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 2017-12-20.

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
61%
16350
29%
48060
21%
16310
68%
16310
44%
25704

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
57%
897
32%
2506
23%
895
66%
895
51%
1286
January16th to endNight
54%
813
34%
2541
26%
813
65%
813
43%
1318
February1st to 15thNight
50%
699
26%
2241
17%
698
61%
698
38%
1213
February16th to endNight
47%
632
33%
1894
19%
632
60%
632
43%
1004
March1st to 15thNight
55%
720
29%
2121
18%
720
64%
720
45%
1125
March16th to endNight
51%
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
73%
510
18%
1360
16%
510
74%
510
37%
816
July16th to endNight
78%
564
26%
1438
23%
531
78%
531
46%
781
August1st to 15thNight
73%
539
19%
1676
20%
536
74%
536
37%
913
August16th to endNight
75%
573
29%
1910
32%
573
77%
573
40%
966
September1st to 15thNight
72%
540
29%
1800
30%
540
75%
540
41%
928
September16th to endNight
73%
537
37%
1938
37%
537
80%
537
46%
893
October1st to 15thNight
62%
702
30%
2142
21%
702
68%
702
45%
1117
October16th to endNight
68%
804
37%
2340
25%
804
73%
804
50%
1186
November1st to 15thNight
65%
950
33%
2470
21%
950
70%
950
55%
1299
November16th to endNight
64%
975
36%
2590
24%
975
69%
975
56%
1347
December1st to 15thNight
56%
975
27%
2730
17%
975
63%
975
47%
1472
December16th to endNight
55%
984
30%
2755
20%
984
63%
984
42%
1565

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%42332445%8%53%
48797
Night
5%423323347%58%
48235
Cloud CoverDay
5%42332446%8%53%
48795
Night
5%42332335%7%58%
48235
TransparencyDay
27%410%24%22%9%
48474
Night
25%411%26%24%8%
48060
SeeingDay
10%6%24%30%20%7%
6137
Night
7%222%47%18%1
16359

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%
2274
16th to endDay
5%213435%6%6%8%51%
2292
September1st to 15thDay
7%21432346%6%57%
2160
16th to endDay
5%412223346%63%
2022
October1st to 15thDay
6%31232335%7%60%
1816
16th to endDay
5%412212336%65%
1872
November1st to 15thDay
142331336%8%61%
1718
16th to endDay
242321235%8%62%
1696
December1st to 15thDay
25%25%32335%9%56%
1560
16th to endDay
35%3432445%7%56%
1568
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%10%52%
1685
16th to endNight
421342446%9%55%
1910
September1st to 15thNight
7%313323348%56%
1800
16th to endNight
6%212312236%66%
1938
October1st to 15thNight
8%413222345%61%
2142
16th to endNight
5%423312336%63%
2340
November1st to 15thNight
3312313346%65%
2470
16th to endNight
2413213336%65%
2590
December1st to 15thNight
25%24422348%58%
2730
16th to endNight
37%3432435%7%54%
2755

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%10%43%
2274
16th to endDay
5%213435%6%7%8%51%
2292
September1st to 15thDay
7%21342345%7%57%
2160
16th to endDay
5%412223346%63%
2022
October1st to 15thDay
6%31232345%6%60%
1816
16th to endDay
5%412212336%65%
1872
November1st to 15thDay
141331425%9%61%
1718
16th to endDay
242221235%9%62%
1696
December1st to 15thDay
25%3432345%9%56%
1560
16th to endDay
35%35%31435%7%56%
1568
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
42144245%7%9%52%
1685
16th to endNight
421343436%9%55%
1910
September1st to 15thNight
7%22333335%8%56%
1800
16th to endNight
6%213313336%65%
1938
October1st to 15thNight
8%5%12313345%61%
2142
16th to endNight
5%422312236%63%
2340
November1st to 15thNight
3313313446%65%
2470
16th to endNight
2423223336%64%
2590
December1st to 15thNight
25%24422348%58%
2730
16th to endNight
37%3432345%7%54%
2755

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
32%7%13%19%15%10%
2259
16th to endDay
26%5%10%24%24%8%
2292
September1st to 15thDay
25%5%9%21%21%15%
2160
16th to endDay
21%46%20%36%10%
2022
October1st to 15thDay
23%311%20%29%12%
1816
16th to endDay
21%27%26%29%13%
1872
November1st to 15thDay
19%38%28%27%12%
1718
16th to endDay
20%17%24%34%11%
1696
December1st to 15thDay
24%311%31%22%6%
1560
16th to endDay
27%314%27%20%6%
1568
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%
1676
16th to endNight
24%5%11%25%25%7%
1910
September1st to 15thNight
26%412%22%21%13%
1800
16th to endNight
21%37%25%33%8%
1938
October1st to 15thNight
24%311%20%27%12%
2142
16th to endNight
22%27%24%29%12%
2340
November1st to 15thNight
19%38%26%28%13%
2470
16th to endNight
20%29%25%31%11%
2590
December1st to 15thNight
25%312%30%21%7%
2730
16th to endNight
28%413%27%21%3
2755

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%323%31%20%10%
315
16th to endDay
8%221%34%21%10%
332
September1st to 15thDay
10%425%30%20%9%
315
16th to endDay
7%327%31%17%11%
177
October1st to 15thDay
8%5%18%33%20%14%
135
16th to endDay
8%322%33%24%7%
144
November1st to 15thDay
1216%44%25%8%
135
16th to endDay
7%5%28%43%12%1
135
December1st to 15thDay
6%438%40%9%
135
16th to endDay
6%27%48%12%3
108
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
5%19%41%38%2
539
16th to endNight
6%10%42%36%2
573
September1st to 15thNight
8%110%43%29%6%
540
16th to endNight
5%115%45%29%3
537
October1st to 15thNight
11%119%46%17%3
702
16th to endNight
8%215%50%20%2
804
November1st to 15thNight
4221%52%15%2
950
16th to endNight
4124%53%14%1
975
December1st to 15thNight
5%228%53%9%
975
16th to endNight
6%226%51%10%1
984
Page generated at 2017-12-21 05:04:56. Version ac04

Copyright 2017 A. Danko


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