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 2005-11-05 to 2017-04-25.

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%
15216
15%
45628
9%
15176
41%
15176
20%
31961

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
17%
898
9%
2506
4%
895
21%
895
12%
1997
January16th to endNight
20%
849
9%
2577
4%
849
25%
849
11%
2031
February1st to 15thNight
17%
701
9%
2269
2%
701
24%
701
11%
1749
February16th to endNight
21%
631
14%
1893
6%
631
29%
631
15%
1408
March1st to 15thNight
26%
720
15%
2072
9%
720
31%
720
17%
1514
March16th to endNight
33%
768
18%
2112
9%
768
40%
768
21%
1502
April1st to 15thNight
29%
596
14%
1811
8%
596
35%
596
19%
1268
April16th to endNight
35%
525
20%
1575
8%
525
45%
525
25%
1024
May1st to 15thNight
39%
495
15%
1485
10%
495
44%
495
23%
1014
May16th to endNight
53%
514
15%
1540
12%
513
58%
513
30%
951
June1st to 15thNight
53%
374
17%
1200
15%
374
60%
374
28%
741
June16th to endNight
60%
393
15%
1218
15%
393
64%
393
30%
748
July1st to 15thNight
63%
465
17%
1240
14%
465
65%
465
39%
739
July16th to endNight
66%
522
16%
1388
13%
489
69%
489
38%
826
August1st to 15thNight
63%
494
20%
1474
15%
491
66%
491
34%
891
August16th to endNight
64%
525
21%
1581
16%
525
67%
525
36%
922
September1st to 15thNight
57%
616
24%
1771
19%
616
60%
616
33%
1079
September16th to endNight
58%
657
22%
1815
17%
657
62%
657
34%
1121
October1st to 15thNight
45%
660
19%
1903
14%
660
51%
660
27%
1261
October16th to endNight
24%
704
13%
2200
7%
704
32%
704
15%
1606
November1st to 15thNight
36%
700
19%
2276
16%
700
42%
700
22%
1474
November16th to endNight
25%
720
13%
2415
9%
720
31%
720
14%
1766
December1st to 15thNight
17%
729
8%
2529
3%
729
22%
729
9%
1970
December16th to endNight
14%
960
6%
2778
2%
960
18%
960
8%
2359

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%9%47%6%35%5%5%7%31%
45991
Night
15%8%46%5%34446%35%
45807
Cloud CoverDay
13%8%47%6%35%5%5%7%31%
46001
Night
15%8%36%5%3445%6%35%
45811
TransparencyDay
50%7%12%18%10%1
45688
Night
48%6%12%20%11%1
45628
SeeingDay
16%8%27%24%15%7%
5205
Night
18%9%29%29%11%1
15222

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
16%15%6%10%9%35%445%16%
1432
16th to endDay
14%18%9%11%7%5%5%5%45%13%
1647
February1st to 15thDay
14%14%7%10%8%5%5%5%45%17%
1591
16th to endDay
13%13%6%11%8%35%446%20%
1580
March1st to 15thDay
16%11%5%7%6%36%45%6%26%
1876
16th to endDay
16%9%6%7%7%45%336%28%
2112
April1st to 15thDay
19%9%5%6%5%24446%30%
2146
16th to endDay
16%8%36%5%23446%37%
2273
May1st to 15thDay
18%8%46%6%35%5%46%31%
2136
16th to endDay
13%5%35%5%3445%8%39%
2223
June1st to 15thDay
11%6%26%5%36%5%5%8%37%
2422
16th to endDay
9%5%36%6%36%7%7%10%34%
2406
July1st to 15thDay
7%5%25%436%6%6%9%42%
2310
16th to endDay
8%6%25%5%46%6%8%10%35%
2368
August1st to 15thDay
9%5%26%7%45%6%7%8%36%
2145
16th to endDay
11%5%25%6%25%5%6%8%39%
2267
September1st to 15thDay
13%6%25%435%46%8%38%
1848
16th to endDay
13%5%25%6%3447%8%37%
1815
October1st to 15thDay
14%9%25%5%3345%6%38%
1727
16th to endDay
22%8%45%5%34436%30%
1672
November1st to 15thDay
15%7%36%6%25%447%35%
1582
16th to endDay
17%11%5%7%7%35%435%27%
1542
December1st to 15thDay
16%14%7%12%5%3445%5%20%
1428
16th to endDay
20%15%8%10%7%3434416%
1443
January1st to 15thNight
21%11%5%8%7%4444423%
2506
16th to endNight
13%12%7%10%7%35%5%46%21%
2577
February1st to 15thNight
15%13%5%9%7%34445%26%
2267
16th to endNight
15%12%48%7%44446%27%
1893
March1st to 15thNight
17%8%47%5%25%345%32%
2060
16th to endNight
14%8%36%5%35%5%46%35%
2112
April1st to 15thNight
18%8%35%5%3445%6%33%
1811
16th to endNight
15%6%35%5%2445%7%40%
1575
May1st to 15thNight
17%7%25%4245%5%8%35%
1485
16th to endNight
12%5%34424448%46%
1538
June1st to 15thNight
9%435%5%35%46%8%44%
1200
16th to endNight
10%5%2442447%8%44%
1218
July1st to 15thNight
8%323424448%53%
1320
16th to endNight
442443446%10%50%
1492
August1st to 15thNight
5%3145%35%5%6%9%48%
1485
16th to endNight
10%5%13423447%51%
1581
September1st to 15thNight
12%5%2433325%5%51%
1771
16th to endNight
11%424424447%47%
1815
October1st to 15thNight
16%5%25%32445%6%42%
1903
16th to endNight
20%9%36%6%245%45%31%
2200
November1st to 15thNight
14%7%35%4245%46%39%
2276
16th to endNight
20%10%48%5%2445%6%28%
2415
December1st to 15thNight
19%13%6%8%5%25%435%23%
2529
16th to endNight
21%16%6%10%7%34345%16%
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
15%15%6%10%9%35%46%6%16%
1432
16th to endDay
14%16%8%11%7%46%6%45%14%
1647
February1st to 15thDay
13%14%7%10%8%45%6%5%5%17%
1591
16th to endDay
12%14%6%11%8%45%445%22%
1580
March1st to 15thDay
17%11%5%7%6%36%446%26%
1887
16th to endDay
16%10%5%8%7%45%435%28%
2111
April1st to 15thDay
18%10%46%5%34446%30%
2146
16th to endDay
16%8%26%5%33347%37%
2273
May1st to 15thDay
18%8%46%5%35%5%5%5%31%
2136
16th to endDay
13%6%25%5%25%45%7%40%
2223
June1st to 15thDay
11%6%26%445%6%5%8%38%
2422
16th to endDay
9%5%35%6%46%6%7%10%34%
2406
July1st to 15thDay
7%425%5%36%5%7%9%42%
2310
16th to endDay
7%5%25%5%37%6%8%10%35%
2368
August1st to 15thDay
8%5%16%6%36%6%6%8%37%
2145
16th to endDay
10%5%35%5%35%5%6%8%39%
2267
September1st to 15thDay
13%5%25%5%35%5%6%8%38%
1848
16th to endDay
12%6%25%5%35%5%6%9%37%
1815
October1st to 15thDay
14%8%25%5%3445%7%38%
1727
16th to endDay
21%10%36%6%23445%31%
1672
November1st to 15thDay
14%7%37%6%35%447%36%
1582
16th to endDay
16%11%5%7%7%35%45%5%27%
1542
December1st to 15thDay
15%12%7%11%6%35%35%6%21%
1428
16th to endDay
20%15%7%9%8%34335%17%
1443
January1st to 15thNight
22%10%5%7%7%35%445%23%
2506
16th to endNight
12%12%7%10%8%345%46%22%
2577
February1st to 15thNight
13%14%5%8%7%35%44427%
2260
16th to endNight
15%10%49%6%345%36%28%
1893
March1st to 15thNight
17%9%48%425%445%33%
2072
16th to endNight
15%7%35%5%26%5%46%36%
2112
April1st to 15thNight
19%8%25%5%24447%33%
1811
16th to endNight
14%7%245%3445%7%40%
1575
May1st to 15thNight
17%6%25%5%2445%8%36%
1484
16th to endNight
11%5%25%4235%48%45%
1538
June1st to 15thNight
9%435%5%35%46%8%43%
1200
16th to endNight
9%5%24335%46%9%44%
1218
July1st to 15thNight
8%41342435%7%53%
1320
16th to endNight
432443446%10%50%
1492
August1st to 15thNight
5%4245%345%7%9%48%
1485
16th to endNight
10%5%1342335%7%52%
1581
September1st to 15thNight
11%5%23424346%50%
1771
16th to endNight
11%415%5%2435%7%48%
1815
October1st to 15thNight
15%5%2443345%6%42%
1903
16th to endNight
20%8%27%5%35%445%31%
2200
November1st to 15thNight
14%7%25%5%3445%6%40%
2276
16th to endNight
19%10%46%5%34446%28%
2415
December1st to 15thNight
20%12%6%8%5%34445%24%
2529
16th to endNight
21%16%6%9%6%35%445%17%
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
68%6%10%10%4
1433
16th to endDay
71%5%9%8%3
1647
February1st to 15thDay
66%7%9%11%5%
1593
16th to endDay
63%5%10%13%6%1
1580
March1st to 15thDay
58%6%11%16%6%
1887
16th to endDay
57%5%10%17%7%1
2112
April1st to 15thDay
53%6%9%19%10%
2146
16th to endDay
46%5%13%16%14%2
2273
May1st to 15thDay
52%7%11%17%9%1
2136
16th to endDay
42%5%13%22%12%2
2227
June1st to 15thDay
41%8%13%21%13%1
2422
16th to endDay
42%8%13%19%15%1
2406
July1st to 15thDay
36%7%11%24%17%2
2161
16th to endDay
38%10%15%19%13%2
2209
August1st to 15thDay
40%10%13%21%12%1
2132
16th to endDay
39%9%11%23%13%2
2267
September1st to 15thDay
41%7%14%23%12%
1848
16th to endDay
41%6%12%27%11%
1815
October1st to 15thDay
43%6%13%21%12%1
1727
16th to endDay
54%5%15%16%6%
1672
November1st to 15thDay
47%6%12%21%10%1
1582
16th to endDay
57%6%13%16%6%
1542
December1st to 15thDay
64%6%12%13%3
1428
16th to endDay
70%5%11%9%3
1443
January1st to 15thNight
63%5%10%13%6%
2506
16th to endNight
61%7%13%13%3
2577
February1st to 15thNight
59%6%10%14%7%
2269
16th to endNight
56%5%12%18%6%
1893
March1st to 15thNight
52%6%9%19%10%1
2072
16th to endNight
48%6%11%22%9%1
2112
April1st to 15thNight
50%411%19%13%
1811
16th to endNight
41%5%12%18%18%3
1575
May1st to 15thNight
45%6%13%20%12%1
1485
16th to endNight
36%6%14%23%15%4
1540
June1st to 15thNight
37%7%13%25%15%1
1200
16th to endNight
34%8%15%22%17%1
1218
July1st to 15thNight
30%5%9%28%22%2
1240
16th to endNight
28%8%17%23%18%3
1388
August1st to 15thNight
29%9%13%29%14%2
1474
16th to endNight
31%5%14%28%17%2
1581
September1st to 15thNight
34%5%12%27%18%1
1771
16th to endNight
35%414%29%15%
1815
October1st to 15thNight
41%6%11%21%18%
1903
16th to endNight
53%6%12%19%6%
2200
November1st to 15thNight
43%6%13%24%11%1
2276
16th to endNight
55%5%13%18%6%
2415
December1st to 15thNight
62%6%12%13%5%
2529
16th to endNight
69%7%10%9%3
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
21%20%42%14%11
90
16th to endDay
28%11%43%14%2
96
February1st to 15thDay
20%20%44%14%1
90
16th to endDay
17%16%44%18%3
81
March1st to 15thDay
31%11%28%21%6%
177
16th to endDay
22%9%33%22%9%2
288
April1st to 15thDay
20%12%32%22%9%2
270
16th to endDay
21%8%31%18%13%8%
250
May1st to 15thDay
25%7%24%23%14%4
228
16th to endDay
19%5%23%25%18%8%
267
June1st to 15thDay
14%6%33%26%15%4
417
16th to endDay
12%5%27%29%18%5%
420
July1st to 15thDay
11%422%31%19%11%
400
16th to endDay
7%325%33%19%10%
354
August1st to 15thDay
9%118%28%22%19%
253
16th to endDay
14%5%14%22%20%21%
268
September1st to 15thDay
13%5%19%17%27%16%
255
16th to endDay
15%415%24%29%11%
254
October1st to 15thDay
15%7%26%23%20%7%
255
16th to endDay
25%9%36%22%41
184
November1st to 15thDay
10%17%31%25%13%2
90
16th to endDay
20%22%35%16%5%
77
December1st to 15thDay
21%25%33%18%1
60
16th to endDay
22%30%38%8%
81
January1st to 15thNight
25%13%36%19%31
900
16th to endNight
18%11%38%26%5%
849
February1st to 15thNight
21%15%37%22%3
704
16th to endNight
22%12%35%25%3
631
March1st to 15thNight
21%11%34%26%6%
720
16th to endNight
17%11%31%29%9%1
768
April1st to 15thNight
21%12%31%28%4
596
16th to endNight
18%8%34%27%9%1
525
May1st to 15thNight
21%427%35%9%1
495
16th to endNight
13%321%40%18%2
515
June1st to 15thNight
10%327%46%12%
374
16th to endNight
10%221%47%17%1
393
July1st to 15thNight
9%119%40%25%3
465
16th to endNight
4120%48%21%3
522
August1st to 15thNight
6%119%39%28%4
494
16th to endNight
11%216%33%31%4
525
September1st to 15thNight
12%5%19%31%24%6%
616
16th to endNight
13%319%32%25%5%
657
October1st to 15thNight
18%6%23%30%17%2
660
16th to endNight
24%13%33%23%5%
704
November1st to 15thNight
18%10%30%25%14%1
700
16th to endNight
24%14%30%22%6%
720
December1st to 15thNight
25%13%36%19%4
729
16th to endNight
28%12%36%19%2
960
Page generated at 2017-04-26 17:21:42. Version ac04

Copyright 2017 A. Danko


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