Carr Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carr Astronomical Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
31%
23103
11%
74677
8%
23060
35%
23060
13%
56827

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
11%
946
2%
2838
1%
946
12%
946
3%
2572
January11th to 20thNight
13%
756
2%
2445
2%
756
14%
756
3%
2229
January21st to endNight
18%
792
4%
2574
2%
792
21%
792
5%
2247
February1st to 10thNight
11%
720
4%
2340
1%
720
15%
720
5%
2040
February11th to 20thNight
18%
700
6%
2275
2%
700
22%
700
7%
1889
February21st to endNight
17%
592
8%
1848
2%
592
23%
592
9%
1492
March1st to 10thNight
22%
720
12%
2009
6%
720
27%
720
15%
1560
March11th to 20thNight
23%
720
16%
1980
7%
720
30%
720
16%
1508
March21st to endNight
33%
792
15%
2178
8%
792
39%
792
19%
1575
April1st to 10thNight
27%
720
12%
1865
5%
720
31%
720
18%
1414
April11th to 20thNight
34%
587
18%
1651
10%
587
38%
587
22%
1146
April21st to endNight
34%
540
15%
1620
10%
540
38%
540
17%
1176
May1st to 10thNight
45%
540
15%
1620
10%
540
48%
540
23%
1086
May11th to 20thNight
48%
395
19%
1457
20%
395
55%
395
22%
894
May21st to endNight
56%
388
17%
1551
19%
388
64%
388
26%
867
June1st to 10thNight
46%
360
12%
1399
14%
360
52%
360
19%
868
June11th to 20thNight
57%
360
17%
1260
19%
360
62%
360
27%
742
June21st to endNight
50%
360
15%
1260
18%
360
55%
360
24%
781
July1st to 10thNight
65%
350
19%
1225
23%
350
69%
350
36%
642
July11th to 20thNight
57%
348
17%
1307
23%
348
61%
348
28%
733
July21st to endNight
61%
587
15%
1669
13%
555
63%
555
30%
1030
August1st to 10thNight
59%
537
17%
1600
14%
534
61%
534
32%
961
August11th to 20thNight
66%
534
21%
1598
16%
534
69%
534
33%
962
August21st to endNight
54%
621
17%
1809
11%
621
57%
621
27%
1169
September1st to 10thNight
53%
720
16%
1800
9%
720
55%
720
33%
1179
September11th to 20thNight
55%
720
22%
1954
15%
720
57%
720
32%
1235
September21st to endNight
45%
720
17%
1983
14%
720
47%
720
22%
1400
October1st to 10thNight
37%
720
14%
2160
12%
720
41%
720
19%
1548
October11th to 20thNight
25%
720
9%
2160
6%
720
31%
720
13%
1687
October21st to endNight
20%
792
9%
2398
6%
792
25%
792
8%
1971
November1st to 10thNight
24%
740
12%
2486
9%
740
29%
740
12%
1889
November11th to 20thNight
17%
760
8%
2660
6%
760
21%
760
8%
2158
November21st to endNight
17%
760
6%
2660
4%
760
20%
760
7%
2265
December1st to 10thNight
12%
760
2%
2660
1%
760
13%
760
3%
2389
December11th to 20thNight
10%
760
2%
3275
0%
759
12%
759
3%
2843
December21st to endNight
8%
966
2%
5103
0%
959
11%
959
1%
4680

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
14%11%48%7%45%5%5%7%29%
74892
Night
14%11%5%9%7%45%5%5%6%27%
74875
TransparencyDay
54%8%11%17%9%1
74600
Night
57%8%11%15%8%1
74704
SeeingDay
17%13%27%26%13%4
13876
Night
19%14%29%26%11%2
23123

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 10thDay
12%15%9%16%13%5%7%6%349%
1328
11th to 20thDay
11%16%8%15%14%8%7%5%448%
1615
21st to endDay
9%14%9%14%15%6%9%6%5%49%
1782
February1st to 10thDay
11%16%7%14%12%5%6%6%5%5%12%
1620
11th to 20thDay
11%11%8%17%13%5%6%5%5%5%15%
1573
21st to endDay
13%17%7%10%11%5%6%44418%
1404
March1st to 10thDay
12%12%6%12%11%5%5%5%46%23%
1946
11th to 20thDay
11%13%7%11%7%45%45%5%28%
1980
21st to endDay
15%12%48%7%45%5%5%5%30%
2178
April1st to 10thDay
15%15%5%9%6%35%45%6%27%
2094
11th to 20thDay
16%11%45%6%34447%35%
2271
21st to endDay
18%12%5%6%5%3445%6%33%
2340
May1st to 10thDay
16%10%36%6%3446%8%35%
2340
11th to 20thDay
15%10%36%5%345%5%6%39%
2435
21st to endDay
12%7%25%5%35%5%6%9%41%
2725
June1st to 10thDay
15%6%35%5%346%6%8%38%
2557
11th to 20thDay
11%6%25%445%5%6%10%41%
2700
21st to endDay
14%6%25%5%346%6%9%39%
2700
July1st to 10thDay
10%5%245%35%5%6%9%45%
2700
11th to 20thDay
10%6%25%5%35%6%6%9%40%
2610
21st to endDay
10%5%27%7%45%5%7%10%38%
2547
August1st to 10thDay
11%6%25%5%35%6%7%9%41%
2327
11th to 20thDay
10%5%26%7%46%5%6%9%41%
2303
21st to endDay
13%6%36%6%45%6%7%9%37%
2527
September1st to 10thDay
15%7%36%5%35%46%8%37%
2160
11th to 20thDay
15%5%26%5%45%5%5%9%39%
2003
21st to endDay
16%7%36%7%45%5%6%7%34%
1976
October1st to 10thDay
18%10%46%6%346%5%8%31%
1800
11th to 20thDay
18%13%48%9%47%5%6%5%22%
1800
21st to endDay
25%18%5%7%7%445%5%5%16%
1955
November1st to 10thDay
13%17%5%9%8%45%5%5%6%25%
1592
11th to 20thDay
13%16%6%11%7%5%7%6%5%6%19%
1520
21st to endDay
15%16%8%12%8%5%6%6%6%6%12%
1520
December1st to 10thDay
11%19%11%15%9%46%5%6%6%8%
1520
11th to 20thDay
14%17%8%16%8%5%7%45%5%11%
1906
21st to endDay
20%19%7%16%8%444449%
2538
January1st to 10thNight
12%16%8%14%12%6%7%7%6%5%9%
2838
11th to 20thNight
14%13%7%15%13%5%8%6%5%5%9%
2445
21st to endNight
9%12%6%15%13%7%8%6%6%6%11%
2574
February1st to 10thNight
11%15%7%14%11%6%7%6%5%5%13%
2340
11th to 20thNight
10%12%7%13%12%6%8%6%5%6%16%
2273
21st to endNight
13%12%5%12%10%5%6%5%5%6%21%
1848
March1st to 10thNight
10%13%7%11%7%35%45%6%28%
1999
11th to 20thNight
11%13%6%9%6%45%5%4432%
1979
21st to endNight
13%10%5%8%6%35%5%5%6%34%
2178
April1st to 10thNight
17%11%5%8%7%4445%6%30%
1865
11th to 20thNight
17%9%36%5%44447%38%
1651
21st to endNight
17%11%48%5%3445%6%32%
1620
May1st to 10thNight
15%8%36%5%45%46%8%37%
1620
11th to 20thNight
16%6%245%345%46%44%
1456
21st to endNight
10%5%245%346%6%7%49%
1550
June1st to 10thNight
14%6%26%6%36%6%5%8%38%
1399
11th to 20thNight
11%424435%6%6%10%42%
1260
21st to endNight
12%7%36%5%245%6%8%43%
1260
July1st to 10thNight
10%324324349%55%
1260
11th to 20thNight
9%4246%35%5%7%9%47%
1349
21st to endNight
9%4245%36%47%8%49%
1767
August1st to 10thNight
9%4245%35%6%6%9%47%
1611
11th to 20thNight
7%425%5%35%5%6%9%49%
1598
21st to endNight
11%5%25%4445%6%8%44%
1809
September1st to 10thNight
12%425%4345%7%10%45%
1800
11th to 20thNight
13%6%144346%5%9%47%
1954
21st to endNight
18%7%36%5%3446%7%38%
1983
October1st to 10thNight
19%8%35%6%45%446%37%
2160
11th to 20thNight
20%12%36%7%35%6%6%7%26%
2160
21st to endNight
23%18%47%6%445%5%6%19%
2398
November1st to 10thNight
15%15%5%7%5%35%5%5%6%28%
2486
11th to 20thNight
14%15%6%10%8%45%6%6%6%19%
2660
21st to endNight
16%16%7%10%8%5%5%6%6%6%16%
2660
December1st to 10thNight
15%17%9%13%8%46%5%6%5%12%
2660
11th to 20thNight
10%18%8%14%9%5%7%5%6%7%12%
3288
21st to endNight
20%18%9%18%8%45%4448%
5117

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
80%7%9%5%1
1329
11th to 20thDay
80%8%6%33
1615
21st to endDay
77%7%8%5%3
1782
February1st to 10thDay
74%7%8%8%2
1620
11th to 20thDay
71%7%8%8%5%1
1582
21st to endDay
70%5%9%10%6%
1404
March1st to 10thDay
61%7%12%12%7%1
1949
11th to 20thDay
58%7%9%15%9%2
1980
21st to endDay
55%5%11%15%12%2
2178
April1st to 10thDay
59%5%10%17%8%1
2094
11th to 20thDay
50%5%9%20%14%1
2271
21st to endDay
52%6%10%18%11%3
2340
May1st to 10thDay
48%6%10%21%13%2
2340
11th to 20thDay
46%5%10%22%15%1
2439
21st to endDay
39%8%13%23%14%2
2725
June1st to 10thDay
42%9%11%22%15%1
2557
11th to 20thDay
38%8%13%23%17%1
2700
21st to endDay
41%7%14%24%13%1
2700
July1st to 10thDay
35%8%14%24%17%2
2626
11th to 20thDay
38%9%13%28%11%1
2530
21st to endDay
41%9%13%22%13%1
2405
August1st to 10thDay
37%10%18%22%12%1
2314
11th to 20thDay
38%11%16%24%11%
2303
21st to endDay
43%8%15%22%11%1
2527
September1st to 10thDay
45%8%13%23%10%2
2160
11th to 20thDay
41%7%14%27%11%
2003
21st to endDay
49%8%12%24%6%1
1976
October1st to 10thDay
51%8%12%17%11%1
1800
11th to 20thDay
63%9%10%11%6%1
1800
21st to endDay
70%7%10%9%5%
1955
November1st to 10thDay
60%8%12%14%6%
1592
11th to 20thDay
66%9%10%9%6%
1520
21st to endDay
74%8%9%7%1
1520
December1st to 10thDay
80%8%7%41
1520
11th to 20thDay
77%8%8%6%1
1906
21st to endDay
81%7%6%5%
2538
January1st to 10thNight
77%9%8%5%1
2838
11th to 20thNight
76%11%8%32
2445
21st to endNight
73%9%10%5%31
2574
February1st to 10thNight
74%8%9%9%1
2340
11th to 20thNight
69%7%10%11%4
2275
21st to endNight
63%9%11%11%6%
1848
March1st to 10thNight
58%7%10%15%9%1
2009
11th to 20thNight
55%7%9%16%11%2
1980
21st to endNight
51%6%10%19%12%2
2178
April1st to 10thNight
56%5%10%18%12%1
1865
11th to 20thNight
48%6%9%19%18%2
1651
21st to endNight
53%6%10%14%15%2
1620
May1st to 10thNight
45%6%10%20%17%2
1620
11th to 20thNight
41%6%9%23%18%3
1457
21st to endNight
32%9%14%26%15%3
1551
June1st to 10thNight
42%7%11%20%18%2
1399
11th to 20thNight
35%7%14%25%18%1
1260
21st to endNight
38%9%13%26%14%1
1260
July1st to 10thNight
27%7%12%28%23%3
1225
11th to 20thNight
32%8%15%30%15%1
1307
21st to endNight
33%10%13%27%16%1
1669
August1st to 10thNight
33%8%17%27%15%1
1600
11th to 20thNight
31%9%16%27%16%2
1598
21st to endNight
38%8%15%26%11%1
1809
September1st to 10thNight
33%10%15%27%13%1
1800
11th to 20thNight
34%8%15%28%15%
1954
21st to endNight
45%9%13%24%9%
1983
October1st to 10thNight
49%8%11%18%13%1
2160
11th to 20thNight
57%10%12%15%6%
2160
21st to endNight
66%8%10%10%5%
2398
November1st to 10thNight
57%8%11%16%7%1
2486
11th to 20thNight
63%10%11%10%41
2660
21st to endNight
68%10%12%7%2
2660
December1st to 10thNight
76%10%9%42
2660
11th to 20thNight
73%10%10%6%1
3288
21st to endNight
83%6%6%5%
5117

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
17%24%31%19%7%1
180
11th to 20thDay
17%20%42%14%5%1
241
21st to endDay
20%17%37%22%5%
264
February1st to 10thDay
22%26%38%12%3
240
11th to 20thDay
18%24%42%14%2
240
21st to endDay
17%34%31%17%
198
March1st to 10thDay
19%17%37%22%5%1
389
11th to 20thDay
16%19%33%25%6%1
420
21st to endDay
26%13%31%22%8%
462
April1st to 10thDay
19%19%32%23%8%
420
11th to 20thDay
27%15%24%19%11%5%
412
21st to endDay
25%12%28%25%9%1
420
May1st to 10thDay
19%13%26%26%13%2
423
11th to 20thDay
19%8%26%26%17%4
447
21st to endDay
15%6%25%28%20%6%
485
June1st to 10thDay
17%9%25%29%17%2
487
11th to 20thDay
13%9%22%35%18%4
630
21st to endDay
16%427%33%16%4
630
July1st to 10thDay
10%6%20%37%22%6%
621
11th to 20thDay
12%7%22%31%19%9%
529
21st to endDay
9%423%40%19%5%
488
August1st to 10thDay
12%419%34%22%10%
446
11th to 20thDay
11%416%34%22%13%
439
21st to endDay
13%9%22%30%20%7%
495
September1st to 10thDay
15%9%22%25%20%8%
450
11th to 20thDay
12%7%23%25%24%10%
450
21st to endDay
13%12%24%26%18%6%
450
October1st to 10thDay
23%13%22%21%15%6%
450
11th to 20thDay
21%21%30%23%6%
450
21st to endDay
31%23%22%18%5%
470
November1st to 10thDay
19%25%28%18%9%1
232
11th to 20thDay
18%29%29%19%32
180
21st to endDay
23%21%41%13%2
180
December1st to 10thDay
17%30%31%18%3
180
11th to 20thDay
19%32%29%16%4
180
21st to endDay
25%26%37%10%2
198
January1st to 10thNight
18%25%33%19%5%
950
11th to 20thNight
22%19%33%20%5%1
756
21st to endNight
14%15%38%25%8%1
792
February1st to 10thNight
20%21%37%19%2
720
11th to 20thNight
16%18%37%24%5%
703
21st to endNight
20%18%37%21%3
592
March1st to 10thNight
17%17%36%24%6%
720
11th to 20thNight
18%17%36%22%6%1
720
21st to endNight
18%12%29%30%10%1
792
April1st to 10thNight
21%14%32%28%5%
720
11th to 20thNight
20%10%30%25%13%1
587
21st to endNight
24%10%24%28%13%
540
May1st to 10thNight
18%5%23%36%15%3
540
11th to 20thNight
18%5%22%39%13%2
395
21st to endNight
11%323%41%21%1
389
June1st to 10thNight
15%6%24%39%14%2
360
11th to 20thNight
12%6%18%41%23%1
360
21st to endNight
15%322%35%23%2
360
July1st to 10thNight
8%416%45%26%1
350
11th to 20thNight
9%423%38%23%4
348
21st to endNight
9%220%43%23%2
587
August1st to 10thNight
12%318%36%29%3
537
11th to 20thNight
8%415%38%29%6%
534
21st to endNight
15%5%20%30%27%2
621
September1st to 10thNight
13%5%22%33%19%7%
720
11th to 20thNight
16%6%19%34%21%5%
720
21st to endNight
19%9%21%28%17%5%
720
October1st to 10thNight
23%9%25%25%15%2
720
11th to 20thNight
25%16%27%23%7%1
720
21st to endNight
33%16%27%19%41
792
November1st to 10thNight
23%15%32%20%9%1
740
11th to 20thNight
20%26%31%17%6%1
760
21st to endNight
25%19%33%19%3
760
December1st to 10thNight
24%24%34%14%3
760
11th to 20thNight
19%24%38%16%21
760
21st to endNight
25%22%35%16%2
978
Page generated at 2024-01-13 01:38:12. Version ac07

Copyright 2024 Attilla Danko


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