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Cedar Drive Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Drive Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
36%
24800
17%
74665
9%
24745
43%
24745
23%
49947

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
24%
950
14%
2648
5%
946
32%
946
19%
1901
January11th to 20thNight
22%
918
13%
2569
5%
918
28%
918
16%
1931
January21st to endNight
21%
990
12%
2772
3%
990
28%
990
17%
2080
February1st to 10thNight
22%
900
15%
2367
3%
900
31%
900
21%
1708
February11th to 20thNight
25%
746
19%
2144
7%
745
35%
745
22%
1462
February21st to endNight
23%
592
18%
1776
5%
592
34%
592
18%
1254
March1st to 10thNight
34%
720
18%
2160
10%
720
40%
720
23%
1429
March11th to 20thNight
33%
691
21%
2118
10%
691
43%
691
25%
1338
March21st to endNight
34%
594
20%
1980
15%
594
43%
594
21%
1315
April1st to 10thNight
26%
540
15%
1800
7%
540
37%
540
19%
1229
April11th to 20thNight
34%
533
20%
1775
14%
533
43%
533
21%
1159
April21st to endNight
34%
540
18%
1656
10%
540
43%
540
23%
1107
May1st to 10thNight
34%
540
15%
1547
9%
540
39%
540
22%
1081
May11th to 20thNight
35%
531
19%
1416
11%
531
42%
531
25%
992
May21st to endNight
48%
583
14%
1552
8%
582
53%
582
31%
991
June1st to 10thNight
49%
540
15%
1440
7%
540
53%
540
33%
918
June11th to 20thNight
46%
540
15%
1440
9%
540
49%
540
31%
946
June21st to endNight
54%
540
16%
1440
9%
540
57%
540
36%
895
July1st to 10thNight
65%
525
18%
1400
10%
525
68%
525
45%
804
July11th to 20thNight
58%
522
19%
1392
11%
522
62%
522
39%
833
July21st to endNight
62%
591
22%
1487
13%
558
68%
558
46%
840
August1st to 10thNight
64%
537
23%
1423
17%
534
67%
534
38%
868
August11th to 20thNight
63%
534
21%
1645
17%
534
69%
534
35%
957
August21st to endNight
60%
594
22%
1980
20%
594
65%
594
34%
1109
September1st to 10thNight
57%
540
23%
1800
22%
540
62%
540
33%
1003
September11th to 20thNight
52%
616
28%
1876
22%
616
60%
616
38%
1038
September21st to endNight
49%
720
21%
1980
14%
720
55%
720
32%
1240
October1st to 10thNight
43%
720
23%
2070
15%
720
50%
720
31%
1272
October11th to 20thNight
31%
720
17%
2200
9%
720
40%
720
22%
1468
October21st to endNight
30%
792
14%
2574
8%
792
38%
792
18%
1773
November1st to 10thNight
31%
740
24%
2406
14%
740
45%
740
25%
1471
November11th to 20thNight
22%
774
18%
2484
7%
774
35%
774
18%
1693
November21st to endNight
28%
950
18%
2660
8%
950
36%
950
23%
1822
December1st to 10thNight
22%
950
13%
2660
3%
950
31%
950
19%
1893
December11th to 20thNight
21%
950
13%
3205
3%
948
30%
948
14%
2335
December21st to endNight
16%
1037
8%
4823
3%
1026
25%
1026
8%
3792

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%8%36%6%35%5%6%8%38%
74800
Night
13%9%46%5%3445%7%39%
74983
TransparencyDay
45%413%24%12%1
74501
Night
46%412%24%13%1
74803
SeeingDay
16%8%29%27%14%5%
14801
Night
17%8%31%32%12%1
24811

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 10thDay
11%9%49%7%46%45%5%35%
1517
11th to 20thDay
13%15%6%10%8%5%7%5%46%23%
1464
21st to endDay
13%14%5%10%7%35%5%46%29%
1584
February1st to 10thDay
9%11%5%8%8%345%6%7%35%
1590
11th to 20thDay
11%10%47%5%35%5%5%6%39%
1702
21st to endDay
13%11%36%6%45%5%6%7%33%
1480
March1st to 10thDay
12%10%47%4345%6%8%37%
1800
11th to 20thDay
12%6%47%5%346%5%8%39%
1856
21st to endDay
17%9%46%6%36%6%5%6%33%
2376
April1st to 10thDay
14%11%5%7%5%45%5%5%6%32%
2160
11th to 20thDay
20%9%35%6%3445%5%36%
2134
21st to endDay
18%9%46%6%36%5%46%33%
2304
May1st to 10thDay
15%8%36%6%445%5%8%35%
2411
11th to 20thDay
15%6%35%5%3446%7%41%
2479
21st to endDay
12%5%25%6%36%6%6%9%40%
2725
June1st to 10thDay
10%5%35%5%35%5%6%8%45%
2520
11th to 20thDay
13%6%25%5%35%5%6%9%41%
2520
21st to endDay
11%5%25%5%35%5%7%9%42%
2520
July1st to 10thDay
6%3245%36%6%8%11%48%
2520
11th to 20thDay
8%4245%35%6%7%10%46%
2520
21st to endDay
8%4245%45%5%6%9%49%
2743
August1st to 10thDay
7%425%6%46%6%8%11%42%
2507
11th to 20thDay
10%5%25%5%45%5%6%9%44%
2253
21st to endDay
12%6%245%35%5%6%8%44%
2376
September1st to 10thDay
13%5%35%6%35%46%7%42%
2160
11th to 20thDay
12%5%25%435%46%8%47%
2066
21st to endDay
12%7%37%445%6%5%8%39%
1980
October1st to 10thDay
14%8%35%5%34447%43%
1887
11th to 20thDay
19%9%37%7%35%5%5%6%31%
1758
21st to endDay
18%8%38%5%34446%35%
1782
November1st to 10thDay
13%7%36%5%3445%9%41%
1672
11th to 20thDay
13%8%5%8%7%45%46%7%32%
1693
21st to endDay
15%9%46%6%35%5%5%7%35%
1520
December1st to 10thDay
13%10%46%7%35%7%7%7%32%
1520
11th to 20thDay
14%12%5%7%6%45%6%6%7%28%
1918
21st to endDay
19%17%6%10%9%45%445%18%
2783
January1st to 10thNight
13%11%5%8%7%35%45%6%34%
2648
11th to 20thNight
15%12%6%10%7%34445%30%
2569
21st to endNight
12%13%6%8%8%35%46%6%27%
2772
February1st to 10thNight
10%12%6%8%8%35%445%35%
2367
11th to 20thNight
10%10%48%6%45%45%7%38%
2143
21st to endNight
16%11%47%6%34445%34%
1776
March1st to 10thNight
14%8%36%5%35%46%5%40%
2160
11th to 20thNight
13%8%35%5%35%45%6%43%
2118
21st to endNight
18%8%36%5%24446%37%
1980
April1st to 10thNight
18%10%37%5%345%5%7%34%
1800
11th to 20thNight
22%6%25%43445%7%38%
1775
21st to endNight
16%9%36%5%3446%7%36%
1656
May1st to 10thNight
17%9%36%435%5%5%8%34%
1547
11th to 20thNight
17%7%35%5%35%6%5%7%38%
1416
21st to endNight
12%5%25%5%35%5%6%9%42%
1551
June1st to 10thNight
11%5%25%6%35%5%6%7%46%
1440
11th to 20thNight
12%6%35%5%35%5%6%8%41%
1440
21st to endNight
7%5%245%346%7%9%48%
1440
July1st to 10thNight
6%315%435%5%5%9%55%
1440
11th to 20thNight
7%425%5%25%5%7%9%50%
1440
21st to endNight
6%3146%2445%9%55%
1575
August1st to 10thNight
6%5%26%5%345%7%10%46%
1432
11th to 20thNight
8%425%5%35%5%6%8%49%
1645
21st to endNight
9%5%25%43445%7%51%
1980
September1st to 10thNight
9%425%5%3445%7%52%
1800
11th to 20thNight
12%42432245%7%55%
1876
21st to endNight
13%5%25%5%4445%7%45%
1980
October1st to 10thNight
13%7%35%42445%7%47%
2070
11th to 20thNight
16%7%35%5%36%5%5%6%37%
2200
21st to endNight
18%10%46%5%345%5%7%33%
2574
November1st to 10thNight
12%8%35%43345%8%44%
2406
11th to 20thNight
13%10%48%6%35%45%6%35%
2484
21st to endNight
15%10%46%5%3445%7%38%
2660
December1st to 10thNight
13%12%48%6%35%45%7%34%
2660
11th to 20thNight
13%14%5%9%7%35%445%32%
3279
21st to endNight
22%18%5%8%6%3443422%
4884

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
52%313%21%10%1
1518
11th to 20thDay
63%5%10%14%7%1
1464
21st to endDay
57%412%19%8%1
1584
February1st to 10thDay
49%413%22%11%1
1590
11th to 20thDay
47%412%23%12%2
1712
21st to endDay
49%5%13%22%10%2
1480
March1st to 10thDay
47%416%22%11%2
1800
11th to 20thDay
44%415%22%13%2
1856
21st to endDay
52%413%21%9%1
2376
April1st to 10thDay
52%5%11%20%12%
2160
11th to 20thDay
51%39%22%13%2
2134
21st to endDay
52%410%20%12%2
2304
May1st to 10thDay
48%413%24%10%1
2411
11th to 20thDay
43%5%12%24%14%2
2483
21st to endDay
41%6%13%26%13%2
2725
June1st to 10thDay
37%5%13%30%14%2
2520
11th to 20thDay
39%5%15%25%15%1
2520
21st to endDay
37%6%15%27%13%2
2520
July1st to 10thDay
30%5%14%33%16%2
2451
11th to 20thDay
31%6%16%29%16%3
2445
21st to endDay
32%415%29%18%2
2591
August1st to 10thDay
34%7%16%30%12%2
2492
11th to 20thDay
37%415%30%14%1
2253
21st to endDay
37%5%14%27%16%1
2376
September1st to 10thDay
40%5%13%26%15%1
2160
11th to 20thDay
36%318%32%10%1
2066
21st to endDay
44%413%29%10%
1980
October1st to 10thDay
43%313%30%10%
1887
11th to 20thDay
53%412%22%9%1
1758
21st to endDay
51%414%20%10%
1782
November1st to 10thDay
41%413%27%14%1
1672
11th to 20thDay
51%414%20%9%1
1693
21st to endDay
48%5%17%23%6%1
1520
December1st to 10thDay
50%5%13%25%6%1
1520
11th to 20thDay
56%5%14%14%9%2
1915
21st to endDay
71%37%14%5%
2783
January1st to 10thNight
52%412%20%12%1
2648
11th to 20thNight
58%411%19%8%
2569
21st to endNight
58%410%17%11%
2772
February1st to 10thNight
51%39%23%11%2
2367
11th to 20thNight
47%411%24%12%2
2144
21st to endNight
53%311%20%11%2
1776
March1st to 10thNight
46%414%24%11%1
2160
11th to 20thNight
42%412%25%16%2
2118
21st to endNight
48%411%23%12%2
1980
April1st to 10thNight
51%47%19%18%1
1800
11th to 20thNight
47%39%22%15%4
1775
21st to endNight
48%311%23%15%1
1656
May1st to 10thNight
48%6%13%21%11%2
1547
11th to 20thNight
46%5%10%24%13%2
1417
21st to endNight
38%5%16%24%15%2
1552
June1st to 10thNight
36%5%12%31%15%1
1440
11th to 20thNight
40%411%26%17%2
1440
21st to endNight
32%7%17%26%15%3
1440
July1st to 10thNight
26%5%13%34%19%3
1400
11th to 20thNight
30%6%14%28%19%4
1392
21st to endNight
26%417%31%18%3
1487
August1st to 10thNight
32%6%15%30%15%2
1423
11th to 20thNight
33%5%15%30%16%1
1645
21st to endNight
33%412%28%20%2
1980
September1st to 10thNight
32%411%31%21%1
1800
11th to 20thNight
31%314%37%15%1
1876
21st to endNight
38%314%30%13%1
1980
October1st to 10thNight
38%410%33%14%1
2070
11th to 20thNight
47%414%23%11%1
2200
21st to endNight
51%413%21%12%
2574
November1st to 10thNight
40%411%27%16%2
2406
11th to 20thNight
50%413%20%13%1
2484
21st to endNight
47%314%26%8%1
2660
December1st to 10thNight
52%314%23%7%1
2660
11th to 20thNight
57%314%18%9%1
3281
21st to endNight
67%48%16%5%
4884

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
14%10%31%30%12%2
270
11th to 20thDay
22%9%31%29%8%1
249
21st to endDay
22%6%27%33%11%2
264
February1st to 10thDay
15%9%39%29%8%
240
11th to 20thDay
12%14%42%22%10%1
240
21st to endDay
22%11%40%25%21
198
March1st to 10thDay
17%13%36%23%12%
240
11th to 20thDay
19%9%29%33%8%3
252
21st to endDay
26%8%28%27%8%3
462
April1st to 10thDay
22%12%31%25%9%1
420
11th to 20thDay
27%13%26%20%11%2
412
21st to endDay
22%9%31%21%15%2
420
May1st to 10thDay
18%10%32%28%8%3
494
11th to 20thDay
18%10%31%27%11%4
625
21st to endDay
16%8%27%28%14%8%
679
June1st to 10thDay
10%6%33%32%15%5%
630
11th to 20thDay
15%8%30%29%14%5%
630
21st to endDay
12%6%29%32%17%5%
630
July1st to 10thDay
8%420%32%26%10%
621
11th to 20thDay
8%5%26%34%18%8%
618
21st to endDay
7%5%25%32%21%10%
684
August1st to 10thDay
8%421%34%24%9%
626
11th to 20thDay
13%417%28%26%12%
481
21st to endDay
15%6%20%26%22%10%
495
September1st to 10thDay
18%6%20%29%19%8%
450
11th to 20thDay
12%424%31%22%8%
450
21st to endDay
15%9%29%22%20%6%
450
October1st to 10thDay
17%11%26%25%17%4
357
11th to 20thDay
21%17%31%23%7%
270
21st to endDay
24%14%34%22%6%
297
November1st to 10thDay
15%13%36%25%10%1
270
11th to 20thDay
15%16%39%20%9%1
270
21st to endDay
23%8%39%24%6%
270
December1st to 10thDay
15%13%42%23%6%
270
11th to 20thDay
22%13%39%17%7%1
270
21st to endDay
29%13%32%19%6%
297
January1st to 10thNight
16%11%37%29%7%
950
11th to 20thNight
20%11%35%25%8%1
918
21st to endNight
19%7%36%29%8%1
990
February1st to 10thNight
15%10%38%29%7%
900
11th to 20thNight
16%10%39%26%8%
748
21st to endNight
22%10%34%29%5%
592
March1st to 10thNight
17%9%32%32%8%1
720
11th to 20thNight
15%11%36%29%7%1
691
21st to endNight
21%7%30%31%9%1
594
April1st to 10thNight
23%8%37%27%5%1
540
11th to 20thNight
26%5%30%30%8%
533
21st to endNight
20%6%32%32%9%1
540
May1st to 10thNight
23%6%32%31%8%1
540
11th to 20thNight
19%6%32%33%9%
531
21st to endNight
14%5%26%38%17%1
584
June1st to 10thNight
12%6%25%41%15%1
540
11th to 20thNight
15%6%26%40%13%1
540
21st to endNight
9%424%44%18%1
540
July1st to 10thNight
7%219%46%24%2
525
11th to 20thNight
8%322%41%24%1
522
21st to endNight
6%221%47%23%1
591
August1st to 10thNight
9%115%47%26%1
537
11th to 20thNight
9%315%40%30%3
534
21st to endNight
10%221%42%23%2
594
September1st to 10thNight
11%423%35%23%4
540
11th to 20thNight
13%5%23%34%21%3
616
21st to endNight
15%6%23%35%19%2
720
October1st to 10thNight
16%8%26%30%19%1
720
11th to 20thNight
19%10%33%29%8%
720
21st to endNight
23%10%31%26%10%1
792
November1st to 10thNight
16%9%39%27%8%1
740
11th to 20thNight
17%14%39%23%6%
774
21st to endNight
19%11%35%26%7%
950
December1st to 10thNight
19%10%39%25%7%
950
11th to 20thNight
21%9%36%25%7%1
950
21st to endNight
27%11%33%25%4
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