This page made possible by the sponsorship of: Martin Wilson.

Chamberlin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chamberlin Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
56%
24574
28%
74470
20%
24525
65%
24525
42%
39689

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 10thNight
50%
947
34%
2647
20%
946
62%
946
50%
1370
January11th to 20thNight
49%
902
33%
2567
20%
902
61%
902
47%
1345
January21st to endNight
49%
792
33%
2574
23%
792
62%
792
40%
1356
February1st to 10thNight
44%
720
28%
2340
16%
720
59%
720
40%
1226
February11th to 20thNight
43%
701
27%
2111
16%
700
54%
700
40%
1174
February21st to endNight
46%
592
35%
1776
18%
592
62%
592
42%
956
March1st to 10thNight
46%
720
29%
2160
16%
720
58%
720
43%
1143
March11th to 20thNight
53%
720
29%
2012
18%
720
61%
720
44%
1117
March21st to endNight
44%
653
29%
2039
15%
653
58%
653
37%
1127
April1st to 10thNight
42%
540
26%
1800
15%
540
57%
540
35%
959
April11th to 20thNight
43%
533
23%
1777
18%
533
54%
533
30%
1011
April21st to endNight
47%
540
23%
1800
19%
540
56%
540
30%
1043
May1st to 10thNight
52%
540
20%
1682
17%
540
58%
540
28%
1043
May11th to 20thNight
58%
531
16%
1436
14%
531
59%
531
32%
899
May21st to endNight
55%
583
20%
1552
14%
582
60%
582
39%
909
June1st to 10thNight
72%
540
24%
1440
20%
540
74%
540
51%
765
June11th to 20thNight
64%
540
26%
1440
19%
540
69%
540
52%
764
June21st to endNight
71%
540
25%
1440
21%
540
73%
540
49%
776
July1st to 10thNight
71%
525
19%
1400
18%
525
71%
525
39%
827
July11th to 20thNight
77%
522
29%
1392
24%
522
80%
522
51%
740
July21st to endNight
74%
591
24%
1522
22%
558
75%
558
40%
871
August1st to 10thNight
70%
537
16%
1608
15%
534
70%
534
34%
920
August11th to 20thNight
72%
534
28%
1778
28%
534
77%
534
41%
900
August21st to endNight
71%
594
29%
1980
31%
594
75%
594
40%
995
September1st to 10thNight
70%
540
30%
1800
30%
540
74%
540
41%
906
September11th to 20thNight
73%
540
37%
1825
37%
540
78%
540
48%
861
September21st to endNight
67%
540
34%
1980
32%
540
75%
540
42%
921
October1st to 10thNight
61%
692
29%
2132
20%
692
67%
692
42%
1130
October11th to 20thNight
63%
720
36%
2160
22%
720
73%
720
56%
1017
October21st to endNight
57%
846
33%
2430
20%
846
64%
846
46%
1290
November1st to 10thNight
60%
925
35%
2405
18%
925
68%
925
58%
1231
November11th to 20thNight
54%
950
37%
2470
20%
950
63%
950
54%
1316
November21st to endNight
57%
950
31%
2550
19%
950
63%
950
49%
1389
December1st to 10thNight
53%
950
30%
2660
17%
950
63%
950
49%
1402
December11th to 20thNight
50%
949
31%
3097
19%
948
60%
948
43%
1576
December21st to endNight
45%
1035
20%
4688
15%
1026
57%
1026
28%
2414

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
5%5%244345%6%8%54%
74800
Night
5%5%2442445%7%58%
75015
TransparencyDay
27%5%10%23%24%11%
74507
Night
26%410%25%26%9%
74830
SeeingDay
8%7%24%33%21%7%
14428
Night
7%326%46%16%1
24592

By Month

Percentage Cloud Cover SW (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 10thDay
25%2332235%9%63%
1518
11th to 20thDay
37%34414347%59%
1520
21st to endDay
17%35%32345%9%58%
1782
February1st to 10thDay
27%37%434447%55%
1620
11th to 20thDay
1435%435%45%8%57%
1735
21st to endDay
27%27%42345%6%56%
1480
March1st to 10thDay
45%3443345%9%56%
1800
11th to 20thDay
6%8%25%33435%8%53%
1944
21st to endDay
6%6%244346%5%10%50%
2317
April1st to 10thDay
7%5%2343346%9%55%
2160
11th to 20thDay
9%7%344345%5%7%48%
2131
21st to endDay
11%6%2443446%9%47%
2160
May1st to 10thDay
12%7%35%5%35%6%7%8%42%
2276
11th to 20thDay
12%7%246%35%5%7%9%39%
2457
21st to endDay
8%4245%35%7%7%10%45%
2724
June1st to 10thDay
6%323436%5%7%10%50%
2520
11th to 20thDay
6%214436%6%6%9%52%
2520
21st to endDay
5%3135%35%7%8%10%50%
2520
July1st to 10thDay
7%324445%6%8%11%46%
2520
11th to 20thDay
4314435%6%7%10%52%
2520
21st to endDay
6%3245%35%7%9%10%46%
2702
August1st to 10thDay
5%3246%47%8%9%11%41%
2320
11th to 20thDay
5%213435%5%7%9%56%
2123
21st to endDay
5%313436%6%7%9%53%
2376
September1st to 10thDay
5%31432445%7%61%
2160
11th to 20thDay
6%31332446%7%60%
2134
21st to endDay
5%413323346%66%
1980
October1st to 10thDay
8%31332435%6%62%
1825
11th to 20thDay
4422222346%68%
1800
21st to endDay
7%6%23222345%63%
1908
November1st to 10thDay
241331335%9%66%
1673
11th to 20thDay
25%33323349%63%
1710
21st to endDay
46%35%31335%6%61%
1625
December1st to 10thDay
26%2443335%9%59%
1520
11th to 20thDay
3425%32345%9%59%
1926
21st to endDay
37%47%5%34446%53%
2794
January1st to 10thNight
16%35%5%22346%64%
2647
11th to 20thNight
25%34324347%63%
2567
21st to endNight
27%36%5%24346%57%
2574
February1st to 10thNight
28%25%424347%57%
2340
11th to 20thNight
27%46%6%25%347%53%
2111
21st to endNight
28%45%423446%58%
1776
March1st to 10thNight
46%25%4245%6%7%57%
2160
11th to 20thNight
7%6%23324436%60%
2012
21st to endNight
7%8%2432335%8%54%
2039
April1st to 10thNight
7%6%2433445%6%57%
1800
11th to 20thNight
11%7%245%23446%51%
1777
21st to endNight
13%7%2433345%7%49%
1800
May1st to 10thNight
13%6%24435%46%7%46%
1682
11th to 20thNight
15%5%2443445%8%47%
1435
21st to endNight
9%42433446%8%54%
1552
June1st to 10thNight
6%2133235%5%11%59%
1440
11th to 20thNight
6%3122235%7%8%62%
1440
21st to endNight
5%214325%5%7%9%58%
1440
July1st to 10thNight
6%423445%47%10%51%
1440
11th to 20thNight
2214435%47%9%58%
1440
21st to endNight
6%314435%6%8%11%48%
1612
August1st to 10thNight
4325%5%45%6%7%10%49%
1617
11th to 20thNight
5%3134235%7%11%56%
1778
21st to endNight
4324435%46%9%56%
1980
September1st to 10thNight
6%32443445%7%58%
1800
11th to 20thNight
7%312323348%64%
1825
21st to endNight
7%313423346%65%
1980
October1st to 10thNight
9%5%2332335%5%61%
2132
11th to 20thNight
4313322337%69%
2160
21st to endNight
6%7%23313335%62%
2430
November1st to 10thNight
3322323446%69%
2405
11th to 20thNight
35%24323345%66%
2470
21st to endNight
46%24323347%62%
2550
December1st to 10thNight
26%35%42335%8%61%
2660
11th to 20thNight
26%2442345%10%58%
3271
21st to endNight
5%8%35%434446%52%
4873

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 10thDay
20%212%30%28%8%
1519
11th to 20thDay
26%37%30%26%7%
1520
21st to endDay
24%48%32%24%8%
1782
February1st to 10thDay
30%310%27%21%9%
1620
11th to 20thDay
25%38%28%28%8%
1745
21st to endDay
27%37%24%27%11%
1480
March1st to 10thDay
26%39%25%28%9%
1800
11th to 20thDay
30%310%24%26%8%
1944
21st to endDay
30%6%11%25%20%8%
2317
April1st to 10thDay
27%5%10%24%22%11%
2160
11th to 20thDay
34%6%9%22%21%9%
2134
21st to endDay
33%6%10%24%22%4
2160
May1st to 10thDay
39%6%11%23%16%5%
2276
11th to 20thDay
39%8%12%25%12%4
2461
21st to endDay
33%8%13%24%15%8%
2724
June1st to 10thDay
27%7%15%24%18%10%
2520
11th to 20thDay
26%7%10%18%22%17%
2520
21st to endDay
26%7%10%20%25%13%
2520
July1st to 10thDay
29%7%11%20%20%13%
2451
11th to 20thDay
25%9%10%23%22%11%
2445
21st to endDay
30%10%14%24%15%7%
2552
August1st to 10thDay
32%9%14%23%14%7%
2305
11th to 20thDay
24%6%11%21%24%13%
2123
21st to endDay
25%6%9%22%27%11%
2376
September1st to 10thDay
23%5%8%20%24%20%
2160
11th to 20thDay
22%49%17%28%19%
2134
21st to endDay
21%45%18%38%14%
1980
October1st to 10thDay
24%48%20%30%14%
1825
11th to 20thDay
18%38%22%33%16%
1800
21st to endDay
24%36%26%25%15%
1908
November1st to 10thDay
17%38%25%29%18%
1673
11th to 20thDay
20%45%27%34%10%
1710
21st to endDay
25%27%21%30%15%
1625
December1st to 10thDay
23%411%29%24%9%
1520
11th to 20thDay
21%49%26%32%7%
1924
21st to endDay
32%29%21%27%8%
2794
January1st to 10thNight
23%39%29%29%8%
2647
11th to 20thNight
23%48%28%29%9%
2567
21st to endNight
28%37%28%26%8%
2574
February1st to 10thNight
27%49%28%24%7%
2340
11th to 20thNight
30%38%28%24%7%
2111
21st to endNight
27%36%24%27%13%
1776
March1st to 10thNight
25%47%25%30%9%
2160
11th to 20thNight
26%410%22%32%6%
2012
21st to endNight
30%5%9%26%26%5%
2039
April1st to 10thNight
27%6%10%23%23%11%
1800
11th to 20thNight
34%410%22%20%9%
1777
21st to endNight
35%5%9%25%21%6%
1800
May1st to 10thNight
36%8%13%23%16%5%
1682
11th to 20thNight
36%6%20%21%12%4
1436
21st to endNight
29%6%17%27%13%8%
1552
June1st to 10thNight
19%7%19%32%15%8%
1440
11th to 20thNight
20%5%13%22%22%18%
1440
21st to endNight
21%6%11%25%28%10%
1440
July1st to 10thNight
27%8%15%22%20%7%
1400
11th to 20thNight
19%6%12%28%24%10%
1392
21st to endNight
26%8%19%28%16%4
1522
August1st to 10thNight
29%9%18%24%14%6%
1608
11th to 20thNight
23%7%10%26%24%10%
1778
21st to endNight
24%6%12%24%26%8%
1980
September1st to 10thNight
24%5%11%21%25%15%
1800
11th to 20thNight
20%49%23%26%17%
1825
21st to endNight
23%46%21%35%12%
1980
October1st to 10thNight
25%5%10%19%28%13%
2132
11th to 20thNight
17%310%22%30%18%
2160
21st to endNight
26%27%23%28%13%
2430
November1st to 10thNight
17%39%25%29%17%
2405
11th to 20thNight
21%27%28%32%10%
2470
21st to endNight
24%38%22%31%12%
2550
December1st to 10thNight
23%312%27%26%9%
2660
11th to 20thNight
23%48%27%33%5%
3272
21st to endNight
32%39%25%25%6%
4873

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 10thDay
6%6%28%41%14%5%
270
11th to 20thDay
7%7%31%41%14%1
255
21st to endDay
3440%39%12%2
264
February1st to 10thDay
413%39%35%8%2
240
11th to 20thDay
4440%40%8%3
240
21st to endDay
48%33%44%11%
198
March1st to 10thDay
5%9%31%37%15%2
240
11th to 20thDay
13%11%31%31%13%2
384
21st to endDay
15%17%30%27%9%1
462
April1st to 10thDay
12%13%32%30%12%2
420
11th to 20thDay
15%18%32%23%9%3
412
21st to endDay
18%11%30%25%13%3
420
May1st to 10thDay
15%10%27%31%15%3
539
11th to 20thDay
18%7%21%28%19%6%
625
21st to endDay
11%9%22%30%21%7%
679
June1st to 10thDay
7%5%19%32%26%13%
630
11th to 20thDay
6%6%25%34%22%6%
630
21st to endDay
6%6%21%32%26%8%
630
July1st to 10thDay
7%314%26%35%14%
621
11th to 20thDay
5%211%31%39%11%
618
21st to endDay
5%311%28%40%13%
644
August1st to 10thDay
6%419%29%27%15%
447
11th to 20thDay
4419%34%27%13%
437
21st to endDay
7%417%33%30%10%
495
September1st to 10thDay
6%320%34%25%12%
450
11th to 20thDay
5%420%36%24%11%
424
21st to endDay
6%6%19%34%23%13%
270
October1st to 10thDay
10%6%22%25%25%13%
270
11th to 20thDay
37%27%38%19%6%
270
21st to endDay
12%8%24%35%17%4
297
November1st to 10thDay
5%7%25%40%16%6%
270
11th to 20thDay
6%6%28%42%13%5%
270
21st to endDay
8%7%27%41%14%3
270
December1st to 10thDay
6%7%29%39%16%2
270
11th to 20thDay
6%437%41%11%1
270
21st to endDay
5%7%30%46%9%2
297
January1st to 10thNight
3433%47%11%2
950
11th to 20thNight
4435%45%10%2
902
21st to endNight
5%332%50%9%1
792
February1st to 10thNight
6%240%46%6%
720
11th to 20thNight
4339%46%7%
704
21st to endNight
7%5%34%50%4
592
March1st to 10thNight
6%238%45%9%
720
11th to 20thNight
10%427%48%11%
720
21st to endNight
9%6%35%42%7%
653
April1st to 10thNight
11%6%36%41%6%
540
11th to 20thNight
15%7%30%38%10%
533
21st to endNight
16%5%27%41%11%1
540
May1st to 10thNight
15%422%44%13%1
540
11th to 20thNight
17%415%44%19%1
531
21st to endNight
11%5%22%39%23%1
584
June1st to 10thNight
6%314%47%27%2
540
11th to 20thNight
8%221%51%18%1
540
21st to endNight
5%215%47%29%1
540
July1st to 10thNight
7%211%41%36%3
525
11th to 20thNight
3111%44%39%2
522
21st to endNight
5%27%42%40%4
591
August1st to 10thNight
5%210%44%37%2
537
11th to 20thNight
5%214%47%31%1
534
21st to endNight
5%114%45%33%3
594
September1st to 10thNight
6%314%45%28%5%
540
11th to 20thNight
7%113%49%27%3
540
21st to endNight
7%217%49%22%3
540
October1st to 10thNight
13%318%44%19%3
692
11th to 20thNight
5%225%50%16%2
720
21st to endNight
9%423%46%15%2
846
November1st to 10thNight
4329%49%13%2
925
11th to 20thNight
5%5%30%50%10%1
950
21st to endNight
7%327%49%12%1
950
December1st to 10thNight
5%432%51%9%
950
11th to 20thNight
5%432%49%9%1
950
21st to endNight
7%335%46%8%1
1045
Page generated at 2024-01-12 23:38:08. Version ac07

Copyright 2024 Attilla Danko


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