Concord Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Concord Observatory clear sky chart from 2005-11-05 to 2017-04-26.

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
65%
14938
27%
45642
23%
14902
70%
14902
41%
24358

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
61%
716
18%
2401
17%
716
64%
716
29%
1422
January16th to endNight
60%
768
24%
2496
25%
768
63%
768
29%
1510
February1st to 15thNight
55%
698
23%
2288
22%
698
61%
698
26%
1410
February16th to endNight
52%
632
24%
1896
19%
632
59%
632
29%
1171
March1st to 15thNight
52%
720
18%
2015
15%
720
56%
720
28%
1300
March16th to endNight
50%
768
21%
2083
14%
768
56%
768
32%
1320
April1st to 15thNight
49%
719
23%
1799
11%
719
55%
719
34%
1154
April16th to endNight
57%
704
25%
1760
12%
704
61%
704
47%
994
May1st to 15thNight
69%
563
27%
1553
17%
563
74%
563
58%
747
May16th to endNight
64%
344
24%
1370
21%
344
72%
344
48%
550
June1st to 15thNight
67%
330
26%
1320
27%
330
77%
330
46%
540
June16th to endNight
79%
330
34%
1320
42%
330
84%
330
69%
433
July1st to 15thNight
86%
327
36%
1257
42%
327
92%
327
74%
404
July16th to endNight
86%
522
34%
1467
30%
489
88%
489
66%
615
August1st to 15thNight
80%
509
36%
1492
28%
506
83%
506
73%
615
August16th to endNight
85%
700
38%
1750
24%
700
86%
700
79%
795
September1st to 15thNight
87%
660
41%
1650
29%
660
89%
660
76%
762
September16th to endNight
82%
656
39%
1795
34%
656
85%
656
66%
832
October1st to 15thNight
71%
660
31%
1980
29%
660
79%
660
48%
981
October16th to endNight
72%
704
33%
2112
34%
704
77%
704
47%
1077
November1st to 15thNight
68%
700
28%
2197
27%
700
74%
700
41%
1144
November16th to endNight
64%
720
25%
2433
26%
720
67%
720
33%
1340
December1st to 15thNight
54%
720
20%
2520
18%
720
60%
720
24%
1569
December16th to endNight
49%
768
20%
2688
17%
768
56%
768
23%
1673

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
6%313313347%61%
46017
Night
7%31332335%7%58%
45828
TransparencyDay
24%410%19%24%16%
45702
Night
26%411%20%21%15%
45643
SeeingDay
9%11%28%33%15%3
5416
Night
8%416%37%27%5%
14950

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 15thDay
16%5%345%2435%7%42%
1534
16th to endDay
15%7%16%425%335%44%
1728
February1st to 15thDay
14%6%25%4245%5%6%41%
1576
16th to endDay
14%5%245%3336%7%40%
1576
March1st to 15thDay
12%5%25%5%25%5%6%9%38%
1944
16th to endDay
10%435%5%35%5%5%7%43%
2139
April1st to 15thDay
12%5%2433445%7%44%
2149
16th to endDay
5%313223438%61%
2111
May1st to 15thDay
3112112447%68%
2064
16th to endDay
4113212348%65%
2389
June1st to 15thDay
2212213348%67%
2310
16th to endDay
11111136%80%
2310
July1st to 15thDay
111225%83%
2289
16th to endDay
112136%81%
2286
August1st to 15thDay
11126%83%
2129
16th to endDay
111226%83%
2100
September1st to 15thDay
1111126%82%
1980
16th to endDay
211212336%74%
1832
October1st to 15thDay
3222213346%67%
1650
16th to endDay
7%313313246%62%
1760
November1st to 15thDay
8%4234235%5%8%52%
1660
16th to endDay
11%6%34424345%48%
1525
December1st to 15thDay
14%9%26%5%23435%42%
1440
16th to endDay
17%7%335%23347%40%
1536
January1st to 15thNight
12%5%243235%5%9%45%
2401
16th to endNight
14%42342445%6%48%
2496
February1st to 15thNight
14%5%245%3345%5%45%
2276
16th to endNight
13%42442445%7%47%
1896
March1st to 15thNight
12%5%34424448%45%
2015
16th to endNight
11%43432345%6%50%
2083
April1st to 15thNight
8%4245%2446%7%50%
1799
16th to endNight
5%213313348%62%
1760
May1st to 15thNight
2112222348%68%
1553
16th to endNight
21211335%10%67%
1370
June1st to 15thNight
21221245%7%69%
1320
16th to endNight
111235%81%
1320
July1st to 15thNight
111225%83%
1338
16th to endNight
1111123411%71%
1575
August1st to 15thNight
111125%13%72%
1501
16th to endNight
1125%10%75%
1750
September1st to 15thNight
1111238%78%
1650
16th to endNight
1111225%8%74%
1795
October1st to 15thNight
3212322447%65%
1980
16th to endNight
5%21231335%7%62%
2112
November1st to 15thNight
7%312213449%57%
2197
16th to endNight
8%423424346%54%
2433
December1st to 15thNight
14%5%24434447%44%
2520
16th to endNight
17%5%24423446%44%
2688

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
40%6%13%15%18%4
1534
16th to endDay
43%5%9%12%20%9%
1728
February1st to 15thDay
42%5%9%19%19%3
1576
16th to endDay
42%6%10%23%13%3
1576
March1st to 15thDay
41%6%11%19%15%5%
1944
16th to endDay
40%6%13%18%17%3
2139
April1st to 15thDay
39%5%13%19%18%3
2149
16th to endDay
22%5%14%26%24%7%
2111
May1st to 15thDay
16%410%26%32%10%
2064
16th to endDay
19%5%16%26%23%8%
2393
June1st to 15thDay
17%5%13%21%23%18%
2310
16th to endDay
8%17%17%34%30%
2310
July1st to 15thDay
6%17%12%25%46%
2141
16th to endDay
6%18%13%24%45%
2131
August1st to 15thDay
7%7%16%27%40%
2113
16th to endDay
6%17%15%37%31%
2100
September1st to 15thDay
7%16%15%33%35%
1980
16th to endDay
13%36%21%33%21%
1832
October1st to 15thDay
19%5%9%20%27%18%
1650
16th to endDay
24%310%23%25%12%
1760
November1st to 15thDay
30%6%12%27%15%7%
1660
16th to endDay
37%5%9%21%21%4
1525
December1st to 15thDay
44%5%9%19%17%3
1440
16th to endDay
43%5%13%18%15%4
1536
January1st to 15thNight
35%5%14%20%16%8%
2401
16th to endNight
36%6%10%15%17%14%
2496
February1st to 15thNight
39%5%10%20%17%7%
2288
16th to endNight
36%5%13%25%15%2
1896
March1st to 15thNight
38%6%12%20%15%6%
2015
16th to endNight
35%6%12%19%19%6%
2083
April1st to 15thNight
33%6%15%20%18%5%
1799
16th to endNight
21%5%13%26%22%9%
1760
May1st to 15thNight
15%416%19%29%14%
1554
16th to endNight
14%5%20%27%23%8%
1370
June1st to 15thNight
15%5%15%20%22%20%
1320
16th to endNight
8%17%16%31%34%
1320
July1st to 15thNight
7%15%15%24%46%
1257
16th to endNight
11%28%22%19%36%
1467
August1st to 15thNight
10%11%19%24%33%
1492
16th to endNight
7%19%21%27%32%
1750
September1st to 15thNight
8%17%16%26%38%
1650
16th to endNight
12%27%23%28%25%
1795
October1st to 15thNight
19%5%9%22%23%19%
1980
16th to endNight
22%310%22%23%16%
2112
November1st to 15thNight
25%413%30%16%9%
2197
16th to endNight
31%410%21%24%8%
2433
December1st to 15thNight
40%5%10%17%19%6%
2520
16th to endNight
40%5%12%15%18%6%
2688

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%9%24%29%12%3
162
16th to endDay
17%10%19%25%22%4
256
February1st to 15thDay
21%10%20%24%20%2
236
16th to endDay
20%14%20%27%15%2
237
March1st to 15thDay
17%15%27%19%15%4
270
16th to endDay
12%21%31%22%10%2
288
April1st to 15thDay
16%21%29%20%9%1
269
16th to endDay
9%25%28%24%9%2
254
May1st to 15thDay
7%15%41%25%9%
228
16th to endDay
7%13%27%39%10%
266
June1st to 15thDay
414%41%32%41
255
16th to endDay
16%33%43%13%1
255
July1st to 15thDay
134%52%11%
245
16th to endDay
1128%51%15%2
271
August1st to 15thDay
15%32%43%16%1
255
16th to endDay
228%51%13%2
268
September1st to 15thDay
2318%49%20%6%
255
16th to endDay
37%25%32%20%10%
255
October1st to 15thDay
5%10%25%32%18%7%
255
16th to endDay
11%8%27%27%21%4
272
November1st to 15thDay
7%9%19%20%33%9%
166
16th to endDay
8%12%27%35%17%
74
December1st to 15thDay
21%20%30%18%10%
60
16th to endDay
12%15%26%17%26%1
64
January1st to 15thNight
14%313%32%28%7%
720
16th to endNight
16%413%32%25%8%
768
February1st to 15thNight
15%5%14%33%24%6%
704
16th to endNight
14%7%18%31%21%4
632
March1st to 15thNight
15%8%16%29%26%4
720
16th to endNight
12%7%23%35%18%2
768
April1st to 15thNight
8%10%25%34%18%2
719
16th to endNight
6%9%23%35%21%3
704
May1st to 15thNight
3220%47%22%3
564
16th to endNight
3326%42%22%
345
June1st to 15thNight
1224%55%15%
330
16th to endNight
18%53%26%
330
July1st to 15thNight
111%53%32%1
327
16th to endNight
18%46%38%4
522
August1st to 15thNight
115%43%35%3
509
16th to endNight
12%48%34%3
700
September1st to 15thNight
19%42%39%6%
660
16th to endNight
1112%38%37%8%
656
October1st to 15thNight
4414%38%30%7%
660
16th to endNight
6%312%34%31%11%
704
November1st to 15thNight
7%116%32%33%8%
700
16th to endNight
9%414%32%29%8%
720
December1st to 15thNight
15%5%14%34%22%6%
720
16th to endNight
17%6%17%32%22%1
768
Page generated at 2017-04-27 14:48:58. Version ac04

Copyright 2017 A. Danko


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