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 2017-09-19.

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
74%
15634
35%
46937
30%
15595
79%
15595
55%
22112

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
67%
719
32%
2327
29%
716
76%
716
45%
1137
January16th to endNight
64%
768
36%
2496
34%
768
73%
768
44%
1243
February1st to 15thNight
67%
698
34%
2199
28%
698
78%
698
52%
1022
February16th to endNight
63%
632
37%
1895
34%
632
71%
632
50%
941
March1st to 15thNight
65%
720
39%
1984
31%
720
73%
720
57%
978
March16th to endNight
70%
768
37%
2112
28%
768
78%
768
60%
1010
April1st to 15thNight
63%
703
30%
1962
18%
703
72%
703
56%
967
April16th to endNight
65%
540
45%
1664
32%
540
77%
540
68%
664
May1st to 15thNight
71%
539
37%
1619
29%
539
78%
539
61%
694
May16th to endNight
72%
561
37%
1684
29%
561
76%
561
67%
703
June1st to 15thNight
77%
540
33%
1620
30%
540
79%
540
72%
654
June16th to endNight
87%
540
35%
1620
32%
540
87%
540
73%
651
July1st to 15thNight
87%
510
23%
1530
20%
510
87%
510
48%
773
July16th to endNight
85%
564
20%
1593
17%
531
85%
531
38%
890
August1st to 15thNight
87%
539
29%
1611
25%
536
87%
536
47%
818
August16th to endNight
88%
630
33%
1836
29%
630
89%
630
47%
962
September1st to 15thNight
85%
720
30%
1980
25%
720
86%
720
50%
1045
September16th to endNight
81%
671
44%
1856
33%
671
87%
671
72%
808
October1st to 15thNight
75%
660
40%
1892
31%
660
81%
660
63%
857
October16th to endNight
79%
704
42%
2112
36%
704
85%
704
64%
927
November1st to 15thNight
76%
700
39%
2169
34%
700
83%
700
62%
950
November16th to endNight
71%
720
40%
2340
38%
720
79%
720
56%
1028
December1st to 15thNight
70%
720
36%
2340
35%
720
76%
720
49%
1091
December16th to endNight
62%
768
32%
2496
30%
768
68%
768
40%
1299

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
3212323446%66%
47873
Night
3212213346%69%
47133
TransparencyDay
18%46%17%28%24%
47568
Night
16%36%17%28%26%
46939
SeeingDay
6%11%26%33%17%4
5447
Night
4214%38%34%5%
15644

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
4212313235%69%
1611
16th to endDay
6%422212336%64%
1728
February1st to 15thDay
3312312336%65%
1661
16th to endDay
5%413333446%59%
1579
March1st to 15thDay
3212212445%68%
1974
16th to endDay
2212313336%68%
2112
April1st to 15thDay
2212213436%70%
1985
16th to endDay
111112236%75%
2293
May1st to 15thDay
212213336%72%
2331
16th to endDay
11221334473%
2429
June1st to 15thDay
11222482%
2340
16th to endDay
11123481%
2340
July1st to 15thDay
2212426%7%8%8%53%
2340
16th to endDay
44246%47%7%9%11%36%
2467
August1st to 15thDay
3214435%7%7%8%50%
2340
16th to endDay
32134345%6%8%54%
2361
September1st to 15thDay
3313225%5%6%7%58%
1980
16th to endDay
2111223478%
1849
October1st to 15thDay
21121234473%
1738
16th to endDay
11122235%76%
1760
November1st to 15thDay
112112345%75%
1687
16th to endDay
5%122122474%
1620
December1st to 15thDay
5%412222335%64%
1620
16th to endDay
8%422313345%58%
1728
January1st to 15thNight
4213223435%65%
2327
16th to endNight
6%412322345%63%
2496
February1st to 15thNight
3312212235%70%
2188
16th to endNight
6%212213446%64%
1895
March1st to 15thNight
3212112246%70%
1984
16th to endNight
221212245%73%
2112
April1st to 15thNight
3211223336%69%
1962
16th to endNight
11111125%80%
1664
May1st to 15thNight
111112345%76%
1619
16th to endNight
1121212480%
1684
June1st to 15thNight
112123481%
1620
16th to endNight
111122483%
1620
July1st to 15thNight
11123246%6%9%59%
1620
16th to endNight
1213435%6%7%14%47%
1701
August1st to 15thNight
2123245%6%10%60%
1620
16th to endNight
1112335%6%7%9%58%
1836
September1st to 15thNight
211332445%8%60%
1980
16th to endNight
211223480%
1856
October1st to 15thNight
211212335%74%
1892
16th to endNight
111111223477%
2112
November1st to 15thNight
2112112236%73%
2169
16th to endNight
42121222475%
2340
December1st to 15thNight
6%312212236%67%
2340
16th to endNight
8%412223436%59%
2496

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
20%35%19%33%16%
1612
16th to endDay
22%38%19%32%14%
1728
February1st to 15thDay
21%38%23%23%20%
1661
16th to endDay
26%37%20%28%13%
1579
March1st to 15thDay
18%3418%36%18%
1974
16th to endDay
17%36%20%34%17%
2112
April1st to 15thDay
16%25%19%34%21%
1985
16th to endDay
13%2415%35%28%
2293
May1st to 15thDay
14%3416%32%28%
2331
16th to endDay
14%3410%34%31%
2432
June1st to 15thDay
8%127%27%52%
2340
16th to endDay
9%125%21%59%
2340
July1st to 15thDay
22%8%10%16%15%25%
2201
16th to endDay
33%12%16%17%15%4
2312
August1st to 15thDay
27%7%9%18%19%17%
2325
16th to endDay
24%7%11%19%24%13%
2361
September1st to 15thDay
23%6%10%16%22%20%
1980
16th to endDay
10%2314%34%35%
1849
October1st to 15thDay
14%3415%30%31%
1738
16th to endDay
12%35%15%33%30%
1760
November1st to 15thDay
12%25%21%34%23%
1687
16th to endDay
15%2319%30%28%
1620
December1st to 15thDay
23%310%24%26%11%
1620
16th to endDay
29%310%23%26%7%
1728
January1st to 15thNight
22%35%21%31%16%
2327
16th to endNight
23%35%19%30%17%
2496
February1st to 15thNight
18%38%21%26%22%
2199
16th to endNight
20%36%21%30%17%
1895
March1st to 15thNight
17%2316%38%21%
1984
16th to endNight
14%36%19%35%20%
2112
April1st to 15thNight
17%25%15%34%24%
1962
16th to endNight
8%2313%36%35%
1664
May1st to 15thNight
11%3416%30%34%
1620
16th to endNight
11%1413%34%35%
1685
June1st to 15thNight
8%117%23%57%
1620
16th to endNight
8%21415%67%
1620
July1st to 15thNight
18%7%14%14%18%27%
1530
16th to endNight
24%9%19%20%17%8%
1593
August1st to 15thNight
18%7%12%19%20%21%
1611
16th to endNight
19%7%11%21%23%16%
1836
September1st to 15thNight
20%6%12%18%20%21%
1980
16th to endNight
9%2311%36%37%
1856
October1st to 15thNight
13%25%18%26%33%
1892
16th to endNight
11%36%12%26%39%
2112
November1st to 15thNight
13%2419%35%24%
2169
16th to endNight
16%2316%30%30%
2340
December1st to 15thNight
19%37%23%27%17%
2340
16th to endNight
26%310%21%29%8%
2496

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%6%22%34%14%1
90
16th to endDay
12%9%19%31%21%5%
96
February1st to 15thDay
5%9%27%36%15%4
176
16th to endDay
14%22%30%20%10%1
238
March1st to 15thDay
8%17%29%25%16%4
270
16th to endDay
7%20%32%23%12%3
288
April1st to 15thDay
9%24%30%20%11%3
269
16th to endDay
8%27%35%18%8%1
270
May1st to 15thDay
6%19%38%22%10%2
288
16th to endDay
419%33%29%10%2
330
June1st to 15thDay
116%35%29%11%4
315
16th to endDay
1227%43%19%5%
315
July1st to 15thDay
1327%43%17%5%
305
16th to endDay
5%210%43%27%11%
327
August1st to 15thDay
2213%45%27%7%
315
16th to endDay
315%43%26%9%
332
September1st to 15thDay
5%325%39%20%6%
315
16th to endDay
6%8%26%37%15%5%
268
October1st to 15thDay
216%28%28%19%5%
178
16th to endDay
6%414%35%34%5%
96
November1st to 15thDay
27%17%27%32%12%
90
16th to endDay
6%15%26%31%17%2
90
December1st to 15thDay
6%314%42%31%2
90
16th to endDay
13%10%18%35%19%2
96
January1st to 15thNight
5%218%43%21%6%
720
16th to endNight
8%218%42%24%3
768
February1st to 15thNight
6%219%44%25%1
704
16th to endNight
8%322%46%17%1
632
March1st to 15thNight
5%322%41%24%2
720
16th to endNight
4418%44%26%2
768
April1st to 15thNight
45%23%42%21%1
703
16th to endNight
17%24%41%22%3
540
May1st to 15thNight
25%16%46%27%1
540
16th to endNight
2319%41%30%3
563
June1st to 15thNight
1214%44%34%2
540
16th to endNight
117%38%47%3
540
July1st to 15thNight
2326%59%7%
510
16th to endNight
2115%60%19%
564
August1st to 15thNight
2217%66%10%
539
16th to endNight
1217%61%16%
630
September1st to 15thNight
3425%55%11%
720
16th to endNight
2112%31%44%8%
671
October1st to 15thNight
2315%42%33%3
660
16th to endNight
2113%37%36%8%
704
November1st to 15thNight
316%45%29%4
700
16th to endNight
5%218%39%28%5%
720
December1st to 15thNight
9%214%43%28%1
720
16th to endNight
11%318%42%20%3
768
Page generated at 2017-09-20 01:49:50. Version ac04

Copyright 2017 A. Danko


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