Cottonwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottonwood clear sky chart from 2005-11-05 to 2017-09-24.

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
64%
15116
27%
46962
24%
15080
68%
15080
40%
25272

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
59%
716
19%
2470
18%
716
63%
716
27%
1472
January16th to endNight
52%
768
25%
2496
24%
768
58%
768
26%
1539
February1st to 15thNight
53%
697
23%
2288
23%
697
58%
697
25%
1442
February16th to endNight
50%
632
22%
1939
19%
632
57%
632
28%
1223
March1st to 15thNight
49%
720
15%
2022
13%
720
52%
720
25%
1356
March16th to endNight
47%
768
20%
2085
13%
768
52%
768
30%
1330
April1st to 15thNight
46%
719
21%
1799
9%
719
52%
719
32%
1172
April16th to endNight
56%
720
26%
1800
12%
720
60%
720
47%
1021
May1st to 15thNight
58%
484
28%
1564
20%
484
66%
484
47%
745
May16th to endNight
59%
375
24%
1496
23%
374
68%
374
34%
724
June1st to 15thNight
64%
360
24%
1440
26%
360
75%
360
37%
665
June16th to endNight
76%
360
32%
1440
43%
360
82%
360
58%
517
July1st to 15thNight
88%
340
32%
1360
45%
340
91%
340
68%
448
July16th to endNight
89%
500
39%
1530
41%
468
91%
468
79%
551
August1st to 15thNight
92%
538
38%
1611
32%
535
93%
535
77%
626
August16th to endNight
91%
735
46%
1881
31%
735
92%
735
86%
797
September1st to 15thNight
88%
720
43%
1800
28%
720
90%
720
83%
797
September16th to endNight
79%
692
41%
1896
34%
692
83%
692
68%
854
October1st to 15thNight
68%
660
32%
1980
29%
660
77%
660
51%
964
October16th to endNight
69%
704
33%
2112
33%
704
74%
704
44%
1099
November1st to 15thNight
66%
700
25%
2234
25%
700
70%
700
35%
1234
November16th to endNight
59%
720
20%
2511
22%
720
62%
720
30%
1446
December1st to 15thNight
52%
720
21%
2520
19%
720
58%
720
25%
1534
December16th to endNight
46%
768
21%
2688
20%
768
52%
768
22%
1716

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
10%212212235%64%
47973
Night
12%312212346%59%
47145
TransparencyDay
23%47%18%24%21%
47655
Night
27%48%19%22%17%
46963
SeeingDay
11%7%19%27%23%10%
5885
Night
12%414%34%29%4
15128

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
18%5%23322348%45%
1466
16th to endDay
22%313322235%47%
1728
February1st to 15thDay
20%313322446%46%
1576
16th to endDay
19%414323338%45%
1535
March1st to 15thDay
22%5%24323349%39%
1937
16th to endDay
17%423313348%46%
2139
April1st to 15thDay
14%5%24424447%46%
2149
16th to endDay
6%312223336%63%
2160
May1st to 15thDay
421212348%67%
2383
16th to endDay
6%213222245%64%
2615
June1st to 15thDay
6%212212335%66%
2520
16th to endDay
3111112480%
2520
July1st to 15thDay
111112386%
2520
16th to endDay
1112289%
2530
August1st to 15thDay
112386%
2340
16th to endDay
111288%
2321
September1st to 15thDay
111112484%
2160
16th to endDay
31111125%79%
1919
October1st to 15thDay
7%21321223469%
1650
16th to endDay
12%213312235%62%
1760
November1st to 15thDay
12%312323447%54%
1623
16th to endDay
16%423223446%49%
1446
December1st to 15thDay
24%412212345%45%
1440
16th to endDay
27%323222236%41%
1536
January1st to 15thNight
16%41432335%7%47%
2470
16th to endNight
21%42331323448%
2496
February1st to 15thNight
19%5%13323346%44%
2276
16th to endNight
20%423423247%44%
1939
March1st to 15thNight
21%423424348%39%
2022
16th to endNight
16%41332245%8%46%
2085
April1st to 15thNight
13%424434347%47%
1799
16th to endNight
9%412212247%62%
1800
May1st to 15thNight
6%213112347%65%
1564
16th to endNight
5%31342335%6%58%
1496
June1st to 15thNight
6%31321345%7%61%
1440
16th to endNight
22111122379%
1440
July1st to 15thNight
1121222381%
1440
16th to endNight
11112287%
1636
August1st to 15thNight
111123383%
1620
16th to endNight
1112387%
1881
September1st to 15thNight
1112486%
1800
16th to endNight
3111223478%
1896
October1st to 15thNight
6%212212335%69%
1980
16th to endNight
9%213213345%62%
2112
November1st to 15thNight
11%31322335%8%53%
2234
16th to endNight
17%313312347%50%
2511
December1st to 15thNight
26%312212336%45%
2520
16th to endNight
27%413212336%41%
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%5%12%18%17%7%
1466
16th to endDay
41%37%16%18%12%
1728
February1st to 15thDay
38%5%11%16%22%4
1576
16th to endDay
38%5%8%27%15%3
1535
March1st to 15thDay
43%6%9%18%14%7%
1937
16th to endDay
36%6%12%20%17%5%
2139
April1st to 15thDay
37%6%10%20%20%4
2149
16th to endDay
22%5%10%24%25%10%
2160
May1st to 15thDay
17%49%21%30%16%
2383
16th to endDay
21%5%9%23%27%12%
2619
June1st to 15thDay
21%48%17%23%24%
2520
16th to endDay
9%25%13%33%36%
2520
July1st to 15thDay
6%1312%29%46%
2371
16th to endDay
5%139%24%54%
2373
August1st to 15thDay
6%1314%30%42%
2324
16th to endDay
41312%32%44%
2321
September1st to 15thDay
6%1411%30%46%
2160
16th to endDay
10%27%21%32%26%
1919
October1st to 15thDay
20%38%19%29%19%
1650
16th to endDay
26%49%20%25%14%
1760
November1st to 15thDay
30%5%10%29%14%9%
1623
16th to endDay
36%5%9%20%17%9%
1446
December1st to 15thDay
40%5%8%17%21%6%
1440
16th to endDay
46%47%18%16%6%
1536
January1st to 15thNight
36%7%12%19%16%7%
2470
16th to endNight
40%46%16%18%13%
2496
February1st to 15thNight
40%5%8%18%19%6%
2288
16th to endNight
39%5%11%22%17%3
1939
March1st to 15thNight
43%5%12%16%14%7%
2022
16th to endNight
35%7%13%21%15%5%
2085
April1st to 15thNight
35%6%13%22%15%6%
1799
16th to endNight
23%411%26%26%7%
1800
May1st to 15thNight
20%49%23%29%13%
1565
16th to endNight
23%7%10%26%21%10%
1496
June1st to 15thNight
23%5%10%20%24%16%
1440
16th to endNight
12%25%13%35%30%
1440
July1st to 15thNight
8%1211%30%45%
1360
16th to endNight
5%1410%22%55%
1530
August1st to 15thNight
7%1317%31%38%
1611
16th to endNight
4216%34%40%
1881
September1st to 15thNight
5%1312%30%47%
1800
16th to endNight
11%26%17%31%30%
1896
October1st to 15thNight
18%46%18%31%20%
1980
16th to endNight
23%47%24%22%17%
2112
November1st to 15thNight
28%6%14%27%13%8%
2234
16th to endNight
34%5%10%21%18%9%
2511
December1st to 15thNight
41%49%15%23%5%
2520
16th to endNight
44%47%16%20%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
36%7%17%21%14%3
94
16th to endDay
22%8%22%16%18%11%
256
February1st to 15thDay
22%8%19%23%22%4
236
16th to endDay
17%10%21%29%15%5%
231
March1st to 15thDay
29%10%22%18%12%7%
270
16th to endDay
20%14%27%19%15%2
288
April1st to 15thDay
18%18%23%25%11%3
269
16th to endDay
11%18%23%28%11%5%
270
May1st to 15thDay
5%12%32%26%17%6%
288
16th to endDay
7%9%20%22%26%13%
330
June1st to 15thDay
7%11%18%29%24%8%
315
16th to endDay
2317%34%29%12%
315
July1st to 15thDay
10%34%37%16%
305
16th to endDay
110%32%38%18%
327
August1st to 15thDay
2113%35%31%15%
315
16th to endDay
215%30%30%20%
332
September1st to 15thDay
2112%32%33%17%
315
16th to endDay
46%21%27%26%14%
288
October1st to 15thDay
10%8%20%25%22%13%
255
16th to endDay
16%6%18%30%21%7%
272
November1st to 15thDay
15%6%15%18%34%10%
129
16th to endDay
19%424%36%13%1
61
December1st to 15thDay
41%321%28%5%
60
16th to endDay
15%114%40%23%4
64
January1st to 15thNight
18%312%37%23%5%
720
16th to endNight
20%415%29%23%6%
768
February1st to 15thNight
21%5%13%34%22%2
704
16th to endNight
20%6%17%35%16%3
632
March1st to 15thNight
19%8%15%31%21%3
720
16th to endNight
17%7%23%30%20%
768
April1st to 15thNight
11%9%27%31%18%2
719
16th to endNight
10%6%23%34%21%3
720
May1st to 15thNight
8%425%35%24%2
485
16th to endNight
6%6%20%33%31%2
375
June1st to 15thNight
5%322%44%22%1
360
16th to endNight
3116%46%30%1
360
July1st to 15thNight
25%39%49%2
340
16th to endNight
16%33%53%5%
500
August1st to 15thNight
1332%54%7%
538
16th to endNight
5%36%51%4
735
September1st to 15thNight
117%33%49%7%
720
16th to endNight
3311%31%39%10%
692
October1st to 15thNight
7%315%34%30%8%
660
16th to endNight
10%410%33%31%9%
704
November1st to 15thNight
11%311%37%29%6%
700
16th to endNight
18%213%34%25%5%
720
December1st to 15thNight
26%213%33%19%4
720
16th to endNight
27%416%32%17%1
768
Page generated at 2017-09-25 06:02:22. Version ac04

Copyright 2017 A. Danko


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