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 2018-03-21.

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%
16416
15%
49242
10%
16376
41%
16376
20%
34356

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
19%
973
10%
2716
4%
970
23%
970
13%
2142
January16th to endNight
19%
919
9%
2791
4%
919
25%
919
11%
2196
February1st to 15thNight
17%
761
9%
2462
2%
761
24%
761
11%
1905
February16th to endNight
20%
683
14%
2049
6%
683
28%
683
14%
1529
March1st to 15thNight
26%
780
15%
2245
9%
780
32%
780
18%
1632
March16th to endNight
34%
792
19%
2178
10%
792
41%
792
21%
1539
April1st to 15thNight
29%
596
14%
1811
8%
596
35%
596
19%
1268
April16th to endNight
35%
540
19%
1620
8%
540
44%
540
25%
1057
May1st to 15thNight
38%
540
14%
1620
9%
540
43%
540
23%
1110
May16th to endNight
51%
562
15%
1684
12%
561
56%
561
28%
1053
June1st to 15thNight
56%
408
16%
1309
14%
408
62%
408
29%
792
June16th to endNight
59%
429
17%
1329
16%
429
64%
429
31%
808
July1st to 15thNight
62%
510
16%
1360
13%
510
65%
510
39%
810
July16th to endNight
67%
564
18%
1508
15%
531
70%
531
39%
884
August1st to 15thNight
64%
539
19%
1609
15%
536
67%
536
34%
973
August16th to endNight
63%
573
23%
1726
17%
573
67%
573
36%
1004
September1st to 15thNight
58%
672
23%
1932
18%
672
61%
672
33%
1169
September16th to endNight
59%
717
24%
1980
18%
717
63%
717
35%
1209
October1st to 15thNight
45%
720
18%
2076
14%
720
50%
720
26%
1394
October16th to endNight
25%
768
15%
2400
9%
768
33%
768
16%
1732
November1st to 15thNight
35%
760
18%
2471
15%
760
41%
760
21%
1623
November16th to endNight
25%
780
14%
2617
9%
780
31%
780
15%
1882
December1st to 15thNight
17%
790
8%
2740
3%
790
23%
790
10%
2113
December16th to endNight
13%
1040
7%
3009
2%
1040
18%
1040
8%
2532

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%32%
49588
Night
15%8%36%5%34446%35%
49421
Cloud CoverDay
13%8%47%6%35%5%5%7%32%
49598
Night
14%8%36%5%3445%6%35%
49425
TransparencyDay
49%7%12%18%10%1
49285
Night
48%6%12%20%11%1
49242
SeeingDay
16%8%28%23%14%7%
6401
Night
18%9%29%29%11%1
16422

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%45%445%17%
1552
16th to endDay
14%18%9%11%6%45%445%15%
1784
February1st to 15thDay
15%14%6%10%8%45%5%45%17%
1728
16th to endDay
14%13%6%11%8%35%446%21%
1710
March1st to 15thDay
16%11%5%7%6%36%45%6%26%
2033
16th to endDay
16%9%6%7%7%45%336%29%
2174
April1st to 15thDay
19%9%5%6%5%24446%30%
2146
16th to endDay
16%8%36%5%3345%7%36%
2340
May1st to 15thDay
18%8%45%6%35%446%32%
2331
16th to endDay
14%6%35%6%3445%8%38%
2431
June1st to 15thDay
10%6%25%5%35%5%5%9%39%
2643
16th to endDay
9%5%26%6%36%7%7%9%34%
2625
July1st to 15thDay
7%5%25%5%36%6%6%9%42%
2520
16th to endDay
7%6%25%6%46%6%7%10%36%
2556
August1st to 15thDay
9%5%26%7%45%7%7%8%36%
2340
16th to endDay
10%6%26%6%35%5%6%8%39%
2474
September1st to 15thDay
12%6%25%5%35%46%8%39%
2016
16th to endDay
12%5%25%5%35%47%8%39%
1980
October1st to 15thDay
15%9%25%5%335%5%6%38%
1884
16th to endDay
21%8%46%5%34436%31%
1824
November1st to 15thDay
15%7%37%6%25%447%34%
1717
16th to endDay
17%11%47%7%35%435%28%
1670
December1st to 15thDay
15%13%7%11%5%3445%5%21%
1547
16th to endDay
21%15%8%9%7%3434416%
1563
January1st to 15thNight
21%11%5%8%6%4444425%
2716
16th to endNight
13%12%7%11%7%35%5%46%21%
2791
February1st to 15thNight
15%14%5%9%7%34445%26%
2460
16th to endNight
16%12%48%7%34446%27%
2049
March1st to 15thNight
17%8%47%5%25%35%5%33%
2233
16th to endNight
14%7%36%5%345%46%36%
2178
April1st to 15thNight
18%8%35%5%3445%6%33%
1811
16th to endNight
15%6%25%5%2445%7%40%
1620
May1st to 15thNight
17%7%26%4245%5%8%35%
1620
16th to endNight
12%5%3442445%8%45%
1682
June1st to 15thNight
8%434425%46%8%45%
1309
16th to endNight
10%42442447%8%45%
1329
July1st to 15thNight
8%323424448%53%
1440
16th to endNight
44244345%6%10%51%
1612
August1st to 15thNight
5%3145%35%5%6%9%47%
1620
16th to endNight
10%5%13423448%51%
1726
September1st to 15thNight
11%42433435%5%50%
1932
16th to endNight
11%42442445%7%48%
1980
October1st to 15thNight
16%6%25%42445%6%41%
2076
16th to endNight
20%9%25%6%245%45%32%
2400
November1st to 15thNight
15%8%35%4245%5%6%38%
2471
16th to endNight
20%10%37%5%2445%6%29%
2617
December1st to 15thNight
18%13%6%8%5%25%435%23%
2740
16th to endNight
20%17%6%9%6%34345%17%
3009

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%45%35%5%18%
1552
16th to endDay
14%16%8%11%7%45%5%45%15%
1784
February1st to 15thDay
14%14%6%10%9%45%5%5%5%17%
1728
16th to endDay
13%13%6%10%8%45%445%22%
1710
March1st to 15thDay
16%11%5%7%6%36%45%6%26%
2044
16th to endDay
16%10%5%8%7%44445%29%
2173
April1st to 15thDay
18%10%46%5%34446%30%
2146
16th to endDay
16%8%26%5%33447%36%
2340
May1st to 15thDay
18%7%46%5%345%45%32%
2331
16th to endDay
13%6%25%5%35%45%8%39%
2431
June1st to 15thDay
10%5%26%445%6%5%9%39%
2643
16th to endDay
8%5%36%6%47%6%7%10%34%
2625
July1st to 15thDay
7%425%5%36%5%6%9%42%
2520
16th to endDay
7%5%26%5%37%6%8%10%36%
2556
August1st to 15thDay
8%5%16%6%46%6%6%8%37%
2340
16th to endDay
10%5%35%5%35%5%6%8%39%
2474
September1st to 15thDay
12%5%25%5%35%5%6%8%39%
2016
16th to endDay
12%6%15%5%35%5%7%8%39%
1980
October1st to 15thDay
14%8%25%5%3445%6%38%
1884
16th to endDay
20%10%36%6%34445%31%
1824
November1st to 15thDay
15%7%37%5%35%447%35%
1717
16th to endDay
15%11%5%7%7%3445%5%28%
1670
December1st to 15thDay
15%12%7%11%6%35%446%22%
1547
16th to endDay
20%15%7%9%8%34335%17%
1563
January1st to 15thNight
21%10%5%7%6%35%445%25%
2716
16th to endNight
12%11%7%10%8%35%5%46%22%
2791
February1st to 15thNight
13%14%5%8%8%35%44426%
2453
16th to endNight
16%11%49%6%34436%28%
2049
March1st to 15thNight
16%9%48%5%25%345%33%
2245
16th to endNight
15%7%35%5%26%5%46%36%
2178
April1st to 15thNight
19%8%25%5%24447%33%
1811
16th to endNight
14%7%245%3445%7%40%
1620
May1st to 15thNight
17%6%25%5%2445%7%36%
1619
16th to endNight
11%4244245%48%44%
1682
June1st to 15thNight
9%434435%5%6%8%45%
1309
16th to endNight
10%5%2433446%8%45%
1329
July1st to 15thNight
7%42442435%7%53%
1440
16th to endNight
43234345%6%10%51%
1612
August1st to 15thNight
44245%345%7%9%47%
1620
16th to endNight
9%5%1442335%7%51%
1726
September1st to 15thNight
10%424424446%50%
1932
16th to endNight
11%415%42435%7%48%
1980
October1st to 15thNight
16%6%245%3345%6%41%
2076
16th to endNight
19%8%27%5%34445%32%
2400
November1st to 15thNight
14%7%25%5%3445%6%39%
2471
16th to endNight
19%10%46%5%34446%29%
2617
December1st to 15thNight
19%12%6%8%5%34445%24%
2740
16th to endNight
20%16%6%9%6%34445%18%
3009

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
67%5%9%10%5%
1553
16th to endDay
70%5%10%9%3
1784
February1st to 15thDay
66%7%8%12%5%
1730
16th to endDay
62%5%9%14%6%1
1710
March1st to 15thDay
57%6%11%16%6%
2044
16th to endDay
56%5%10%18%7%1
2174
April1st to 15thDay
53%6%9%19%10%
2146
16th to endDay
47%5%14%16%14%2
2340
May1st to 15thDay
51%7%11%18%9%2
2331
16th to endDay
43%5%13%22%12%2
2435
June1st to 15thDay
39%8%13%22%13%1
2643
16th to endDay
42%8%13%19%14%1
2625
July1st to 15thDay
36%7%11%24%17%2
2371
16th to endDay
38%10%14%19%13%2
2397
August1st to 15thDay
40%9%12%22%11%1
2327
16th to endDay
39%9%11%23%13%1
2474
September1st to 15thDay
40%7%14%24%12%
2016
16th to endDay
39%6%12%28%11%
1980
October1st to 15thDay
44%6%13%21%12%1
1884
16th to endDay
54%5%15%17%7%
1824
November1st to 15thDay
48%5%12%21%9%1
1717
16th to endDay
56%6%13%16%6%
1670
December1st to 15thDay
62%6%12%13%4
1547
16th to endDay
70%5%11%9%3
1563
January1st to 15thNight
61%5%11%13%7%
2716
16th to endNight
61%7%13%13%4
2791
February1st to 15thNight
60%6%10%14%7%
2462
16th to endNight
57%411%18%7%
2049
March1st to 15thNight
52%6%9%19%11%1
2245
16th to endNight
47%6%11%22%10%1
2178
April1st to 15thNight
50%411%19%13%
1811
16th to endNight
41%5%12%18%17%3
1620
May1st to 15thNight
46%5%12%20%12%2
1620
16th to endNight
36%7%13%23%15%3
1684
June1st to 15thNight
34%8%13%27%15%1
1309
16th to endNight
33%7%14%24%18%1
1329
July1st to 15thNight
29%6%10%29%22%2
1360
16th to endNight
27%8%17%24%20%2
1508
August1st to 15thNight
29%10%13%30%14%2
1609
16th to endNight
31%5%13%29%17%2
1726
September1st to 15thNight
33%5%12%28%18%1
1932
16th to endNight
34%414%30%15%
1980
October1st to 15thNight
42%6%11%21%17%1
2076
16th to endNight
52%6%12%20%7%
2400
November1st to 15thNight
44%6%13%23%11%1
2471
16th to endNight
54%5%14%18%6%
2617
December1st to 15thNight
61%6%12%13%5%
2740
16th to endNight
68%6%10%10%4
3009

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
20%19%42%14%21
135
16th to endDay
29%11%45%12%2
144
February1st to 15thDay
25%17%41%14%
135
16th to endDay
25%15%42%15%2
120
March1st to 15thDay
27%11%32%20%6%
229
16th to endDay
21%9%33%25%8%2
311
April1st to 15thDay
20%12%32%22%9%2
270
16th to endDay
21%10%31%17%12%7%
270
May1st to 15thDay
25%7%26%23%13%3
288
16th to endDay
20%6%26%22%16%7%
331
June1st to 15thDay
12%5%34%27%15%4
492
16th to endDay
11%7%31%27%15%5%
495
July1st to 15thDay
10%424%31%19%10%
475
16th to endDay
7%325%31%21%10%
416
August1st to 15thDay
9%318%27%23%18%
313
16th to endDay
14%5%16%23%20%19%
332
September1st to 15thDay
10%5%20%19%26%17%
315
16th to endDay
14%415%22%29%14%
314
October1st to 15thDay
17%7%26%22%19%7%
315
16th to endDay
22%11%34%25%41
240
November1st to 15thDay
17%13%34%20%12%2
135
16th to endDay
19%22%37%16%4
115
December1st to 15thDay
22%26%31%15%4
90
16th to endDay
23%25%39%9%
121
January1st to 15thNight
24%13%36%20%41
975
16th to endNight
18%11%38%26%5%
919
February1st to 15thNight
21%14%37%22%2
764
16th to endNight
22%12%35%24%3
683
March1st to 15thNight
20%11%35%26%5%
780
16th to endNight
16%11%31%29%9%1
792
April1st to 15thNight
21%12%31%28%4
596
16th to endNight
17%8%35%27%9%1
540
May1st to 15thNight
20%428%35%9%1
540
16th to endNight
13%323%39%17%2
563
June1st to 15thNight
9%225%48%12%
408
16th to endNight
10%223%47%16%
429
July1st to 15thNight
9%120%40%25%3
510
16th to endNight
4119%48%22%3
564
August1st to 15thNight
6%119%39%28%4
539
16th to endNight
11%217%32%31%4
573
September1st to 15thNight
11%419%31%24%6%
672
16th to endNight
13%319%31%26%6%
717
October1st to 15thNight
18%7%23%30%17%2
720
16th to endNight
23%12%33%24%5%
768
November1st to 15thNight
19%10%29%26%13%1
760
16th to endNight
23%14%32%22%6%
780
December1st to 15thNight
24%13%36%19%5%
790
16th to endNight
28%12%37%18%2
1040
Page generated at 2018-03-22 11:34:26. Version ac04

Copyright 2018 A. Danko


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