Borman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Borman Observatory clear sky chart from 2005-11-05 to 2017-04-28.

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
44%
15312
21%
45579
15%
15268
51%
15268
28%
28865

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
26%
900
19%
2506
8%
895
36%
895
22%
1736
January16th to endNight
25%
936
18%
2565
8%
936
33%
936
22%
1802
February1st to 15thNight
23%
704
18%
2112
7%
701
32%
701
19%
1464
February16th to endNight
23%
631
18%
1893
7%
631
33%
631
22%
1271
March1st to 15thNight
28%
720
17%
2160
9%
720
35%
720
21%
1460
March16th to endNight
38%
651
16%
2022
11%
651
45%
651
20%
1377
April1st to 15thNight
40%
539
22%
1797
15%
539
52%
539
28%
1073
April16th to endNight
43%
534
21%
1756
17%
534
50%
534
27%
1084
May1st to 15thNight
44%
494
18%
1484
11%
494
51%
494
24%
989
May16th to endNight
61%
513
19%
1493
16%
513
63%
513
30%
941
June1st to 15thNight
64%
495
23%
1320
17%
495
68%
495
38%
795
June16th to endNight
71%
495
22%
1320
17%
495
73%
495
43%
767
July1st to 15thNight
67%
465
20%
1240
17%
465
69%
465
37%
768
July16th to endNight
77%
522
22%
1332
19%
489
79%
489
43%
774
August1st to 15thNight
78%
494
26%
1585
28%
491
79%
491
42%
819
August16th to endNight
75%
525
25%
1750
30%
525
77%
525
38%
940
September1st to 15thNight
68%
525
29%
1680
29%
525
71%
525
35%
956
September16th to endNight
59%
657
27%
1815
20%
657
63%
657
35%
1096
October1st to 15thNight
56%
660
31%
1841
24%
660
61%
660
38%
1084
October16th to endNight
41%
704
26%
2216
19%
704
51%
704
29%
1343
November1st to 15thNight
44%
700
29%
2276
23%
700
55%
700
32%
1282
November16th to endNight
36%
720
24%
2340
17%
720
47%
720
26%
1427
December1st to 15thNight
31%
768
15%
2388
10%
768
38%
768
19%
1667
December16th to endNight
24%
960
16%
2688
6%
960
32%
960
19%
1950

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
13%6%25%5%3445%8%40%
46124
Night
13%6%25%42445%7%43%
45758
TransparencyDay
41%5%12%23%14%2
45805
Night
40%411%23%16%3
45581
SeeingDay
15%5%21%24%21%11%
5151
Night
16%6%25%30%17%2
15315

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
21%7%37%5%24445%33%
1432
16th to endDay
13%9%36%6%3435%7%37%
1656
February1st to 15thDay
16%9%46%433347%36%
1750
16th to endDay
13%7%48%5%46%5%5%6%32%
1580
March1st to 15thDay
19%9%35%43343438%
1800
16th to endDay
17%9%36%425%45%7%33%
2210
April1st to 15thDay
13%5%25%43445%7%42%
2151
16th to endDay
16%6%25%5%24447%40%
2149
May1st to 15thDay
19%6%26%5%3445%8%33%
2136
16th to endDay
9%6%36%5%45%5%6%8%38%
2267
June1st to 15thDay
8%425%426%5%6%9%44%
2310
16th to endDay
5%325%5%26%5%7%10%43%
2310
July1st to 15thDay
12%425%435%5%8%10%37%
2310
16th to endDay
5%3146%37%6%7%12%41%
2429
August1st to 15thDay
6%4245%35%6%6%10%44%
2032
16th to endDay
7%4245%345%6%11%45%
2100
September1st to 15thDay
10%425%6%4446%8%42%
1939
16th to endDay
12%425%5%24346%49%
1815
October1st to 15thDay
11%413324347%51%
1788
16th to endDay
14%5%24413345%49%
1653
November1st to 15thDay
10%5%24324447%49%
1582
16th to endDay
20%6%34423335%43%
1620
December1st to 15thDay
22%8%46%42423435%
1569
16th to endDay
20%11%36%423235%36%
1536
January1st to 15thNight
19%7%46%433345%37%
2506
16th to endNight
15%9%36%6%2345%6%35%
2565
February1st to 15thNight
17%9%46%5%2345%5%35%
2103
16th to endNight
15%7%46%42445%6%37%
1893
March1st to 15thNight
17%7%35%434435%38%
2160
16th to endNight
17%6%35%5%25%45%7%36%
2022
April1st to 15thNight
14%5%23423446%47%
1797
16th to endNight
16%5%35%423447%43%
1756
May1st to 15thNight
15%6%37%43345%8%37%
1484
16th to endNight
6%435%5%5%5%5%6%9%43%
1492
June1st to 15thNight
6%4244445%6%10%47%
1320
16th to endNight
5%2133145%7%11%50%
1320
July1st to 15thNight
7%325%42446%10%48%
1320
16th to endNight
5%2135%25%47%10%51%
1430
August1st to 15thNight
5%21422446%9%55%
1596
16th to endNight
432342446%11%52%
1750
September1st to 15thNight
8%4144235%6%7%50%
1680
16th to endNight
10%5%345%23347%49%
1815
October1st to 15thNight
10%415%423335%55%
1841
16th to endNight
16%5%2432334449%
2216
November1st to 15thNight
12%433423446%51%
2276
16th to endNight
18%6%24323345%46%
2340
December1st to 15thNight
22%8%35%3235%45%34%
2388
16th to endNight
21%10%35%5%34345%32%
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
52%411%20%11%
1433
16th to endDay
46%312%28%8%
1656
February1st to 15thDay
48%311%24%10%1
1752
16th to endDay
51%5%12%20%10%
1580
March1st to 15thDay
50%39%22%12%1
1800
16th to endDay
50%5%13%23%6%1
2211
April1st to 15thDay
40%5%12%24%17%
2151
16th to endDay
43%412%25%12%2
2149
May1st to 15thDay
48%6%13%20%10%
2136
16th to endDay
41%7%15%19%13%3
2271
June1st to 15thDay
33%6%12%25%18%2
2310
16th to endDay
32%8%14%21%17%4
2310
July1st to 15thDay
39%6%13%21%15%4
2161
16th to endDay
30%8%19%25%13%1
2264
August1st to 15thDay
33%6%14%23%18%2
2019
16th to endDay
31%5%14%22%19%5%
2100
September1st to 15thDay
37%6%9%21%19%4
1939
16th to endDay
36%46%22%25%4
1815
October1st to 15thDay
31%49%26%22%4
1788
16th to endDay
36%28%28%19%3
1653
November1st to 15thDay
34%410%23%19%7%
1582
16th to endDay
44%37%25%15%2
1620
December1st to 15thDay
53%212%20%10%1
1569
16th to endDay
50%313%22%8%
1536
January1st to 15thNight
49%39%22%14%1
2506
16th to endNight
48%412%22%10%1
2565
February1st to 15thNight
50%310%24%9%1
2112
16th to endNight
46%413%23%11%
1893
March1st to 15thNight
47%410%21%12%3
2160
16th to endNight
46%6%14%20%10%1
2022
April1st to 15thNight
37%411%24%18%4
1797
16th to endNight
40%39%25%16%4
1756
May1st to 15thNight
43%5%12%23%13%
1485
16th to endNight
35%8%13%20%16%5%
1494
June1st to 15thNight
31%5%14%24%20%2
1320
16th to endNight
24%8%16%23%21%5%
1320
July1st to 15thNight
32%6%12%26%17%5%
1240
16th to endNight
26%6%16%31%15%2
1332
August1st to 15thNight
24%5%16%25%23%4
1585
16th to endNight
26%6%12%26%22%5%
1750
September1st to 15thNight
30%5%8%26%21%7%
1680
16th to endNight
34%38%21%24%7%
1815
October1st to 15thNight
32%37%22%26%6%
1841
16th to endNight
39%26%28%17%5%
2216
November1st to 15thNight
33%39%21%24%8%
2276
16th to endNight
40%39%25%18%2
2340
December1st to 15thNight
51%411%20%11%1
2388
16th to endNight
53%311%19%10%1
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
37%7%34%12%7%
90
16th to endDay
14%26%39%17%2
96
February1st to 15thDay
22%14%45%14%3
90
16th to endDay
20%18%33%22%4
81
March1st to 15thDay
27%11%44%14%2
90
16th to endDay
21%11%30%26%10%
261
April1st to 15thDay
16%10%32%25%14%
270
16th to endDay
19%5%25%25%18%5%
259
May1st to 15thDay
23%7%26%22%13%7%
228
16th to endDay
15%322%24%18%16%
311
June1st to 15thDay
10%5%18%26%26%12%
420
16th to endDay
7%322%31%23%12%
420
July1st to 15thDay
14%216%27%23%15%
400
16th to endDay
6%7%25%35%24%
415
August1st to 15thDay
13%17%18%30%28%
253
16th to endDay
12%8%20%40%18%
268
September1st to 15thDay
9%410%20%31%23%
255
16th to endDay
16%312%22%29%16%
254
October1st to 15thDay
11%222%25%28%10%
228
16th to endDay
16%232%29%18%1
96
November1st to 15thDay
7%7%23%30%20%11%
90
16th to endDay
33%6%27%22%8%1
90
December1st to 15thDay
17%14%33%25%44
90
16th to endDay
30%15%41%8%4
96
January1st to 15thNight
23%12%34%25%5%
900
16th to endNight
20%12%37%26%2
936
February1st to 15thNight
22%12%34%27%2
704
16th to endNight
19%12%39%25%2
631
March1st to 15thNight
21%9%34%29%4
720
16th to endNight
20%8%27%33%9%
651
April1st to 15thNight
16%7%32%32%9%1
539
16th to endNight
19%5%25%32%15%1
534
May1st to 15thNight
17%5%25%33%16%1
495
16th to endNight
7%220%33%31%5%
515
June1st to 15thNight
10%217%39%28%2
495
16th to endNight
5%213%41%34%3
495
July1st to 15thNight
9%112%33%40%3
465
16th to endNight
6%16%31%42%12%
522
August1st to 15thNight
6%1431%45%9%
494
16th to endNight
7%7%33%42%7%
525
September1st to 15thNight
9%210%29%39%8%
525
16th to endNight
13%314%27%34%6%
657
October1st to 15thNight
12%320%30%26%6%
660
16th to endNight
19%5%29%30%13%1
704
November1st to 15thNight
13%7%28%31%18%1
700
16th to endNight
21%8%29%27%11%1
720
December1st to 15thNight
27%7%28%27%7%1
768
16th to endNight
26%10%34%24%3
960
Page generated at 2017-04-29 08:45:05. Version ac04

Copyright 2017 A. Danko


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