Charles E. Daniel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charles E. Daniel Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
47%
16162
22%
48467
14%
16121
55%
16121
27%
30691

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
30%
780
23%
2522
10%
776
47%
776
24%
1540
January16th to endNight
28%
788
26%
2560
13%
788
45%
788
25%
1553
February1st to 15thNight
30%
701
25%
2175
11%
700
46%
700
27%
1306
February16th to endNight
27%
631
26%
1893
11%
631
43%
631
28%
1152
March1st to 15thNight
33%
720
25%
1998
13%
720
43%
720
29%
1261
March16th to endNight
36%
768
19%
2112
10%
768
43%
768
27%
1392
April1st to 15thNight
41%
718
24%
1970
13%
718
50%
718
33%
1198
April16th to endNight
46%
564
25%
1644
15%
564
54%
564
31%
1007
May1st to 15thNight
44%
540
17%
1620
8%
540
51%
540
25%
1062
May16th to endNight
59%
561
15%
1683
11%
561
62%
561
26%
1105
June1st to 15thNight
62%
540
12%
1620
9%
540
64%
540
24%
1100
June16th to endNight
69%
540
14%
1620
12%
540
71%
540
26%
1082
July1st to 15thNight
67%
510
9%
1530
8%
510
68%
510
20%
1105
July16th to endNight
70%
564
13%
1595
10%
531
72%
531
24%
1080
August1st to 15thNight
65%
539
13%
1609
12%
536
66%
536
23%
1115
August16th to endNight
64%
621
16%
1842
14%
621
65%
621
22%
1294
September1st to 15thNight
63%
720
17%
1980
15%
720
64%
720
28%
1309
September16th to endNight
53%
717
21%
1980
15%
717
58%
717
26%
1341
October1st to 15thNight
53%
720
28%
2064
24%
720
59%
720
33%
1265
October16th to endNight
51%
768
35%
2304
26%
768
65%
768
38%
1271
November1st to 15thNight
51%
760
28%
2372
23%
760
60%
760
34%
1339
November16th to endNight
44%
780
28%
2535
20%
780
56%
780
30%
1451
December1st to 15thNight
40%
780
24%
2535
16%
780
52%
780
25%
1570
December16th to endNight
34%
832
22%
2704
15%
832
44%
832
21%
1793

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
13%4244245%5%8%43%
49052
Night
13%5%2442445%7%44%
48665
TransparencyDay
37%7%12%19%17%4
48753
Night
37%6%11%18%19%5%
48468
SeeingDay
16%5%19%24%21%12%
5945
Night
15%6%23%29%21%3
16167

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
17%5%23324435%46%
1746
16th to endDay
16%42432434448%
1768
February1st to 15thDay
14%5%24333446%48%
1684
16th to endDay
15%5%15%323335%48%
1580
March1st to 15thDay
16%423323346%48%
1962
16th to endDay
17%5%2442445%6%43%
2111
April1st to 15thDay
13%42432345%9%47%
1975
16th to endDay
11%325%4345%46%47%
2325
May1st to 15thDay
11%5%245%25%45%8%43%
2331
16th to endDay
10%4245%35%6%6%9%40%
2431
June1st to 15thDay
8%4346%37%7%6%12%34%
2340
16th to endDay
5%2245%37%7%8%11%40%
2340
July1st to 15thDay
9%5%36%6%46%6%7%10%33%
2340
16th to endDay
7%425%6%48%6%7%12%32%
2465
August1st to 15thDay
11%6%25%6%46%5%6%11%31%
2340
16th to endDay
12%5%36%6%45%6%6%10%33%
2345
September1st to 15thDay
10%4245%35%6%6%9%41%
1980
16th to endDay
15%5%244245%5%7%42%
1980
October1st to 15thDay
15%413312235%57%
1894
16th to endDay
10%41341222461%
1920
November1st to 15thDay
13%413222436%53%
1813
16th to endDay
15%423412445%51%
1755
December1st to 15thDay
17%6%24424345%43%
1755
16th to endDay
23%6%24413335%39%
1872
January1st to 15thNight
17%42332333449%
2522
16th to endNight
17%5%24323345%47%
2560
February1st to 15thNight
14%5%13324445%50%
2166
16th to endNight
13%5%24423346%48%
1893
March1st to 15thNight
14%5%15%42345%6%46%
1998
16th to endNight
14%5%25%42445%5%45%
2112
April1st to 15thNight
13%413323446%51%
1970
16th to endNight
11%5%24424445%49%
1644
May1st to 15thNight
12%5%35%6%445%6%6%40%
1619
16th to endNight
9%425%6%37%5%6%8%39%
1682
June1st to 15thNight
10%425%6%36%6%8%10%34%
1620
16th to endNight
6%325%5%36%8%7%11%37%
1620
July1st to 15thNight
8%6%25%6%5%7%8%9%10%28%
1620
16th to endNight
7%425%437%8%9%13%32%
1703
August1st to 15thNight
12%5%35%6%45%5%8%10%33%
1620
16th to endNight
11%6%26%5%36%6%6%10%34%
1842
September1st to 15thNight
11%5%35%5%3446%11%38%
1980
16th to endNight
15%5%25%5%3445%5%42%
1980
October1st to 15thNight
13%5%14313335%52%
2064
16th to endNight
10%31331433459%
2304
November1st to 15thNight
12%414323236%55%
2372
16th to endNight
15%313323346%51%
2535
December1st to 15thNight
17%5%145%23445%45%
2535
16th to endNight
21%6%25%424445%39%
2704

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
40%6%7%17%22%5%
1747
16th to endDay
38%46%20%21%9%
1768
February1st to 15thDay
36%49%20%23%4
1686
16th to endDay
37%49%22%19%5%
1580
March1st to 15thDay
37%47%23%20%6%
1962
16th to endDay
40%6%12%21%17%2
2112
April1st to 15thDay
33%5%11%22%21%5%
1975
16th to endDay
36%6%10%20%19%6%
2325
May1st to 15thDay
38%7%14%19%17%2
2331
16th to endDay
36%9%16%22%13%1
2435
June1st to 15thDay
39%11%18%21%7%1
2340
16th to endDay
32%12%17%20%13%2
2340
July1st to 15thDay
41%12%18%17%7%2
2201
16th to endDay
38%11%22%17%8%1
2310
August1st to 15thDay
45%11%14%17%9%
2327
16th to endDay
42%11%18%17%9%1
2345
September1st to 15thDay
36%9%13%18%18%3
1980
16th to endDay
39%7%12%17%17%5%
1980
October1st to 15thDay
31%411%20%27%5%
1894
16th to endDay
28%26%21%29%11%
1920
November1st to 15thDay
32%47%18%26%9%
1813
16th to endDay
35%47%19%25%7%
1755
December1st to 15thDay
42%48%20%18%6%
1755
16th to endDay
47%38%17%16%5%
1872
January1st to 15thNight
39%48%15%24%7%
2522
16th to endNight
38%36%19%23%8%
2560
February1st to 15thNight
36%37%20%23%7%
2175
16th to endNight
36%49%21%23%5%
1893
March1st to 15thNight
37%410%17%21%8%
1998
16th to endNight
39%6%10%18%19%4
2112
April1st to 15thNight
33%48%22%24%6%
1970
16th to endNight
35%5%9%19%21%7%
1644
May1st to 15thNight
41%7%13%19%17%2
1620
16th to endNight
36%11%13%23%12%1
1684
June1st to 15thNight
39%12%18%20%8%1
1620
16th to endNight
35%13%17%18%12%3
1620
July1st to 15thNight
43%14%18%15%6%2
1530
16th to endNight
36%14%21%17%7%2
1595
August1st to 15thNight
42%10%19%16%10%
1609
16th to endNight
41%12%17%16%10%1
1842
September1st to 15thNight
38%8%17%18%13%2
1980
16th to endNight
42%7%11%16%16%5%
1980
October1st to 15thNight
34%6%8%18%25%6%
2064
16th to endNight
28%45%19%29%12%
2304
November1st to 15thNight
32%36%18%27%11%
2372
16th to endNight
34%46%17%27%9%
2535
December1st to 15thNight
40%49%19%18%7%
2535
16th to endNight
46%49%15%18%5%
2704

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
22%14%33%22%7%
135
16th to endDay
15%22%44%13%3
109
February1st to 15thDay
20%22%45%10%2
90
16th to endDay
22%9%34%29%3
81
March1st to 15thDay
16%13%32%29%8%
252
16th to endDay
19%10%31%24%13%1
288
April1st to 15thDay
15%10%24%27%18%3
270
16th to endDay
15%425%25%19%9%
270
May1st to 15thDay
14%6%31%19%17%9%
288
16th to endDay
14%315%24%27%15%
331
June1st to 15thDay
11%411%25%27%19%
315
16th to endDay
9%14%27%20%26%
315
July1st to 15thDay
10%110%22%30%23%
305
16th to endDay
6%6%27%33%25%
326
August1st to 15thDay
20%18%17%27%24%
313
16th to endDay
14%9%23%25%27%
332
September1st to 15thDay
14%113%18%28%23%
315
16th to endDay
21%213%23%27%11%
314
October1st to 15thDay
21%218%27%21%7%
315
16th to endDay
12%7%17%29%27%5%
336
November1st to 15thDay
25%6%19%26%16%5%
231
16th to endDay
10%6%25%31%21%5%
135
December1st to 15thDay
26%8%34%22%8%
135
16th to endDay
28%13%38%15%4
144
January1st to 15thNight
20%10%33%26%7%
780
16th to endNight
20%12%35%27%3
788
February1st to 15thNight
17%11%36%31%2
704
16th to endNight
15%11%41%27%3
631
March1st to 15thNight
17%11%34%29%7%
720
16th to endNight
15%8%34%29%12%
768
April1st to 15thNight
16%11%28%29%13%
718
16th to endNight
13%5%27%33%18%1
564
May1st to 15thNight
13%5%27%32%19%2
540
16th to endNight
13%213%32%33%5%
563
June1st to 15thNight
11%113%30%34%9%
540
16th to endNight
7%12%29%38%11%
540
July1st to 15thNight
11%18%31%38%9%
510
16th to endNight
7%7%27%45%10%
564
August1st to 15thNight
15%17%23%43%8%
539
16th to endNight
13%8%25%43%7%
621
September1st to 15thNight
13%110%27%37%9%
720
16th to endNight
18%216%29%29%4
717
October1st to 15thNight
17%420%25%27%5%
720
16th to endNight
12%426%30%21%3
768
November1st to 15thNight
14%424%33%17%4
760
16th to endNight
16%8%26%31%16%1
780
December1st to 15thNight
19%8%25%33%13%
780
16th to endNight
23%6%28%32%8%
832
Page generated at 2018-01-21 12:19:33. Version ac04

Copyright 2018 A. Danko


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