CSM Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CSM Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
63%
15416
23%
46918
21%
15379
67%
15379
34%
27191

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%
717
17%
2366
17%
716
63%
716
27%
1461
January16th to endNight
57%
768
24%
2496
25%
768
60%
768
26%
1574
February1st to 15thNight
53%
700
22%
2288
21%
700
58%
700
24%
1463
February16th to endNight
50%
632
20%
1905
17%
632
55%
632
24%
1259
March1st to 15thNight
53%
720
17%
1992
15%
720
56%
720
26%
1338
March16th to endNight
52%
768
19%
2097
14%
768
56%
768
28%
1397
April1st to 15thNight
49%
719
20%
1799
11%
719
53%
719
30%
1204
April16th to endNight
57%
720
23%
1800
11%
720
60%
720
42%
1065
May1st to 15thNight
68%
605
23%
1685
16%
605
70%
605
43%
932
May16th to endNight
62%
414
19%
1537
17%
414
68%
414
29%
843
June1st to 15thNight
68%
360
20%
1440
20%
360
75%
360
32%
719
June16th to endNight
84%
360
31%
1440
40%
360
87%
360
52%
555
July1st to 15thNight
84%
402
25%
1422
28%
402
86%
402
56%
580
July16th to endNight
75%
564
24%
1593
23%
531
78%
531
44%
811
August1st to 15thNight
75%
547
22%
1620
18%
544
75%
544
44%
824
August16th to endNight
79%
764
26%
1910
16%
764
79%
764
52%
1051
September1st to 15thNight
81%
720
32%
1800
23%
720
82%
720
57%
953
September16th to endNight
76%
664
34%
1823
31%
664
78%
664
54%
924
October1st to 15thNight
70%
660
26%
1980
28%
660
74%
660
40%
1086
October16th to endNight
70%
704
29%
2112
30%
704
73%
704
37%
1202
November1st to 15thNight
67%
700
26%
2166
27%
700
70%
700
36%
1230
November16th to endNight
64%
720
23%
2439
25%
720
66%
720
31%
1385
December1st to 15thNight
53%
720
20%
2520
19%
720
59%
720
22%
1602
December16th to endNight
46%
768
19%
2688
17%
768
52%
768
21%
1733

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%5%24423347%53%
47851
Night
7%42442445%8%49%
47107
TransparencyDay
28%7%11%17%21%13%
47540
Night
29%7%12%17%19%12%
46919
SeeingDay
8%9%23%34%18%5%
6045
Night
9%413%29%33%8%
15425

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
13%5%26%4235%37%44%
1569
16th to endDay
14%5%245%3445%6%43%
1728
February1st to 15thDay
14%7%35%434445%41%
1576
16th to endDay
15%6%36%5%3345%7%37%
1568
March1st to 15thDay
11%6%37%5%35%47%9%36%
1965
16th to endDay
10%5%25%7%345%5%8%40%
2127
April1st to 15thDay
12%5%26%4245%5%6%44%
2149
16th to endDay
6%424323248%57%
2160
May1st to 15thDay
342431336%9%58%
2262
16th to endDay
6%7%34313448%51%
2575
June1st to 15thDay
5%5%2332445%8%56%
2520
16th to endDay
2212212347%70%
2520
July1st to 15thDay
1322323348%64%
2449
16th to endDay
1313313348%65%
2468
August1st to 15thDay
13243233410%60%
2329
16th to endDay
323323349%64%
2292
September1st to 15thDay
1313313339%65%
2160
16th to endDay
3313212238%66%
1838
October1st to 15thDay
6%423322337%60%
1650
16th to endDay
7%423433346%56%
1760
November1st to 15thDay
7%5%24425%45%8%49%
1690
16th to endDay
11%6%35%5%24445%47%
1520
December1st to 15thDay
13%8%37%5%24445%39%
1440
16th to endDay
16%6%45%5%33347%39%
1536
January1st to 15thNight
13%7%1442445%8%42%
2366
16th to endNight
14%6%35%423346%45%
2496
February1st to 15thNight
11%6%27%435%35%6%42%
2276
16th to endNight
13%6%24425%45%8%40%
1905
March1st to 15thNight
13%5%36%4235%5%7%41%
1992
16th to endNight
10%6%445%34346%45%
2097
April1st to 15thNight
8%5%3443446%9%44%
1799
16th to endNight
5%413413448%57%
1800
May1st to 15thNight
141342345%10%57%
1685
16th to endNight
5%425%4235%5%8%51%
1536
June1st to 15thNight
33243145%7%10%54%
1440
16th to endNight
112222448%68%
1440
July1st to 15thNight
2222245%6%13%56%
1507
16th to endNight
13245%46%6%8%13%43%
1701
August1st to 15thNight
13146%35%7%8%14%42%
1629
16th to endNight
2144347%8%14%47%
1910
September1st to 15thNight
111242345%11%58%
1800
16th to endNight
1213423338%65%
1823
October1st to 15thNight
44235%23446%59%
1980
16th to endNight
5%41442345%6%54%
2112
November1st to 15thNight
7%5%2342335%8%53%
2166
16th to endNight
7%5%24434347%51%
2439
December1st to 15thNight
13%7%26%5%24347%42%
2520
16th to endNight
16%6%35%423445%43%
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
38%6%11%18%15%9%
1569
16th to endDay
41%7%8%12%18%12%
1728
February1st to 15thDay
43%6%8%17%20%4
1576
16th to endDay
46%6%7%22%12%3
1568
March1st to 15thDay
42%8%11%18%13%5%
1965
16th to endDay
41%8%14%18%14%2
2127
April1st to 15thDay
39%8%13%19%16%2
2149
16th to endDay
26%7%15%23%20%6%
2160
May1st to 15thDay
20%10%11%23%26%6%
2262
16th to endDay
29%10%13%21%19%4
2579
June1st to 15thDay
24%10%14%18%20%12%
2520
16th to endDay
12%6%10%16%31%23%
2520
July1st to 15thDay
12%7%13%9%18%37%
2305
16th to endDay
12%6%12%11%23%33%
2313
August1st to 15thDay
16%7%12%10%27%25%
2313
16th to endDay
14%6%11%14%32%21%
2292
September1st to 15thDay
15%6%8%13%27%28%
2160
16th to endDay
17%47%23%28%19%
1838
October1st to 15thDay
24%5%9%19%25%15%
1650
16th to endDay
27%5%11%21%20%12%
1760
November1st to 15thDay
32%6%12%25%15%7%
1690
16th to endDay
37%6%10%15%25%4
1520
December1st to 15thDay
44%6%11%15%17%4
1440
16th to endDay
45%412%16%16%4
1536
January1st to 15thNight
38%6%13%18%15%9%
2366
16th to endNight
40%6%9%11%16%15%
2496
February1st to 15thNight
40%7%9%17%17%7%
2288
16th to endNight
40%8%12%23%12%2
1905
March1st to 15thNight
41%6%12%18%14%5%
1992
16th to endNight
39%7%12%18%17%5%
2097
April1st to 15thNight
34%10%15%20%16%2
1799
16th to endNight
24%7%14%25%19%8%
1800
May1st to 15thNight
20%10%12%20%25%10%
1686
16th to endNight
26%11%16%20%18%5%
1537
June1st to 15thNight
20%13%15%17%20%12%
1440
16th to endNight
11%6%10%14%31%25%
1440
July1st to 15thNight
10%7%17%10%19%34%
1422
16th to endNight
17%10%20%10%13%26%
1593
August1st to 15thNight
19%9%20%9%20%21%
1620
16th to endNight
15%10%18%10%22%22%
1910
September1st to 15thNight
14%8%11%11%23%30%
1800
16th to endNight
17%5%9%20%26%20%
1823
October1st to 15thNight
25%7%9%19%21%17%
1980
16th to endNight
27%8%8%20%21%13%
2112
November1st to 15thNight
28%7%14%25%16%7%
2166
16th to endNight
32%6%10%22%19%8%
2439
December1st to 15thNight
40%8%8%15%20%6%
2520
16th to endNight
43%6%11%15%16%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%7%21%30%14%6%
198
16th to endDay
14%10%22%28%18%5%
256
February1st to 15thDay
17%13%23%22%18%3
236
16th to endDay
18%13%23%28%14%1
236
March1st to 15thDay
15%16%26%22%15%2
270
16th to endDay
11%16%35%27%7%1
288
April1st to 15thDay
14%18%36%20%8%1
269
16th to endDay
7%22%32%25%8%2
270
May1st to 15thDay
6%13%36%30%10%1
288
16th to endDay
10%15%25%29%13%5%
330
June1st to 15thDay
6%13%30%36%12%1
315
16th to endDay
1321%43%24%6%
315
July1st to 15thDay
1217%51%22%4
305
16th to endDay
216%45%26%8%
327
August1st to 15thDay
1218%43%26%6%
315
16th to endDay
1115%46%27%8%
332
September1st to 15thDay
1415%43%25%9%
315
16th to endDay
36%19%33%26%10%
260
October1st to 15thDay
6%7%20%39%19%6%
255
16th to endDay
10%7%26%29%20%5%
272
November1st to 15thDay
9%6%19%24%29%10%
196
16th to endDay
5%13%27%27%26%
73
December1st to 15thDay
15%11%31%23%16%1
60
16th to endDay
10%15%14%23%28%7%
64
January1st to 15thNight
15%5%11%30%30%7%
720
16th to endNight
16%5%12%29%27%8%
768
February1st to 15thNight
12%8%16%30%27%5%
704
16th to endNight
16%6%19%30%21%5%
632
March1st to 15thNight
14%7%15%27%29%5%
720
16th to endNight
13%8%20%32%22%3
768
April1st to 15thNight
11%9%22%32%20%4
719
16th to endNight
7%8%21%29%25%7%
720
May1st to 15thNight
4317%38%29%7%
606
16th to endNight
6%5%18%33%28%8%
415
June1st to 15thNight
3219%38%32%3
360
16th to endNight
118%38%46%3
360
July1st to 15thNight
16%24%52%13%
402
16th to endNight
117%19%51%17%
564
August1st to 15thNight
426%23%51%12%
547
16th to endNight
117%29%48%11%
764
September1st to 15thNight
37%24%48%15%
720
16th to endNight
3210%26%43%14%
664
October1st to 15thNight
7%211%28%38%10%
660
16th to endNight
8%39%28%33%15%
704
November1st to 15thNight
8%213%30%34%10%
700
16th to endNight
10%412%34%29%9%
720
December1st to 15thNight
15%6%14%30%24%7%
720
16th to endNight
18%7%19%29%20%3
768
Page generated at 2017-09-18 05:38:24. Version ac04

Copyright 2017 A. Danko


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