Chamberlin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chamberlin Observatory clear sky chart from 2005-11-05 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
61%
15825
28%
46504
21%
15785
67%
15785
44%
24924

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
58%
897
32%
2506
23%
895
66%
895
51%
1286
January16th to endNight
55%
813
34%
2541
26%
813
66%
813
43%
1318
February1st to 15thNight
49%
699
26%
2241
17%
698
60%
698
38%
1213
February16th to endNight
46%
632
33%
1894
18%
632
60%
632
43%
1004
March1st to 15thNight
55%
720
29%
2121
18%
720
65%
720
45%
1125
March16th to endNight
50%
675
28%
2019
18%
675
61%
675
42%
1090
April1st to 15thNight
48%
539
25%
1798
20%
539
59%
539
37%
947
April16th to endNight
47%
540
23%
1800
19%
540
56%
540
29%
1059
May1st to 15thNight
57%
540
20%
1613
17%
540
61%
540
30%
1014
May16th to endNight
56%
562
18%
1498
12%
561
61%
561
39%
868
June1st to 15thNight
71%
540
23%
1440
17%
540
74%
540
52%
763
June16th to endNight
77%
540
26%
1440
22%
540
80%
540
56%
734
July1st to 15thNight
72%
510
18%
1360
16%
510
73%
510
37%
816
July16th to endNight
77%
564
26%
1438
23%
531
78%
531
46%
781
August1st to 15thNight
73%
527
19%
1637
20%
524
74%
524
37%
891
August16th to endNight
75%
525
27%
1750
30%
525
77%
525
40%
896
September1st to 15thNight
70%
495
30%
1650
31%
495
74%
495
40%
860
September16th to endNight
76%
492
37%
1776
39%
492
81%
492
49%
792
October1st to 15thNight
61%
643
30%
1963
22%
643
67%
643
44%
1030
October16th to endNight
68%
737
35%
2145
24%
737
73%
737
50%
1088
November1st to 15thNight
65%
875
34%
2275
21%
875
69%
875
55%
1197
November16th to endNight
64%
900
35%
2391
24%
900
69%
900
55%
1255
December1st to 15thNight
55%
900
27%
2520
17%
900
63%
900
46%
1367
December16th to endNight
54%
960
29%
2688
19%
960
62%
960
42%
1530

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%42332446%8%53%
47486
Night
5%42332335%7%58%
46679
Cloud CoverDay
5%42332446%8%53%
47484
Night
5%42332335%7%57%
46679
TransparencyDay
27%410%24%22%9%
47163
Night
25%411%26%23%8%
46504
SeeingDay
10%6%24%30%21%7%
5710
Night
7%222%47%18%1
15834

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 15thDay
26%23312247%62%
1432
16th to endDay
25%23212348%62%
1695
February1st to 15thDay
26%26%334447%54%
1621
16th to endDay
26%25%423347%57%
1580
March1st to 15thDay
4425%43335%8%55%
1836
16th to endDay
6%6%233235%5%9%51%
2205
April1st to 15thDay
7%5%1332345%8%53%
2150
16th to endDay
11%6%2342346%7%46%
2160
May1st to 15thDay
10%7%245%2446%7%43%
2335
16th to endDay
9%4245%25%6%6%10%43%
2616
June1st to 15thDay
5%214425%6%6%9%50%
2520
16th to endDay
2112325%6%7%9%54%
2520
July1st to 15thDay
7%3135%35%5%7%11%44%
2520
16th to endDay
5%3244346%8%10%46%
2629
August1st to 15thDay
5%3145%37%7%8%9%43%
2227
16th to endDay
5%213435%6%6%8%51%
2100
September1st to 15thDay
7%21332445%6%56%
1980
16th to endDay
4312223346%64%
1854
October1st to 15thDay
6%31332335%7%59%
1665
16th to endDay
6%412212336%65%
1716
November1st to 15thDay
142331336%8%61%
1583
16th to endDay
242321235%8%62%
1566
December1st to 15thDay
25%25%22335%9%55%
1440
16th to endDay
35%3432435%7%55%
1536
January1st to 15thNight
334322346%64%
2506
16th to endNight
26%25%414235%61%
2541
February1st to 15thNight
37%2441435%6%55%
2231
16th to endNight
18%24424435%57%
1894
March1st to 15thNight
45%1332346%6%58%
2121
16th to endNight
6%5%23223347%57%
2019
April1st to 15thNight
7%5%1332335%6%56%
1798
16th to endNight
14%7%24313346%49%
1800
May1st to 15thNight
14%5%1332445%8%45%
1612
16th to endNight
8%32432345%8%53%
1497
June1st to 15thNight
5%222135%6%9%60%
1440
16th to endNight
2122135%7%8%62%
1440
July1st to 15thNight
5%3135%35%37%10%49%
1440
16th to endNight
5%213325%5%7%10%52%
1536
August1st to 15thNight
33144345%7%9%52%
1646
16th to endNight
421342446%9%54%
1750
September1st to 15thNight
8%313324348%55%
1650
16th to endNight
5%212312236%67%
1776
October1st to 15thNight
7%413222345%60%
1963
16th to endNight
5%423312336%63%
2145
November1st to 15thNight
3312313345%66%
2275
16th to endNight
35%13223336%64%
2391
December1st to 15thNight
25%24412349%57%
2520
16th to endNight
37%3432445%7%54%
2688

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
26%23213247%62%
1432
16th to endDay
15%33212248%62%
1695
February1st to 15thDay
26%36%324437%54%
1621
16th to endDay
26%2441335%7%57%
1580
March1st to 15thDay
4425%42335%9%54%
1836
16th to endDay
6%6%2332345%9%51%
2203
April1st to 15thDay
7%5%1332345%7%53%
2150
16th to endDay
11%6%2342336%7%46%
2160
May1st to 15thDay
10%6%24425%46%7%43%
2335
16th to endDay
8%424425%6%6%10%43%
2616
June1st to 15thDay
6%314425%5%7%9%50%
2520
16th to endDay
2113425%6%8%10%54%
2520
July1st to 15thDay
7%3145%35%5%7%11%45%
2520
16th to endDay
4314435%6%8%10%46%
2629
August1st to 15thDay
5%3245%36%7%8%9%43%
2227
16th to endDay
5%213435%6%7%8%51%
2100
September1st to 15thDay
7%21342445%6%57%
1980
16th to endDay
4412223346%65%
1854
October1st to 15thDay
6%31232345%7%59%
1665
16th to endDay
5%412212236%65%
1716
November1st to 15thDay
241331435%9%60%
1583
16th to endDay
242321235%8%62%
1566
December1st to 15thDay
25%3432345%9%55%
1440
16th to endDay
35%35%31435%7%55%
1536
January1st to 15thNight
334313346%64%
2506
16th to endNight
35%25%323245%60%
2541
February1st to 15thNight
37%2442445%7%54%
2231
16th to endNight
28%34424335%57%
1894
March1st to 15thNight
45%1332345%6%57%
2121
16th to endNight
6%6%23323347%57%
2019
April1st to 15thNight
7%5%13323447%55%
1798
16th to endNight
14%6%24322345%49%
1800
May1st to 15thNight
14%5%1343445%8%45%
1612
16th to endNight
8%31432245%8%53%
1497
June1st to 15thNight
5%222135%6%8%60%
1440
16th to endNight
21122145%7%9%62%
1440
July1st to 15thNight
5%3145%35%47%10%48%
1440
16th to endNight
42124246%8%10%51%
1536
August1st to 15thNight
42244246%6%9%52%
1646
16th to endNight
421343447%8%55%
1750
September1st to 15thNight
8%32433335%8%55%
1650
16th to endNight
5%212313236%67%
1776
October1st to 15thNight
7%5%13313345%60%
1963
16th to endNight
5%422312336%62%
2145
November1st to 15thNight
2313313345%66%
2275
16th to endNight
2423223336%64%
2391
December1st to 15thNight
36%24422349%57%
2520
16th to endNight
37%3432345%7%54%
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
23%111%31%25%5%
1433
16th to endDay
21%37%34%24%7%
1695
February1st to 15thDay
29%212%34%16%5%
1622
16th to endDay
26%27%28%27%6%
1580
March1st to 15thDay
26%29%26%25%8%
1836
16th to endDay
29%5%12%23%21%7%
2205
April1st to 15thDay
29%311%26%20%8%
2150
16th to endDay
35%5%11%22%19%5%
2160
May1st to 15thDay
40%5%11%23%15%4
2335
16th to endDay
34%7%12%23%13%6%
2620
June1st to 15thDay
27%6%13%20%19%12%
2520
16th to endDay
21%6%10%19%28%12%
2520
July1st to 15thDay
32%6%11%21%16%12%
2371
16th to endDay
29%8%12%24%16%7%
2464
August1st to 15thDay
33%7%13%19%15%11%
2212
16th to endDay
27%5%10%24%23%8%
2100
September1st to 15thDay
26%5%9%21%20%16%
1980
16th to endDay
20%45%21%37%10%
1854
October1st to 15thDay
23%311%21%29%10%
1665
16th to endDay
21%27%26%29%11%
1716
November1st to 15thDay
19%38%27%26%13%
1583
16th to endDay
21%16%25%32%12%
1566
December1st to 15thDay
25%312%32%22%4
1440
16th to endDay
27%314%27%20%7%
1536
January1st to 15thNight
21%310%32%26%6%
2506
16th to endNight
26%27%28%25%9%
2541
February1st to 15thNight
28%411%31%19%4
2241
16th to endNight
26%27%27%25%9%
1894
March1st to 15thNight
24%38%26%29%7%
2121
16th to endNight
27%310%25%27%6%
2019
April1st to 15thNight
27%411%24%22%9%
1798
16th to endNight
36%410%23%18%6%
1800
May1st to 15thNight
36%6%14%21%15%5%
1613
16th to endNight
28%5%21%24%12%7%
1498
June1st to 15thNight
18%6%17%29%15%12%
1440
16th to endNight
16%5%11%24%29%12%
1440
July1st to 15thNight
28%8%15%21%16%9%
1360
16th to endNight
22%6%16%29%19%5%
1438
August1st to 15thNight
26%7%16%24%16%8%
1637
16th to endNight
24%6%12%26%23%7%
1750
September1st to 15thNight
27%412%20%21%14%
1650
16th to endNight
19%27%26%35%8%
1776
October1st to 15thNight
24%411%20%28%10%
1963
16th to endNight
22%28%25%29%11%
2145
November1st to 15thNight
19%38%25%27%14%
2275
16th to endNight
20%28%25%31%11%
2391
December1st to 15thNight
25%312%32%20%5%
2520
16th to endNight
28%414%27%21%3
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
7%7%20%36%22%5%
90
16th to endDay
9%120%46%19%2
96
February1st to 15thDay
37%36%43%8%
90
16th to endDay
6%328%39%20%1
81
March1st to 15thDay
5%11%26%42%11%1
126
16th to endDay
16%21%33%21%6%
288
April1st to 15thDay
14%17%31%23%10%2
269
16th to endDay
22%16%32%17%9%1
270
May1st to 15thDay
15%8%25%30%17%2
426
16th to endDay
16%7%21%27%19%7%
517
June1st to 15thDay
7%324%32%22%9%
495
16th to endDay
4424%29%27%9%
495
July1st to 15thDay
9%216%24%34%12%
475
16th to endDay
6%114%26%35%14%
488
August1st to 15thDay
11%324%31%19%10%
300
16th to endDay
10%322%35%19%8%
268
September1st to 15thDay
10%5%29%32%18%3
255
16th to endDay
3223%32%21%16%
129
October1st to 15thDay
5%312%36%25%16%
90
16th to endDay
9%216%35%27%9%
96
November1st to 15thDay
1211%36%35%13%
90
16th to endDay
7%7%28%41%12%2
90
December1st to 15thDay
7%5%35%43%6%1
90
16th to endDay
7%129%50%8%4
96
January1st to 15thNight
2228%52%11%2
900
16th to endNight
5%229%51%10%1
813
February1st to 15thNight
6%231%51%7%
704
16th to endNight
7%334%47%6%
632
March1st to 15thNight
5%230%49%11%
720
16th to endNight
9%330%47%8%
675
April1st to 15thNight
11%5%30%44%7%
539
16th to endNight
18%325%40%11%
540
May1st to 15thNight
17%219%45%14%1
540
16th to endNight
10%223%38%23%1
563
June1st to 15thNight
6%117%47%24%1
540
16th to endNight
4112%50%31%
540
July1st to 15thNight
6%19%38%40%3
510
16th to endNight
5%7%37%44%4
564
August1st to 15thNight
6%19%41%38%2
527
16th to endNight
6%11%42%36%2
525
September1st to 15thNight
9%111%45%27%4
495
16th to endNight
413%45%30%4
492
October1st to 15thNight
11%220%44%18%3
643
16th to endNight
8%215%50%21%2
737
November1st to 15thNight
4221%51%16%2
875
16th to endNight
4223%53%15%1
900
December1st to 15thNight
5%229%52%9%
900
16th to endNight
6%227%51%9%1
960
Page generated at 2017-08-13 12:16:18. Version ac04

Copyright 2017 A. Danko


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