Bloomington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bloomington clear sky chart from 2005-11-06 to 2024-01-31.

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
35%
24378
19%
74825
12%
24320
43%
24320
22%
49450

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
17%
950
15%
2648
4%
946
26%
946
14%
1935
January11th to 20thNight
12%
950
12%
2660
3%
950
19%
950
13%
2041
January21st to endNight
15%
965
14%
2794
4%
965
26%
965
14%
2076
February1st to 10thNight
15%
720
12%
2160
4%
720
22%
720
12%
1639
February11th to 20thNight
14%
702
16%
2099
6%
700
23%
700
15%
1484
February21st to endNight
14%
592
17%
1776
5%
592
25%
592
13%
1297
March1st to 10thNight
20%
720
17%
2160
9%
720
27%
720
18%
1478
March11th to 20thNight
22%
720
16%
2065
6%
720
30%
720
19%
1408
March21st to endNight
24%
691
16%
2077
7%
691
33%
691
17%
1474
April1st to 10thNight
30%
540
21%
1800
11%
540
43%
540
22%
1115
April11th to 20thNight
31%
533
21%
1775
14%
533
42%
533
22%
1124
April21st to endNight
26%
540
19%
1679
6%
540
38%
540
21%
1101
May1st to 10thNight
29%
540
15%
1620
6%
540
37%
540
21%
1126
May11th to 20thNight
39%
531
17%
1593
10%
531
45%
531
24%
1061
May21st to endNight
52%
582
18%
1697
12%
582
57%
582
29%
1074
June1st to 10thNight
54%
540
20%
1440
13%
540
59%
540
37%
880
June11th to 20thNight
55%
540
24%
1440
16%
540
60%
540
39%
850
June21st to endNight
59%
540
23%
1440
14%
540
64%
540
40%
838
July1st to 10thNight
62%
525
18%
1400
13%
525
65%
525
36%
883
July11th to 20thNight
65%
522
22%
1392
16%
522
68%
522
42%
820
July21st to endNight
65%
591
26%
1559
20%
558
70%
558
40%
897
August1st to 10thNight
70%
537
22%
1600
20%
534
72%
534
36%
931
August11th to 20thNight
66%
534
23%
1742
22%
534
71%
534
36%
966
August21st to endNight
68%
594
26%
1980
27%
594
72%
594
40%
1035
September1st to 10thNight
60%
540
24%
1800
23%
540
65%
540
31%
1029
September11th to 20thNight
62%
719
34%
1979
24%
719
69%
719
42%
1115
September21st to endNight
50%
720
28%
1980
19%
720
56%
720
36%
1172
October1st to 10thNight
52%
720
30%
1980
20%
720
60%
720
40%
1133
October11th to 20thNight
35%
720
27%
2102
15%
720
48%
720
28%
1299
October21st to endNight
27%
792
21%
2574
14%
792
38%
792
20%
1659
November1st to 10thNight
33%
740
26%
2406
17%
740
46%
740
28%
1387
November11th to 20thNight
27%
760
25%
2470
12%
760
44%
760
21%
1550
November21st to endNight
25%
760
20%
2470
12%
760
36%
760
17%
1667
December1st to 10thNight
20%
760
15%
2470
7%
760
30%
760
16%
1739
December11th to 20thNight
22%
907
16%
3155
7%
906
29%
906
14%
2256
December21st to endNight
14%
1041
8%
4843
4%
1026
23%
1026
7%
3911

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%8%46%5%35%5%5%7%38%
75006
Night
15%9%46%5%3445%7%39%
75136
TransparencyDay
45%411%23%15%2
74713
Night
46%410%23%15%3
74950
SeeingDay
20%13%28%22%12%4
14426
Night
20%13%27%25%13%2
24386

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
17%13%5%9%43445%5%32%
1517
11th to 20thDay
19%12%6%8%6%34445%28%
1520
21st to endDay
15%16%5%8%6%35%345%30%
1784
February1st to 10thDay
19%12%6%9%6%34446%29%
1800
11th to 20thDay
15%11%5%8%6%345%47%30%
1748
21st to endDay
17%13%5%10%5%2345%6%31%
1480
March1st to 10thDay
18%10%36%5%34445%38%
1800
11th to 20thDay
19%9%46%5%3445%6%35%
1894
21st to endDay
19%11%5%8%6%34346%29%
2294
April1st to 10thDay
14%8%46%5%35%45%8%38%
2160
11th to 20thDay
17%9%36%43445%6%39%
2134
21st to endDay
20%7%36%6%3445%7%35%
2281
May1st to 10thDay
18%8%37%6%4446%7%34%
2340
11th to 20thDay
20%8%46%5%35%45%5%35%
2301
21st to endDay
9%6%36%8%45%7%7%9%34%
2575
June1st to 10thDay
11%5%25%5%46%5%5%9%43%
2520
11th to 20thDay
8%5%35%5%45%6%7%9%43%
2520
21st to endDay
9%5%35%5%36%6%6%8%42%
2520
July1st to 10thDay
11%5%36%5%35%6%7%10%38%
2520
11th to 20thDay
7%435%5%36%6%8%10%44%
2520
21st to endDay
9%425%5%36%7%7%9%43%
2663
August1st to 10thDay
9%4245%36%6%7%11%43%
2327
11th to 20thDay
10%5%26%6%36%6%7%10%39%
2155
21st to endDay
6%4245%45%5%7%9%48%
2376
September1st to 10thDay
13%6%25%5%35%46%8%44%
2142
11th to 20thDay
10%5%25%5%345%7%7%47%
1980
21st to endDay
12%3335%2445%7%52%
1980
October1st to 10thDay
12%5%245%245%5%7%49%
1980
11th to 20thDay
14%6%25%43445%7%44%
1852
21st to endDay
20%9%36%5%35%446%37%
1782
November1st to 10thDay
10%5%345%2345%6%53%
1672
11th to 20thDay
16%8%47%5%2345%7%40%
1710
21st to endDay
20%10%35%5%23346%39%
1710
December1st to 10thDay
19%12%5%8%5%24335%33%
1710
11th to 20thDay
16%14%6%8%434446%31%
1956
21st to endDay
21%19%8%7%5%34445%19%
2783
January1st to 10thNight
16%11%5%9%7%35%5%45%30%
2648
11th to 20thNight
19%14%7%9%6%34345%26%
2660
21st to endNight
17%13%6%8%7%34445%29%
2794
February1st to 10thNight
20%12%6%8%6%35%46%5%26%
2160
11th to 20thNight
14%11%5%8%7%35%45%6%32%
2098
21st to endNight
20%13%49%43435%5%31%
1776
March1st to 10thNight
18%10%46%5%2345%5%37%
2160
11th to 20thNight
18%8%36%5%35%447%37%
2065
21st to endNight
21%9%47%5%3445%7%32%
2077
April1st to 10thNight
12%8%47%4345%47%42%
1800
11th to 20thNight
16%9%36%5%2345%7%41%
1775
21st to endNight
17%7%46%43446%7%37%
1679
May1st to 10thNight
16%8%47%6%35%449%34%
1620
11th to 20thNight
14%6%46%5%45%5%48%40%
1592
21st to endNight
8%5%26%7%47%5%6%11%39%
1696
June1st to 10thNight
10%5%35%5%35%45%10%47%
1440
11th to 20thNight
8%335%6%3445%11%49%
1440
21st to endNight
7%2244346%7%11%50%
1440
July1st to 10thNight
8%435%6%345%6%9%47%
1440
11th to 20thNight
6%414435%5%8%9%51%
1440
21st to endNight
6%5%345%3335%7%54%
1651
August1st to 10thNight
7%315%5%35%6%6%8%50%
1611
11th to 20thNight
7%325%5%35%5%7%9%48%
1742
21st to endNight
5%3244346%49%55%
1980
September1st to 10thNight
11%6%25%4345%47%50%
1800
11th to 20thNight
7%4244235%6%7%55%
1979
21st to endNight
11%435%5%33447%51%
1980
October1st to 10thNight
9%4245%2435%6%57%
1980
11th to 20thNight
16%7%34324446%47%
2102
21st to endNight
19%8%35%5%34446%41%
2574
November1st to 10thNight
11%7%34434447%49%
2406
11th to 20thNight
15%8%36%5%3445%7%41%
2470
21st to endNight
20%9%47%5%34346%36%
2470
December1st to 10thNight
18%12%48%6%3345%5%31%
2470
11th to 20thNight
18%13%5%8%5%24445%32%
3237
21st to endNight
23%20%6%8%6%3443419%
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
54%39%19%13%2
1518
11th to 20thDay
60%210%19%8%
1520
21st to endDay
57%310%24%5%2
1784
February1st to 10thDay
57%38%21%9%2
1800
11th to 20thDay
53%39%23%9%2
1758
21st to endDay
56%37%22%10%3
1480
March1st to 10thDay
49%38%25%14%1
1800
11th to 20thDay
51%311%21%12%2
1894
21st to endDay
57%310%22%8%1
2294
April1st to 10thDay
46%313%22%16%1
2160
11th to 20thDay
46%39%25%13%3
2134
21st to endDay
50%39%22%12%4
2281
May1st to 10thDay
50%413%22%10%1
2340
11th to 20thDay
50%412%18%15%1
2305
21st to endDay
43%6%15%19%14%2
2575
June1st to 10thDay
38%410%28%17%3
2520
11th to 20thDay
36%413%24%19%3
2520
21st to endDay
38%6%14%21%17%4
2520
July1st to 10thDay
40%5%13%22%15%3
2451
11th to 20thDay
33%6%15%27%18%1
2445
21st to endDay
36%6%15%24%16%3
2515
August1st to 10thDay
35%6%13%29%15%2
2314
11th to 20thDay
39%5%13%26%16%2
2155
21st to endDay
31%5%13%26%18%7%
2376
September1st to 10thDay
39%411%25%18%4
2142
11th to 20thDay
35%49%29%20%3
1980
21st to endDay
33%39%27%25%3
1980
October1st to 10thDay
35%49%26%24%3
1980
11th to 20thDay
40%38%26%22%2
1852
21st to endDay
49%38%24%14%1
1782
November1st to 10thDay
32%410%31%19%5%
1672
11th to 20thDay
45%39%23%17%4
1710
21st to endDay
49%29%23%16%1
1710
December1st to 10thDay
56%210%20%11%1
1710
11th to 20thDay
56%26%24%10%1
1953
21st to endDay
68%29%13%7%1
2783
January1st to 10thNight
55%38%21%11%1
2648
11th to 20thNight
61%211%18%8%1
2660
21st to endNight
58%310%19%9%1
2794
February1st to 10thNight
60%411%18%5%1
2160
11th to 20thNight
54%310%21%12%1
2099
21st to endNight
57%39%19%10%3
1776
March1st to 10thNight
49%47%23%15%2
2160
11th to 20thNight
48%313%22%12%2
2065
21st to endNight
53%311%23%7%2
2077
April1st to 10thNight
42%311%28%14%2
1800
11th to 20thNight
44%39%20%18%6%
1775
21st to endNight
46%39%25%13%4
1679
May1st to 10thNight
49%5%11%23%10%2
1620
11th to 20thNight
44%6%13%20%16%1
1593
21st to endNight
38%6%15%22%13%5%
1697
June1st to 10thNight
35%311%26%22%4
1440
11th to 20thNight
32%413%26%21%5%
1440
21st to endNight
27%8%15%25%20%5%
1440
July1st to 10thNight
34%6%15%23%19%4
1400
11th to 20thNight
29%5%15%29%19%4
1392
21st to endNight
30%412%32%19%4
1559
August1st to 10thNight
32%5%15%28%18%3
1600
11th to 20thNight
30%5%15%28%19%2
1742
21st to endNight
26%5%12%29%21%7%
1980
September1st to 10thNight
35%410%27%17%7%
1800
11th to 20thNight
28%48%30%26%5%
1979
21st to endNight
34%310%24%24%5%
1980
October1st to 10thNight
29%410%26%27%5%
1980
11th to 20thNight
40%26%26%21%4
2102
21st to endNight
46%37%24%17%3
2574
November1st to 10thNight
36%38%26%22%5%
2406
11th to 20thNight
44%28%23%19%3
2470
21st to endNight
51%29%23%14%1
2470
December1st to 10thNight
55%310%20%12%1
2470
11th to 20thNight
55%38%20%13%1
3239
21st to endNight
71%27%12%7%1
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
31%21%28%16%3
270
11th to 20thDay
36%22%31%9%1
270
21st to endDay
32%26%30%10%11
294
February1st to 10thDay
35%25%30%8%2
240
11th to 20thDay
36%24%30%8%1
240
21st to endDay
34%23%36%6%1
198
March1st to 10thDay
31%25%35%8%1
240
11th to 20thDay
31%18%35%10%5%1
334
21st to endDay
32%21%28%15%4
462
April1st to 10thDay
26%18%31%17%7%1
420
11th to 20thDay
27%21%22%19%9%1
412
21st to endDay
29%20%32%11%7%1
420
May1st to 10thDay
27%14%35%16%6%2
423
11th to 20thDay
25%12%30%22%7%4
447
21st to endDay
15%11%29%22%16%8%
529
June1st to 10thDay
13%7%31%29%16%4
630
11th to 20thDay
12%8%29%30%17%5%
630
21st to endDay
13%8%34%24%16%6%
630
July1st to 10thDay
13%5%20%26%23%12%
621
11th to 20thDay
8%5%26%33%19%9%
618
21st to endDay
10%5%23%34%20%8%
604
August1st to 10thDay
13%415%34%24%10%
446
11th to 20thDay
15%423%29%21%6%
439
21st to endDay
9%420%33%23%11%
495
September1st to 10thDay
13%6%20%33%22%7%
450
11th to 20thDay
12%318%31%27%9%
450
21st to endDay
16%10%22%24%22%6%
450
October1st to 10thDay
11%9%31%31%12%5%
450
11th to 20thDay
20%20%35%16%7%2
370
21st to endDay
34%13%39%13%
297
November1st to 10thDay
14%23%32%24%6%1
270
11th to 20thDay
26%20%30%17%5%1
270
21st to endDay
29%13%40%14%5%
270
December1st to 10thDay
26%24%29%17%41
270
11th to 20thDay
30%19%36%12%3
270
21st to endDay
38%21%30%9%21
297
January1st to 10thNight
27%22%29%18%3
950
11th to 20thNight
30%22%33%14%2
950
21st to endNight
27%18%35%18%2
965
February1st to 10thNight
31%19%32%17%2
720
11th to 20thNight
25%25%33%16%2
703
21st to endNight
30%20%33%16%1
592
March1st to 10thNight
26%20%31%20%2
720
11th to 20thNight
25%19%32%18%6%1
720
21st to endNight
27%16%29%22%6%
691
April1st to 10thNight
19%16%31%28%6%1
540
11th to 20thNight
20%17%28%25%10%
533
21st to endNight
23%11%36%22%7%1
540
May1st to 10thNight
20%12%34%24%9%1
540
11th to 20thNight
17%9%29%27%15%3
531
21st to endNight
11%6%24%33%23%3
584
June1st to 10thNight
13%423%36%23%1
540
11th to 20thNight
10%5%24%41%20%1
540
21st to endNight
6%426%37%25%2
540
July1st to 10thNight
11%214%32%30%10%
525
11th to 20thNight
8%5%16%34%31%6%
522
21st to endNight
9%314%38%31%5%
591
August1st to 10thNight
9%213%38%32%7%
537
11th to 20thNight
7%214%38%34%5%
534
21st to endNight
6%218%34%34%7%
594
September1st to 10thNight
14%5%15%34%29%4
540
11th to 20thNight
9%5%18%30%33%6%
719
21st to endNight
14%8%21%29%24%4
720
October1st to 10thNight
12%7%24%30%23%4
720
11th to 20thNight
19%13%29%24%13%2
720
21st to endNight
25%15%31%21%7%1
792
November1st to 10thNight
16%11%34%26%12%1
740
11th to 20thNight
24%17%28%23%8%1
760
21st to endNight
26%17%26%23%6%
760
December1st to 10thNight
28%17%33%18%5%
760
11th to 20thNight
28%15%30%21%6%1
908
21st to endNight
36%16%29%16%3
1045
Page generated at 2024-01-28 05:26:34. Version ac07

Copyright 2024 Attilla Danko


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