Centennial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Centennial Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
55%
14911
22%
46811
18%
14880
60%
14880
32%
27317

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
44%
716
13%
2506
10%
716
48%
716
18%
1715
January16th to endNight
47%
768
14%
2637
13%
768
50%
768
21%
1726
February1st to 15thNight
44%
700
12%
2238
11%
699
47%
699
20%
1532
February16th to endNight
42%
632
17%
1895
13%
632
50%
632
26%
1219
March1st to 15thNight
45%
720
16%
2103
12%
720
51%
720
27%
1367
March16th to endNight
40%
768
17%
2112
11%
768
45%
768
26%
1403
April1st to 15thNight
43%
710
21%
1798
8%
710
50%
710
31%
1176
April16th to endNight
50%
540
26%
1620
16%
540
56%
540
35%
926
May1st to 15thNight
57%
539
24%
1619
18%
539
63%
539
38%
897
May16th to endNight
60%
503
19%
1624
19%
501
63%
501
32%
934
June1st to 15thNight
60%
360
19%
1440
22%
360
69%
360
32%
718
June16th to endNight
71%
360
29%
1440
36%
360
82%
360
54%
537
July1st to 15thNight
82%
340
25%
1360
35%
340
86%
340
48%
560
July16th to endNight
81%
421
33%
1458
39%
396
85%
396
58%
564
August1st to 15thNight
77%
539
31%
1611
25%
536
81%
536
54%
773
August16th to endNight
76%
636
39%
1782
27%
636
80%
636
60%
849
September1st to 15thNight
75%
720
33%
1902
23%
720
80%
720
60%
954
September16th to endNight
72%
667
37%
1847
30%
667
76%
667
52%
954
October1st to 15thNight
62%
660
32%
1862
24%
660
69%
660
46%
993
October16th to endNight
60%
704
26%
2240
23%
704
66%
704
38%
1210
November1st to 15thNight
51%
700
24%
2275
21%
700
58%
700
30%
1332
November16th to endNight
48%
720
20%
2340
14%
720
56%
720
28%
1396
December1st to 15thNight
41%
720
9%
2414
6%
720
45%
720
20%
1655
December16th to endNight
38%
768
13%
2688
11%
768
43%
768
15%
1927

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
6%5%2442445%7%53%
48001
Night
7%5%2442445%7%50%
46988
TransparencyDay
31%5%11%21%19%10%
47677
Night
33%5%12%22%16%9%
46813
SeeingDay
8%8%24%29%20%7%
5336
Night
10%5%22%36%21%3
14920

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
9%10%5%9%5%2246%6%36%
1432
16th to endDay
10%10%26%6%35%5%5%6%37%
1586
February1st to 15thDay
8%8%37%425%46%9%38%
1622
16th to endDay
7%9%45%435%45%7%41%
1579
March1st to 15thDay
7%7%36%5%36%5%7%9%37%
1857
16th to endDay
10%8%35%5%25%45%9%38%
2112
April1st to 15thDay
7%5%25%5%35%5%6%9%43%
2149
16th to endDay
8%5%2442445%7%50%
2340
May1st to 15thDay
6%31332445%8%55%
2331
16th to endDay
6%4245%35%46%8%46%
2486
June1st to 15thDay
6%423435%5%5%7%52%
2520
16th to endDay
221212345%74%
2520
July1st to 15thDay
22221335%6%68%
2520
16th to endDay
312224345%70%
2609
August1st to 15thDay
422324445%65%
2340
16th to endDay
212212345%73%
2418
September1st to 15thDay
3212212236%70%
2058
16th to endDay
5%31222333467%
1838
October1st to 15thDay
7%42331445%6%55%
1768
16th to endDay
6%314434448%53%
1631
November1st to 15thDay
8%5%245%24446%48%
1584
16th to endDay
8%8%36%6%35%45%6%41%
1620
December1st to 15thDay
14%8%36%5%34446%36%
1545
16th to endDay
12%12%7%8%6%34347%29%
1536
January1st to 15thNight
10%10%36%6%35%45%7%36%
2506
16th to endNight
11%9%35%424346%41%
2637
February1st to 15thNight
10%9%26%6%345%5%7%37%
2227
16th to endNight
8%7%35%5%26%5%6%9%39%
1895
March1st to 15thNight
6%7%26%6%36%5%6%8%40%
2103
16th to endNight
10%6%35%5%36%5%6%6%40%
2112
April1st to 15thNight
7%6%35%5%36%5%6%7%44%
1798
16th to endNight
6%5%15%43436%8%51%
1620
May1st to 15thNight
6%41442445%7%54%
1619
16th to endNight
6%414425%5%6%8%48%
1624
June1st to 15thNight
5%223325%6%6%7%52%
1440
16th to endNight
2211212235%74%
1440
July1st to 15thNight
11123245%5%7%65%
1440
16th to endNight
121222334473%
1557
August1st to 15thNight
21241345%7%64%
1620
16th to endNight
21232335%6%69%
1782
September1st to 15thNight
3212322335%70%
1902
16th to endNight
5%22323345%66%
1847
October1st to 15thNight
7%313413347%60%
1862
16th to endNight
7%313425%45%8%53%
2240
November1st to 15thNight
10%5%24424346%50%
2275
16th to endNight
7%5%245%35%5%5%7%46%
2340
December1st to 15thNight
12%8%46%445%5%5%8%35%
2414
16th to endNight
17%10%5%7%423446%33%
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
50%8%19%18%31
1432
16th to endDay
46%10%19%16%5%1
1586
February1st to 15thDay
43%9%18%21%5%1
1622
16th to endDay
42%7%15%25%7%1
1579
March1st to 15thDay
41%7%18%23%7%1
1857
16th to endDay
44%6%14%23%10%
2112
April1st to 15thDay
38%6%14%24%15%1
2149
16th to endDay
33%411%28%19%2
2340
May1st to 15thDay
26%5%8%29%24%4
2331
16th to endDay
34%6%11%27%16%2
2489
June1st to 15thDay
30%411%25%22%5%
2520
16th to endDay
13%25%18%40%19%
2520
July1st to 15thDay
15%3316%33%27%
2371
16th to endDay
15%2310%22%45%
2446
August1st to 15thDay
19%3414%27%30%
2325
16th to endDay
13%3317%36%25%
2418
September1st to 15thDay
16%35%16%33%24%
2058
16th to endDay
21%35%25%30%13%
1838
October1st to 15thDay
29%312%29%18%5%
1768
16th to endDay
30%412%30%19%2
1631
November1st to 15thDay
37%6%13%29%11%1
1584
16th to endDay
42%5%18%23%9%
1620
December1st to 15thDay
49%8%19%17%4
1545
16th to endDay
56%7%18%13%3
1536
January1st to 15thNight
47%7%18%19%5%
2506
16th to endNight
43%6%17%24%5%
2637
February1st to 15thNight
46%8%17%21%6%
2238
16th to endNight
39%6%18%27%6%
1895
March1st to 15thNight
39%6%17%23%10%2
2103
16th to endNight
42%5%13%26%10%1
2112
April1st to 15thNight
37%6%12%28%13%2
1798
16th to endNight
30%410%27%23%2
1620
May1st to 15thNight
27%48%25%28%4
1620
16th to endNight
32%5%10%27%20%4
1625
June1st to 15thNight
27%5%12%21%25%7%
1440
16th to endNight
14%2416%33%28%
1440
July1st to 15thNight
16%4413%29%32%
1360
16th to endNight
13%229%22%49%
1458
August1st to 15thNight
17%3416%20%36%
1611
16th to endNight
15%3312%28%35%
1782
September1st to 15thNight
16%3414%34%27%
1902
16th to endNight
19%4421%33%17%
1847
October1st to 15thNight
24%310%29%24%8%
1862
16th to endNight
28%412%29%20%4
2240
November1st to 15thNight
36%313%25%17%3
2275
16th to endNight
36%5%17%28%11%
2340
December1st to 15thNight
47%6%22%18%4
2414
16th to endNight
53%6%16%19%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
20%8%18%26%18%8%
60
16th to endDay
20%6%21%23%21%5%
73
February1st to 15thDay
18%327%21%25%3
137
16th to endDay
12%17%31%26%11%
238
March1st to 15thDay
11%13%37%24%12%1
270
16th to endDay
15%18%33%23%8%
288
April1st to 15thDay
7%19%32%19%15%5%
269
16th to endDay
13%15%30%25%12%4
270
May1st to 15thDay
5%13%25%33%15%6%
288
16th to endDay
6%10%19%29%23%10%
330
June1st to 15thDay
7%10%28%26%20%7%
315
16th to endDay
16%25%33%22%10%
315
July1st to 15thDay
2116%35%34%9%
305
16th to endDay
2220%40%23%10%
327
August1st to 15thDay
6%121%37%26%6%
315
16th to endDay
1217%31%33%14%
332
September1st to 15thDay
4321%28%24%18%
315
16th to endDay
6%6%12%36%24%14%
264
October1st to 15thDay
10%5%27%26%21%8%
208
16th to endDay
16%9%21%29%18%4
96
November1st to 15thDay
14%18%24%38%3
90
16th to endDay
18%20%17%28%12%2
90
December1st to 15thDay
32%7%28%25%5%
77
16th to endDay
17%9%20%28%17%7%
64
January1st to 15thNight
15%7%22%32%20%1
720
16th to endNight
17%7%19%30%22%3
768
February1st to 15thNight
15%6%24%34%18%
704
16th to endNight
12%8%29%31%15%1
632
March1st to 15thNight
9%7%31%32%16%2
720
16th to endNight
13%9%31%33%10%1
768
April1st to 15thNight
9%8%30%33%15%1
710
16th to endNight
7%7%29%36%16%2
540
May1st to 15thNight
8%6%22%36%22%3
540
16th to endNight
8%420%32%28%6%
503
June1st to 15thNight
7%224%38%24%1
360
16th to endNight
2218%46%26%3
360
July1st to 15thNight
111%51%32%2
340
16th to endNight
110%46%36%4
421
August1st to 15thNight
2114%48%31%2
539
16th to endNight
214%46%30%4
636
September1st to 15thNight
4114%36%32%10%
720
16th to endNight
5%413%36%29%10%
667
October1st to 15thNight
7%321%39%22%4
660
16th to endNight
9%419%37%23%4
704
November1st to 15thNight
12%8%21%32%22%3
700
16th to endNight
10%6%27%32%17%4
720
December1st to 15thNight
15%330%31%15%2
720
16th to endNight
20%8%22%33%12%2
768
Page generated at 2017-09-19 05:32:27. Version ac04

Copyright 2017 A. Danko


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