Shepherd University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shepherd University Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
38%
23406
13%
74702
8%
23360
45%
23360
13%
56515

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
20%
757
13%
2578
4%
757
32%
757
9%
1990
January11th to 20thNight
25%
732
12%
2378
5%
732
34%
732
9%
1883
January21st to endNight
22%
792
14%
2574
6%
792
32%
792
10%
1964
February1st to 10thNight
25%
720
13%
2340
5%
720
35%
720
10%
1786
February11th to 20thNight
17%
700
10%
2265
2%
700
28%
700
8%
1751
February21st to endNight
17%
592
13%
1776
4%
592
28%
592
9%
1419
March1st to 10thNight
23%
720
16%
1980
5%
720
35%
720
15%
1466
March11th to 20thNight
26%
720
14%
1980
7%
720
33%
720
12%
1536
March21st to endNight
23%
792
13%
2170
5%
792
30%
792
13%
1698
April1st to 10thNight
24%
720
10%
1800
2%
720
30%
720
13%
1451
April11th to 20thNight
34%
711
14%
1775
6%
711
37%
711
16%
1375
April21st to endNight
34%
716
14%
1796
5%
716
38%
716
17%
1398
May1st to 10thNight
41%
540
13%
1620
7%
540
45%
540
13%
1254
May11th to 20thNight
43%
446
13%
1507
9%
446
47%
446
11%
1176
May21st to endNight
53%
388
12%
1551
13%
388
56%
388
12%
1119
June1st to 10thNight
55%
360
14%
1440
14%
360
61%
360
15%
1006
June11th to 20thNight
54%
360
13%
1440
15%
360
57%
360
12%
1061
June21st to endNight
59%
360
13%
1440
12%
360
64%
360
14%
1021
July1st to 10thNight
60%
350
10%
1400
12%
350
62%
350
10%
1069
July11th to 20thNight
68%
445
10%
1489
9%
445
69%
445
14%
1109
July21st to endNight
68%
591
10%
1672
8%
558
71%
558
18%
1235
August1st to 10thNight
65%
537
12%
1600
9%
534
67%
534
16%
1226
August11th to 20thNight
61%
567
13%
1631
9%
567
63%
567
15%
1263
August21st to endNight
62%
792
9%
1980
5%
792
63%
792
16%
1596
September1st to 10thNight
57%
720
16%
1800
8%
720
60%
720
19%
1392
September11th to 20thNight
56%
720
21%
1806
16%
720
60%
720
21%
1361
September21st to endNight
48%
720
12%
2075
8%
720
52%
720
14%
1604
October1st to 10thNight
47%
720
13%
2160
11%
720
52%
720
16%
1628
October11th to 20thNight
42%
720
16%
2160
11%
720
51%
720
16%
1599
October21st to endNight
36%
792
18%
2376
11%
792
44%
792
15%
1772
November1st to 10thNight
42%
740
19%
2287
14%
740
49%
740
17%
1638
November11th to 20thNight
34%
760
16%
2546
11%
760
42%
760
12%
1902
November21st to endNight
33%
760
12%
2660
8%
760
41%
760
11%
2017
December1st to 10thNight
23%
760
13%
2660
4%
760
34%
760
9%
2037
December11th to 20thNight
27%
760
13%
3186
7%
759
35%
759
9%
2332
December21st to endNight
28%
826
8%
4804
4%
817
37%
817
6%
3381

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%6%35%5%35%5%6%8%41%
74667
Night
14%6%25%5%35%5%6%7%42%
75077
TransparencyDay
27%38%8%15%10%2
74378
Night
26%38%8%15%11%2
74885
SeeingDay
18%13%25%23%16%6%
13769
Night
17%11%27%31%12%1
23423

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
13%6%35%5%35%5%6%7%40%
1583
11th to 20thDay
14%8%46%5%35%5%5%8%37%
1644
21st to endDay
15%9%46%6%35%446%38%
1782
February1st to 10thDay
15%8%37%6%45%5%5%7%36%
1620
11th to 20thDay
15%7%37%6%45%35%6%39%
1582
21st to endDay
18%8%46%5%25%35%6%38%
1480
March1st to 10thDay
13%6%25%5%3445%7%46%
1978
11th to 20thDay
16%7%45%5%346%5%7%38%
1980
21st to endDay
18%7%36%6%35%45%6%37%
2186
April1st to 10thDay
13%6%36%6%45%46%8%39%
2160
11th to 20thDay
13%6%25%5%35%46%7%44%
2134
21st to endDay
19%6%25%5%345%5%6%40%
2178
May1st to 10thDay
16%6%35%5%35%6%5%9%36%
2340
11th to 20thDay
20%5%345%35%46%8%36%
2384
21st to endDay
14%6%26%5%345%7%9%40%
2725
June1st to 10thDay
12%425%5%345%7%10%43%
2520
11th to 20thDay
11%5%25%5%47%6%6%9%38%
2520
21st to endDay
10%315%5%35%5%6%11%44%
2520
July1st to 10thDay
8%435%6%46%6%7%9%42%
2520
11th to 20thDay
6%425%5%47%7%8%9%44%
2417
21st to endDay
9%6%36%6%46%6%7%10%38%
2547
August1st to 10thDay
8%6%26%6%46%7%8%9%37%
2327
11th to 20thDay
11%6%26%5%35%5%7%9%41%
2250
21st to endDay
10%425%6%35%6%7%8%42%
2376
September1st to 10thDay
16%5%2443445%8%44%
2160
11th to 20thDay
12%425%5%335%6%8%48%
2151
21st to endDay
18%6%35%5%345%5%7%39%
1883
October1st to 10thDay
17%425%434448%45%
1800
11th to 20thDay
16%425%435%45%6%46%
1800
21st to endDay
14%6%25%43445%5%48%
1980
November1st to 10thDay
12%5%25%43445%7%50%
1788
11th to 20thDay
16%5%2343445%7%46%
1630
21st to endDay
15%6%35%5%35%5%47%43%
1520
December1st to 10thDay
16%9%36%5%245%7%7%35%
1520
11th to 20thDay
17%435%5%35%5%5%7%39%
1910
21st to endDay
17%6%26%7%5%6%6%7%8%30%
2772
January1st to 10thNight
14%7%26%5%445%5%7%41%
2578
11th to 20thNight
17%7%36%5%345%6%6%37%
2378
21st to endNight
14%8%36%5%35%447%40%
2574
February1st to 10thNight
15%7%36%5%35%46%7%39%
2340
11th to 20thNight
16%8%35%5%35%45%6%39%
2263
21st to endNight
17%9%35%6%35%45%7%36%
1776
March1st to 10thNight
13%5%25%5%35%5%6%6%46%
1980
11th to 20thNight
17%7%2443445%7%42%
1980
21st to endNight
15%6%37%6%3445%6%40%
2170
April1st to 10thNight
15%6%46%6%45%6%6%5%38%
1800
11th to 20thNight
13%5%26%6%345%5%8%43%
1775
21st to endNight
19%4245%36%45%8%42%
1796
May1st to 10thNight
16%5%36%6%35%5%6%8%38%
1620
11th to 20thNight
16%6%36%5%25%46%8%38%
1507
21st to endNight
12%6%245%35%6%7%10%40%
1550
June1st to 10thNight
10%5%35%425%47%10%45%
1440
11th to 20thNight
10%5%35%5%46%6%6%9%40%
1440
21st to endNight
8%4246%35%6%7%10%44%
1440
July1st to 10thNight
9%6%25%6%5%5%6%7%9%40%
1440
11th to 20thNight
5%4345%45%6%8%8%47%
1538
21st to endNight
8%4145%27%6%10%11%41%
1771
August1st to 10thNight
8%427%6%46%6%7%9%41%
1611
11th to 20thNight
10%6%26%6%35%6%6%8%41%
1631
21st to endNight
10%6%25%5%35%5%7%8%43%
1980
September1st to 10thNight
14%6%25%5%35%5%5%6%45%
1800
11th to 20thNight
10%6%35%5%33347%51%
1806
21st to endNight
17%6%25%5%45%446%43%
2075
October1st to 10thNight
19%4245%34446%45%
2160
11th to 20thNight
13%5%25%42445%6%50%
2160
21st to endNight
17%5%2432445%7%48%
2376
November1st to 10thNight
11%5%2442336%6%53%
2287
11th to 20thNight
14%6%3443445%7%46%
2546
21st to endNight
14%5%245%345%6%8%44%
2660
December1st to 10thNight
16%8%36%6%345%5%7%38%
2660
11th to 20thNight
17%6%25%6%45%5%5%7%39%
3285
21st to endNight
16%7%35%5%46%6%7%9%32%
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
25%41%7%19%7%
1584
11th to 20thDay
28%42%9%13%8%
1644
21st to endDay
31%37%8%14%8%1
1782
February1st to 10thDay
29%37%8%17%8%1
1620
11th to 20thDay
31%37%7%16%8%2
1591
21st to endDay
31%37%8%12%10%2
1480
March1st to 10thDay
23%36%10%18%12%1
1978
11th to 20thDay
27%37%8%12%11%4
1980
21st to endDay
33%37%7%13%9%2
2186
April1st to 10thDay
25%38%10%13%12%3
2160
11th to 20thDay
26%36%7%13%13%4
2134
21st to endDay
28%38%6%14%11%3
2178
May1st to 10thDay
28%39%8%12%11%1
2340
11th to 20thDay
31%39%7%10%10%3
2388
21st to endDay
26%39%8%17%9%1
2725
June1st to 10thDay
22%39%10%16%11%1
2520
11th to 20thDay
27%39%11%14%8%1
2520
21st to endDay
21%40%10%18%10%1
2520
July1st to 10thDay
25%40%8%15%10%2
2450
11th to 20thDay
22%39%10%16%10%2
2343
21st to endDay
25%42%8%12%11%2
2405
August1st to 10thDay
25%40%11%16%8%
2314
11th to 20thDay
27%36%8%15%12%1
2250
21st to endDay
27%39%10%15%7%3
2376
September1st to 10thDay
25%38%6%12%14%4
2160
11th to 20thDay
22%37%7%17%14%2
2151
21st to endDay
29%37%6%13%13%1
1883
October1st to 10thDay
24%37%8%17%12%2
1800
11th to 20thDay
27%37%8%16%11%1
1800
21st to endDay
26%38%5%16%14%1
1980
November1st to 10thDay
17%40%8%19%13%2
1788
11th to 20thDay
26%40%8%13%11%3
1630
21st to endDay
26%41%8%16%9%1
1520
December1st to 10thDay
28%42%8%16%5%1
1520
11th to 20thDay
28%34%8%21%6%2
1906
21st to endDay
34%31%14%15%6%
2772
January1st to 10thNight
26%41%7%17%8%
2578
11th to 20thNight
28%42%9%14%7%
2378
21st to endNight
28%38%8%18%8%1
2574
February1st to 10thNight
28%37%7%16%11%1
2340
11th to 20thNight
30%37%8%14%9%2
2265
21st to endNight
32%38%7%12%8%3
1776
March1st to 10thNight
22%37%9%19%12%1
1980
11th to 20thNight
27%38%8%14%11%2
1980
21st to endNight
29%37%8%13%10%3
2170
April1st to 10thNight
31%37%7%10%12%3
1800
11th to 20thNight
26%37%7%12%14%5%
1775
21st to endNight
26%37%9%16%9%4
1796
May1st to 10thNight
27%39%8%14%9%3
1620
11th to 20thNight
29%39%8%11%12%2
1508
21st to endNight
22%40%12%15%9%1
1551
June1st to 10thNight
21%38%9%19%11%3
1440
11th to 20thNight
25%40%9%15%9%2
1440
21st to endNight
22%39%10%16%11%2
1440
July1st to 10thNight
26%43%9%13%7%3
1400
11th to 20thNight
23%41%10%13%11%2
1489
21st to endNight
18%42%13%15%11%1
1672
August1st to 10thNight
24%40%10%15%10%
1600
11th to 20thNight
28%37%8%14%11%2
1631
21st to endNight
28%40%9%13%8%2
1980
September1st to 10thNight
25%38%7%12%15%4
1800
11th to 20thNight
24%36%6%18%16%2
1806
21st to endNight
28%38%7%13%13%2
2075
October1st to 10thNight
26%37%6%17%12%2
2160
11th to 20thNight
23%38%8%17%13%2
2160
21st to endNight
24%38%6%17%15%1
2376
November1st to 10thNight
18%40%5%19%16%2
2287
11th to 20thNight
24%41%6%16%11%3
2546
21st to endNight
25%41%7%14%12%1
2660
December1st to 10thNight
27%41%6%18%8%1
2660
11th to 20thNight
30%34%7%15%12%2
3288
21st to endNight
33%31%14%15%7%
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
27%27%27%15%31
211
11th to 20thDay
26%29%27%14%4
248
21st to endDay
24%34%26%11%32
264
February1st to 10thDay
27%24%35%10%3
240
11th to 20thDay
32%27%31%8%1
249
21st to endDay
30%18%30%19%2
346
March1st to 10thDay
20%25%29%23%3
420
11th to 20thDay
23%22%30%17%7%1
420
21st to endDay
22%20%30%20%6%2
462
April1st to 10thDay
21%21%27%21%7%2
420
11th to 20thDay
17%14%33%16%15%5%
412
21st to endDay
27%15%28%19%10%2
420
May1st to 10thDay
24%17%25%19%11%3
423
11th to 20thDay
19%14%27%22%15%3
447
21st to endDay
16%8%21%26%21%9%
485
June1st to 10thDay
15%7%27%24%19%8%
450
11th to 20thDay
14%8%27%26%19%6%
450
21st to endDay
11%6%24%30%23%6%
450
July1st to 10thDay
9%418%27%29%13%
445
11th to 20thDay
6%418%27%32%12%
444
21st to endDay
11%419%31%25%10%
488
August1st to 10thDay
10%417%28%28%14%
446
11th to 20thDay
13%5%15%30%23%13%
439
21st to endDay
10%319%29%24%14%
495
September1st to 10thDay
18%5%16%25%23%12%
450
11th to 20thDay
12%419%30%23%11%
450
21st to endDay
22%9%21%24%19%5%
450
October1st to 10thDay
20%7%18%26%23%6%
450
11th to 20thDay
17%12%26%29%14%2
450
21st to endDay
17%15%31%25%10%2
495
November1st to 10thDay
17%12%28%25%15%3
422
11th to 20thDay
22%14%30%21%11%2
290
21st to endDay
20%17%34%21%7%2
180
December1st to 10thDay
23%21%33%18%41
180
11th to 20thDay
26%22%26%19%8%
180
21st to endDay
20%20%30%19%9%1
198
January1st to 10thNight
17%19%38%23%3
760
11th to 20thNight
22%15%31%28%4
732
21st to endNight
18%19%36%26%2
792
February1st to 10thNight
18%19%33%28%2
720
11th to 20thNight
23%21%33%22%1
703
21st to endNight
24%20%34%19%3
592
March1st to 10thNight
19%17%37%23%4
720
11th to 20thNight
24%19%29%23%6%
720
21st to endNight
20%14%37%24%41
792
April1st to 10thNight
19%19%33%24%5%
720
11th to 20thNight
16%12%33%28%10%
711
21st to endNight
20%12%29%30%7%1
716
May1st to 10thNight
20%7%26%33%13%
540
11th to 20thNight
19%6%24%40%11%1
446
21st to endNight
16%420%40%20%1
389
June1st to 10thNight
12%225%36%24%1
360
11th to 20thNight
11%6%21%41%20%2
360
21st to endNight
8%320%51%17%1
360
July1st to 10thNight
12%217%39%27%4
350
11th to 20thNight
8%211%40%34%4
445
21st to endNight
10%214%40%31%3
591
August1st to 10thNight
11%210%43%31%3
537
11th to 20thNight
12%313%39%30%4
567
21st to endNight
11%314%41%27%4
792
September1st to 10thNight
16%216%36%27%3
720
11th to 20thNight
12%418%35%27%3
720
21st to endNight
19%5%19%34%20%2
720
October1st to 10thNight
20%6%20%31%20%3
720
11th to 20thNight
15%11%27%34%12%1
720
21st to endNight
21%8%31%29%10%1
792
November1st to 10thNight
13%8%31%36%11%2
740
11th to 20thNight
18%15%28%31%8%1
760
21st to endNight
16%15%31%31%7%
760
December1st to 10thNight
22%14%34%23%7%
760
11th to 20thNight
19%11%37%29%4
760
21st to endNight
20%13%33%32%3
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