This page made possible by the sponsorship of: In memory of Maurice L. Battin, Jr..

Bloomington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bloomington clear sky chart from 2005-11-05 to 2017-09-10.

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
36%
15744
20%
46730
12%
15701
44%
15701
24%
30493

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
14%
900
15%
2506
4%
895
24%
895
15%
1845
January16th to endNight
14%
910
15%
2608
3%
910
25%
910
15%
1907
February1st to 15thNight
16%
703
14%
2112
4%
701
25%
701
15%
1507
February16th to endNight
16%
631
16%
1893
5%
631
25%
631
14%
1347
March1st to 15thNight
20%
720
15%
2155
8%
720
27%
720
17%
1508
March16th to endNight
26%
700
16%
2044
7%
700
34%
700
18%
1409
April1st to 15thNight
30%
539
20%
1797
11%
539
43%
539
22%
1132
April16th to endNight
32%
540
21%
1719
11%
540
44%
540
25%
1077
May1st to 15thNight
32%
540
16%
1620
7%
540
39%
540
20%
1126
May16th to endNight
49%
561
17%
1651
12%
561
53%
561
27%
1068
June1st to 15thNight
53%
540
20%
1440
13%
540
58%
540
38%
868
June16th to endNight
59%
540
21%
1440
14%
540
64%
540
42%
842
July1st to 15thNight
61%
510
17%
1360
12%
510
64%
510
39%
835
July16th to endNight
72%
564
25%
1465
20%
531
75%
531
46%
808
August1st to 15thNight
70%
539
22%
1645
20%
536
73%
536
40%
911
August16th to endNight
70%
573
25%
1910
26%
573
75%
573
38%
1016
September1st to 15thNight
59%
580
27%
1805
23%
580
66%
580
35%
1026
September16th to endNight
55%
657
27%
1815
19%
657
59%
657
35%
1098
October1st to 15thNight
48%
660
33%
1815
22%
660
58%
660
38%
1059
October16th to endNight
30%
704
22%
2253
15%
704
41%
704
23%
1391
November1st to 15thNight
34%
700
27%
2276
17%
700
48%
700
26%
1340
November16th to endNight
26%
720
20%
2340
12%
720
38%
720
18%
1542
December1st to 15thNight
21%
753
13%
2373
8%
753
27%
753
14%
1754
December16th to endNight
15%
960
13%
2688
3%
960
24%
960
12%
2077

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%7%35%5%3445%7%38%
47894
Night
14%7%35%424446%40%
46904
Cloud CoverDay
14%7%35%5%3445%7%38%
47903
Night
14%7%35%5%24446%40%
46909
TransparencyDay
44%411%23%14%2
47586
Night
43%311%23%15%2
46730
SeeingDay
18%9%27%23%14%6%
5769
Night
19%12%26%24%14%2
15747

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
20%10%39%42434430%
1432
16th to endDay
12%14%5%6%5%34345%35%
1613
February1st to 15thDay
16%11%47%5%24446%31%
1750
16th to endDay
13%12%5%7%5%345%5%6%30%
1580
March1st to 15thDay
22%8%25%5%24445%33%
1793
16th to endDay
16%10%47%5%2435%6%32%
2190
April1st to 15thDay
17%6%35%42335%7%39%
2151
16th to endDay
19%7%25%424446%37%
2241
May1st to 15thDay
21%7%36%5%2335%6%33%
2331
16th to endDay
13%6%35%6%35%5%7%8%35%
2461
June1st to 15thDay
10%4245%25%5%6%8%44%
2520
16th to endDay
9%5%24435%5%6%9%41%
2520
July1st to 15thDay
12%5%25%5%35%5%7%9%38%
2520
16th to endDay
6%325%5%36%6%7%10%42%
2601
August1st to 15thDay
9%324445%5%6%10%43%
2301
16th to endDay
7%5%245%45%5%6%8%44%
2292
September1st to 15thDay
13%425%425%45%6%44%
2031
16th to endDay
12%5%15%42446%5%47%
1815
October1st to 15thDay
13%5%25%4245%47%44%
1815
16th to endDay
16%6%25%324446%42%
1615
November1st to 15thDay
12%4235%235%5%5%50%
1582
16th to endDay
20%9%35%422346%38%
1620
December1st to 15thDay
23%11%46%42433431%
1584
16th to endDay
21%13%47%323246%29%
1536
January1st to 15thNight
18%10%48%6%34445%29%
2506
16th to endNight
16%12%6%7%5%23345%31%
2608
February1st to 15thNight
15%12%5%8%42446%5%30%
2110
16th to endNight
16%11%5%7%43435%5%32%
1893
March1st to 15thNight
18%9%45%5%24446%35%
2142
16th to endNight
17%8%36%5%34346%35%
2044
April1st to 15thNight
15%7%35%424435%43%
1797
16th to endNight
14%6%35%32445%7%41%
1719
May1st to 15thNight
18%7%35%5%3445%9%34%
1620
16th to endNight
10%5%25%6%46%5%5%8%39%
1649
June1st to 15thNight
7%425%435%3410%47%
1440
16th to endNight
8%2224146%6%12%48%
1440
July1st to 15thNight
8%42442346%8%49%
1440
16th to endNight
432343345%8%55%
1565
August1st to 15thNight
5%2145%35%5%5%9%51%
1656
16th to endNight
43144345%5%8%53%
1910
September1st to 15thNight
10%5%24323446%51%
1805
16th to endNight
11%325%5%23337%49%
1815
October1st to 15thNight
10%414323346%54%
1815
16th to endNight
18%6%2442334445%
2253
November1st to 15thNight
11%5%34424346%48%
2276
16th to endNight
19%8%35%433346%37%
2340
December1st to 15thNight
22%12%47%5%23445%27%
2373
16th to endNight
23%12%46%434345%26%
2688

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
20%11%49%424345%30%
1432
16th to endDay
12%14%5%7%5%24345%34%
1613
February1st to 15thDay
15%11%5%7%5%23446%31%
1750
16th to endDay
13%12%49%5%3445%6%30%
1580
March1st to 15thDay
22%8%35%42344433%
1803
16th to endDay
16%10%47%5%3435%7%32%
2189
April1st to 15thDay
17%6%3442335%7%39%
2151
16th to endDay
18%6%36%42345%6%37%
2241
May1st to 15thDay
21%7%36%5%34346%33%
2331
16th to endDay
12%6%35%6%35%6%6%7%35%
2461
June1st to 15thDay
10%425%435%5%5%9%43%
2520
16th to endDay
8%4245%36%5%6%9%41%
2520
July1st to 15thDay
11%5%25%5%35%5%6%9%37%
2520
16th to endDay
6%325%5%36%6%7%9%42%
2601
August1st to 15thDay
8%3245%36%6%6%10%42%
2301
16th to endDay
7%425%6%35%5%6%8%44%
2292
September1st to 15thDay
13%424425%5%6%7%44%
2031
16th to endDay
12%42442446%6%46%
1815
October1st to 15thDay
13%5%244245%5%6%44%
1815
16th to endDay
16%5%25%423346%42%
1615
November1st to 15thDay
11%4245%23446%49%
1582
16th to endDay
20%9%34422336%38%
1620
December1st to 15thDay
23%11%46%414325%30%
1584
16th to endDay
21%13%47%333245%29%
1536
January1st to 15thNight
18%10%48%6%3434429%
2506
16th to endNight
16%13%6%7%5%24335%30%
2608
February1st to 15thNight
15%12%6%7%42436%5%30%
2103
16th to endNight
16%11%47%434345%31%
1893
March1st to 15thNight
18%9%45%424446%34%
2155
16th to endNight
17%7%35%5%35%45%6%35%
2044
April1st to 15thNight
14%7%36%324445%42%
1797
16th to endNight
14%6%35%42335%7%41%
1719
May1st to 15thNight
17%6%36%5%345%49%33%
1619
16th to endNight
10%425%6%47%45%9%39%
1649
June1st to 15thNight
8%425%5%244411%47%
1440
16th to endNight
7%2223245%6%11%49%
1440
July1st to 15thNight
7%42442446%9%49%
1440
16th to endNight
43135%3436%8%55%
1565
August1st to 15thNight
5%3145%35%5%5%8%51%
1656
16th to endNight
43144345%5%9%52%
1910
September1st to 15thNight
10%4244235%46%52%
1805
16th to endNight
11%325%5%23337%49%
1815
October1st to 15thNight
10%41341335%6%54%
1815
16th to endNight
17%7%24423335%45%
2253
November1st to 15thNight
11%5%245%33346%47%
2276
16th to endNight
19%8%36%424246%37%
2340
December1st to 15thNight
21%12%5%7%5%23445%27%
2373
16th to endNight
24%13%46%423445%26%
2688

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
56%211%17%11%1
1433
16th to endDay
51%311%24%7%
1613
February1st to 15thDay
53%310%22%8%1
1752
16th to endDay
53%411%23%7%
1580
March1st to 15thDay
52%39%23%10%1
1803
16th to endDay
51%312%22%8%
2190
April1st to 15thDay
44%311%23%15%
2151
16th to endDay
47%39%22%12%4
2241
May1st to 15thDay
52%312%18%12%
2331
16th to endDay
44%6%13%18%14%2
2465
June1st to 15thDay
35%412%27%16%3
2520
16th to endDay
36%5%13%22%17%3
2520
July1st to 15thDay
41%5%12%19%17%2
2371
16th to endDay
33%6%16%26%15%1
2438
August1st to 15thDay
35%6%11%25%18%2
2288
16th to endDay
34%5%11%25%17%5%
2292
September1st to 15thDay
37%310%24%18%5%
2031
16th to endDay
37%37%24%24%2
1815
October1st to 15thDay
37%47%25%21%2
1815
16th to endDay
41%311%26%16%
1615
November1st to 15thDay
34%411%23%19%5%
1582
16th to endDay
48%19%23%15%1
1620
December1st to 15thDay
57%210%18%9%
1584
16th to endDay
56%211%21%5%1
1536
January1st to 15thNight
55%38%20%10%
2506
16th to endNight
55%311%20%8%
2608
February1st to 15thNight
53%313%21%7%
2112
16th to endNight
53%312%20%9%
1893
March1st to 15thNight
50%49%21%11%1
2155
16th to endNight
49%314%23%7%1
2044
April1st to 15thNight
42%310%24%15%2
1797
16th to endNight
42%29%23%14%6%
1719
May1st to 15thNight
47%6%11%21%12%
1620
16th to endNight
39%6%13%18%15%5%
1651
June1st to 15thNight
33%310%27%21%3
1440
16th to endNight
26%7%16%23%21%5%
1440
July1st to 15thNight
31%5%15%22%20%4
1360
16th to endNight
25%413%34%18%3
1465
August1st to 15thNight
28%416%25%20%3
1645
16th to endNight
26%6%12%29%20%5%
1910
September1st to 15thNight
32%38%25%22%7%
1805
16th to endNight
34%38%21%25%5%
1815
October1st to 15thNight
30%38%28%22%5%
1815
16th to endNight
42%27%28%16%2
2253
November1st to 15thNight
37%38%22%22%6%
2276
16th to endNight
48%29%22%15%
2340
December1st to 15thNight
58%210%17%9%
2373
16th to endNight
61%39%16%8%
2688

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
43%17%28%5%4
90
16th to endDay
17%40%35%6%
96
February1st to 15thDay
33%27%30%7%1
90
16th to endDay
19%19%50%7%2
81
March1st to 15thDay
36%22%30%10%
93
16th to endDay
24%15%34%17%6%1
288
April1st to 15thDay
24%14%28%21%9%1
270
16th to endDay
26%10%30%18%11%2
270
May1st to 15thDay
31%11%30%15%7%2
288
16th to endDay
20%9%29%19%11%9%
361
June1st to 15thDay
11%6%29%31%16%4
495
16th to endDay
14%7%35%23%13%6%
495
July1st to 15thDay
15%6%26%27%15%9%
475
16th to endDay
8%319%32%22%13%
461
August1st to 15thDay
15%212%30%23%16%
313
16th to endDay
11%218%27%28%11%
332
September1st to 15thDay
10%5%19%28%24%10%
294
16th to endDay
17%7%15%22%27%9%
254
October1st to 15thDay
12%10%26%25%16%7%
255
16th to endDay
19%14%40%24%
102
November1st to 15thDay
13%12%27%32%10%4
90
16th to endDay
32%14%33%12%7%
90
December1st to 15thDay
26%22%27%20%12
90
16th to endDay
34%29%30%5%1
96
January1st to 15thNight
28%20%33%14%2
900
16th to endNight
25%20%35%17%1
910
February1st to 15thNight
26%20%32%19%1
704
16th to endNight
24%19%35%18%1
631
March1st to 15thNight
26%18%31%20%2
720
16th to endNight
21%18%29%21%8%
700
April1st to 15thNight
20%16%30%24%7%
539
16th to endNight
19%9%32%26%10%
540
May1st to 15thNight
20%10%30%25%10%1
540
16th to endNight
12%6%26%30%21%3
563
June1st to 15thNight
10%425%38%20%
540
16th to endNight
7%325%37%24%1
540
July1st to 15thNight
10%218%35%29%4
510
16th to endNight
5%211%36%33%9%
564
August1st to 15thNight
7%114%34%34%8%
539
16th to endNight
5%114%35%36%6%
573
September1st to 15thNight
12%416%31%30%4
580
16th to endNight
14%6%17%28%28%5%
657
October1st to 15thNight
14%8%22%26%22%5%
660
16th to endNight
21%14%30%21%9%
704
November1st to 15thNight
16%13%30%24%13%1
700
16th to endNight
27%16%25%22%8%
720
December1st to 15thNight
32%14%28%17%6%
753
16th to endNight
34%14%30%16%3
960
Page generated at 2017-09-11 19:35:34. Version ac04

Copyright 2017 A. Danko


Bloomington Clear Sky Chart | Charts Home