight
26%10%36%6%24345%26%
2180
November1st to 15thNight
17%11%35%4345%45%33%
2334
16th to endNight
22%11%48%6%35%335%25%
2520
December1st to 15thNight
20%16%5%9%5%33335%22%
2520
16th to endNight
24%14%5%8%5%3444420%
2688

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
21%15%47%6%345%4422%
1432
16th to endDay
15%13%5%10%9%45%44422%
1612
February1st to 15thDay
14%13%6%10%8%44445%23%
1575
16th to endDay
19%14%5%7%6%35%33426%
1515
March1st to 15thDay
18%12%48%8%45%33426%
1878
16th to endDay
17%9%45%424235%41%
2175
April1st to 15thDay
21%10%35%424335%34%
2152
16th to endDay
19%8%35%5%23445%37%
2225
May1st to 15thDay
20%6%36%5%24348%33%
2511
16th to endDay
14%6%25%6%35%45%8%36%
2618
June1st to 15thDay
21%7%45%5%25%447%31%
2520
16th to endDay
17%6%25%6%35%45%8%33%
2520
July1st to 15thDay
11%5%25%5%25%6%6%8%39%
2520
16th to endDay
12%5%25%5%26%6%7%8%35%
2654
August1st to 15thDay
12%6%36%5%35%45%8%37%
2348
16th to endDay
12%5%145%335%6%8%42%
2143
September1st to 15thDay
17%5%26%42445%6%41%
1980
16th to endDay
17%6%24433346%44%
1828
October1st to 15thDay
21%7%35%5%23347%34%
1650
16th to endDay
27%10%37%6%33345%25%
1691
November1st to 15thDay
14%8%47%6%45%446%34%
1521
16th to endDay
23%11%47%5%2445%426%
1440
December1st to 15thDay
23%15%48%5%34445%19%
1440
16th to endDay
24%14%6%8%6%2433420%
1536
January1st to 15thNight
19%14%5%10%7%35%44420%
2506
16th to endNight
14%13%6%9%6%44446%25%
2610
February1st to 15thNight
14%14%6%9%7%445%5%5%23%
2278
16th to endNight
15%13%47%7%34336%28%
1957
March1st to 15thNight
20%11%37%6%23335%31%
2079
16th to endNight
16%8%47%423445%41%
2047
April1st to 15thNight
23%7%45%423335%35%
1796
16th to endNight
18%8%25%5%23437%37%
1746
May1st to 15thNight
21%7%25%4225%45%37%
1440
16th to endNight
14%5%26%42435%9%39%
1495
June1st to 15thNight
18%7%35%5%345%6%6%34%
1440
16th to endNight
14%6%245%35%5%7%8%36%
1440
July1st to 15thNight
10%5%25%5%245%5%8%46%
1440
16th to endNight
9%4134346%7%8%47%
1514
August1st to 15thNight
9%5%346%3347%8%43%
1524
16th to endNight
10%41441345%8%50%
1695
September1st to 15thNight
15%4245%33446%44%
1650
16th to endNight
16%5%14322346%48%
1801
October1st to 15thNight
21%6%35%5%25%45%5%34%
1980
16th to endNight
27%9%27%5%2434426%
2180
November1st to 15thNight
19%9%35%42445%6%33%
2334
16th to endNight
22%12%48%6%24435%26%
2520
December1st to 15thNight
20%17%5%8%6%2333422%
2520
16th to endNight
24%14%5%9%5%3434419%
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
65%29%15%6%1
1433
16th to endDay
64%38%12%9%
1612
February1st to 15thDay
63%39%18%5%
1577
16th to endDay
63%19%12%10%1
1515
March1st to 15thDay
63%29%15%7%1
1878
16th to endDay
47%28%19%15%5%
2176
April1st to 15thDay
54%26%19%14%2
2152
16th to endDay
48%27%21%15%3
2225
May1st to 15thDay
51%28%19%15%2
2511
16th to endDay
45%413%22%12%2
2622
June1st to 15thDay
52%410%21%10%
2520
16th to endDay
48%311%22%12%
2520
July1st to 15thDay
39%412%30%11%
2371
16th to endDay
43%5%14%26%9%
2487
August1st to 15thDay
44%415%23%11%
2334
16th to endDay
38%315%29%12%
2143
September1st to 15thDay
42%412%27%12%
1980
16th to endDay
41%310%31%12%
1828
October1st to 15thDay
50%212%23%10%
1650
16th to endDay
62%310%17%5%
1691
November1st to 15thDay
50%314%19%10%
1521
16th to endDay
60%312%14%8%1
1440
December1st to 15thDay
67%313%12%3
1440
16th to endDay
68%310%11%5%
1536
January1st to 15thNight
68%39%12%5%
2506
16th to endNight
60%29%17%8%
2610
February1st to 15thNight
62%311%16%5%
2287
16th to endNight
58%39%18%10%
1957
March1st to 15thNight
56%211%20%8%
2079
16th to endNight
46%29%20%17%3
2047
April1st to 15thNight
51%26%20%16%1
1796
16th to endNight
47%38%19%17%3
1746
May1st to 15thNight
48%37%20%15%4
1440
16th to endNight
42%314%21%15%2
1497
June1st to 15thNight
48%5%12%21%11%
1440
16th to endNight
43%5%12%21%14%
1440
July1st to 15thNight
33%412%30%18%1
1360
16th to endNight
32%5%15%29%15%1
1418
August1st to 15thNight
37%416%26%13%
1514
16th to endNight
32%316%33%14%
1695
September1st to 15thNight
39%411%32%11%
1650
16th to endNight
38%311%33%12%
1801
October1st to 15thNight
50%49%22%12%
1980
16th to endNight
60%212%16%7%
2180
November1st to 15thNight
51%214%18%12%1
2334
16th to endNight
61%39%17%5%1
2520
December1st to 15thNight
65%312%14%4
2520
16th to endNight
68%310%11%5%
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
30%21%25%13%10%
60
16th to endDay
40%11%28%12%6%
77
February1st to 15thDay
36%24%31%7%
90
16th to endDay
37%14%28%13%6%
174
March1st to 15thDay
26%15%30%21%6%
270
16th to endDay
26%14%31%14%10%1
288
April1st to 15thDay
29%21%26%12%10%
270
16th to endDay
22%18%28%17%8%5%
270
May1st to 15thDay
28%12%27%19%9%3
288
16th to endDay
21%14%33%18%10%3
331
June1st to 15thDay
26%8%27%24%11%2
315
16th to endDay
20%8%29%23%13%3
315
July1st to 15thDay
16%7%27%29%13%6%
305
16th to endDay
13%5%31%27%15%6%
326
August1st to 15thDay
13%5%25%34%14%7%
297
16th to endDay
14%426%28%13%12%
268
September1st to 15thDay
17%6%27%20%14%13%
255
16th to endDay
22%6%29%19%14%7%
254
October1st to 15thDay
27%10%25%21%10%3
255
16th to endDay
32%15%27%18%5%
259
November1st to 15thDay
17%13%30%27%10%1
175
16th to endDay
30%8%33%15%13%
60
December1st to 15thDay
31%11%36%11%8%
60
16th to endDay
50%25%25%
64
January1st to 15thNight
30%16%30%18%4
720
16th to endNight
23%13%33%22%5%
768
February1st to 15thNight
21%18%36%20%2
704
16th to endNight
24%14%35%20%5%
631
March1st to 15thNight
29%14%29%23%2
720
16th to endNight
22%16%26%23%10%
768
April1st to 15thNight
28%14%30%21%4
718
16th to endNight
24%14%28%21%9%
666
May1st to 15thNight
22%8%26%31%8%1
360
16th to endNight
13%10%36%26%12%
375
June1st to 15thNight
20%9%26%31%11%1
360
16th to endNight
16%326%36%16%
360
July1st to 15thNight
11%427%37%17%
340
16th to endNight
8%327%42%17%1
376
August1st to 15thNight
13%423%34%22%1
465
16th to endNight
11%425%35%20%2
645
September1st to 15thNight
18%5%24%29%20%1
660
16th to endNight
19%8%23%24%21%2
657
October1st to 15thNight
25%10%25%24%12%1
660
16th to endNight
32%11%25%24%5%
704
November1st to 15thNight
27%10%29%20%11%
700
16th to endNight
32%15%24%19%8%
720
December1st to 15thNight
30%19%29%16%4
720
16th to endNight
33%14%31%17%11
768
Page generated at 2017-08-13 14:16:40. Version ac04

Copyright 2017 A. Danko


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