Concord Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Concord Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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
61%
23902
26%
80718
23%
23815
68%
23815
37%
43629

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
53%
751
19%
4249
17%
736
57%
736
16%
2312
January11th to 20thNight
55%
750
15%
4094
17%
740
62%
740
14%
2802
January21st to endNight
55%
829
14%
4458
23%
814
60%
814
14%
3086
February1st to 10thNight
53%
760
26%
2470
23%
760
61%
760
29%
1472
February11th to 20thNight
51%
740
25%
2311
20%
740
59%
740
30%
1352
February21st to endNight
51%
628
25%
1884
20%
628
59%
628
34%
1075
March1st to 10thNight
45%
760
17%
2144
13%
760
50%
760
25%
1418
March11th to 20thNight
48%
760
24%
2090
19%
760
54%
760
30%
1336
March21st to endNight
46%
820
20%
2214
11%
820
52%
820
33%
1368
April1st to 10thNight
49%
720
23%
1800
11%
720
55%
720
36%
1129
April11th to 20thNight
46%
711
29%
1779
11%
711
54%
711
42%
1039
April21st to endNight
54%
720
29%
1800
12%
720
61%
720
53%
963
May1st to 10thNight
59%
653
28%
1733
15%
653
65%
653
51%
897
May11th to 20thNight
65%
448
27%
1510
21%
448
72%
448
54%
646
May21st to endNight
56%
388
25%
1552
19%
388
69%
388
46%
623
June1st to 10thNight
60%
360
25%
1440
22%
360
72%
360
43%
617
June11th to 20thNight
67%
360
36%
1440
36%
360
79%
360
63%
483
June21st to endNight
70%
360
36%
1440
39%
360
80%
360
67%
464
July1st to 10thNight
74%
350
36%
1400
37%
350
86%
350
77%
424
July11th to 20thNight
80%
465
37%
1509
33%
465
85%
465
73%
563
July21st to endNight
77%
591
39%
1674
28%
558
84%
558
72%
673
August1st to 10thNight
69%
537
35%
1602
23%
534
76%
534
67%
676
August11th to 20thNight
76%
650
38%
1718
22%
650
80%
650
80%
733
August21st to endNight
80%
792
40%
1980
24%
792
83%
792
79%
892
September1st to 10thNight
79%
720
44%
1800
27%
720
84%
720
81%
804
September11th to 20thNight
73%
720
39%
1800
26%
720
80%
720
65%
902
September21st to endNight
77%
720
41%
2038
36%
720
83%
720
69%
886
October1st to 10thNight
71%
720
32%
2160
29%
720
80%
720
56%
991
October11th to 20thNight
71%
720
35%
2160
35%
720
78%
720
50%
1046
October21st to endNight
71%
792
37%
2376
37%
792
77%
792
52%
1148
November1st to 10thNight
67%
740
30%
2279
28%
740
73%
740
42%
1178
November11th to 20thNight
66%
760
27%
2470
27%
760
71%
760
36%
1349
November21st to endNight
63%
760
27%
2617
28%
760
69%
760
37%
1355
December1st to 10thNight
56%
760
22%
2660
20%
760
62%
760
27%
1570
December11th to 20thNight
52%
760
17%
3242
20%
759
56%
759
16%
2259
December21st to endNight
45%
827
13%
4825
16%
817
54%
817
12%
3098

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
7%424323347%61%
78915
Night
8%42442345%8%57%
81114
TransparencyDay
25%5%10%20%23%18%
78632
Night
28%5%12%21%20%15%
80918
SeeingDay
8%11%27%33%18%3
14475
Night
8%6%20%38%24%4
23942

By Month

Percentage Cloud Cover SW (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%7%37%7%35%5%6%6%36%
2645
11th to 20thDay
13%11%5%9%7%35%346%34%
2860
21st to endDay
18%9%37%6%35%5%6%6%31%
3146
February1st to 10thDay
13%6%35%5%345%5%7%45%
1710
11th to 20thDay
11%5%25%6%35%46%7%45%
1756
21st to endDay
11%5%245%4445%7%49%
1570
March1st to 10thDay
12%6%37%6%45%6%6%8%37%
2033
11th to 20thDay
11%6%36%6%35%5%6%8%42%
2090
21st to endDay
10%425%5%35%45%9%48%
2296
April1st to 10thDay
11%6%35%4345%5%8%46%
2160
11th to 20thDay
7%423323447%59%
2129
21st to endDay
432332345%9%64%
2160
May1st to 10thDay
421332345%7%66%
2222
11th to 20thDay
3212223348%69%
2381
21st to endDay
321322335%9%68%
2723
June1st to 10thDay
3212313449%67%
2520
11th to 20thDay
11111225%6%80%
2520
21st to endDay
2111111125%83%
2520
July1st to 10thDay
1111136%85%
2520
11th to 20thDay
11112237%83%
2395
21st to endDay
11112236%82%
2546
August1st to 10thDay
111212236%81%
2328
11th to 20thDay
1111336%84%
2183
21st to endDay
11111226%85%
2376
September1st to 10thDay
111111125%86%
2160
11th to 20thDay
211221235%8%74%
2160
21st to endDay
2212222236%79%
1917
October1st to 10thDay
2222223336%73%
1800
11th to 20thDay
421331335%6%69%
1800
21st to endDay
5%413323347%65%
1980
November1st to 10thDay
7%4234335%6%8%56%
1798
11th to 20thDay
8%5%35%5%26%5%5%7%50%
1710
21st to endDay
10%5%25%32336%6%55%
1559
December1st to 10thDay
11%7%35%5%345%5%7%46%
1520
11th to 20thDay
19%11%48%7%2445%5%31%
1928
21st to endDay
14%9%47%6%35%46%8%34%
2794
January1st to 10thNight
13%7%25%5%2445%7%45%
4299
11th to 20thNight
15%9%38%6%345%6%6%33%
4110
21st to endNight
17%8%37%6%45%5%5%7%33%
4521
February1st to 10thNight
13%5%245%3345%5%51%
2470
11th to 20thNight
10%425%435%46%8%49%
2309
21st to endNight
10%42442435%7%55%
1884
March1st to 10thNight
12%6%35%5%35%448%44%
2144
11th to 20thNight
12%5%25%5%345%5%8%46%
2090
21st to endNight
11%435%42335%7%53%
2214
April1st to 10thNight
7%425%5%3446%7%51%
1800
11th to 20thNight
6%42332335%7%62%
1779
21st to endNight
321332345%10%65%
1800
May1st to 10thNight
421323345%8%66%
1733
11th to 20thNight
211221335%11%67%
1510
21st to endNight
311121335%10%70%
1552
June1st to 10thNight
321242336%8%68%
1440
11th to 20thNight
11111335%82%
1440
21st to endNight
111112236%81%
1440
July1st to 10thNight
11133486%
1440
11th to 20thNight
1111112226%83%
1559
21st to endNight
11111245%11%73%
1773
August1st to 10thNight
211111125%11%73%
1611
11th to 20thNight
111225%11%76%
1718
21st to endNight
111111249%80%
1980
September1st to 10thNight
11112237%83%
1800
11th to 20thNight
221111235%10%72%
1800
21st to endNight
1111212247%79%
2038
October1st to 10thNight
3212322346%74%
2160
11th to 20thNight
3212323449%67%
2160
21st to endNight
5%21221336%7%67%
2376
November1st to 10thNight
5%32332445%9%59%
2279
11th to 20thNight
8%4243245%6%8%54%
2470
21st to endNight
8%41342345%7%59%
2617
December1st to 10thNight
11%6%25%44445%7%49%
2660
11th to 20thNight
19%7%37%6%45%5%7%7%32%
3276
21st to endNight
14%7%36%6%46%5%5%7%37%
4862

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
43%11%12%25%8%2
2645
11th to 20thDay
53%6%11%14%12%5%
2860
21st to endDay
52%7%10%15%13%3
3146
February1st to 10thDay
39%5%10%20%19%7%
1710
11th to 20thDay
38%6%10%18%22%6%
1765
21st to endDay
35%6%10%23%20%7%
1570
March1st to 10thDay
44%7%11%19%16%3
2033
11th to 20thDay
40%6%10%22%15%6%
2090
21st to endDay
35%7%16%20%18%4
2296
April1st to 10thDay
38%6%13%19%20%5%
2160
11th to 20thDay
26%5%14%24%23%7%
2132
21st to endDay
19%5%14%29%27%5%
2160
May1st to 10thDay
18%5%11%26%30%9%
2222
11th to 20thDay
16%412%28%30%10%
2384
21st to endDay
17%6%18%28%24%7%
2724
June1st to 10thDay
17%6%12%25%28%12%
2520
11th to 20thDay
7%310%23%33%23%
2520
21st to endDay
8%26%16%30%37%
2520
July1st to 10thDay
5%26%13%24%50%
2451
11th to 20thDay
7%29%16%20%46%
2322
21st to endDay
5%16%12%25%50%
2405
August1st to 10thDay
9%27%19%26%37%
2312
11th to 20thDay
5%17%14%31%41%
2183
21st to endDay
5%27%17%32%37%
2376
September1st to 10thDay
6%25%11%30%46%
2160
11th to 20thDay
13%310%23%33%19%
2160
21st to endDay
10%37%19%35%26%
1917
October1st to 10thDay
15%48%16%30%27%
1800
11th to 20thDay
18%5%10%20%23%25%
1800
21st to endDay
21%410%20%26%20%
1980
November1st to 10thDay
26%5%11%25%21%12%
1798
11th to 20thDay
33%7%10%23%22%6%
1710
21st to endDay
30%410%20%26%9%
1559
December1st to 10thDay
37%7%11%20%17%8%
1520
11th to 20thDay
55%6%8%13%14%3
1928
21st to endDay
46%8%14%18%11%2
2794
January1st to 10thNight
36%8%20%23%10%3
4299
11th to 20thNight
50%8%13%12%10%7%
4110
21st to endNight
51%7%11%13%12%5%
4521
February1st to 10thNight
36%5%9%20%20%10%
2470
11th to 20thNight
34%5%12%19%21%9%
2311
21st to endNight
31%5%12%28%19%5%
1884
March1st to 10thNight
40%7%14%17%17%5%
2144
11th to 20thNight
38%5%8%22%19%7%
2090
21st to endNight
33%6%15%21%18%6%
2214
April1st to 10thNight
33%5%16%19%20%7%
1800
11th to 20thNight
24%6%13%26%19%11%
1779
21st to endNight
17%6%14%31%25%7%
1800
May1st to 10thNight
18%6%13%22%30%12%
1733
11th to 20thNight
15%419%27%25%10%
1510
21st to endNight
13%7%24%26%23%7%
1552
June1st to 10thNight
17%7%14%24%26%12%
1440
11th to 20thNight
8%411%20%32%25%
1440
21st to endNight
8%17%24%26%33%
1440
July1st to 10thNight
5%26%20%23%45%
1400
11th to 20thNight
8%27%22%19%42%
1509
21st to endNight
9%27%26%20%37%
1674
August1st to 10thNight
12%111%24%23%29%
1602
11th to 20thNight
6%29%22%23%37%
1718
21st to endNight
7%29%25%25%32%
1980
September1st to 10thNight
5%36%16%25%45%
1800
11th to 20thNight
15%211%27%25%20%
1800
21st to endNight
10%38%22%28%29%
2038
October1st to 10thNight
14%5%10%20%23%28%
2160
11th to 20thNight
18%410%20%21%26%
2160
21st to endNight
19%39%22%24%23%
2376
November1st to 10thNight
24%5%12%26%17%15%
2279
11th to 20thNight
29%5%11%25%22%8%
2470
21st to endNight
27%5%11%19%26%12%
2617
December1st to 10thNight
36%6%11%19%17%12%
2660
11th to 20thNight
51%6%10%13%16%3
3276
21st to endNight
46%10%14%15%12%4
4862

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
24%13%28%21%14%1
247
11th to 20thDay
17%10%22%33%15%3
370
21st to endDay
14%10%23%28%23%3
407
February1st to 10thDay
17%14%20%28%18%3
370
11th to 20thDay
16%19%25%23%16%2
409
21st to endDay
14%14%27%29%13%2
382
March1st to 10thDay
17%18%30%22%10%2
460
11th to 20thDay
17%17%26%21%15%4
460
21st to endDay
13%20%32%24%10%1
491
April1st to 10thDay
14%18%30%23%12%2
420
11th to 20thDay
13%19%34%21%9%4
412
21st to endDay
5%23%28%27%13%5%
420
May1st to 10thDay
7%17%35%28%13%1
423
11th to 20thDay
6%15%38%25%15%1
448
21st to endDay
5%13%30%37%13%2
485
June1st to 10thDay
414%34%30%15%3
450
11th to 20thDay
212%34%40%11%1
450
21st to endDay
17%33%41%16%2
450
July1st to 10thDay
431%49%15%
446
11th to 20thDay
227%50%19%2
444
21st to endDay
1130%46%19%4
487
August1st to 10thDay
26%30%43%17%3
447
11th to 20thDay
328%44%19%6%
437
21st to endDay
223%47%23%3
495
September1st to 10thDay
1420%45%23%6%
450
11th to 20thDay
38%27%39%17%6%
450
21st to endDay
28%25%35%25%6%
450
October1st to 10thDay
37%29%29%26%6%
450
11th to 20thDay
5%9%21%28%29%8%
450
21st to endDay
8%8%21%31%26%6%
495
November1st to 10thDay
8%12%19%25%29%7%
394
11th to 20thDay
6%10%19%32%26%8%
270
21st to endDay
10%8%25%33%24%1
198
December1st to 10thDay
14%14%22%24%19%6%
180
11th to 20thDay
18%11%23%24%22%2
180
21st to endDay
19%12%28%24%16%2
198
January1st to 10thNight
16%5%18%33%22%6%
760
11th to 20thNight
14%6%16%36%23%6%
760
21st to endNight
16%6%15%35%23%4
836
February1st to 10thNight
16%7%17%34%22%4
760
11th to 20thNight
12%10%20%33%20%5%
744
21st to endNight
12%10%22%34%19%2
628
March1st to 10thNight
18%9%21%30%20%3
760
11th to 20thNight
13%11%21%33%19%3
760
21st to endNight
11%10%28%34%15%2
820
April1st to 10thNight
9%9%27%36%17%2
720
11th to 20thNight
7%13%30%30%17%3
711
21st to endNight
49%30%35%20%2
720
May1st to 10thNight
47%27%41%18%3
653
11th to 20thNight
35%24%45%22%1
448
21st to endNight
37%32%41%16%1
389
June1st to 10thNight
3429%49%13%1
360
11th to 20thNight
1425%53%16%1
360
21st to endNight
325%49%22%1
360
July1st to 10thNight
124%53%22%
350
11th to 20thNight
1117%52%25%4
465
21st to endNight
1118%45%32%2
591
August1st to 10thNight
3124%41%28%3
537
11th to 20thNight
122%48%27%2
650
21st to endNight
1116%49%30%3
792
September1st to 10thNight
1118%43%32%5%
720
11th to 20thNight
2320%44%27%4
720
21st to endNight
1316%41%33%6%
720
October1st to 10thNight
4419%37%31%6%
720
11th to 20thNight
45%16%38%31%6%
720
21st to endNight
6%5%14%35%31%10%
792
November1st to 10thNight
6%417%33%32%8%
740
11th to 20thNight
9%217%38%29%6%
760
21st to endNight
10%416%35%28%7%
760
December1st to 10thNight
12%7%17%35%24%5%
760
11th to 20thNight
19%7%13%35%22%3
760
21st to endNight
17%8%20%32%20%2
836
Page generated at 2024-03-24 20:37:03. Version ac07

Copyright © 2024 Attilla Danko.


Concord Observatory Clear Sky Chart |Charts Home