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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 2018-03-11.

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%
15706
10%
48958
8%
15671
35%
15671
14%
37253

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
11%
915
2%
2806
1%
915
12%
915
3%
2549
January16th to endNight
16%
832
4%
2704
2%
832
18%
832
4%
2403
February1st to 15thNight
13%
761
4%
2482
1%
761
17%
761
5%
2152
February16th to endNight
19%
683
7%
2165
2%
683
24%
683
8%
1763
March1st to 15thNight
21%
764
10%
2122
5%
764
25%
764
13%
1674
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%
374
15%
1497
16%
374
57%
374
23%
874
June1st to 15thNight
47%
360
11%
1352
12%
360
53%
360
20%
847
June16th to endNight
55%
360
14%
1260
16%
360
59%
360
26%
773
July1st to 15thNight
63%
340
16%
1190
21%
340
66%
340
35%
631
July16th to endNight
57%
502
15%
1534
14%
470
59%
470
28%
929
August1st to 15thNight
60%
539
15%
1609
12%
536
63%
536
30%
985
August16th to endNight
60%
592
19%
1738
13%
592
63%
592
30%
1089
September1st to 15thNight
53%
720
16%
1843
10%
720
55%
720
30%
1226
September16th to endNight
53%
717
20%
1983
15%
717
54%
717
27%
1323
October1st to 15thNight
36%
720
14%
2160
11%
720
41%
720
18%
1567
October16th to endNight
21%
768
8%
2319
4%
768
26%
768
9%
1903
November1st to 15thNight
24%
760
12%
2591
10%
760
28%
760
10%
2010
November16th to endNight
18%
780
7%
2730
5%
780
22%
780
7%
2293
December1st to 15thNight
10%
780
2%
2730
1%
780
11%
780
3%
2466
December16th to endNight
8%
930
3%
3010
0%
930
10%
930
2%
2757

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%
49655
Night
14%10%48%7%45%5%5%6%27%
49129
Cloud CoverDay
14%9%48%6%35%5%5%7%29%
49665
Night
14%10%48%7%35%5%5%6%28%
49133
TransparencyDay
54%7%11%16%8%
49345
Night
56%7%10%15%8%
48958
SeeingDay
18%9%25%26%14%5%
6221
Night
19%12%28%26%11%1
15715

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%7%16%12%6%7%5%448%
1454
16th to endDay
9%15%8%14%14%7%7%6%448%
1872
February1st to 15thDay
11%14%7%14%11%5%7%6%5%411%
1710
16th to endDay
14%15%7%11%10%46%44416%
1591
March1st to 15thDay
12%12%6%11%9%45%445%25%
2062
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%39%
2618
June1st to 15thDay
15%6%25%4246%6%8%36%
2604
16th to endDay
13%5%25%5%35%5%6%10%36%
2700
July1st to 15thDay
10%5%245%35%5%6%9%41%
2700
16th to endDay
10%5%26%6%36%47%9%37%
2525
August1st to 15thDay
10%6%25%5%35%5%6%8%40%
2340
16th to endDay
11%5%27%6%45%5%6%8%36%
2451
September1st to 15thDay
18%6%25%5%3435%8%35%
2115
16th to endDay
16%6%25%5%3445%8%37%
1977
October1st to 15thDay
18%9%46%7%34447%29%
1800
16th to endDay
24%15%46%7%35%45%417%
1902
November1st to 15thDay
13%15%49%6%35%5%45%24%
1597
16th to endDay
15%15%8%9%7%5%6%5%5%6%13%
1560
December1st to 15thDay
12%18%11%12%9%46%5%5%5%8%
1560
16th to endDay
16%17%8%14%9%5%5%35%48%
1560
January1st to 15thNight
13%14%6%13%12%5%7%6%5%5%8%
2806
16th to endNight
9%12%6%13%12%5%8%6%6%6%11%
2704
February1st to 15thNight
10%14%6%12%12%6%8%45%5%13%
2480
16th to endNight
11%11%6%11%9%46%5%6%6%19%
2165
March1st to 15thNight
13%13%6%9%7%34445%27%
2110
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
12%5%245%246%46%45%
1495
June1st to 15thNight
14%425%5%25%6%5%8%38%
1352
16th to endNight
9%5%25%5%25%45%9%43%
1260
July1st to 15thNight
8%323414348%54%
1260
16th to endNight
9%3135%26%47%8%47%
1640
August1st to 15thNight
8%4145%35%5%6%9%45%
1620
16th to endNight
9%415%4335%5%7%47%
1738
September1st to 15thNight
15%41332346%9%42%
1843
16th to endNight
14%6%244235%5%7%43%
1983
October1st to 15thNight
17%8%35%6%3435%7%35%
2160
16th to endNight
23%14%36%6%445%5%5%20%
2319
November1st to 15thNight
16%14%46%6%345%6%6%24%
2591
16th to endNight
16%14%6%9%7%35%5%5%6%18%
2730
December1st to 15thNight
14%17%8%11%9%5%6%5%5%410%
2730
16th to endNight
17%14%9%15%9%46%6%447%
3010

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%16%11%6%7%5%448%
1454
16th to endDay
9%15%8%14%14%7%7%6%448%
1872
February1st to 15thDay
12%14%7%14%11%5%6%5%5%5%11%
1710
16th to endDay
14%14%7%11%10%5%5%435%17%
1591
March1st to 15thDay
12%11%6%11%9%5%5%445%25%
2073
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%7%25%42445%8%40%
2618
June1st to 15thDay
15%5%25%425%6%6%8%36%
2604
16th to endDay
13%5%25%5%35%5%5%9%37%
2700
July1st to 15thDay
10%5%25%435%5%6%9%41%
2700
16th to endDay
10%5%26%6%35%5%7%9%38%
2525
August1st to 15thDay
10%6%26%425%5%5%8%40%
2340
16th to endDay
11%427%6%35%5%6%9%36%
2451
September1st to 15thDay
18%6%25%5%3435%8%36%
2115
16th to endDay
16%5%25%5%3445%8%37%
1977
October1st to 15thDay
18%9%46%6%34447%30%
1800
16th to endDay
24%15%37%6%35%46%417%
1902
November1st to 15thDay
13%14%5%8%5%35%5%5%6%24%
1597
16th to endDay
15%16%8%9%6%46%6%5%6%13%
1560
December1st to 15thDay
12%18%10%13%9%46%5%6%5%8%
1560
16th to endDay
16%17%9%13%9%5%445%5%8%
1560
January1st to 15thNight
13%14%7%13%11%5%7%6%5%5%8%
2806
16th to endNight
10%12%6%14%12%5%8%6%5%6%11%
2704
February1st to 15thNight
10%14%6%12%12%5%8%5%5%5%13%
2473
16th to endNight
11%11%5%12%9%5%5%5%6%6%19%
2165
March1st to 15thNight
13%13%7%8%7%345%46%27%
2122
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
12%5%245%235%5%6%45%
1495
June1st to 15thNight
14%425%5%26%6%5%8%38%
1352
16th to endNight
9%5%25%425%45%9%44%
1260
July1st to 15thNight
8%323414348%54%
1260
16th to endNight
9%3135%35%47%8%47%
1640
August1st to 15thNight
8%4145%45%5%6%9%45%
1620
16th to endNight
10%425%4335%5%7%47%
1738
September1st to 15thNight
16%41332446%9%43%
1843
16th to endNight
14%6%2432445%6%44%
1983
October1st to 15thNight
17%7%35%6%34447%34%
2160
16th to endNight
23%15%35%6%35%5%5%5%19%
2319
November1st to 15thNight
16%13%47%5%345%6%7%24%
2591
16th to endNight
17%14%6%9%6%35%46%5%19%
2730
December1st to 15thNight
14%17%8%11%9%46%5%5%5%11%
2730
16th to endNight
17%14%8%15%9%46%5%5%47%
3010

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
1455
16th to endDay
79%6%7%41
1872
February1st to 15thDay
74%7%8%8%1
1712
16th to endDay
70%5%8%8%5%
1591
March1st to 15thDay
62%5%10%13%7%
2073
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
42%7%12%22%14%1
2622
June1st to 15thDay
43%8%12%22%12%
2604
16th to endDay
42%7%15%21%12%
2700
July1st to 15thDay
37%7%14%23%14%1
2541
16th to endDay
42%8%13%23%11%1
2369
August1st to 15thDay
40%8%15%20%13%
2327
16th to endDay
43%8%15%22%9%
2451
September1st to 15thDay
48%6%12%22%9%1
2115
16th to endDay
45%6%12%26%8%
1977
October1st to 15thDay
54%6%10%17%10%1
1800
16th to endDay
69%7%10%7%4
1902
November1st to 15thDay
61%7%11%12%6%
1597
16th to endDay
72%8%9%7%1
1560
December1st to 15thDay
79%8%7%3
1560
16th to endDay
81%7%5%4
1560
January1st to 15thNight
77%8%7%41
2806
16th to endNight
73%10%8%41
2704
February1st to 15thNight
73%7%8%8%1
2482
16th to endNight
64%8%10%9%6%
2165
March1st to 15thNight
59%6%10%15%7%
2122
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
37%7%13%26%13%2
1497
June1st to 15thNight
42%6%12%22%15%1
1352
16th to endNight
36%8%13%26%15%
1260
July1st to 15thNight
28%5%14%28%21%2
1190
16th to endNight
33%9%12%26%16%1
1534
August1st to 15thNight
33%8%17%24%14%
1609
16th to endNight
35%7%14%26%13%1
1738
September1st to 15thNight
36%8%15%26%11%
1843
16th to endNight
39%8%13%26%11%
1983
October1st to 15thNight
50%8%10%19%11%
2160
16th to endNight
64%8%12%10%4
2319
November1st to 15thNight
59%8%11%12%5%1
2591
16th to endNight
66%10%10%9%2
2730
December1st to 15thNight
77%8%8%31
2730
16th to endNight
80%7%6%4
3010

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
14%26%36%18%2
101
16th to endDay
22%17%36%21%1
144
February1st to 15thDay
22%22%42%12%
135
16th to endDay
22%23%35%18%
120
March1st to 15thDay
19%15%33%24%6%
289
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%25%27%19%5%
331
June1st to 15thDay
19%6%23%28%19%3
399
16th to endDay
15%325%35%16%4
495
July1st to 15thDay
11%5%22%35%18%7%
475
16th to endDay
9%222%34%21%9%
326
August1st to 15thDay
10%119%33%22%12%
313
16th to endDay
13%318%31%23%9%
332
September1st to 15thDay
15%420%21%25%12%
315
16th to endDay
16%6%16%27%21%10%
314
October1st to 15thDay
21%11%25%25%12%4
315
16th to endDay
31%19%24%20%4
318
November1st to 15thDay
21%13%27%26%9%2
107
16th to endDay
28%22%35%8%4
90
December1st to 15thDay
13%35%30%20%1
90
16th to endDay
17%31%40%10%
96
January1st to 15thNight
20%23%32%18%4
920
16th to endNight
15%17%37%23%6%
832
February1st to 15thNight
18%20%37%20%3
764
16th to endNight
18%13%37%24%5%
683
March1st to 15thNight
20%15%35%21%6%
764
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
14%325%36%19%
375
June1st to 15thNight
15%5%22%36%19%
360
16th to endNight
12%321%40%21%1
360
July1st to 15thNight
8%318%43%22%2
340
16th to endNight
9%223%40%21%2
502
August1st to 15thNight
11%217%39%26%2
539
16th to endNight
12%317%34%27%3
592
September1st to 15thNight
17%320%31%16%9%
720
16th to endNight
17%6%17%30%20%6%
717
October1st to 15thNight
21%9%26%25%13%2
720
16th to endNight
32%16%27%19%4
768
November1st to 15thNight
24%14%30%19%10%
760
16th to endNight
24%21%29%18%5%
780
December1st to 15thNight
23%23%36%14%2
780
16th to endNight
23%21%36%15%2
930
Page generated at 2018-03-12 13:28:07. Version ac04

Copyright 2018 A. Danko


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