Cedar Springs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Springs Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
33%
15642
14%
46852
8%
15600
39%
15600
20%
32610

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
17%
900
8%
2506
2%
895
22%
895
11%
2013
January16th to endNight
19%
939
9%
2667
2%
939
25%
939
13%
2090
February1st to 15thNight
18%
701
10%
2268
3%
701
26%
701
12%
1709
February16th to endNight
22%
631
12%
1893
5%
631
30%
631
13%
1449
March1st to 15thNight
27%
720
15%
2097
8%
720
32%
720
20%
1475
March16th to endNight
31%
768
18%
2112
10%
768
37%
768
23%
1443
April1st to 15thNight
25%
556
15%
1778
7%
556
34%
556
19%
1225
April16th to endNight
34%
540
20%
1620
9%
540
43%
540
24%
1087
May1st to 15thNight
39%
540
14%
1620
9%
540
44%
540
22%
1084
May16th to endNight
42%
550
16%
1571
9%
549
51%
549
29%
989
June1st to 15thNight
43%
360
14%
1260
12%
360
50%
360
26%
758
June16th to endNight
50%
360
15%
1260
12%
360
56%
360
27%
767
July1st to 15thNight
62%
507
16%
1357
12%
507
65%
507
43%
789
July16th to endNight
59%
564
16%
1431
11%
531
62%
531
38%
868
August1st to 15thNight
60%
539
19%
1609
13%
536
65%
536
37%
927
August16th to endNight
60%
573
22%
1737
16%
573
65%
573
36%
1004
September1st to 15thNight
55%
645
22%
1905
17%
645
59%
645
35%
1114
September16th to endNight
53%
665
21%
1837
15%
665
57%
665
33%
1142
October1st to 15thNight
35%
660
19%
1892
10%
660
44%
660
26%
1254
October16th to endNight
24%
704
12%
2243
7%
704
31%
704
15%
1624
November1st to 15thNight
28%
700
17%
2276
13%
700
37%
700
19%
1536
November16th to endNight
21%
720
9%
2447
4%
720
28%
720
11%
1885
December1st to 15thNight
14%
840
7%
2640
2%
840
19%
840
10%
2098
December16th to endNight
16%
960
9%
2826
2%
960
22%
960
10%
2280

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%7%36%6%35%5%5%7%33%
47919
Night
14%8%36%5%3445%7%35%
47023
Cloud CoverDay
13%7%37%6%35%5%5%7%33%
47928
Night
14%8%46%5%3445%7%35%
47028
TransparencyDay
48%7%13%19%9%1
47608
Night
47%6%13%20%10%1
46852
SeeingDay
16%11%31%24%11%5%
5927
Night
18%9%32%27%10%1
15646

By Month

Percentage Cloud Cover NE (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
16%12%5%10%7%45%5%6%6%19%
1432
16th to endDay
14%14%8%9%9%46%5%5%6%14%
1557
February1st to 15thDay
14%11%5%11%8%5%6%5%45%20%
1593
16th to endDay
12%12%410%8%47%5%5%6%21%
1580
March1st to 15thDay
13%7%47%7%46%5%47%29%
1853
16th to endDay
14%8%5%8%7%44445%32%
2112
April1st to 15thDay
19%10%46%5%23446%31%
2181
16th to endDay
15%7%35%6%34446%37%
2340
May1st to 15thDay
18%6%35%5%245%47%34%
2331
16th to endDay
12%5%25%5%3445%6%43%
2539
June1st to 15thDay
12%5%26%5%35%5%5%8%38%
2700
16th to endDay
10%5%35%6%35%6%6%9%37%
2698
July1st to 15thDay
6%425%6%45%5%7%10%41%
2520
16th to endDay
8%325%6%46%5%6%9%42%
2637
August1st to 15thDay
7%426%6%45%6%7%9%40%
2340
16th to endDay
11%6%25%5%4446%7%41%
2462
September1st to 15thDay
13%415%5%35%45%8%42%
2043
16th to endDay
11%5%35%5%35%5%6%10%38%
1829
October1st to 15thDay
17%6%36%6%34346%36%
1736
16th to endDay
21%10%47%6%36%45%7%23%
1628
November1st to 15thDay
14%10%37%6%36%5%46%30%
1582
16th to endDay
19%14%48%7%35%6%4421%
1512
December1st to 15thDay
15%13%49%6%35%6%5%6%22%
1319
16th to endDay
21%15%7%9%6%34345%17%
1395
January1st to 15thNight
19%12%5%8%7%45%5%45%22%
2506
16th to endNight
11%12%6%8%8%46%5%6%7%22%
2667
February1st to 15thNight
13%13%5%7%6%345%5%6%27%
2266
16th to endNight
15%13%6%8%7%3445%6%25%
1893
March1st to 15thNight
14%9%46%6%35%446%35%
2084
16th to endNight
15%8%45%424435%40%
2112
April1st to 15thNight
18%7%35%6%2445%7%33%
1778
16th to endNight
17%8%25%5%34345%40%
1620
May1st to 15thNight
13%6%35%6%445%5%7%38%
1620
16th to endNight
13%425%33445%9%42%
1569
June1st to 15thNight
13%5%24325%45%10%42%
1260
16th to endNight
8%325%6%36%46%9%44%
1260
July1st to 15thNight
6%215%3245%5%7%55%
1437
16th to endNight
5%315%42447%8%50%
1528
August1st to 15thNight
6%4134345%6%8%51%
1620
16th to endNight
9%323334347%53%
1737
September1st to 15thNight
10%424313346%53%
1905
16th to endNight
10%415%5%3345%8%47%
1837
October1st to 15thNight
14%7%25%5%23447%41%
1892
16th to endNight
21%8%36%6%3445%7%30%
2243
November1st to 15thNight
12%7%37%6%345%6%7%35%
2276
16th to endNight
18%11%47%6%445%46%24%
2447
December1st to 15thNight
19%13%5%8%6%35%5%45%22%
2640
16th to endNight
20%15%6%7%6%345%46%20%
2826

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
16%12%5%9%8%45%5%6%6%19%
1432
16th to endDay
13%14%8%9%10%46%5%5%6%14%
1557
February1st to 15thDay
13%12%6%10%9%47%5%45%21%
1593
16th to endDay
12%12%410%8%47%5%6%6%22%
1580
March1st to 15thDay
14%7%47%8%46%5%5%6%29%
1863
16th to endDay
14%8%5%8%7%35%445%31%
2111
April1st to 15thDay
19%10%46%42335%6%32%
2181
16th to endDay
15%7%26%6%3445%6%37%
2340
May1st to 15thDay
18%6%36%5%345%5%7%34%
2331
16th to endDay
12%425%5%35%45%7%43%
2539
June1st to 15thDay
12%6%36%5%25%5%6%8%37%
2700
16th to endDay
10%5%35%6%35%6%7%9%37%
2698
July1st to 15thDay
5%425%5%45%5%7%10%41%
2520
16th to endDay
8%325%5%35%5%7%8%42%
2637
August1st to 15thDay
7%5%25%6%45%6%7%9%39%
2340
16th to endDay
10%6%25%5%4446%7%42%
2462
September1st to 15thDay
12%5%25%4345%5%9%41%
2043
16th to endDay
11%5%36%5%25%5%6%9%39%
1829
October1st to 15thDay
16%7%26%6%34446%36%
1736
16th to endDay
19%10%48%6%36%45%6%23%
1628
November1st to 15thDay
13%9%37%7%36%45%7%30%
1582
16th to endDay
17%13%7%8%8%246%5%421%
1512
December1st to 15thDay
15%12%5%9%6%45%5%5%6%23%
1319
16th to endDay
21%14%7%9%7%35%445%17%
1395
January1st to 15thNight
19%11%5%8%7%35%446%21%
2506
16th to endNight
11%12%6%9%8%36%6%6%6%22%
2667
February1st to 15thNight
13%12%5%8%6%35%5%6%6%27%
2259
16th to endNight
15%13%5%8%7%3445%6%24%
1893
March1st to 15thNight
14%9%36%7%35%346%35%
2097
16th to endNight
15%8%46%424445%40%
2112
April1st to 15thNight
18%7%36%5%235%5%7%33%
1778
16th to endNight
16%7%25%5%34345%39%
1620
May1st to 15thNight
12%7%35%5%445%48%37%
1619
16th to endNight
12%425%425%35%9%42%
1569
June1st to 15thNight
12%434425%45%9%42%
1260
16th to endNight
8%325%5%35%46%9%43%
1260
July1st to 15thNight
5%22342446%8%54%
1437
16th to endNight
5%315%42447%8%50%
1528
August1st to 15thNight
6%424325%5%6%8%51%
1620
16th to endNight
9%41342335%7%52%
1737
September1st to 15thNight
10%42432335%7%52%
1905
16th to endNight
9%5%2443345%8%47%
1837
October1st to 15thNight
13%7%25%5%24447%41%
1892
16th to endNight
20%9%36%5%3435%7%29%
2243
November1st to 15thNight
12%7%36%6%345%6%7%35%
2276
16th to endNight
18%11%5%8%6%35%5%46%24%
2447
December1st to 15thNight
18%13%5%9%6%35%5%45%23%
2640
16th to endNight
20%15%6%7%5%3445%6%20%
2826

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
63%7%11%13%3
1433
16th to endDay
69%6%10%10%3
1557
February1st to 15thDay
65%6%10%13%3
1595
16th to endDay
60%7%12%13%5%1
1580
March1st to 15thDay
53%6%14%17%7%
1863
16th to endDay
53%5%13%17%8%1
2112
April1st to 15thDay
53%5%9%20%10%
2181
16th to endDay
46%5%14%14%15%2
2340
May1st to 15thDay
47%6%10%22%10%2
2331
16th to endDay
39%6%14%24%14%1
2543
June1st to 15thDay
42%7%14%22%12%
2700
16th to endDay
40%7%15%22%12%
2698
July1st to 15thDay
33%8%14%25%16%1
2371
16th to endDay
38%8%14%21%14%2
2471
August1st to 15thDay
37%8%14%25%12%
2327
16th to endDay
38%7%13%25%12%1
2462
September1st to 15thDay
38%6%13%29%10%1
2043
16th to endDay
39%7%17%25%9%
1829
October1st to 15thDay
48%5%11%22%10%
1736
16th to endDay
59%7%15%12%4
1628
November1st to 15thDay
51%8%13%18%7%
1582
16th to endDay
63%7%11%11%4
1512
December1st to 15thDay
60%9%13%12%4
1319
16th to endDay
68%6%12%9%2
1395
January1st to 15thNight
62%6%11%13%6%
2506
16th to endNight
59%7%14%14%3
2667
February1st to 15thNight
56%7%11%16%6%
2268
16th to endNight
58%6%12%16%5%
1893
March1st to 15thNight
50%413%20%10%1
2097
16th to endNight
46%412%21%13%1
2112
April1st to 15thNight
49%5%10%20%13%1
1778
16th to endNight
46%49%20%16%3
1620
May1st to 15thNight
44%6%11%21%13%2
1620
16th to endNight
36%6%13%26%12%4
1571
June1st to 15thNight
37%6%14%22%17%1
1260
16th to endNight
34%9%13%24%16%1
1260
July1st to 15thNight
25%7%14%29%21%1
1357
16th to endNight
30%6%17%28%15%1
1431
August1st to 15thNight
28%7%16%31%15%
1609
16th to endNight
29%6%14%30%16%1
1737
September1st to 15thNight
30%5%12%33%16%
1905
16th to endNight
34%5%15%32%9%
1837
October1st to 15thNight
42%5%13%26%11%
1892
16th to endNight
53%6%13%19%6%
2243
November1st to 15thNight
44%8%16%21%9%
2276
16th to endNight
59%7%14%12%5%
2447
December1st to 15thNight
62%6%12%12%5%
2640
16th to endNight
64%6%12%12%4
2826

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
21%17%44%13%3
90
16th to endDay
30%9%35%21%3
96
February1st to 15thDay
21%23%46%8%
90
16th to endDay
16%27%38%13%4
81
March1st to 15thDay
23%16%32%22%3
153
16th to endDay
25%7%30%22%11%2
288
April1st to 15thDay
27%13%28%20%9%1
270
16th to endDay
18%14%32%19%10%4
270
May1st to 15thDay
23%12%31%17%9%5%
288
16th to endDay
15%12%34%23%10%3
430
June1st to 15thDay
14%13%33%25%8%3
495
16th to endDay
11%9%37%25%10%4
495
July1st to 15thDay
7%7%33%30%14%6%
475
16th to endDay
8%6%32%32%11%7%
497
August1st to 15thDay
9%225%30%18%13%
313
16th to endDay
12%5%20%27%18%14%
332
September1st to 15thDay
14%321%26%21%12%
315
16th to endDay
16%5%24%23%20%9%
259
October1st to 15thDay
19%10%31%23%12%1
255
16th to endDay
22%20%37%15%3
140
November1st to 15thDay
8%17%41%21%10%1
90
16th to endDay
18%31%30%13%5%
72
December1st to 15thDay
21%33%30%10%31
60
16th to endDay
28%38%26%6%
73
January1st to 15thNight
24%14%35%19%4
900
16th to endNight
17%10%39%26%5%
939
February1st to 15thNight
19%15%39%21%3
704
16th to endNight
23%12%32%25%4
631
March1st to 15thNight
16%13%37%26%6%
720
16th to endNight
20%11%31%29%5%1
768
April1st to 15thNight
21%10%37%23%5%1
556
16th to endNight
21%8%31%26%10%1
540
May1st to 15thNight
12%8%32%34%10%1
540
16th to endNight
15%5%30%31%15%1
551
June1st to 15thNight
14%433%33%13%
360
16th to endNight
8%330%35%20%1
360
July1st to 15thNight
7%222%44%21%1
507
16th to endNight
8%124%39%23%2
564
August1st to 15thNight
9%121%39%24%2
539
16th to endNight
10%320%36%26%2
573
September1st to 15thNight
12%6%21%32%21%5%
645
16th to endNight
14%5%21%32%20%5%
665
October1st to 15thNight
17%8%32%26%13%1
660
16th to endNight
24%14%33%22%4
704
November1st to 15thNight
15%13%36%21%11%1
700
16th to endNight
23%13%35%20%6%
720
December1st to 15thNight
25%16%35%19%3
840
16th to endNight
25%14%35%20%3
960
Page generated at 2017-09-18 08:38:22. Version ac04

Copyright 2017 A. Danko


Cedar Springs Observatory Clear Sky Chart | Charts Home