CBA Concord Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CBA Concord Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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%
15468
27%
47240
23%
15432
70%
15432
42%
24973

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
60%
716
18%
2396
17%
716
64%
716
29%
1419
January16th to endNight
59%
768
24%
2496
25%
768
62%
768
29%
1510
February1st to 15thNight
55%
698
23%
2288
22%
698
61%
698
26%
1410
February16th to endNight
52%
632
24%
1898
19%
632
59%
632
29%
1171
March1st to 15thNight
52%
720
18%
2010
15%
720
55%
720
28%
1299
March16th to endNight
49%
768
21%
2085
14%
768
55%
768
32%
1320
April1st to 15thNight
49%
719
23%
1799
11%
719
54%
719
34%
1154
April16th to endNight
56%
720
26%
1800
12%
720
60%
720
47%
1010
May1st to 15thNight
69%
611
26%
1691
17%
611
72%
611
59%
805
May16th to endNight
64%
379
25%
1501
23%
379
72%
379
48%
603
June1st to 15thNight
66%
360
25%
1440
25%
360
76%
360
47%
585
June16th to endNight
79%
360
36%
1440
44%
360
85%
360
70%
465
July1st to 15thNight
87%
364
34%
1384
39%
364
92%
364
75%
444
July16th to endNight
85%
564
36%
1593
32%
531
87%
531
68%
659
August1st to 15thNight
79%
553
34%
1626
26%
550
82%
550
72%
672
August16th to endNight
84%
764
39%
1910
26%
764
85%
764
79%
862
September1st to 15thNight
84%
720
39%
1800
26%
720
87%
720
75%
839
September16th to endNight
81%
716
42%
1962
36%
716
85%
716
67%
898
October1st to 15thNight
71%
720
31%
2160
29%
720
78%
720
50%
1041
October16th to endNight
71%
708
33%
2124
34%
708
75%
708
48%
1081
November1st to 15thNight
68%
700
28%
2193
27%
700
73%
700
41%
1143
November16th to endNight
64%
720
25%
2436
26%
720
68%
720
33%
1341
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%313323346%60%
48175
Night
7%31332345%8%56%
47427
TransparencyDay
23%410%19%24%17%
47861
Night
25%411%20%21%16%
47241
SeeingDay
8%10%27%33%17%3
6109
Night
8%416%38%27%5%
15480

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%3343445%7%41%
1540
16th to endDay
15%6%15%5%34345%43%
1728
February1st to 15thDay
14%7%25%425%446%41%
1576
16th to endDay
15%5%25%5%3446%7%39%
1574
March1st to 15thDay
11%6%35%5%3447%8%38%
1947
16th to endDay
10%5%36%6%345%5%7%42%
2138
April1st to 15thDay
12%6%25%43435%7%43%
2149
16th to endDay
5%323223347%60%
2160
May1st to 15thDay
322113348%67%
2257
16th to endDay
4213312348%63%
2607
June1st to 15thDay
321321445%7%64%
2520
16th to endDay
1111247%77%
2520
July1st to 15thDay
1112235%80%
2491
16th to endDay
1112235%79%
2468
August1st to 15thDay
11112236%77%
2325
16th to endDay
1112235%79%
2292
September1st to 15thDay
11211237%77%
2160
16th to endDay
112213236%73%
1993
October1st to 15thDay
3212223336%67%
1800
16th to endDay
6%313322345%61%
1768
November1st to 15thDay
8%3233245%6%7%51%
1664
16th to endDay
10%6%35%43345%5%47%
1522
December1st to 15thDay
14%9%35%424436%41%
1440
16th to endDay
17%7%34414347%40%
1536
January1st to 15thNight
12%5%243235%5%8%45%
2396
16th to endNight
14%5%2442345%6%47%
2496
February1st to 15thNight
13%6%25%434446%44%
2276
16th to endNight
13%5%2442445%7%45%
1898
March1st to 15thNight
13%5%3442345%8%43%
2010
16th to endNight
11%5%3442345%6%48%
2085
April1st to 15thNight
8%425%42446%7%48%
1799
16th to endNight
4222313348%61%
1800
May1st to 15thNight
221221345%8%65%
1691
16th to endNight
2122135%6%10%61%
1501
June1st to 15thNight
21122135%5%8%65%
1440
16th to endNight
1112246%77%
1440
July1st to 15thNight
1112349%75%
1466
16th to endNight
11121347%12%63%
1701
August1st to 15thNight
111135%8%15%59%
1635
16th to endNight
121247%12%66%
1910
September1st to 15thNight
11113449%70%
1800
16th to endNight
11121235%7%72%
1962
October1st to 15thNight
4113323347%65%
2160
16th to endNight
5%31332446%6%59%
2124
November1st to 15thNight
7%32332345%9%56%
2193
16th to endNight
8%5%2332345%6%53%
2436
December1st to 15thNight
13%6%24424347%43%
2520
16th to endNight
16%5%2442435%5%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
1540
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
1574
March1st to 15thDay
41%6%11%19%15%5%
1947
16th to endDay
40%6%13%18%17%3
2138
April1st to 15thDay
39%5%13%19%18%3
2149
16th to endDay
22%5%14%26%24%7%
2160
May1st to 15thDay
15%410%27%32%9%
2257
16th to endDay
19%5%15%26%23%8%
2611
June1st to 15thDay
17%5%12%22%24%17%
2520
16th to endDay
7%16%17%33%32%
2520
July1st to 15thDay
6%17%11%24%49%
2344
16th to endDay
6%17%12%22%49%
2313
August1st to 15thDay
8%17%16%27%39%
2309
16th to endDay
5%17%16%36%32%
2292
September1st to 15thDay
8%17%16%32%33%
2160
16th to endDay
12%37%21%34%20%
1993
October1st to 15thDay
17%48%19%26%23%
1800
16th to endDay
24%310%23%24%12%
1768
November1st to 15thDay
29%6%12%27%15%7%
1664
16th to endDay
37%5%9%21%21%4
1522
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%
2396
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
1898
March1st to 15thNight
38%6%12%20%15%6%
2010
16th to endNight
35%6%12%19%19%6%
2085
April1st to 15thNight
33%6%15%20%18%5%
1799
16th to endNight
21%5%13%26%23%9%
1800
May1st to 15thNight
14%415%21%30%13%
1692
16th to endNight
14%5%20%27%23%9%
1501
June1st to 15thNight
15%5%15%21%24%18%
1440
16th to endNight
7%17%17%30%35%
1440
July1st to 15thNight
6%15%14%22%49%
1384
16th to endNight
10%27%21%18%39%
1593
August1st to 15thNight
10%10%20%24%32%
1626
16th to endNight
7%19%20%27%33%
1910
September1st to 15thNight
9%28%17%25%37%
1800
16th to endNight
11%27%24%28%24%
1962
October1st to 15thNight
17%5%8%20%23%24%
2160
16th to endNight
22%310%22%23%16%
2124
November1st to 15thNight
25%413%30%16%9%
2193
16th to endNight
31%410%21%24%8%
2436
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
20%8%25%28%13%2
168
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%23%10%2
270
May1st to 15thDay
6%14%40%28%10%
288
16th to endDay
6%12%27%37%14%1
330
June1st to 15thDay
5%15%39%30%7%1
315
16th to endDay
15%31%42%18%
315
July1st to 15thDay
129%50%17%
305
16th to endDay
126%49%17%4
327
August1st to 15thDay
1428%42%19%2
315
16th to endDay
124%46%22%4
332
September1st to 15thDay
2319%47%20%6%
315
16th to endDay
27%25%34%21%9%
315
October1st to 15thDay
49%28%31%19%6%
315
16th to endDay
10%7%26%27%21%5%
276
November1st to 15thDay
7%9%19%20%34%10%
170
16th to endDay
8%12%27%34%17%
73
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%24%35%21%3
720
May1st to 15thNight
3320%46%22%3
612
16th to endNight
3326%42%23%
380
June1st to 15thNight
2223%54%15%
360
16th to endNight
18%53%26%
360
July1st to 15thNight
110%53%32%1
364
16th to endNight
18%47%37%4
564
August1st to 15thNight
214%43%35%3
553
16th to endNight
11%48%34%4
764
September1st to 15thNight
1110%42%38%6%
720
16th to endNight
1212%39%35%8%
716
October1st to 15thNight
4415%39%30%7%
720
16th to endNight
6%312%34%31%11%
708
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 2017-10-17 13:35:19. Version ac04

Copyright 2017 A. Danko


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