Shady Grove Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shady Grove Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
47%
24191
27%
74302
18%
24130
56%
24130
35%
42053

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
33%
949
28%
2458
11%
946
45%
946
35%
1521
January11th to 20thNight
28%
921
27%
2393
9%
921
40%
921
33%
1490
January21st to endNight
34%
990
33%
2574
13%
990
46%
990
38%
1541
February1st to 10thNight
30%
900
22%
2340
7%
900
38%
900
30%
1518
February11th to 20thNight
25%
753
21%
2148
7%
749
34%
749
26%
1356
February21st to endNight
24%
531
27%
1715
11%
531
39%
531
24%
1042
March1st to 10thNight
35%
540
25%
1980
16%
540
45%
540
25%
1129
March11th to 20thNight
32%
540
22%
1980
14%
540
44%
540
25%
1151
March21st to endNight
32%
594
23%
2178
14%
594
46%
594
25%
1262
April1st to 10thNight
30%
540
23%
1976
14%
540
44%
540
27%
1076
April11th to 20thNight
37%
533
26%
1775
19%
533
50%
533
30%
996
April21st to endNight
35%
540
24%
1700
15%
540
51%
540
31%
1004
May1st to 10thNight
42%
540
24%
1620
17%
540
53%
540
33%
965
May11th to 20thNight
50%
531
22%
1594
19%
531
58%
531
33%
958
May21st to endNight
55%
584
23%
1746
18%
582
65%
582
35%
1023
June1st to 10thNight
71%
540
24%
1620
24%
540
75%
540
46%
844
June11th to 20thNight
69%
540
26%
1620
26%
540
72%
540
49%
818
June21st to endNight
77%
540
29%
1620
28%
540
80%
540
58%
752
July1st to 10thNight
79%
525
22%
1575
24%
525
81%
525
41%
855
July11th to 20thNight
85%
522
28%
1566
32%
522
86%
522
59%
715
July21st to endNight
84%
591
29%
1673
36%
558
85%
558
50%
832
August1st to 10thNight
83%
537
27%
1601
32%
534
84%
534
47%
819
August11th to 20thNight
79%
534
33%
1600
38%
534
80%
534
46%
838
August21st to endNight
81%
594
27%
1935
32%
594
81%
594
46%
956
September1st to 10thNight
74%
540
28%
1934
34%
540
75%
540
38%
977
September11th to 20thNight
69%
540
27%
1980
30%
540
72%
540
32%
1071
September21st to endNight
69%
540
36%
1980
35%
540
75%
540
44%
918
October1st to 10thNight
63%
642
33%
2082
27%
642
68%
642
42%
1061
October11th to 20thNight
46%
720
33%
2160
17%
720
57%
720
39%
1179
October21st to endNight
44%
792
31%
2376
19%
792
53%
792
34%
1370
November1st to 10thNight
47%
740
33%
2220
18%
740
60%
740
42%
1191
November11th to 20thNight
43%
878
30%
2398
15%
878
53%
878
40%
1362
November21st to endNight
35%
950
29%
2470
14%
950
45%
950
36%
1504
December1st to 10thNight
36%
950
29%
2470
12%
950
46%
950
34%
1536
December11th to 20thNight
30%
949
28%
2883
11%
948
40%
948
26%
1795
December21st to endNight
28%
1041
17%
4362
9%
1026
40%
1026
20%
2628

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
12%5%25%43445%7%49%
74968
Night
11%5%24423447%55%
74831
TransparencyDay
35%6%11%24%20%5%
74693
Night
31%5%10%24%23%7%
74626
SeeingDay
13%7%22%28%22%7%
14214
Night
13%8%27%33%17%2
24197

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
11%8%36%323346%49%
1707
11th to 20thDay
12%7%35%333346%50%
1656
21st to endDay
15%7%24323447%50%
1782
February1st to 10thDay
17%9%35%5%24335%43%
1620
11th to 20thDay
15%8%35%5%33446%44%
1713
21st to endDay
19%9%35%323435%43%
1539
March1st to 10thDay
15%7%24434435%49%
1980
11th to 20thDay
18%8%35%5%3434443%
1980
21st to endDay
17%9%25%43445%7%40%
2178
April1st to 10thDay
11%5%24435%45%7%49%
1984
11th to 20thDay
16%6%24433446%47%
2134
21st to endDay
17%7%26%5%33446%42%
2256
May1st to 10thDay
15%6%35%5%3435%5%45%
2340
11th to 20thDay
13%6%35%6%345%5%7%42%
2302
21st to endDay
12%436%6%46%5%5%9%40%
2531
June1st to 10thDay
8%5%25%5%245%7%9%49%
2340
11th to 20thDay
7%425%5%345%7%9%49%
2340
21st to endDay
5%32343445%8%60%
2340
July1st to 10thDay
7%325%6%46%7%7%10%43%
2340
11th to 20thDay
421342446%10%58%
2340
21st to endDay
5%3245%35%6%7%9%51%
2546
August1st to 10thDay
4425%5%35%5%7%9%52%
2328
11th to 20thDay
9%425%5%35%45%8%50%
2301
21st to endDay
6%3245%35%5%6%9%52%
2418
September1st to 10thDay
11%42443445%6%54%
2022
11th to 20thDay
12%425%435%46%7%49%
1980
21st to endDay
8%31443445%6%58%
1980
October1st to 10thDay
7%425%5%3345%6%57%
1859
11th to 20thDay
12%41432322462%
1800
21st to endDay
17%6%2442324453%
1980
November1st to 10thDay
10%6%24313446%57%
1858
11th to 20thDay
11%5%24323345%61%
1778
21st to endDay
16%6%23213346%53%
1710
December1st to 10thDay
14%6%15%5%23446%50%
1710
11th to 20thDay
16%7%44434345%45%
2161
21st to endDay
17%9%25%6%35%446%39%
3135
January1st to 10thNight
12%5%245%34346%54%
2458
11th to 20thNight
14%6%24323346%53%
2393
21st to endNight
12%6%24423345%57%
2574
February1st to 10thNight
15%7%26%423345%48%
2340
11th to 20thNight
15%8%44422246%48%
2148
21st to endNight
15%9%35%323345%48%
1715
March1st to 10thNight
15%5%25%5%23447%48%
1980
11th to 20thNight
16%6%24423246%50%
1980
21st to endNight
14%5%25%434446%49%
2178
April1st to 10thNight
11%5%344235%5%7%52%
1976
11th to 20thNight
13%5%245%23346%53%
1775
21st to endNight
14%5%26%32435%7%50%
1700
May1st to 10thNight
11%5%235%245%5%9%49%
1620
11th to 20thNight
12%5%2443445%8%50%
1593
21st to endNight
8%4245%35%5%6%10%48%
1745
June1st to 10thNight
431442346%9%60%
1620
11th to 20thNight
6%21232346%9%61%
1620
21st to endNight
321222245%8%69%
1620
July1st to 10thNight
43245%35%5%7%12%51%
1620
11th to 20thNight
221232346%10%65%
1620
21st to endNight
32134245%6%10%59%
1772
August1st to 10thNight
2213335%6%6%9%59%
1611
11th to 20thNight
43244336%6%10%56%
1600
21st to endNight
32145%345%6%9%58%
1935
September1st to 10thNight
9%424323346%59%
1934
11th to 20thNight
10%4244245%6%6%52%
1980
21st to endNight
6%324323445%65%
1980
October1st to 10thNight
7%324423446%60%
2082
11th to 20thNight
12%41342333362%
2160
21st to endNight
17%42332322457%
2376
November1st to 10thNight
10%5%23322335%62%
2220
11th to 20thNight
8%5%23423345%61%
2398
21st to endNight
14%6%23313435%55%
2470
December1st to 10thNight
13%6%2442335%6%52%
2470
11th to 20thNight
14%6%35%423335%51%
3036
21st to endNight
16%8%25%424346%46%
4532

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
38%39%23%23%4
1708
11th to 20thDay
36%49%23%24%3
1656
21st to endDay
36%5%7%25%23%5%
1782
February1st to 10thDay
46%410%19%17%4
1620
11th to 20thDay
43%48%24%16%5%
1723
21st to endDay
46%36%16%21%8%
1539
March1st to 10thDay
39%48%20%18%12%
1980
11th to 20thDay
46%48%21%15%6%
1980
21st to endDay
44%5%10%24%14%3
2178
April1st to 10thDay
36%6%11%23%18%6%
1984
11th to 20thDay
39%412%23%17%5%
2134
21st to endDay
43%5%10%20%19%2
2256
May1st to 10thDay
41%5%11%22%18%3
2340
11th to 20thDay
40%7%13%25%14%1
2306
21st to endDay
40%8%14%23%13%1
2531
June1st to 10thDay
31%8%16%29%14%3
2340
11th to 20thDay
29%8%14%28%19%2
2340
21st to endDay
23%6%14%30%23%4
2340
July1st to 10thDay
33%9%18%25%14%1
2276
11th to 20thDay
20%6%15%32%24%3
2271
21st to endDay
25%9%16%34%15%
2405
August1st to 10thDay
27%8%15%27%20%2
2314
11th to 20thDay
31%6%14%25%21%3
2301
21st to endDay
26%7%16%29%17%4
2418
September1st to 10thDay
30%6%8%24%23%9%
2022
11th to 20thDay
33%7%11%22%20%7%
1980
21st to endDay
26%6%8%23%29%8%
1980
October1st to 10thDay
28%5%11%21%25%10%
1859
11th to 20thDay
28%37%18%31%13%
1800
21st to endDay
37%38%22%20%9%
1980
November1st to 10thDay
27%5%9%25%27%7%
1858
11th to 20thDay
28%38%26%26%9%
1778
21st to endDay
32%49%21%26%7%
1710
December1st to 10thDay
37%410%25%20%3
1710
11th to 20thDay
42%46%19%24%6%
2159
21st to endDay
46%7%8%19%18%3
3135
January1st to 10thNight
34%48%22%27%5%
2458
11th to 20thNight
35%48%23%24%6%
2393
21st to endNight
32%35%25%26%8%
2574
February1st to 10thNight
40%310%23%18%5%
2340
11th to 20thNight
40%47%24%20%6%
2148
21st to endNight
39%47%17%22%10%
1715
March1st to 10thNight
37%48%19%20%12%
1980
11th to 20thNight
38%411%21%19%7%
1980
21st to endNight
37%5%10%26%18%4
2178
April1st to 10thNight
32%6%11%21%20%11%
1976
11th to 20thNight
33%5%9%26%17%10%
1775
21st to endNight
35%5%9%26%23%2
1700
May1st to 10thNight
33%6%13%23%19%7%
1620
11th to 20thNight
34%6%13%29%16%2
1594
21st to endNight
30%7%17%28%15%2
1746
June1st to 10thNight
21%7%16%32%21%3
1620
11th to 20thNight
20%5%14%33%24%4
1620
21st to endNight
14%5%15%30%28%8%
1620
July1st to 10thNight
24%8%17%27%22%2
1575
11th to 20thNight
13%6%14%36%27%5%
1566
21st to endNight
18%6%16%34%24%1
1673
August1st to 10thNight
20%7%15%31%23%4
1601
11th to 20thNight
22%6%13%26%29%4
1600
21st to endNight
21%5%14%31%23%6%
1935
September1st to 10thNight
26%5%8%27%24%10%
1934
11th to 20thNight
30%6%10%20%24%9%
1980
21st to endNight
22%47%25%33%9%
1980
October1st to 10thNight
25%411%23%25%12%
2082
11th to 20thNight
29%35%17%30%16%
2160
21st to endNight
33%35%22%25%12%
2376
November1st to 10thNight
26%47%25%27%10%
2220
11th to 20thNight
28%48%22%29%10%
2398
21st to endNight
33%47%21%28%7%
2470
December1st to 10thNight
35%410%23%22%8%
2470
11th to 20thNight
38%47%20%24%7%
3037
21st to endNight
39%6%9%21%19%6%
4532

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
20%14%34%23%8%1
270
11th to 20thDay
22%19%34%20%5%
252
21st to endDay
17%14%39%21%8%1
264
February1st to 10thDay
26%12%33%21%8%
240
11th to 20thDay
24%18%36%18%4
240
21st to endDay
29%16%38%14%31
198
March1st to 10thDay
20%16%35%24%5%1
240
11th to 20thDay
26%15%34%18%6%2
240
21st to endDay
20%14%44%17%5%1
264
April1st to 10thDay
16%14%40%21%7%2
244
11th to 20thDay
22%11%33%28%7%
412
21st to endDay
20%13%34%23%8%2
516
May1st to 10thDay
15%8%36%30%11%1
603
11th to 20thDay
16%6%25%33%16%4
625
21st to endDay
12%5%27%28%21%7%
679
June1st to 10thDay
8%212%35%33%10%
630
11th to 20thDay
7%216%42%26%8%
630
21st to endDay
3218%37%32%9%
630
July1st to 10thDay
8%19%30%36%17%
621
11th to 20thDay
5%15%32%44%14%
618
21st to endDay
5%1427%44%19%
684
August1st to 10thDay
5%16%37%42%9%
626
11th to 20thDay
10%16%33%39%11%
615
21st to endDay
6%1427%40%22%
537
September1st to 10thDay
10%17%19%39%24%
312
11th to 20thDay
437%31%37%19%
270
21st to endDay
11%314%24%35%13%
270
October1st to 10thDay
6%324%34%21%11%
270
11th to 20thDay
11%6%33%32%16%2
270
21st to endDay
28%10%25%24%12%2
297
November1st to 10thDay
16%5%38%27%11%4
270
11th to 20thDay
15%9%33%31%10%2
270
21st to endDay
20%12%37%22%9%
270
December1st to 10thDay
14%16%31%28%10%1
270
11th to 20thDay
26%9%38%21%6%
270
21st to endDay
21%14%36%23%6%
297
January1st to 10thNight
15%12%35%30%7%
950
11th to 20thNight
16%15%37%28%4
921
21st to endNight
14%10%38%33%5%
990
February1st to 10thNight
20%12%34%29%5%
900
11th to 20thNight
21%15%37%24%3
753
21st to endNight
20%14%38%25%3
531
March1st to 10thNight
18%11%34%34%4
540
11th to 20thNight
19%10%36%30%5%
540
21st to endNight
14%12%38%28%7%
594
April1st to 10thNight
13%11%39%29%7%
540
11th to 20thNight
14%12%33%32%9%
533
21st to endNight
16%9%37%29%9%1
540
May1st to 10thNight
12%6%36%36%10%1
540
11th to 20thNight
13%426%40%16%2
531
21st to endNight
9%326%36%22%3
584
June1st to 10thNight
5%214%38%37%3
540
11th to 20thNight
6%118%50%24%1
540
21st to endNight
3114%46%31%6%
540
July1st to 10thNight
416%40%42%6%
525
11th to 20thNight
217%38%46%6%
522
21st to endNight
32439%46%6%
591
August1st to 10thNight
36%41%46%5%
537
11th to 20thNight
6%16%38%45%4
534
21st to endNight
415%35%48%6%
594
September1st to 10thNight
10%17%36%43%4
540
11th to 20thNight
12%110%36%37%5%
540
21st to endNight
8%116%37%33%6%
540
October1st to 10thNight
8%321%36%28%4
642
11th to 20thNight
15%6%29%37%14%
720
21st to endNight
19%7%27%32%14%1
792
November1st to 10thNight
13%5%33%36%13%1
740
11th to 20thNight
10%12%31%36%10%
878
21st to endNight
18%10%34%30%8%
950
December1st to 10thNight
16%12%32%33%7%
950
11th to 20thNight
21%10%34%30%5%
950
21st to endNight
18%12%38%27%5%
1045
Page generated at 2024-01-11 21:33:49. Version ac07

Copyright 2024 Attilla Danko


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