StarBourne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the StarBourne Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
50%
15508
24%
47611
17%
15462
57%
15462
30%
28728

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
30%
900
24%
2327
8%
895
41%
895
27%
1516
January16th to endNight
26%
918
24%
2454
8%
918
36%
918
26%
1630
February1st to 15thNight
30%
704
26%
2112
11%
701
42%
701
27%
1314
February16th to endNight
24%
631
24%
1893
8%
631
37%
631
23%
1212
March1st to 15thNight
30%
597
24%
2037
13%
597
41%
597
22%
1260
March16th to endNight
39%
576
23%
2053
16%
576
49%
576
28%
1142
April1st to 15thNight
39%
539
24%
1797
17%
539
50%
539
28%
1041
April16th to endNight
45%
540
26%
1800
20%
540
58%
540
34%
988
May1st to 15thNight
51%
539
22%
1800
16%
539
62%
539
33%
1005
May16th to endNight
64%
563
21%
1869
22%
561
68%
561
33%
1053
June1st to 15thNight
73%
540
16%
1538
15%
540
74%
540
33%
951
June16th to endNight
73%
540
17%
1606
17%
540
75%
540
32%
969
July1st to 15thNight
78%
510
16%
1530
18%
510
79%
510
30%
946
July16th to endNight
77%
564
13%
1658
16%
531
77%
531
27%
1061
August1st to 15thNight
81%
539
14%
1788
17%
536
81%
536
31%
1073
August16th to endNight
69%
573
17%
1910
21%
573
70%
573
23%
1260
September1st to 15thNight
72%
540
20%
1800
22%
540
73%
540
30%
1091
September16th to endNight
72%
666
29%
1929
26%
666
73%
666
38%
1121
October1st to 15thNight
64%
720
31%
2125
25%
720
68%
720
43%
1140
October16th to endNight
55%
768
35%
2304
28%
768
62%
768
40%
1252
November1st to 15thNight
52%
700
33%
2101
24%
700
61%
700
37%
1178
November16th to endNight
44%
720
31%
2340
23%
720
55%
720
33%
1293
December1st to 15thNight
36%
720
24%
2340
16%
720
46%
720
25%
1457
December16th to endNight
30%
901
18%
2500
10%
901
36%
901
20%
1775

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
11%6%26%6%35%5%5%7%38%
48080
Night
10%5%2442445%8%46%
47816
TransparencyDay
42%6%10%17%17%5%
47788
Night
35%5%12%19%19%8%
47613
SeeingDay
12%5%15%26%26%13%
5578
Night
13%7%22%29%21%5%
15509

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
18%8%25%413335%44%
1611
16th to endDay
18%6%2442333345%
1767
February1st to 15thDay
15%7%35%434346%42%
1750
16th to endDay
13%7%45%423446%42%
1580
March1st to 15thDay
16%8%245%345%45%40%
1932
16th to endDay
11%6%36%435%45%6%42%
2167
April1st to 15thDay
11%6%26%5%345%5%7%40%
2151
16th to endDay
8%6%25%7%36%5%6%8%39%
2160
May1st to 15thDay
11%6%35%7%36%5%6%6%36%
2151
16th to endDay
8%438%5%47%6%6%8%35%
2244
June1st to 15thDay
6%5%27%8%5%9%7%7%9%30%
2400
16th to endDay
5%5%36%7%7%8%8%8%8%29%
2340
July1st to 15thDay
7%5%37%8%6%9%7%8%9%24%
2340
16th to endDay
8%6%37%9%5%9%8%8%9%23%
2397
August1st to 15thDay
6%437%9%48%7%7%9%29%
2160
16th to endDay
12%6%27%7%5%6%6%6%8%29%
2292
September1st to 15thDay
11%5%36%8%46%5%5%6%36%
2160
16th to endDay
10%5%25%5%35%45%7%43%
2019
October1st to 15thDay
7%415%42345%6%53%
1831
16th to endDay
9%413323335%58%
1919
November1st to 15thDay
9%5%2442335%6%52%
1755
16th to endDay
11%6%24323336%53%
1620
December1st to 15thDay
15%9%45%5%24345%39%
1620
16th to endDay
17%8%35%5%34345%38%
1714
January1st to 15thNight
15%7%25%323346%46%
2327
16th to endNight
19%6%33423345%43%
2454
February1st to 15thNight
13%7%24414346%45%
2103
16th to endNight
16%6%35%423345%44%
1893
March1st to 15thNight
15%7%24424347%43%
2037
16th to endNight
10%5%2442435%6%50%
2053
April1st to 15thNight
8%5%15%5%3345%7%48%
1797
16th to endNight
7%4134345%6%9%50%
1800
May1st to 15thNight
7%5%2432446%10%49%
1799
16th to endNight
5%3245%35%46%10%47%
1869
June1st to 15thNight
3435%5%45%6%7%11%42%
1538
16th to endNight
33245%36%8%8%11%43%
1606
July1st to 15thNight
43246%36%6%7%11%42%
1620
16th to endNight
44245%46%6%8%13%38%
1771
August1st to 15thNight
43145%35%8%9%15%38%
1800
16th to endNight
8%5%25%6%35%5%7%11%37%
1910
September1st to 15thNight
7%425%5%35%6%7%9%44%
1800
16th to endNight
8%5%143345%6%8%50%
1929
October1st to 15thNight
6%324323446%58%
2125
16th to endNight
10%41331323460%
2304
November1st to 15thNight
9%5%14323336%55%
2101
16th to endNight
11%6%23323335%55%
2340
December1st to 15thNight
15%6%35%424336%44%
2340
16th to endNight
18%11%36%433336%35%
2500

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%2415%24%9%
1612
16th to endDay
43%2414%25%8%
1767
February1st to 15thDay
42%27%16%20%9%
1752
16th to endDay
43%36%17%21%8%
1580
March1st to 15thDay
44%47%17%19%5%
1932
16th to endDay
40%5%8%17%21%5%
2169
April1st to 15thDay
42%48%17%19%6%
2151
16th to endDay
40%6%10%20%19%4
2160
May1st to 15thDay
44%6%12%15%16%5%
2151
16th to endDay
43%6%12%23%13%
2248
June1st to 15thDay
44%8%14%21%10%
2400
16th to endDay
46%10%13%18%9%1
2340
July1st to 15thDay
48%11%16%14%6%1
2201
16th to endDay
50%11%16%14%5%
2247
August1st to 15thDay
45%8%18%16%8%1
2148
16th to endDay
50%9%15%14%8%2
2292
September1st to 15thDay
45%7%13%16%11%5%
2160
16th to endDay
38%5%10%18%19%6%
2019
October1st to 15thDay
30%49%17%24%13%
1831
16th to endDay
29%3312%35%15%
1919
November1st to 15thDay
32%37%16%30%9%
1755
16th to endDay
33%26%15%26%15%
1620
December1st to 15thDay
47%29%18%15%6%
1620
16th to endDay
48%36%19%17%4
1714
January1st to 15thNight
40%35%15%24%10%
2327
16th to endNight
42%35%16%22%8%
2454
February1st to 15thNight
40%26%17%21%11%
2112
16th to endNight
43%3418%20%10%
1893
March1st to 15thNight
41%38%16%22%6%
2037
16th to endNight
33%412%20%23%6%
2053
April1st to 15thNight
34%410%21%19%9%
1797
16th to endNight
29%5%12%22%22%7%
1800
May1st to 15thNight
30%6%14%23%18%6%
1800
16th to endNight
30%6%16%25%18%2
1871
June1st to 15thNight
32%8%17%26%14%
1538
16th to endNight
30%9%22%21%14%1
1606
July1st to 15thNight
31%11%23%22%7%3
1530
16th to endNight
33%13%25%20%6%
1658
August1st to 15thNight
28%12%28%18%10%1
1788
16th to endNight
38%11%19%16%10%3
1910
September1st to 15thNight
32%9%18%18%13%6%
1800
16th to endNight
30%5%13%21%19%9%
1929
October1st to 15thNight
26%39%19%25%15%
2125
16th to endNight
28%3413%27%22%
2304
November1st to 15thNight
30%36%17%29%13%
2101
16th to endNight
32%25%17%24%17%
2340
December1st to 15thNight
42%29%20%20%5%
2340
16th to endNight
51%36%14%18%5%
2500

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
23%20%28%17%7%2
90
16th to endDay
15%31%37%12%3
96
February1st to 15thDay
17%15%44%17%4
90
16th to endDay
19%18%37%23%1
81
March1st to 15thDay
31%21%35%12%
90
16th to endDay
22%10%22%29%14%
153
April1st to 15thDay
18%12%25%28%14%1
270
16th to endDay
14%9%22%35%15%2
270
May1st to 15thDay
16%6%22%31%18%4
288
16th to endDay
11%322%29%22%9%
331
June1st to 15thDay
10%16%37%32%11%
453
16th to endDay
7%211%28%29%19%
495
July1st to 15thDay
6%16%26%41%17%
475
16th to endDay
5%2418%44%24%
446
August1st to 15thDay
10%1218%38%27%
313
16th to endDay
13%5%18%39%22%
332
September1st to 15thDay
11%18%19%33%24%
315
16th to endDay
11%19%26%32%18%
314
October1st to 15thDay
4419%33%24%12%
166
16th to endDay
14%6%20%31%21%4
144
November1st to 15thDay
23%432%27%8%3
90
16th to endDay
8%13%45%17%8%5%
90
December1st to 15thDay
23%11%40%18%33
90
16th to endDay
29%12%30%25%21
96
January1st to 15thNight
20%15%31%24%8%
900
16th to endNight
23%14%33%23%5%
918
February1st to 15thNight
20%14%32%26%5%
704
16th to endNight
20%18%32%23%4
631
March1st to 15thNight
19%14%32%27%5%
597
16th to endNight
14%8%34%31%10%
576
April1st to 15thNight
13%11%33%28%12%
539
16th to endNight
10%8%32%35%12%
540
May1st to 15thNight
10%428%35%17%2
540
16th to endNight
5%119%42%26%3
563
June1st to 15thNight
5%16%40%38%6%
540
16th to endNight
417%30%38%16%
540
July1st to 15thNight
41230%45%16%
510
16th to endNight
5%1324%45%18%
564
August1st to 15thNight
5%318%48%22%
539
16th to endNight
9%1423%41%19%
573
September1st to 15thNight
9%26%28%41%12%
540
16th to endNight
9%17%32%40%8%
666
October1st to 15thNight
8%118%31%33%6%
720
16th to endNight
13%5%21%29%26%3
768
November1st to 15thNight
11%7%24%35%18%3
700
16th to endNight
15%9%28%29%15%1
720
December1st to 15thNight
20%10%30%28%10%
720
16th to endNight
24%10%29%26%7%
901
Page generated at 2017-11-01 16:23:35. Version ac04

Copyright 2017 A. Danko


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