Apache-Sitgreaves Research Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apache-Sitgreaves Research Center clear sky chart from 2005-11-05 to 2017-09-10.

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
54%
15456
33%
46820
21%
15414
67%
15414
44%
23136

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
46%
720
30%
2327
20%
716
62%
716
40%
1143
January16th to endNight
43%
768
34%
2496
20%
768
63%
768
37%
1268
February1st to 15thNight
45%
701
31%
2264
21%
700
62%
700
42%
1103
February16th to endNight
36%
632
37%
1838
19%
632
57%
632
40%
911
March1st to 15thNight
45%
720
36%
1980
18%
720
62%
720
46%
1013
March16th to endNight
46%
768
36%
2112
16%
768
63%
768
50%
1039
April1st to 15thNight
36%
650
31%
1909
12%
650
54%
650
43%
922
April16th to endNight
42%
540
40%
1761
20%
540
65%
540
53%
711
May1st to 15thNight
49%
540
36%
1619
20%
539
64%
539
55%
711
May16th to endNight
51%
561
34%
1684
21%
561
63%
561
55%
736
June1st to 15thNight
57%
540
33%
1620
22%
540
65%
540
64%
684
June16th to endNight
70%
540
30%
1620
25%
540
73%
540
61%
726
July1st to 15thNight
69%
510
18%
1530
15%
510
70%
510
33%
899
July16th to endNight
71%
564
14%
1593
13%
531
71%
531
24%
1054
August1st to 15thNight
80%
539
21%
1611
19%
536
80%
536
35%
949
August16th to endNight
78%
573
26%
1839
25%
573
80%
573
34%
1032
September1st to 15thNight
74%
662
28%
1887
22%
662
78%
662
42%
1047
September16th to endNight
69%
656
39%
1815
24%
656
78%
656
60%
842
October1st to 15thNight
57%
660
37%
1939
22%
660
70%
660
54%
897
October16th to endNight
62%
704
40%
2112
26%
704
75%
704
56%
961
November1st to 15thNight
57%
700
38%
2100
24%
700
70%
700
53%
955
November16th to endNight
50%
720
38%
2328
26%
720
66%
720
47%
1027
December1st to 15thNight
47%
720
34%
2340
22%
720
64%
720
39%
1159
December16th to endNight
41%
768
30%
2496
20%
768
55%
768
32%
1347

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
231442445%6%59%
47800
Night
2213323447%65%
47016
TransparencyDay
24%5%7%17%28%17%
47495
Night
19%48%18%29%18%
46822
SeeingDay
7%16%28%29%13%3
5301
Night
412%25%31%21%5%
15461

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
1425%424235%62%
1611
16th to endDay
241432335%6%62%
1728
February1st to 15thDay
15%34323336%62%
1596
16th to endDay
131433446%6%60%
1633
March1st to 15thDay
121232445%6%63%
1980
16th to endDay
2213323325%67%
2112
April1st to 15thDay
111232335%7%66%
2037
16th to endDay
1313323235%69%
2196
May1st to 15thDay
1113224346%69%
2331
16th to endDay
321331334467%
2429
June1st to 15thDay
111212236%75%
2340
16th to endDay
11232434470%
2340
July1st to 15thDay
4326%7%47%7%7%8%37%
2340
16th to endDay
8%438%7%49%9%9%11%23%
2467
August1st to 15thDay
6%427%7%5%7%7%6%8%34%
2340
16th to endDay
5%425%6%46%8%7%8%40%
2361
September1st to 15thDay
5%4146%35%6%7%8%45%
1956
16th to endDay
221232335%5%67%
1815
October1st to 15thDay
322323335%70%
1691
16th to endDay
1212223235%73%
1760
November1st to 15thDay
1212212236%72%
1759
16th to endDay
1313312335%71%
1630
December1st to 15thDay
24245%1245%6%61%
1620
16th to endDay
1415%4345%6%7%55%
1728
January1st to 15thNight
1313434347%63%
2327
16th to endNight
2323323346%64%
2496
February1st to 15thNight
2323323337%65%
2253
16th to endNight
2232445%9%63%
1838
March1st to 15thNight
1312314447%66%
1980
16th to endNight
111221235%6%69%
2112
April1st to 15thNight
11332345%7%65%
1909
16th to endNight
1221233476%
1761
May1st to 15thNight
11222346%72%
1619
16th to endNight
1111212235%75%
1684
June1st to 15thNight
21112235%76%
1620
16th to endNight
11222333473%
1620
July1st to 15thNight
5%3246%35%5%8%10%46%
1620
16th to endNight
5%325%7%37%6%8%12%36%
1701
August1st to 15thNight
23145%46%5%7%9%48%
1620
16th to endNight
23235%36%7%8%11%45%
1839
September1st to 15thNight
331343446%8%55%
1887
16th to endNight
112212226%75%
1815
October1st to 15thNight
21221233474%
1939
16th to endNight
111222123476%
2112
November1st to 15thNight
1112223345%72%
2100
16th to endNight
122213336%72%
2328
December1st to 15thNight
2314322447%62%
2340
16th to endNight
231443445%7%57%
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
25%37%21%31%9%
1612
16th to endDay
24%38%18%34%11%
1728
February1st to 15thDay
25%28%23%23%16%
1596
16th to endDay
23%5%6%22%31%11%
1633
March1st to 15thDay
20%35%17%37%14%
1980
16th to endDay
21%26%19%36%12%
2112
April1st to 15thDay
17%36%19%35%16%
2037
16th to endDay
18%25%16%36%20%
2196
May1st to 15thDay
16%36%19%30%23%
2331
16th to endDay
19%3413%37%20%
2432
June1st to 15thDay
13%239%31%40%
2340
16th to endDay
16%35%8%24%41%
2340
July1st to 15thDay
38%9%12%12%8%17%
2201
16th to endDay
47%13%17%13%6%
2312
August1st to 15thDay
42%8%12%12%16%8%
2325
16th to endDay
37%10%12%16%17%6%
2361
September1st to 15thDay
34%7%9%17%19%11%
1956
16th to endDay
17%46%14%33%23%
1815
October1st to 15thDay
19%35%16%29%24%
1691
16th to endDay
15%36%13%43%18%
1760
November1st to 15thDay
16%25%23%33%17%
1759
16th to endDay
18%2417%34%21%
1630
December1st to 15thDay
25%410%23%25%10%
1620
16th to endDay
29%410%25%24%5%
1728
January1st to 15thNight
22%38%21%33%9%
2327
16th to endNight
24%47%19%34%10%
2496
February1st to 15thNight
22%38%22%24%19%
2264
16th to endNight
18%48%24%29%14%
1838
March1st to 15thNight
18%35%17%38%15%
1980
16th to endNight
15%47%22%36%13%
2112
April1st to 15thNight
18%26%20%34%16%
1909
16th to endNight
11%26%20%39%20%
1761
May1st to 15thNight
12%36%23%29%23%
1620
16th to endNight
12%26%13%40%23%
1685
June1st to 15thNight
10%227%28%47%
1620
16th to endNight
14%346%22%48%
1620
July1st to 15thNight
32%7%13%16%11%18%
1530
16th to endNight
37%12%19%19%8%2
1593
August1st to 15thNight
27%10%16%15%17%12%
1611
16th to endNight
27%9%17%19%18%7%
1839
September1st to 15thNight
25%5%15%20%19%13%
1887
16th to endNight
13%25%16%34%27%
1815
October1st to 15thNight
15%36%19%28%25%
1939
16th to endNight
14%36%14%38%23%
2112
November1st to 15thNight
15%36%22%34%17%
2100
16th to endNight
16%36%16%33%23%
2328
December1st to 15thNight
22%48%21%28%14%
2340
16th to endNight
27%5%11%21%27%5%
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
10%30%35%15%6%2
90
16th to endDay
6%26%30%20%11%5%
96
February1st to 15thDay
6%15%38%24%10%4
111
16th to endDay
14%36%24%16%6%1
238
March1st to 15thDay
7%28%32%20%8%2
270
16th to endDay
6%29%35%21%5%1
288
April1st to 15thDay
6%28%37%16%8%2
269
16th to endDay
11%31%36%15%5%
270
May1st to 15thDay
324%42%21%6%1
288
16th to endDay
423%36%27%6%1
330
June1st to 15thDay
5%15%36%27%13%1
315
16th to endDay
3329%41%17%3
315
July1st to 15thDay
6%121%48%18%3
305
16th to endDay
12%112%38%25%10%
327
August1st to 15thDay
9%13%40%26%9%
315
16th to endDay
8%213%37%33%5%
332
September1st to 15thDay
10%5%22%45%12%3
294
16th to endDay
8%12%26%32%16%5%
255
October1st to 15thDay
314%33%29%11%7%
131
16th to endDay
8%8%33%32%14%3
96
November1st to 15thDay
5%14%22%34%13%10%
90
16th to endDay
5%34%34%20%5%
90
December1st to 15thDay
6%20%33%24%10%5%
90
16th to endDay
5%29%35%25%32
96
January1st to 15thNight
6%14%30%28%16%4
720
16th to endNight
5%17%30%26%16%3
768
February1st to 15thNight
413%32%31%14%3
704
16th to endNight
325%33%24%10%2
632
March1st to 15thNight
5%17%29%29%14%3
720
16th to endNight
317%30%30%14%2
768
April1st to 15thNight
322%35%27%10%1
650
16th to endNight
219%34%28%12%2
540
May1st to 15thNight
210%35%37%13%1
540
16th to endNight
113%29%33%19%2
563
June1st to 15thNight
25%32%40%16%1
540
16th to endNight
1120%48%26%1
540
July1st to 15thNight
7%9%45%32%4
510
16th to endNight
7%7%29%43%10%
564
August1st to 15thNight
5%328%47%14%
539
16th to endNight
46%30%45%12%
573
September1st to 15thNight
5%112%35%37%7%
662
16th to endNight
27%16%31%32%9%
656
October1st to 15thNight
210%27%33%20%5%
660
16th to endNight
28%23%34%23%7%
704
November1st to 15thNight
112%26%32%21%5%
700
16th to endNight
5%16%26%29%15%7%
720
December1st to 15thNight
5%16%26%27%21%2
720
16th to endNight
421%30%28%12%3
768
Page generated at 2017-09-11 16:35:24. Version ac04

Copyright 2017 A. Danko


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