Cottontail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottontail Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
58%
15744
30%
48475
24%
15716
66%
15716
44%
23803

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
54%
776
24%
2716
20%
776
64%
776
34%
1381
January16th to endNight
52%
788
27%
2597
23%
788
61%
788
34%
1396
February1st to 15thNight
49%
699
27%
2196
23%
698
57%
698
34%
1165
February16th to endNight
49%
632
28%
1895
21%
632
60%
632
36%
1027
March1st to 15thNight
47%
720
24%
2139
17%
720
56%
720
38%
1106
March16th to endNight
42%
768
24%
2004
13%
768
50%
768
37%
1118
April1st to 15thNight
45%
719
22%
1799
10%
719
51%
719
37%
1075
April16th to endNight
51%
720
24%
1800
11%
720
55%
720
42%
1011
May1st to 15thNight
55%
581
28%
1661
18%
581
60%
581
47%
827
May16th to endNight
61%
385
26%
1507
25%
385
68%
385
36%
708
June1st to 15thNight
61%
360
27%
1440
28%
360
72%
360
44%
600
June16th to endNight
71%
360
35%
1440
39%
360
81%
360
65%
469
July1st to 15thNight
82%
340
32%
1360
39%
340
87%
340
61%
481
July16th to endNight
77%
409
37%
1447
39%
385
82%
385
54%
585
August1st to 15thNight
76%
647
35%
1721
21%
644
81%
644
68%
801
August16th to endNight
75%
764
43%
1910
25%
764
78%
764
75%
883
September1st to 15thNight
77%
720
41%
1800
26%
720
82%
720
73%
836
September16th to endNight
69%
716
43%
1954
33%
716
77%
716
59%
926
October1st to 15thNight
68%
720
33%
2109
29%
720
75%
720
52%
1005
October16th to endNight
67%
768
40%
2343
37%
768
77%
768
55%
1046
November1st to 15thNight
61%
760
32%
2470
29%
760
71%
760
46%
1151
November16th to endNight
51%
780
33%
2535
25%
780
65%
780
42%
1204
December1st to 15thNight
52%
780
23%
2720
19%
780
59%
780
35%
1350
December16th to endNight
43%
832
26%
2912
20%
832
53%
832
25%
1652

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
242432445%7%59%
49058
Night
131332335%7%63%
48651
TransparencyDay
24%49%20%24%16%
48733
Night
19%411%24%26%13%
48476
SeeingDay
8%24%30%22%10%2
6133
Night
311%21%32%23%7%
15755

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
13243336%6%9%54%
1552
16th to endDay
27%25%425%5%6%8%48%
1727
February1st to 15thDay
5%3432336%11%53%
1665
16th to endDay
5%36%42445%8%52%
1579
March1st to 15thDay
15%343245%6%10%50%
1818
16th to endDay
1433325%6%7%10%50%
2220
April1st to 15thDay
35%25%5%3446%9%48%
2149
16th to endDay
25%24323446%60%
2160
May1st to 15thDay
5%6%2332335%6%57%
2287
16th to endDay
7%8%24434446%48%
2602
June1st to 15thDay
4324434446%58%
2520
16th to endDay
211221233474%
2520
July1st to 15thDay
3213334345%62%
2520
16th to endDay
432342434463%
2621
August1st to 15thDay
221442435%464%
2229
16th to endDay
231331332370%
2292
September1st to 15thDay
231332333468%
2160
16th to endDay
2212212336%71%
2004
October1st to 15thDay
3413212335%67%
1848
16th to endDay
2322213346%67%
1881
November1st to 15thDay
242321445%6%61%
1719
16th to endDay
21322446%10%60%
1755
December1st to 15thDay
13343245%5%9%56%
1566
16th to endDay
1437%336%7%7%10%43%
1664
January1st to 15thNight
142443446%9%53%
2716
16th to endNight
16%244245%6%8%52%
2597
February1st to 15thNight
434425%47%10%52%
2185
16th to endNight
15%3432346%9%55%
1895
March1st to 15thNight
4233235%6%9%57%
2139
16th to endNight
42442345%8%59%
2004
April1st to 15thNight
24234245%6%9%53%
1799
16th to endNight
35%3232433463%
1800
May1st to 15thNight
3413123347%64%
1661
16th to endNight
6%5%13313236%60%
1507
June1st to 15thNight
3312212346%67%
1440
16th to endNight
11222283%
1440
July1st to 15thNight
11121223477%
1440
16th to endNight
322212235%72%
1545
August1st to 15thNight
1222233477%
1730
16th to endNight
1111123480%
1910
September1st to 15thNight
1111122480%
1800
16th to endNight
111221223474%
1954
October1st to 15thNight
231223345%69%
2109
16th to endNight
1212212246%71%
2343
November1st to 15thNight
1312213449%65%
2470
16th to endNight
131332335%8%62%
2535
December1st to 15thNight
122442447%9%56%
2720
16th to endNight
1336%5%36%5%8%10%45%
2912

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
23%7%17%26%20%4
1552
16th to endDay
31%6%13%19%20%8%
1727
February1st to 15thDay
24%5%16%24%21%7%
1665
16th to endDay
30%5%11%26%23%2
1579
March1st to 15thDay
28%6%16%22%19%6%
1818
16th to endDay
26%7%18%26%16%4
2220
April1st to 15thDay
31%6%12%26%18%5%
2149
16th to endDay
26%5%15%27%19%5%
2160
May1st to 15thDay
27%312%27%23%5%
2287
16th to endDay
35%49%23%21%5%
2606
June1st to 15thDay
26%38%19%27%13%
2520
16th to endDay
15%2213%36%28%
2520
July1st to 15thDay
21%338%22%40%
2371
16th to endDay
22%2410%18%40%
2457
August1st to 15thDay
21%3311%18%42%
2213
16th to endDay
19%218%33%34%
2292
September1st to 15thDay
20%2310%33%28%
2160
16th to endDay
16%3324%33%19%
2004
October1st to 15thDay
21%3423%29%17%
1848
16th to endDay
16%46%25%32%13%
1881
November1st to 15thDay
21%5%11%27%24%10%
1719
16th to endDay
18%5%12%28%28%6%
1755
December1st to 15thDay
23%6%15%28%19%6%
1566
16th to endDay
32%8%13%19%21%4
1664
January1st to 15thNight
26%414%26%23%4
2716
16th to endNight
26%6%13%22%20%10%
2597
February1st to 15thNight
25%5%13%29%17%9%
2196
16th to endNight
24%6%14%29%20%4
1895
March1st to 15thNight
21%5%18%26%20%7%
2139
16th to endNight
23%5%20%29%17%3
2004
April1st to 15thNight
26%6%16%28%19%3
1799
16th to endNight
23%417%29%20%4
1800
May1st to 15thNight
19%412%30%28%4
1662
16th to endNight
25%210%28%25%5%
1507
June1st to 15thNight
18%311%23%30%12%
1440
16th to endNight
8%1419%33%31%
1440
July1st to 15thNight
10%2310%31%41%
1360
16th to endNight
16%2311%26%40%
1447
August1st to 15thNight
11%2316%23%41%
1721
16th to endNight
8%1315%39%31%
1910
September1st to 15thNight
9%1416%38%29%
1800
16th to endNight
14%2323%36%19%
1954
October1st to 15thNight
17%27%28%29%13%
2109
16th to endNight
15%28%25%36%11%
2343
November1st to 15thNight
16%6%9%31%24%11%
2470
16th to endNight
19%412%27%30%6%
2535
December1st to 15thNight
22%6%17%25%20%6%
2720
16th to endNight
30%8%11%22%21%5%
2912

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
10%23%32%20%12%2
90
16th to endDay
8%24%30%21%11%3
230
February1st to 15thDay
7%26%28%22%15%
252
16th to endDay
8%31%30%21%7%
238
March1st to 15thDay
12%33%24%19%8%1
270
16th to endDay
9%37%30%17%4
288
April1st to 15thDay
11%38%26%15%7%
269
16th to endDay
14%36%27%16%4
270
May1st to 15thDay
15%27%28%18%7%2
288
16th to endDay
16%23%25%20%10%3
330
June1st to 15thDay
11%28%30%19%8%2
315
16th to endDay
6%19%37%22%9%4
315
July1st to 15thDay
5%16%32%26%12%4
305
16th to endDay
7%17%34%25%11%5%
327
August1st to 15thDay
321%34%25%11%3
315
16th to endDay
416%34%24%13%5%
332
September1st to 15thDay
7%15%35%26%12%3
315
16th to endDay
8%17%32%30%10%1
315
October1st to 15thDay
8%24%29%26%8%2
315
16th to endDay
7%18%29%27%13%4
297
November1st to 15thDay
222%22%20%25%6%
135
16th to endDay
425%22%32%12%2
135
December1st to 15thDay
7%26%27%19%13%5%
91
16th to endDay
414%28%32%17%3
96
January1st to 15thNight
412%23%30%20%9%
780
16th to endNight
5%11%25%32%17%8%
788
February1st to 15thNight
314%25%29%21%5%
704
16th to endNight
416%25%30%15%6%
632
March1st to 15thNight
319%26%28%16%5%
720
16th to endNight
223%27%25%17%2
768
April1st to 15thNight
6%17%26%30%15%3
719
16th to endNight
6%16%21%29%19%6%
720
May1st to 15thNight
6%9%25%32%19%5%
582
16th to endNight
9%6%17%36%27%2
386
June1st to 15thNight
5%6%23%36%23%3
360
16th to endNight
1419%46%23%5%
360
July1st to 15thNight
1111%48%33%3
340
16th to endNight
3112%43%33%6%
409
August1st to 15thNight
1216%38%34%6%
647
16th to endNight
1317%38%31%8%
764
September1st to 15thNight
1115%35%36%9%
720
16th to endNight
27%17%29%33%9%
716
October1st to 15thNight
410%14%36%24%10%
720
16th to endNight
38%16%29%28%13%
768
November1st to 15thNight
39%22%32%22%8%
760
16th to endNight
415%23%28%18%8%
780
December1st to 15thNight
314%24%32%18%7%
780
16th to endNight
415%30%30%15%4
832
Page generated at 2018-01-21 09:19:31. Version ac04

Copyright 2018 A. Danko


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