McMath-Hulbert Observatory
Clear Sky Chart
History

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

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
34%
24082
15%
74867
9%
24024
40%
24024
19%
52654

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
18%
949
11%
2648
4%
946
24%
946
13%
2072
January11th to 20thNight
17%
905
7%
2533
3%
905
20%
905
11%
2062
January21st to endNight
21%
822
9%
2604
5%
822
26%
822
11%
2044
February1st to 10thNight
16%
720
8%
2340
2%
720
22%
720
9%
1854
February11th to 20thNight
19%
700
13%
2155
6%
699
26%
699
13%
1635
February21st to endNight
14%
592
15%
1776
3%
592
26%
592
14%
1316
March1st to 10thNight
25%
720
15%
2118
9%
720
31%
720
17%
1518
March11th to 20thNight
27%
720
20%
1980
9%
720
37%
720
21%
1375
March21st to endNight
28%
792
16%
2178
8%
792
35%
792
18%
1596
April1st to 10thNight
26%
626
15%
1886
7%
626
33%
626
20%
1294
April11th to 20thNight
29%
533
20%
1624
8%
533
39%
533
22%
1100
April21st to endNight
34%
540
17%
1620
6%
540
43%
540
22%
1089
May1st to 10thNight
35%
540
13%
1620
8%
540
39%
540
21%
1130
May11th to 20thNight
41%
531
18%
1592
11%
531
48%
531
25%
1033
May21st to endNight
55%
583
15%
1745
11%
582
60%
582
30%
1077
June1st to 10thNight
53%
432
17%
1334
14%
432
59%
432
30%
806
June11th to 20thNight
53%
360
20%
1260
20%
360
60%
360
27%
733
June21st to endNight
57%
464
20%
1364
16%
464
63%
464
32%
831
July1st to 10thNight
64%
525
16%
1400
14%
525
66%
525
39%
834
July11th to 20thNight
61%
522
21%
1392
16%
522
66%
522
39%
832
July21st to endNight
65%
591
17%
1627
13%
558
69%
558
37%
953
August1st to 10thNight
65%
537
19%
1600
16%
534
68%
534
36%
942
August11th to 20thNight
62%
534
22%
1598
16%
534
66%
534
33%
954
August21st to endNight
60%
594
23%
1792
16%
594
65%
594
35%
1039
September1st to 10thNight
56%
648
19%
1908
14%
648
59%
648
29%
1190
September11th to 20thNight
60%
720
27%
1980
20%
720
63%
720
37%
1184
September21st to endNight
50%
720
22%
1980
16%
720
55%
720
30%
1280
October1st to 10thNight
43%
720
20%
2034
15%
720
49%
720
28%
1327
October11th to 20thNight
29%
720
15%
2160
7%
720
39%
720
18%
1547
October21st to endNight
23%
792
14%
2519
8%
792
31%
792
15%
1844
November1st to 10thNight
35%
740
21%
2406
15%
740
43%
740
23%
1522
November11th to 20thNight
23%
760
15%
2470
9%
760
32%
760
16%
1751
November21st to endNight
22%
760
13%
2590
8%
760
29%
760
14%
1890
December1st to 10thNight
16%
760
8%
2660
4%
760
21%
760
9%
2089
December11th to 20thNight
17%
869
8%
3407
2%
867
24%
867
9%
2595
December21st to endNight
12%
1041
4%
4967
1%
1026
18%
1026
5%
4316

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
13%9%47%6%45%5%6%7%33%
74587
Night
15%10%47%6%35%5%5%7%35%
75099
TransparencyDay
48%8%12%19%11%1
74296
Night
48%7%12%20%11%1
74910
SeeingDay
17%12%30%22%13%5%
14243
Night
18%11%30%28%11%1
24091

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
14%13%6%12%10%36%46%6%21%
1517
11th to 20thDay
15%15%6%12%8%5%6%5%5%5%16%
1440
21st to endDay
15%17%9%11%8%46%5%45%17%
1750
February1st to 10thDay
14%14%6%11%10%5%5%5%5%5%19%
1620
11th to 20thDay
14%11%6%11%10%5%5%5%5%5%23%
1688
21st to endDay
14%15%6%10%8%345%5%5%25%
1480
March1st to 10thDay
15%11%5%7%7%46%5%5%6%28%
1841
11th to 20thDay
12%12%5%8%7%4445%6%32%
1980
21st to endDay
17%12%5%9%7%45%445%27%
2178
April1st to 10thDay
15%12%48%5%35%5%5%7%30%
2089
11th to 20thDay
16%10%37%6%35%5%6%7%33%
2284
21st to endDay
18%9%37%6%4445%7%34%
2340
May1st to 10thDay
17%9%46%6%45%5%5%7%33%
2340
11th to 20thDay
17%8%36%6%35%5%5%7%35%
2301
21st to endDay
13%6%26%5%35%5%7%8%40%
2531
June1st to 10thDay
10%5%26%5%45%5%6%10%41%
2612
11th to 20thDay
10%6%36%5%45%5%5%9%41%
2700
21st to endDay
10%6%36%5%46%6%7%10%37%
2587
July1st to 10thDay
7%425%6%36%6%6%10%45%
2520
11th to 20thDay
8%5%35%5%36%6%8%9%42%
2520
21st to endDay
7%5%36%5%47%7%7%10%40%
2594
August1st to 10thDay
8%5%26%6%5%6%7%7%9%40%
2327
11th to 20thDay
9%6%26%7%5%6%6%7%9%39%
2303
21st to endDay
10%6%36%6%45%6%6%9%41%
2560
September1st to 10thDay
11%7%36%5%47%6%6%8%38%
2034
11th to 20thDay
10%6%245%35%5%8%8%44%
1980
21st to endDay
13%7%26%6%36%5%7%9%36%
1980
October1st to 10thDay
14%7%36%6%45%5%6%6%40%
1926
11th to 20thDay
17%11%37%6%35%6%47%32%
1800
21st to endDay
20%12%47%6%4445%6%29%
1836
November1st to 10thDay
12%8%38%5%45%5%5%9%36%
1672
11th to 20thDay
14%11%48%7%45%5%6%5%31%
1710
21st to endDay
17%11%5%8%6%34446%29%
1585
December1st to 10thDay
13%14%8%12%8%45%45%6%22%
1520
11th to 20thDay
17%14%6%10%6%35%5%7%6%23%
1751
21st to endDay
24%20%7%10%8%34435%11%
2691
January1st to 10thNight
17%10%6%10%7%5%5%5%46%25%
2648
11th to 20thNight
17%13%7%11%7%45%5%5%6%20%
2533
21st to endNight
12%12%8%12%10%35%5%46%23%
2604
February1st to 10thNight
15%15%6%9%9%5%6%45%5%23%
2340
11th to 20thNight
13%12%6%9%9%45%5%5%6%27%
2155
21st to endNight
18%13%48%6%345%46%29%
1776
March1st to 10thNight
14%10%48%6%35%45%7%33%
2118
11th to 20thNight
14%8%36%6%36%5%5%6%38%
1980
21st to endNight
19%9%38%6%36%445%34%
2178
April1st to 10thNight
16%9%36%6%35%5%5%7%35%
1886
11th to 20thNight
18%7%26%6%3445%8%37%
1624
21st to endNight
16%9%25%5%345%5%8%38%
1620
May1st to 10thNight
16%8%37%6%445%5%7%34%
1620
11th to 20thNight
18%6%35%4245%5%8%41%
1592
21st to endNight
9%5%34435%6%6%9%46%
1744
June1st to 10thNight
10%5%35%5%25%46%8%47%
1334
11th to 20thNight
10%5%26%435%5%6%8%45%
1260
21st to endNight
9%6%35%44445%9%48%
1364
July1st to 10thNight
7%4245%35%35%8%54%
1440
11th to 20thNight
8%42443346%9%52%
1440
21st to endNight
5%4245%45%6%6%11%49%
1723
August1st to 10thNight
6%4244345%7%10%49%
1611
11th to 20thNight
6%5%246%35%6%6%9%49%
1598
21st to endNight
9%5%2442346%8%52%
1792
September1st to 10thNight
9%6%35%5%35%5%5%7%46%
1908
11th to 20thNight
10%415%435%447%53%
1980
21st to endNight
14%5%26%5%2445%7%44%
1980
October1st to 10thNight
14%7%345%3345%6%45%
2034
11th to 20thNight
18%9%38%5%445%5%6%34%
2160
21st to endNight
21%9%37%6%45%446%31%
2519
November1st to 10thNight
13%7%35%5%3445%7%43%
2406
11th to 20thNight
15%9%48%7%35%6%6%6%31%
2470
21st to endNight
18%13%5%7%5%35%5%5%6%28%
2590
December1st to 10thNight
17%13%7%11%8%35%5%5%6%22%
2660
11th to 20thNight
13%14%6%10%7%45%5%5%6%24%
3441
21st to endNight
26%23%7%9%5%3433412%
4971

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
64%6%10%12%6%1
1518
11th to 20thDay
68%8%12%8%5%
1440
21st to endDay
69%6%8%11%5%1
1750
February1st to 10thDay
65%7%9%12%7%
1620
11th to 20thDay
61%7%9%15%7%1
1697
21st to endDay
59%7%10%15%7%2
1480
March1st to 10thDay
55%7%14%16%8%1
1841
11th to 20thDay
51%6%11%18%11%3
1980
21st to endDay
58%6%10%16%8%1
2178
April1st to 10thDay
52%8%11%18%10%1
2089
11th to 20thDay
48%8%11%18%13%2
2284
21st to endDay
49%7%14%16%13%1
2340
May1st to 10thDay
49%8%11%20%9%2
2340
11th to 20thDay
47%7%11%19%13%2
2305
21st to endDay
40%7%15%22%14%2
2531
June1st to 10thDay
38%8%14%25%14%2
2612
11th to 20thDay
38%8%13%23%15%2
2700
21st to endDay
39%9%13%22%15%2
2587
July1st to 10thDay
33%10%12%25%18%3
2451
11th to 20thDay
34%8%15%24%17%2
2445
21st to endDay
35%10%14%21%17%3
2450
August1st to 10thDay
36%11%15%25%12%1
2314
11th to 20thDay
38%11%14%23%12%2
2303
21st to endDay
38%8%12%25%15%1
2560
September1st to 10thDay
41%9%15%21%12%2
2034
11th to 20thDay
34%8%14%33%12%1
1980
21st to endDay
42%8%14%24%12%
1980
October1st to 10thDay
41%8%13%24%13%2
1926
11th to 20thDay
51%7%14%18%9%1
1800
21st to endDay
54%6%14%17%8%
1836
November1st to 10thDay
45%7%14%22%11%1
1672
11th to 20thDay
53%7%13%17%9%1
1710
21st to endDay
55%6%14%17%7%1
1585
December1st to 10thDay
63%7%11%15%4
1520
11th to 20thDay
59%8%14%14%5%
1747
21st to endDay
75%7%9%6%3
2691
January1st to 10thNight
59%7%11%16%6%1
2648
11th to 20thNight
65%6%12%11%5%
2533
21st to endNight
61%8%11%15%5%1
2604
February1st to 10thNight
63%7%10%13%6%1
2340
11th to 20thNight
58%6%10%16%9%1
2156
21st to endNight
55%6%12%17%8%1
1776
March1st to 10thNight
50%7%11%21%10%1
2118
11th to 20thNight
45%7%10%21%15%2
1980
21st to endNight
52%6%9%20%11%1
2178
April1st to 10thNight
48%5%12%21%13%2
1886
11th to 20thNight
44%7%12%17%18%2
1624
21st to endNight
43%7%12%19%15%3
1620
May1st to 10thNight
48%7%12%20%12%2
1620
11th to 20thNight
41%6%12%19%18%3
1593
21st to endNight
33%10%14%24%15%3
1745
June1st to 10thNight
34%7%12%28%17%2
1334
11th to 20thNight
33%9%14%25%17%2
1260
21st to endNight
33%7%13%26%20%1
1364
July1st to 10thNight
28%8%11%27%23%3
1400
11th to 20thNight
30%6%13%31%18%2
1392
21st to endNight
26%10%19%22%20%3
1627
August1st to 10thNight
28%10%16%30%14%1
1600
11th to 20thNight
29%11%15%30%12%3
1598
21st to endNight
29%8%15%29%18%1
1792
September1st to 10thNight
35%9%13%26%15%2
1908
11th to 20thNight
30%7%13%30%19%1
1980
21st to endNight
38%6%13%29%13%1
1980
October1st to 10thNight
40%6%11%24%18%1
2034
11th to 20thNight
48%9%12%18%11%1
2160
21st to endNight
54%6%11%20%8%1
2519
November1st to 10thNight
41%6%13%26%14%1
2406
11th to 20thNight
50%8%14%19%8%1
2470
21st to endNight
55%6%13%19%6%
2590
December1st to 10thNight
63%7%11%14%5%
2660
11th to 20thNight
58%10%13%14%6%1
3444
21st to endNight
75%7%9%6%2
4971

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
23%22%38%13%5%
270
11th to 20thDay
21%15%47%15%21
240
21st to endDay
27%16%36%16%41
264
February1st to 10thDay
24%24%38%13%1
240
11th to 20thDay
24%21%39%14%1
240
21st to endDay
25%30%33%10%2
198
March1st to 10thDay
28%22%33%12%4
281
11th to 20thDay
23%13%35%22%6%1
420
21st to endDay
27%15%32%20%5%1
462
April1st to 10thDay
17%18%37%20%8%1
420
11th to 20thDay
25%18%30%15%7%5%
412
21st to endDay
25%15%30%19%10%3
420
May1st to 10thDay
23%14%27%22%11%3
423
11th to 20thDay
22%9%30%22%12%6%
447
21st to endDay
16%7%24%28%17%8%
485
June1st to 10thDay
12%9%31%29%15%3
624
11th to 20thDay
13%8%32%26%17%3
630
21st to endDay
12%8%30%30%15%4
630
July1st to 10thDay
8%6%21%32%21%12%
621
11th to 20thDay
10%6%30%28%19%8%
618
21st to endDay
8%5%26%30%22%9%
535
August1st to 10thDay
9%324%24%26%13%
446
11th to 20thDay
12%421%28%21%14%
439
21st to endDay
12%6%24%27%19%12%
495
September1st to 10thDay
13%6%25%24%22%10%
450
11th to 20thDay
10%422%23%27%14%
450
21st to endDay
14%11%24%23%20%7%
450
October1st to 10thDay
17%11%28%20%17%8%
450
11th to 20thDay
20%17%31%24%7%1
450
21st to endDay
26%18%37%15%31
351
November1st to 10thDay
16%21%37%17%9%1
270
11th to 20thDay
21%23%34%16%5%1
270
21st to endDay
23%19%40%14%4
210
December1st to 10thDay
22%27%32%13%7%
180
11th to 20thDay
26%27%34%9%31
180
21st to endDay
24%27%36%13%1
272
January1st to 10thNight
20%16%38%20%5%1
950
11th to 20thNight
24%14%36%22%31
905
21st to endNight
18%14%35%27%6%
822
February1st to 10thNight
23%15%38%22%2
720
11th to 20thNight
21%15%36%23%4
703
21st to endNight
26%17%37%18%2
592
March1st to 10thNight
19%14%36%26%5%
720
11th to 20thNight
18%14%36%26%5%1
720
21st to endNight
21%13%31%27%8%1
792
April1st to 10thNight
20%15%35%27%4
626
11th to 20thNight
22%11%34%25%7%2
533
21st to endNight
20%10%33%29%8%
540
May1st to 10thNight
19%8%31%32%9%1
540
11th to 20thNight
21%428%33%12%1
531
21st to endNight
11%324%41%19%2
584
June1st to 10thNight
12%426%44%13%
432
11th to 20thNight
11%5%26%48%11%
360
21st to endNight
10%5%23%45%17%1
464
July1st to 10thNight
7%318%40%28%4
525
11th to 20thNight
10%221%41%22%4
522
21st to endNight
5%320%49%21%2
591
August1st to 10thNight
7%318%41%28%3
537
11th to 20thNight
8%221%35%30%4
534
21st to endNight
9%420%34%30%3
594
September1st to 10thNight
12%5%20%35%23%5%
648
11th to 20thNight
11%5%18%34%27%5%
720
21st to endNight
15%7%23%30%20%5%
720
October1st to 10thNight
17%9%26%28%17%3
720
11th to 20thNight
22%16%28%26%8%1
720
21st to endNight
26%13%34%23%4
792
November1st to 10thNight
18%13%29%27%12%1
740
11th to 20thNight
21%16%35%21%6%1
760
21st to endNight
24%15%36%21%5%
760
December1st to 10thNight
23%16%36%19%6%
760
11th to 20thNight
22%15%39%21%3
869
21st to endNight
30%14%37%17%2
1045
Page generated at 2024-01-08 11:14:20. Version ac07

Copyright 2024 Attilla Danko


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