Chamberlain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chamberlain Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
43%
15929
22%
47082
14%
15883
50%
15883
29%
29442

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
27%
899
19%
2506
8%
895
36%
895
23%
1693
January16th to endNight
24%
960
19%
2500
6%
960
33%
960
23%
1765
February1st to 15thNight
25%
830
15%
2238
5%
827
31%
827
20%
1590
February16th to endNight
26%
631
21%
1893
7%
631
36%
631
24%
1224
March1st to 15thNight
26%
669
18%
2109
8%
669
35%
669
20%
1411
March16th to endNight
33%
576
15%
2026
10%
576
40%
576
19%
1351
April1st to 15thNight
35%
539
21%
1797
14%
539
48%
539
27%
1075
April16th to endNight
39%
540
23%
1800
18%
540
48%
540
27%
1106
May1st to 15thNight
45%
540
18%
1645
12%
539
51%
539
24%
1073
May16th to endNight
55%
563
21%
1497
14%
561
59%
561
34%
965
June1st to 15thNight
64%
540
22%
1440
15%
540
68%
540
44%
826
June16th to endNight
64%
540
22%
1440
15%
540
68%
540
42%
845
July1st to 15thNight
70%
510
20%
1360
16%
510
71%
510
42%
797
July16th to endNight
74%
564
24%
1469
21%
531
77%
531
44%
826
August1st to 15thNight
77%
539
24%
1679
26%
536
79%
536
41%
896
August16th to endNight
74%
573
25%
1910
29%
573
77%
573
38%
1015
September1st to 15thNight
64%
540
28%
1800
29%
540
68%
540
35%
992
September16th to endNight
62%
669
34%
1932
26%
669
68%
669
40%
1071
October1st to 15thNight
54%
684
29%
2040
21%
684
60%
684
38%
1158
October16th to endNight
38%
704
26%
2138
18%
704
47%
704
31%
1262
November1st to 15thNight
40%
700
28%
2276
18%
700
54%
700
33%
1242
November16th to endNight
33%
759
23%
2379
15%
759
43%
759
27%
1466
December1st to 15thNight
29%
900
15%
2520
8%
900
37%
900
20%
1808
December16th to endNight
23%
960
15%
2688
5%
960
32%
960
18%
1985

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
12%6%25%5%3445%7%42%
48122
Night
13%6%25%42445%6%44%
47262
TransparencyDay
40%412%24%15%2
47806
Night
39%311%25%17%3
47084
SeeingDay
13%421%27%22%9%
5952
Night
16%6%26%32%16%1
15930

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
14%9%5%9%5%24345%34%
1432
16th to endDay
13%8%47%5%24347%37%
1722
February1st to 15thDay
15%7%6%6%42445%7%35%
1624
16th to endDay
12%10%37%5%34346%38%
1580
March1st to 15thDay
16%9%46%42443438%
1861
16th to endDay
18%8%35%6%35%45%7%29%
2195
April1st to 15thDay
15%7%245%3435%6%42%
2151
16th to endDay
16%6%35%6%34446%38%
2160
May1st to 15thDay
18%5%25%43446%8%35%
2301
16th to endDay
11%5%25%5%36%45%7%41%
2617
June1st to 15thDay
8%3145%35%5%6%9%45%
2520
16th to endDay
6%3145%35%6%6%11%45%
2520
July1st to 15thDay
8%3145%35%6%6%9%43%
2520
16th to endDay
5%314436%6%6%11%47%
2596
August1st to 15thDay
7%425%6%35%5%7%8%43%
2271
16th to endDay
7%425%5%35%6%6%8%44%
2292
September1st to 15thDay
13%5%2442445%7%47%
2160
16th to endDay
8%425%42345%7%51%
2016
October1st to 15thDay
15%424333435%49%
1715
16th to endDay
13%5%24323245%52%
1733
November1st to 15thDay
13%414413448%50%
1582
16th to endDay
17%8%34334336%42%
1578
December1st to 15thDay
18%9%46%425%435%34%
1440
16th to endDay
18%10%45%42345%5%34%
1536
January1st to 15thNight
14%7%46%5%34445%39%
2506
16th to endNight
13%10%36%6%34346%36%
2500
February1st to 15thNight
14%9%5%6%435%45%5%35%
2229
16th to endNight
13%8%35%5%2324444%
1893
March1st to 15thNight
20%7%25%424445%39%
2109
16th to endNight
18%7%35%5%345%6%7%34%
2026
April1st to 15thNight
13%6%24334446%47%
1797
16th to endNight
16%5%25%424448%43%
1800
May1st to 15thNight
16%6%2342445%6%41%
1645
16th to endNight
9%425%6%345%5%7%46%
1496
June1st to 15thNight
6%32432446%8%52%
1440
16th to endNight
7%3144245%6%11%49%
1440
July1st to 15thNight
8%32342345%8%51%
1440
16th to endNight
3324435%5%6%10%52%
1569
August1st to 15thNight
5%3134245%7%7%54%
1689
16th to endNight
5%3143245%5%8%54%
1910
September1st to 15thNight
10%32443435%7%51%
1800
16th to endNight
8%424323446%56%
1932
October1st to 15thNight
11%41432335%7%52%
2040
16th to endNight
16%5%24312345%51%
2138
November1st to 15thNight
10%5%24323246%54%
2276
16th to endNight
16%7%2432335%5%45%
2379
December1st to 15thNight
21%9%35%424346%33%
2520
16th to endNight
20%12%36%42443432%
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
51%39%21%12%
1433
16th to endDay
47%313%26%8%
1722
February1st to 15thDay
48%313%25%8%
1626
16th to endDay
48%412%22%11%1
1580
March1st to 15thDay
49%411%23%10%1
1861
16th to endDay
52%5%14%18%8%
2197
April1st to 15thDay
42%310%25%15%1
2151
16th to endDay
46%311%23%12%1
2160
May1st to 15thDay
44%6%13%25%10%
2301
16th to endDay
41%5%14%20%15%2
2621
June1st to 15thDay
33%5%15%23%19%2
2520
16th to endDay
31%6%17%24%18%3
2520
July1st to 15thDay
34%5%13%27%15%4
2371
16th to endDay
27%6%16%30%17%1
2434
August1st to 15thDay
35%5%12%27%18%1
2257
16th to endDay
33%5%14%22%18%5%
2292
September1st to 15thDay
36%37%26%20%4
2160
16th to endDay
31%48%32%20%2
2016
October1st to 15thDay
38%38%25%20%3
1715
16th to endDay
35%29%31%18%3
1733
November1st to 15thDay
33%312%22%22%5%
1582
16th to endDay
44%311%27%11%1
1578
December1st to 15thDay
52%213%21%9%
1440
16th to endDay
51%312%21%8%2
1536
January1st to 15thNight
46%29%25%14%
2506
16th to endNight
48%311%24%10%
2500
February1st to 15thNight
49%410%21%13%1
2238
16th to endNight
45%212%25%13%
1893
March1st to 15thNight
48%49%23%12%2
2109
16th to endNight
47%5%13%22%10%
2026
April1st to 15thNight
38%410%25%18%3
1797
16th to endNight
40%39%26%16%3
1800
May1st to 15thNight
42%5%11%22%16%
1646
16th to endNight
36%5%14%21%17%4
1498
June1st to 15thNight
26%414%30%21%1
1440
16th to endNight
28%5%14%26%20%6%
1440
July1st to 15thNight
29%311%31%17%5%
1360
16th to endNight
26%415%31%19%1
1469
August1st to 15thNight
25%5%14%28%23%2
1679
16th to endNight
27%5%11%25%25%5%
1910
September1st to 15thNight
32%29%24%22%8%
1800
16th to endNight
28%39%27%27%4
1932
October1st to 15thNight
31%310%26%21%6%
2040
16th to endNight
36%27%27%20%4
2138
November1st to 15thNight
31%210%24%21%7%
2276
16th to endNight
40%29%27%17%1
2379
December1st to 15thNight
52%311%21%10%
2520
16th to endNight
55%311%17%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
27%11%40%15%41
90
16th to endDay
11%17%46%20%3
96
February1st to 15thDay
20%12%37%26%3
90
16th to endDay
13%17%34%28%6%
81
March1st to 15thDay
34%436%17%5%1
90
16th to endDay
25%7%34%22%9%
181
April1st to 15thDay
15%11%30%27%14%1
270
16th to endDay
20%5%27%29%12%4
270
May1st to 15thDay
19%6%26%29%13%4
324
16th to endDay
15%427%30%15%6%
517
June1st to 15thDay
9%320%29%26%11%
495
16th to endDay
8%224%34%24%6%
495
July1st to 15thDay
11%212%33%28%12%
475
16th to endDay
5%11%27%37%17%
515
August1st to 15thDay
10%8%27%34%19%
424
16th to endDay
8%19%25%39%15%
332
September1st to 15thDay
13%213%22%33%14%
315
16th to endDay
9%411%28%31%14%
314
October1st to 15thDay
14%418%33%21%6%
116
16th to endDay
11%5%32%35%15%
96
November1st to 15thDay
8%223%24%30%11%
90
16th to endDay
32%14%32%13%6%1
90
December1st to 15thDay
16%11%38%22%6%4
90
16th to endDay
27%13%43%12%3
96
January1st to 15thNight
18%12%36%25%6%
900
16th to endNight
18%12%37%27%3
960
February1st to 15thNight
18%13%34%29%3
830
16th to endNight
18%11%35%31%2
631
March1st to 15thNight
25%8%34%25%5%
669
16th to endNight
22%6%30%33%7%
576
April1st to 15thNight
14%10%36%29%9%
539
16th to endNight
19%332%32%11%1
540
May1st to 15thNight
18%325%37%13%1
540
16th to endNight
9%323%42%19%1
563
June1st to 15thNight
7%218%44%26%1
540
16th to endNight
10%116%42%26%2
540
July1st to 15thNight
9%18%41%33%4
510
16th to endNight
49%36%43%5%
564
August1st to 15thNight
7%6%40%41%4
539
16th to endNight
7%8%34%42%6%
573
September1st to 15thNight
11%211%32%33%8%
540
16th to endNight
11%315%29%33%6%
669
October1st to 15thNight
14%222%30%25%3
684
16th to endNight
18%7%29%33%9%
704
November1st to 15thNight
13%7%34%31%12%1
700
16th to endNight
22%8%32%27%8%
759
December1st to 15thNight
25%9%31%27%5%
900
16th to endNight
26%9%33%26%3
960
Page generated at 2017-10-07 13:07:46. Version ac04

Copyright 2017 A. Danko


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