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 2017-08-12.

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
33%
15387
14%
46458
8%
15346
39%
15346
19%
32664

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
24%
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
29%
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
38%
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
63%
527
17%
1575
14%
524
65%
524
32%
969
August16th to endNight
59%
525
21%
1575
15%
525
63%
525
34%
929
September1st to 15thNight
53%
616
21%
1760
16%
616
57%
616
30%
1107
September16th to endNight
54%
657
21%
1815
15%
657
58%
657
32%
1148
October1st to 15thNight
40%
660
17%
1911
13%
660
46%
660
25%
1276
October16th to endNight
22%
704
11%
2203
6%
704
29%
704
13%
1644
November1st to 15thNight
29%
700
18%
2276
14%
700
35%
700
18%
1547
November16th to endNight
22%
720
11%
2472
7%
720
29%
720
11%
1855
December1st to 15thNight
14%
762
7%
2562
2%
762
20%
762
9%
2006
December16th to endNight
13%
960
8%
2844
2%
960
19%
960
9%
2347

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%47%6%35%45%7%33%
47501
Night
14%9%46%5%3445%6%34%
46635
Cloud CoverDay
14%9%47%5%35%45%7%33%
47511
Night
15%9%46%5%3445%6%34%
46639
TransparencyDay
50%6%12%19%10%1
47196
Night
49%6%12%20%10%1
46458
SeeingDay
17%10%28%23%13%5%
5704
Night
19%10%30%27%10%1
15392

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
9%5%25%6%36%6%6%8%37%
2288
16th to endDay
12%6%245%25%5%5%8%41%
2275
September1st to 15thDay
14%5%25%6%25%6%6%8%37%
1856
16th to endDay
13%6%35%5%35%45%10%37%
1815
October1st to 15thDay
17%8%36%6%34446%35%
1719
16th to endDay
23%11%36%5%24346%27%
1667
November1st to 15thDay
15%12%37%6%2446%5%31%
1582
16th to endDay
16%14%5%9%8%35%5%5%422%
1486
December1st to 15thDay
15%15%6%10%7%4434422%
1395
16th to endDay
20%16%7%9%7%34345%17%
1377
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%7%8%45%
1586
16th to endNight
9%434423347%51%
1575
September1st to 15thNight
12%5%25%5%235%5%7%46%
1760
16th to endNight
11%6%2442445%7%46%
1815
October1st to 15thNight
15%6%35%43435%7%40%
1911
16th to endNight
22%9%47%5%34436%27%
2203
November1st to 15thNight
14%8%36%6%35%45%6%34%
2276
16th to endNight
20%12%47%6%3445%6%24%
2472
December1st to 15thNight
19%15%5%7%5%35%44423%
2562
16th to endNight
19%15%7%10%5%3445%5%18%
2844

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%6%25%6%36%6%6%8%37%
2288
16th to endDay
12%5%24435%5%5%8%41%
2275
September1st to 15thDay
14%426%5%35%6%6%7%38%
1856
16th to endDay
14%6%25%5%35%45%10%36%
1815
October1st to 15thDay
17%8%26%6%23446%35%
1719
16th to endDay
23%10%46%5%24346%27%
1667
November1st to 15thDay
16%11%37%6%2445%6%31%
1582
16th to endDay
16%14%5%10%6%35%45%5%22%
1486
December1st to 15thDay
16%15%5%10%6%3444422%
1395
16th to endDay
20%16%7%9%5%35%345%17%
1377
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%
1586
16th to endNight
10%424423446%51%
1575
September1st to 15thNight
12%425%424446%46%
1760
16th to endNight
11%6%25%424348%46%
1815
October1st to 15thNight
15%6%35%43445%7%40%
1911
16th to endNight
22%9%37%434346%28%
2203
November1st to 15thNight
14%8%36%7%345%5%6%35%
2276
16th to endNight
21%12%5%6%5%3445%6%24%
2472
December1st to 15thNight
19%15%5%7%5%3444423%
2562
16th to endNight
20%15%7%9%5%3445%5%18%
2844

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
2275
16th to endDay
39%8%12%25%12%1
2275
September1st to 15thDay
41%9%14%24%9%
1856
16th to endDay
42%7%12%25%11%
1815
October1st to 15thDay
49%5%10%20%12%1
1719
16th to endDay
58%5%16%15%4
1667
November1st to 15thDay
52%6%12%19%8%
1582
16th to endDay
62%5%13%12%4
1486
December1st to 15thDay
66%5%13%11%3
1395
16th to endDay
68%5%11%11%2
1377
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%16%1
1575
16th to endNight
32%6%11%30%17%1
1575
September1st to 15thNight
36%6%12%29%13%
1760
16th to endNight
35%6%11%32%13%
1815
October1st to 15thNight
41%7%11%23%14%
1911
16th to endNight
56%6%13%17%5%
2203
November1st to 15thNight
47%6%13%22%8%1
2276
16th to endNight
58%6%14%14%5%
2472
December1st to 15thNight
62%6%13%12%4
2562
16th to endNight
67%5%10%11%4
2844

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
10%321%25%22%16%
297
16th to endDay
16%6%14%24%21%16%
268
September1st to 15thDay
14%5%21%21%23%12%
255
16th to endDay
16%6%18%25%22%9%
254
October1st to 15thDay
21%9%23%25%16%3
255
16th to endDay
27%15%33%17%5%1
179
November1st to 15thDay
14%16%33%24%10%1
90
16th to endDay
19%25%35%10%8%
67
December1st to 15thDay
30%28%23%18%
60
16th to endDay
31%28%36%2
69
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%117%40%28%2
527
16th to endNight
11%221%33%26%4
525
September1st to 15thNight
15%422%32%19%5%
616
16th to endNight
15%5%19%33%21%5%
657
October1st to 15thNight
18%7%29%27%16%1
660
16th to endNight
27%13%32%20%4
704
November1st to 15thNight
18%14%32%21%12%
700
16th to endNight
27%15%30%21%5%
720
December1st to 15thNight
27%17%34%17%3
762
16th to endNight
27%14%36%18%2
960
Page generated at 2017-08-13 14:16:26. Version ac04

Copyright 2017 A. Danko


Beckstrom Observatory Clear Sky Chart | Charts Home