Beckstrom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beckstrom Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
33%
15895
14%
48021
9%
15854
39%
15854
19%
33707

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
15%
899
9%
2506
2%
895
21%
895
11%
2009
January16th to endNight
18%
871
9%
2599
3%
871
25%
871
12%
2039
February1st to 15thNight
16%
701
10%
2286
2%
701
24%
701
10%
1748
February16th to endNight
24%
631
13%
1893
5%
631
32%
631
13%
1415
March1st to 15thNight
24%
720
14%
2070
7%
720
30%
720
17%
1511
March16th to endNight
33%
768
18%
2112
10%
768
39%
768
22%
1482
April1st to 15thNight
26%
596
15%
1799
8%
596
33%
596
20%
1259
April16th to endNight
32%
540
19%
1620
7%
540
41%
540
23%
1078
May1st to 15thNight
37%
540
15%
1620
9%
540
43%
540
22%
1088
May16th to endNight
41%
523
16%
1618
10%
522
48%
522
26%
1012
June1st to 15thNight
43%
360
15%
1260
14%
360
49%
360
24%
773
June16th to endNight
51%
360
17%
1260
17%
360
57%
360
29%
736
July1st to 15thNight
63%
483
16%
1333
14%
483
65%
483
40%
782
July16th to endNight
60%
564
16%
1489
11%
531
63%
531
35%
904
August1st to 15thNight
64%
539
17%
1609
14%
536
66%
536
32%
991
August16th to endNight
57%
573
22%
1719
16%
573
62%
573
34%
1016
September1st to 15thNight
55%
672
21%
1920
16%
672
58%
672
31%
1191
September16th to endNight
56%
717
23%
1980
17%
717
60%
717
33%
1240
October1st to 15thNight
39%
720
16%
2085
12%
720
45%
720
25%
1408
October16th to endNight
22%
768
12%
2403
7%
768
30%
768
14%
1770
November1st to 15thNight
29%
760
17%
2471
14%
760
35%
760
17%
1706
November16th to endNight
21%
780
12%
2678
7%
780
28%
780
11%
1985
December1st to 15thNight
14%
826
8%
2776
2%
826
21%
826
9%
2161
December16th to endNight
13%
984
8%
2915
2%
984
19%
984
8%
2403

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
14%9%37%6%35%45%7%33%
48805
Night
14%9%46%5%3445%6%34%
48198
Cloud CoverDay
14%9%37%5%35%45%7%33%
48815
Night
15%9%46%5%3445%6%34%
48202
TransparencyDay
50%6%12%19%10%1
48500
Night
48%6%12%20%10%1
48021
SeeingDay
18%11%28%22%13%5%
6136
Night
19%10%30%26%11%1
15900

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
16%16%6%9%8%34445%19%
1432
16th to endDay
14%16%7%11%9%4445%415%
1623
February1st to 15thDay
12%16%6%10%7%46%5%5%6%18%
1575
16th to endDay
13%14%5%8%9%2435%5%26%
1580
March1st to 15thDay
15%10%5%9%8%34346%26%
1879
16th to endDay
17%9%5%10%6%34245%29%
2112
April1st to 15thDay
19%11%46%5%24346%31%
2157
16th to endDay
15%8%245%3446%6%37%
2340
May1st to 15thDay
18%7%35%435%347%36%
2331
16th to endDay
11%6%25%5%35%447%41%
2491
June1st to 15thDay
11%6%25%435%47%8%39%
2700
16th to endDay
11%6%35%5%35%5%6%9%38%
2700
July1st to 15thDay
6%436%5%36%5%6%9%43%
2544
16th to endDay
8%426%5%36%46%10%40%
2577
August1st to 15thDay
10%5%25%6%36%6%6%9%37%
2340
16th to endDay
12%6%245%35%5%5%7%41%
2483
September1st to 15thDay
13%5%25%6%25%6%6%8%38%
2025
16th to endDay
13%5%25%5%35%45%9%38%
1980
October1st to 15thDay
17%8%35%6%34445%35%
1875
16th to endDay
22%11%36%5%34346%27%
1818
November1st to 15thDay
16%12%37%5%2446%5%31%
1717
16th to endDay
15%14%5%9%7%35%5%5%423%
1610
December1st to 15thDay
15%16%6%10%7%4444422%
1511
16th to endDay
20%16%7%9%7%34345%17%
1405
January1st to 15thNight
20%12%5%9%6%44446%22%
2506
16th to endNight
13%12%7%9%7%46%446%22%
2599
February1st to 15thNight
13%15%5%8%7%35%445%25%
2284
16th to endNight
15%12%48%7%36%45%6%26%
1893
March1st to 15thNight
14%11%47%6%35%5%45%32%
2058
16th to endNight
15%8%46%5%24446%36%
2112
April1st to 15thNight
19%9%5%5%32435%8%32%
1799
16th to endNight
16%7%35%5%24436%41%
1620
May1st to 15thNight
13%8%35%6%3445%6%37%
1620
16th to endNight
12%5%15%435%447%44%
1616
June1st to 15thNight
11%4245%35%5%5%8%42%
1260
16th to endNight
9%4145%25%5%6%10%45%
1260
July1st to 15thNight
7%42432345%8%52%
1413
16th to endNight
6%3244345%6%8%49%
1591
August1st to 15thNight
8%424435%6%6%8%45%
1620
16th to endNight
9%4345%24346%51%
1719
September1st to 15thNight
11%425%5%235%5%7%46%
1920
16th to endNight
10%6%2442445%7%47%
1980
October1st to 15thNight
15%6%35%43435%7%39%
2085
16th to endNight
21%9%37%5%34446%29%
2403
November1st to 15thNight
14%8%36%6%35%45%6%33%
2471
16th to endNight
19%11%47%6%3445%6%24%
2678
December1st to 15thNight
18%14%5%7%6%35%45%423%
2776
16th to endNight
19%15%7%10%5%34445%18%
2915

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
16%17%6%9%8%34445%19%
1432
16th to endDay
14%16%8%10%9%45%445%15%
1623
February1st to 15thDay
12%17%5%10%7%46%5%45%19%
1575
16th to endDay
13%14%5%9%8%3345%5%26%
1580
March1st to 15thDay
16%10%5%10%7%34346%26%
1890
16th to endDay
17%10%5%10%6%24345%29%
2111
April1st to 15thDay
19%11%36%5%34346%31%
2157
16th to endDay
15%8%25%5%3446%7%37%
2340
May1st to 15thDay
18%6%35%435%346%37%
2331
16th to endDay
12%6%25%6%35%447%41%
2491
June1st to 15thDay
11%6%36%43446%8%40%
2700
16th to endDay
11%5%35%5%35%5%5%9%38%
2700
July1st to 15thDay
6%435%5%35%5%6%8%43%
2544
16th to endDay
8%5%26%5%35%5%6%9%40%
2577
August1st to 15thDay
9%5%25%6%36%6%6%8%37%
2340
16th to endDay
12%6%24435%5%5%8%41%
2483
September1st to 15thDay
13%426%5%35%6%6%7%38%
2025
16th to endDay
13%5%25%5%35%45%9%38%
1980
October1st to 15thDay
18%8%25%6%24445%36%
1875
16th to endDay
22%10%36%5%24446%27%
1818
November1st to 15thDay
16%11%37%6%3345%5%31%
1717
16th to endDay
16%14%410%6%3445%5%22%
1610
December1st to 15thDay
15%16%6%10%7%3444423%
1511
16th to endDay
20%16%7%9%5%25%345%17%
1405
January1st to 15thNight
20%12%6%8%6%34446%22%
2506
16th to endNight
13%12%8%9%8%45%445%23%
2599
February1st to 15thNight
13%15%6%8%6%35%45%5%25%
2277
16th to endNight
15%11%5%8%6%35%5%5%6%26%
1893
March1st to 15thNight
14%11%47%6%35%445%32%
2070
16th to endNight
15%8%46%5%25%446%36%
2112
April1st to 15thNight
20%8%45%42345%7%32%
1799
16th to endNight
15%8%25%434445%41%
1620
May1st to 15thNight
13%8%35%6%34446%38%
1619
16th to endNight
12%5%25%435%45%7%44%
1616
June1st to 15thNight
10%5%246%35%5%5%8%43%
1260
16th to endNight
9%4244345%5%10%45%
1260
July1st to 15thNight
7%42332345%8%53%
1413
16th to endNight
7%314435%5%6%8%50%
1591
August1st to 15thNight
8%414445%6%6%8%45%
1620
16th to endNight
10%424424446%51%
1719
September1st to 15thNight
12%415%424447%47%
1920
16th to endNight
10%6%24324448%47%
1980
October1st to 15thNight
16%6%35%43435%7%40%
2085
16th to endNight
21%10%37%434346%29%
2403
November1st to 15thNight
15%8%36%6%345%5%6%33%
2471
16th to endNight
20%11%46%5%3445%7%25%
2678
December1st to 15thNight
18%14%5%8%5%3445%424%
2776
16th to endNight
20%15%7%9%5%2445%5%18%
2915

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
66%5%10%13%3
1433
16th to endDay
69%6%9%9%3
1623
February1st to 15thDay
66%6%10%12%3
1577
16th to endDay
59%5%10%16%7%
1580
March1st to 15thDay
59%6%11%15%7%
1890
16th to endDay
56%5%11%18%7%1
2112
April1st to 15thDay
54%410%19%10%
2157
16th to endDay
45%7%14%17%13%2
2340
May1st to 15thDay
48%5%10%22%10%2
2331
16th to endDay
42%6%12%21%15%1
2495
June1st to 15thDay
40%8%11%24%14%
2700
16th to endDay
41%7%13%21%14%
2700
July1st to 15thDay
36%7%11%25%16%2
2395
16th to endDay
39%8%13%21%14%2
2416
August1st to 15thDay
40%9%13%22%12%1
2327
16th to endDay
40%7%12%24%13%1
2483
September1st to 15thDay
40%9%14%24%10%1
2025
16th to endDay
41%6%12%26%11%
1980
October1st to 15thDay
49%5%10%20%12%1
1875
16th to endDay
57%5%15%15%5%
1818
November1st to 15thDay
52%6%13%18%8%
1717
16th to endDay
61%5%14%12%4
1610
December1st to 15thDay
65%5%13%11%3
1511
16th to endDay
68%5%11%11%2
1405
January1st to 15thNight
62%6%10%14%7%
2506
16th to endNight
61%6%13%15%3
2599
February1st to 15thNight
60%6%10%16%6%
2286
16th to endNight
56%6%11%18%7%
1893
March1st to 15thNight
53%5%12%20%7%1
2070
16th to endNight
47%5%11%22%11%1
2112
April1st to 15thNight
49%410%20%13%
1799
16th to endNight
44%5%9%18%18%3
1620
May1st to 15thNight
45%5%10%21%13%3
1620
16th to endNight
38%6%11%24%14%4
1618
June1st to 15thNight
37%8%11%24%16%1
1260
16th to endNight
33%7%15%24%17%1
1260
July1st to 15thNight
28%6%9%31%20%2
1333
16th to endNight
30%8%16%24%17%2
1489
August1st to 15thNight
32%8%12%28%15%1
1609
16th to endNight
32%6%11%30%16%1
1719
September1st to 15thNight
35%6%12%30%14%
1920
16th to endNight
34%6%11%32%13%
1980
October1st to 15thNight
43%6%11%23%14%1
2085
16th to endNight
55%5%13%18%6%
2403
November1st to 15thNight
49%6%13%21%8%
2471
16th to endNight
57%6%15%14%5%
2678
December1st to 15thNight
61%6%13%13%5%
2776
16th to endNight
67%5%10%11%4
2915

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
22%23%37%15%1
90
16th to endDay
33%17%34%13%1
96
February1st to 15thDay
23%23%46%5%1
90
16th to endDay
19%22%39%14%3
81
March1st to 15thDay
31%15%27%23%2
180
16th to endDay
27%11%26%21%10%2
288
April1st to 15thDay
25%14%27%20%10%1
270
16th to endDay
19%14%31%16%12%5%
270
May1st to 15thDay
22%13%29%20%10%4
288
16th to endDay
14%12%31%21%13%5%
355
June1st to 15thDay
13%10%31%28%12%3
495
16th to endDay
14%8%33%24%13%4
495
July1st to 15thDay
9%6%32%29%14%7%
475
16th to endDay
9%5%28%29%18%8%
437
August1st to 15thDay
11%221%26%22%15%
313
16th to endDay
16%7%17%24%20%14%
332
September1st to 15thDay
13%5%22%21%23%13%
315
16th to endDay
14%7%16%25%23%12%
314
October1st to 15thDay
23%9%23%25%15%3
315
16th to endDay
26%16%33%18%41
234
November1st to 15thDay
20%16%34%19%8%
135
16th to endDay
20%26%35%10%5%
101
December1st to 15thDay
30%25%26%16%1
90
16th to endDay
35%28%33%2
77
January1st to 15thNight
26%18%33%17%3
900
16th to endNight
18%12%39%23%5%
871
February1st to 15thNight
21%18%37%18%4
704
16th to endNight
22%16%28%26%4
631
March1st to 15thNight
21%13%33%26%5%
720
16th to endNight
19%10%31%28%9%1
768
April1st to 15thNight
24%13%32%23%5%
596
16th to endNight
20%9%34%25%8%1
540
May1st to 15thNight
18%6%30%34%9%1
540
16th to endNight
15%5%32%29%15%1
524
June1st to 15thNight
12%432%38%11%
360
16th to endNight
11%230%38%17%
360
July1st to 15thNight
11%118%42%23%2
483
16th to endNight
7%124%43%21%1
564
August1st to 15thNight
10%116%41%27%2
539
16th to endNight
11%222%32%26%4
573
September1st to 15thNight
14%322%32%20%5%
672
16th to endNight
15%419%32%23%4
717
October1st to 15thNight
18%7%29%27%15%1
720
16th to endNight
26%13%32%21%4
768
November1st to 15thNight
19%14%31%22%11%
760
16th to endNight
26%16%30%20%5%
780
December1st to 15thNight
25%17%34%17%3
826
16th to endNight
27%15%36%17%2
984
Page generated at 2017-12-21 07:04:51. Version ac04

Copyright 2017 A. Danko


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