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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 2005-11-05 to 2017-05-24.

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%
14683
10%
45722
7%
14648
34%
14648
13%
34886

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
9%
844
2%
2589
1%
844
11%
844
3%
2362
January16th to endNight
16%
768
3%
2496
2%
768
19%
768
4%
2229
February1st to 15thNight
13%
701
4%
2287
1%
701
16%
701
5%
1986
February16th to endNight
20%
631
7%
2000
2%
631
25%
631
8%
1635
March1st to 15thNight
20%
720
10%
1999
6%
720
24%
720
13%
1590
March16th to endNight
34%
768
18%
2112
10%
768
40%
768
20%
1516
April1st to 15thNight
28%
694
13%
1814
5%
694
33%
694
20%
1341
April16th to endNight
39%
540
18%
1620
12%
540
43%
540
20%
1124
May1st to 15thNight
48%
507
15%
1587
13%
507
52%
507
23%
1058
May16th to endNight
50%
360
15%
1441
16%
360
57%
360
23%
838
June1st to 15thNight
46%
330
12%
1240
12%
330
52%
330
19%
790
June16th to endNight
56%
330
13%
1155
16%
330
59%
330
26%
706
July1st to 15thNight
64%
310
17%
1085
22%
310
67%
310
36%
567
July16th to endNight
57%
465
13%
1413
12%
433
59%
433
28%
859
August1st to 15thNight
59%
494
16%
1474
12%
491
62%
491
29%
910
August16th to endNight
61%
542
18%
1592
12%
542
63%
542
30%
995
September1st to 15thNight
52%
660
16%
1689
10%
660
54%
660
29%
1142
September16th to endNight
51%
657
18%
1818
13%
657
53%
657
26%
1221
October1st to 15thNight
35%
660
14%
1980
11%
660
40%
660
17%
1447
October16th to endNight
19%
704
6%
2126
3%
704
23%
704
7%
1780
November1st to 15thNight
25%
700
13%
2387
10%
700
29%
700
11%
1827
November16th to endNight
19%
720
7%
2520
6%
720
23%
720
7%
2124
December1st to 15thNight
10%
720
2%
2520
1%
720
11%
720
3%
2291
December16th to endNight
8%
858
2%
2778
0%
858
10%
858
2%
2548

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%10%47%7%35%45%7%28%
46538
Night
14%10%48%7%35%5%5%6%27%
45893
Cloud CoverDay
14%9%47%6%35%5%5%7%29%
46548
Night
14%10%48%7%35%5%5%6%28%
45897
TransparencyDay
54%7%11%16%9%
46228
Night
56%7%10%14%8%
45722
SeeingDay
18%8%25%27%14%5%
5219
Night
19%12%28%26%10%1
14692

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
13%13%6%17%12%5%7%5%449%
1341
16th to endDay
8%15%8%15%15%7%7%6%448%
1728
February1st to 15thDay
11%14%8%14%11%5%7%6%5%410%
1575
16th to endDay
14%15%7%11%10%46%445%15%
1470
March1st to 15thDay
11%12%6%10%9%45%445%24%
1948
16th to endDay
12%10%48%6%3445%6%31%
2112
April1st to 15thDay
16%11%46%5%3435%6%30%
2142
16th to endDay
15%10%445%2445%7%36%
2340
May1st to 15thDay
16%8%35%5%3446%6%36%
2363
16th to endDay
12%8%25%5%2445%8%40%
2517
June1st to 15thDay
15%6%25%425%6%7%8%34%
2387
16th to endDay
13%5%25%5%35%5%5%10%38%
2475
July1st to 15thDay
10%5%245%35%5%6%9%42%
2475
16th to endDay
10%5%25%6%36%47%9%37%
2338
August1st to 15thDay
11%6%25%5%245%5%8%41%
2145
16th to endDay
11%426%6%45%5%6%9%36%
2246
September1st to 15thDay
19%7%35%5%3435%8%34%
1939
16th to endDay
17%6%25%5%3445%8%36%
1812
October1st to 15thDay
18%10%46%6%34447%29%
1650
16th to endDay
25%16%45%7%35%5%6%415%
1744
November1st to 15thDay
13%15%48%6%36%5%46%26%
1471
16th to endDay
15%15%8%9%7%5%6%6%5%6%12%
1440
December1st to 15thDay
13%18%10%12%9%45%45%5%8%
1440
16th to endDay
16%18%9%13%9%5%5%35%48%
1440
January1st to 15thNight
14%15%6%14%12%5%7%5%5%5%7%
2589
16th to endNight
10%12%6%13%13%5%8%5%6%6%10%
2496
February1st to 15thNight
10%14%6%12%12%5%8%45%5%12%
2285
16th to endNight
11%11%6%12%9%5%6%5%6%6%19%
2000
March1st to 15thNight
13%13%6%9%7%34445%26%
1987
16th to endNight
11%8%5%8%5%35%44437%
2112
April1st to 15thNight
18%9%46%6%33346%32%
1814
16th to endNight
16%8%36%5%35%346%37%
1620
May1st to 15thNight
14%7%25%435%45%8%37%
1587
16th to endNight
11%5%245%246%46%45%
1439
June1st to 15thNight
14%425%5%25%6%5%7%38%
1240
16th to endNight
9%6%25%425%45%9%44%
1155
July1st to 15thNight
7%323414348%54%
1155
16th to endNight
8%2135%36%5%8%8%47%
1519
August1st to 15thNight
9%4145%35%5%5%8%45%
1485
16th to endNight
10%415%3335%5%7%48%
1592
September1st to 15thNight
16%42332346%9%41%
1689
16th to endNight
15%6%25%4235%5%6%43%
1818
October1st to 15thNight
17%8%35%6%34446%34%
1980
16th to endNight
23%15%36%6%35%5%5%5%18%
2126
November1st to 15thNight
15%14%46%5%345%6%6%25%
2387
16th to endNight
17%13%6%9%7%35%5%5%6%18%
2520
December1st to 15thNight
15%17%8%11%9%5%7%5%5%410%
2520
16th to endNight
17%14%9%15%8%46%6%447%
2778

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
13%13%6%17%11%6%7%5%5%49%
1341
16th to endDay
8%15%8%14%14%7%7%6%448%
1728
February1st to 15thDay
12%14%7%14%10%5%6%5%5%5%11%
1575
16th to endDay
14%15%7%11%11%5%5%435%15%
1470
March1st to 15thDay
12%11%6%10%9%5%5%445%24%
1959
16th to endDay
12%9%5%8%7%3445%6%31%
2111
April1st to 15thDay
16%11%5%6%5%35%35%6%30%
2142
16th to endDay
16%9%35%42345%7%36%
2340
May1st to 15thDay
16%8%26%5%3446%7%36%
2363
16th to endDay
12%8%25%42445%8%40%
2517
June1st to 15thDay
15%5%26%425%6%6%8%35%
2387
16th to endDay
13%5%25%5%35%5%5%9%38%
2475
July1st to 15thDay
10%425%435%5%6%9%42%
2475
16th to endDay
10%5%25%6%36%5%7%9%37%
2338
August1st to 15thDay
11%5%26%425%5%6%8%41%
2145
16th to endDay
11%427%6%35%5%6%9%37%
2246
September1st to 15thDay
19%6%25%5%2435%8%34%
1939
16th to endDay
16%5%25%5%3445%8%36%
1812
October1st to 15thDay
18%10%46%6%34447%29%
1650
16th to endDay
25%16%36%6%35%46%416%
1744
November1st to 15thDay
13%14%5%8%5%35%5%5%6%26%
1471
16th to endDay
15%16%8%9%7%46%7%5%6%12%
1440
December1st to 15thDay
13%18%10%13%8%46%45%5%8%
1440
16th to endDay
16%17%10%12%9%5%445%48%
1440
January1st to 15thNight
14%14%7%13%11%5%6%5%5%5%8%
2589
16th to endNight
10%12%6%14%12%5%8%6%5%6%10%
2496
February1st to 15thNight
10%14%6%12%12%5%8%5%5%5%13%
2278
16th to endNight
11%11%5%12%9%5%5%6%6%6%19%
2000
March1st to 15thNight
13%13%7%8%8%345%45%26%
1999
16th to endNight
11%9%5%8%5%3444437%
2112
April1st to 15thNight
18%9%46%5%33346%32%
1814
16th to endNight
16%8%36%5%25%346%37%
1620
May1st to 15thNight
15%6%25%435%45%8%37%
1586
16th to endNight
11%5%25%5%246%5%6%45%
1439
June1st to 15thNight
14%425%5%26%6%5%8%38%
1240
16th to endNight
9%5%25%425%45%9%44%
1155
July1st to 15thNight
7%323414448%55%
1155
16th to endNight
8%2225%35%5%8%9%46%
1519
August1st to 15thNight
9%4145%45%5%5%8%46%
1485
16th to endNight
10%425%43345%7%48%
1592
September1st to 15thNight
16%42332446%9%41%
1689
16th to endNight
15%6%2432445%6%43%
1818
October1st to 15thNight
17%8%35%6%34447%34%
1980
16th to endNight
24%15%35%6%35%5%5%5%18%
2126
November1st to 15thNight
15%13%46%5%345%6%7%25%
2387
16th to endNight
17%14%6%10%6%35%46%5%19%
2520
December1st to 15thNight
15%17%8%10%9%47%5%5%5%10%
2520
16th to endNight
17%14%9%15%8%36%5%5%47%
2778

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
79%7%6%41
1342
16th to endDay
79%5%7%41
1728
February1st to 15thDay
74%7%8%8%1
1577
16th to endDay
71%5%8%8%5%
1470
March1st to 15thDay
61%6%10%14%6%
1959
16th to endDay
53%5%11%15%12%1
2112
April1st to 15thDay
55%5%9%19%9%
2142
16th to endDay
47%5%10%20%13%2
2340
May1st to 15thDay
47%5%10%21%13%1
2363
16th to endDay
41%6%12%22%14%1
2521
June1st to 15thDay
44%8%12%21%12%
2387
16th to endDay
41%7%15%21%13%
2475
July1st to 15thDay
37%7%13%24%14%2
2316
16th to endDay
42%8%13%22%11%1
2182
August1st to 15thDay
40%7%15%20%14%
2132
16th to endDay
42%9%15%22%9%1
2246
September1st to 15thDay
49%6%12%22%7%
1939
16th to endDay
46%6%12%24%8%1
1812
October1st to 15thDay
55%6%10%16%10%
1650
16th to endDay
70%7%10%7%3
1744
November1st to 15thDay
60%7%11%13%6%
1471
16th to endDay
72%7%9%7%1
1440
December1st to 15thDay
80%8%7%3
1440
16th to endDay
82%6%5%4
1440
January1st to 15thNight
78%8%7%41
2589
16th to endNight
74%10%8%41
2496
February1st to 15thNight
73%7%8%8%1
2287
16th to endNight
64%8%10%9%6%
2000
March1st to 15thNight
60%7%10%15%6%
1999
16th to endNight
49%6%8%18%14%1
2112
April1st to 15thNight
53%410%18%13%
1814
16th to endNight
48%5%9%15%18%2
1620
May1st to 15thNight
45%5%10%19%16%2
1587
16th to endNight
36%7%13%26%13%2
1441
June1st to 15thNight
43%7%11%21%15%1
1240
16th to endNight
36%8%13%25%16%
1155
July1st to 15thNight
26%6%15%27%22%1
1085
16th to endNight
33%10%13%25%16%1
1413
August1st to 15thNight
34%8%16%23%15%
1474
16th to endNight
35%7%14%27%13%1
1592
September1st to 15thNight
38%9%15%26%10%
1689
16th to endNight
40%8%13%25%11%
1818
October1st to 15thNight
51%8%10%18%11%
1980
16th to endNight
66%8%11%8%3
2126
November1st to 15thNight
57%8%11%13%6%1
2387
16th to endNight
67%9%10%9%2
2520
December1st to 15thNight
77%9%8%31
2520
16th to endNight
80%7%6%4
2778

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
11%23%43%17%2
67
16th to endDay
21%15%35%26%1
96
February1st to 15thDay
22%21%42%14%
90
16th to endDay
24%16%37%22%
81
March1st to 15thDay
19%15%32%25%6%
249
16th to endDay
21%9%29%27%11%1
288
April1st to 15thDay
21%11%34%21%9%1
270
16th to endDay
24%8%26%20%13%5%
270
May1st to 15thDay
23%7%21%26%16%5%
288
16th to endDay
16%5%24%28%19%5%
302
June1st to 15thDay
18%7%24%26%19%3
332
16th to endDay
13%322%37%18%4
420
July1st to 15thDay
11%5%22%35%18%7%
400
16th to endDay
8%324%34%20%10%
270
August1st to 15thDay
11%118%32%21%13%
253
16th to endDay
13%217%32%24%10%
268
September1st to 15thDay
16%5%21%21%23%10%
255
16th to endDay
17%5%18%30%18%8%
254
October1st to 15thDay
20%10%25%27%12%3
255
16th to endDay
34%17%25%18%3
256
November1st to 15thDay
18%11%26%28%11%4
71
16th to endDay
31%15%36%10%6%
60
December1st to 15thDay
15%35%26%21%1
60
16th to endDay
15%35%40%7%
64
January1st to 15thNight
21%24%32%17%4
849
16th to endNight
14%16%37%24%6%
768
February1st to 15thNight
18%19%37%20%3
704
16th to endNight
18%12%37%25%5%
631
March1st to 15thNight
21%16%35%21%5%
720
16th to endNight
16%9%32%27%11%1
768
April1st to 15thNight
23%11%31%26%6%
694
16th to endNight
22%8%25%29%14%1
540
May1st to 15thNight
18%322%36%15%3
507
16th to endNight
13%325%37%19%
361
June1st to 15thNight
16%6%22%36%18%
330
16th to endNight
13%320%39%22%1
330
July1st to 15thNight
7%318%45%22%2
310
16th to endNight
7%224%40%21%3
465
August1st to 15thNight
11%217%39%25%2
494
16th to endNight
13%318%34%27%3
542
September1st to 15thNight
18%320%32%15%9%
660
16th to endNight
18%7%18%32%17%5%
657
October1st to 15thNight
22%10%26%24%13%2
660
16th to endNight
33%16%26%18%4
704
November1st to 15thNight
23%15%30%19%10%1
700
16th to endNight
25%20%29%19%5%
720
December1st to 15thNight
24%23%35%13%2
720
16th to endNight
24%20%36%16%2
858
Page generated at 2017-05-25 13:27:34. Version ac04

Copyright 2017 A. Danko


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