Grand Canyon Star Party (South Rim)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Canyon Star Party (South Rim) clear sky chart from 2005-11-05 to 2017-08-12.

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%
15477
33%
46546
24%
15435
68%
15435
46%
23171

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
55%
720
30%
2327
25%
716
66%
716
41%
1169
January16th to endNight
52%
768
34%
2496
26%
768
65%
768
38%
1304
February1st to 15thNight
56%
700
31%
2219
27%
700
65%
700
44%
1107
February16th to endNight
45%
632
34%
1895
25%
632
59%
632
39%
1004
March1st to 15thNight
50%
720
36%
1998
24%
720
63%
720
45%
1019
March16th to endNight
50%
768
34%
2112
19%
768
63%
768
47%
1082
April1st to 15thNight
42%
695
28%
1954
12%
695
54%
695
39%
1026
April16th to endNight
46%
540
41%
1635
20%
540
65%
540
49%
730
May1st to 15thNight
48%
540
35%
1619
21%
539
58%
539
49%
748
May16th to endNight
50%
562
33%
1684
19%
561
61%
561
45%
802
June1st to 15thNight
52%
540
31%
1620
23%
540
60%
540
58%
706
June16th to endNight
66%
540
33%
1620
27%
540
72%
540
64%
684
July1st to 15thNight
71%
510
21%
1530
16%
510
74%
510
41%
822
July16th to endNight
72%
564
21%
1593
19%
531
72%
531
34%
939
August1st to 15thNight
77%
527
29%
1575
23%
524
79%
524
43%
830
August16th to endNight
76%
563
34%
1653
27%
563
80%
563
48%
845
September1st to 15thNight
73%
660
29%
1815
23%
660
76%
660
45%
1011
September16th to endNight
73%
656
43%
1815
29%
656
81%
656
64%
828
October1st to 15thNight
61%
660
37%
1895
23%
660
72%
660
54%
909
October16th to endNight
65%
704
41%
2112
31%
704
75%
704
53%
975
November1st to 15thNight
59%
700
36%
2203
26%
700
72%
700
51%
1016
November16th to endNight
59%
720
38%
2340
32%
720
70%
720
48%
1074
December1st to 15thNight
57%
720
32%
2340
25%
720
69%
720
42%
1159
December16th to endNight
50%
768
29%
2496
25%
768
58%
768
33%
1382

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
3313324446%60%
47428
Night
3313323346%64%
46742
TransparencyDay
26%35%18%28%17%
47123
Night
21%36%21%29%18%
46548
SeeingDay
10%17%33%26%9%2
5274
Night
6%9%21%32%24%5%
15482

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
3314313336%64%
1611
16th to endDay
6%5%1431335%6%58%
1728
February1st to 15thDay
25%24413348%59%
1643
16th to endDay
6%6%2432445%5%54%
1579
March1st to 15thDay
332232345%6%62%
1962
16th to endDay
3323323348%61%
2112
April1st to 15thDay
3324423346%60%
1994
16th to endDay
1313323336%66%
2322
May1st to 15thDay
2223324448%60%
2331
16th to endDay
3313333446%64%
2429
June1st to 15thDay
112212335%76%
2340
16th to endDay
11221223477%
2340
July1st to 15thDay
3326%5%46%6%6%7%46%
2340
16th to endDay
45%38%7%48%8%6%9%32%
2467
August1st to 15thDay
3426%7%5%6%7%7%8%40%
2290
16th to endDay
3325%6%45%6%5%7%49%
2193
September1st to 15thDay
4314436%5%5%6%53%
1815
16th to endDay
221222334469%
1815
October1st to 15thDay
231231334468%
1735
16th to endDay
212323345%70%
1760
November1st to 15thDay
1211212237%71%
1654
16th to endDay
431221332471%
1620
December1st to 15thDay
441332435%7%58%
1620
16th to endDay
8%7%22324446%53%
1728
January1st to 15thNight
4423313345%63%
2327
16th to endNight
7%5%13323436%59%
2496
February1st to 15thNight
2413323346%64%
2208
16th to endNight
441332245%6%59%
1895
March1st to 15thNight
231322336%7%63%
1998
16th to endNight
221231245%7%64%
2112
April1st to 15thNight
2223324345%65%
1954
16th to endNight
2112212246%72%
1635
May1st to 15thNight
2212223346%68%
1619
16th to endNight
112323446%69%
1684
June1st to 15thNight
12212236%75%
1620
16th to endNight
112111245%78%
1620
July1st to 15thNight
2213425%5%6%9%55%
1620
16th to endNight
3326%5%35%6%8%11%43%
1701
August1st to 15thNight
323435%5%5%8%57%
1584
16th to endNight
1243245%7%10%57%
1653
September1st to 15thNight
232442445%7%57%
1815
16th to endNight
1121233477%
1815
October1st to 15thNight
212212335%71%
1895
16th to endNight
2212212236%72%
2112
November1st to 15thNight
1212224347%68%
2203
16th to endNight
3311213246%70%
2340
December1st to 15thNight
441321345%7%61%
2340
16th to endNight
7%5%23423447%53%
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
24%26%28%30%7%
1612
16th to endDay
28%37%24%27%7%
1728
February1st to 15thDay
25%27%27%21%14%
1643
16th to endDay
32%16%20%30%8%
1579
March1st to 15thDay
21%3326%37%8%
1962
16th to endDay
24%35%25%29%11%
2112
April1st to 15thDay
26%3321%29%14%
1994
16th to endDay
20%3323%34%16%
2322
May1st to 15thDay
23%3416%37%14%
2331
16th to endDay
23%3315%34%18%
2432
June1st to 15thDay
13%218%30%43%
2340
16th to endDay
13%25%24%53%
2340
July1st to 15thDay
36%46%9%15%26%
2201
16th to endDay
46%6%12%14%13%7%
2312
August1st to 15thDay
40%47%12%18%15%
2275
16th to endDay
35%45%17%24%12%
2193
September1st to 15thDay
30%47%15%18%23%
1815
16th to endDay
18%3214%33%27%
1815
October1st to 15thDay
21%2318%32%21%
1735
16th to endDay
18%3417%38%17%
1760
November1st to 15thDay
15%16%28%31%16%
1654
16th to endDay
19%25%22%35%14%
1620
December1st to 15thDay
26%310%28%26%3
1620
16th to endDay
32%210%25%21%6%
1728
January1st to 15thNight
25%27%25%32%7%
2327
16th to endNight
29%16%21%30%10%
2496
February1st to 15thNight
23%36%26%25%14%
2219
16th to endNight
26%35%23%30%10%
1895
March1st to 15thNight
20%2426%36%8%
1998
16th to endNight
19%35%26%31%12%
2112
April1st to 15thNight
23%2419%34%15%
1954
16th to endNight
15%1324%37%17%
1635
May1st to 15thNight
17%2320%37%17%
1620
16th to endNight
18%3318%37%18%
1685
June1st to 15thNight
13%217%30%44%
1620
16th to endNight
11%215%23%56%
1620
July1st to 15thNight
26%410%14%14%28%
1530
16th to endNight
32%5%15%20%15%10%
1593
August1st to 15thNight
25%39%20%23%17%
1575
16th to endNight
20%5%8%23%25%16%
1653
September1st to 15thNight
26%37%19%19%24%
1815
16th to endNight
11%2216%32%33%
1815
October1st to 15thNight
17%26%19%30%24%
1895
16th to endNight
16%2415%37%22%
2112
November1st to 15thNight
18%26%22%32%17%
2203
16th to endNight
18%2321%34%18%
2340
December1st to 15thNight
22%48%28%27%8%
2340
16th to endNight
32%210%26%20%6%
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
23%22%27%17%8%
90
16th to endDay
13%16%28%26%15%
96
February1st to 15thDay
7%18%34%25%12%1
158
16th to endDay
20%31%31%14%1
238
March1st to 15thDay
12%22%34%22%5%2
270
16th to endDay
13%27%33%19%32
288
April1st to 15thDay
14%27%32%15%7%2
269
16th to endDay
17%30%31%15%5%
270
May1st to 15thDay
10%23%43%17%4
288
16th to endDay
12%22%36%20%6%1
330
June1st to 15thDay
6%15%45%20%9%2
315
16th to endDay
37%41%32%13%
315
July1st to 15thDay
6%7%37%32%12%3
305
16th to endDay
9%5%23%40%17%3
327
August1st to 15thDay
5%7%26%39%17%3
300
16th to endDay
8%7%27%38%14%3
268
September1st to 15thDay
7%8%38%36%5%4
255
16th to endDay
11%12%29%27%13%4
255
October1st to 15thDay
9%23%30%23%8%4
175
16th to endDay
10%16%28%33%11%
96
November1st to 15thDay
6%13%25%27%24%2
90
16th to endDay
13%20%36%22%7%
90
December1st to 15thDay
315%34%32%13%1
90
16th to endDay
16%26%20%28%7%1
96
January1st to 15thNight
9%9%23%33%19%5%
720
16th to endNight
12%8%23%30%20%5%
768
February1st to 15thNight
7%8%24%35%20%3
704
16th to endNight
10%12%30%31%14%2
632
March1st to 15thNight
7%15%25%29%18%4
720
16th to endNight
6%12%27%33%17%2
768
April1st to 15thNight
7%20%27%26%15%3
695
16th to endNight
6%17%27%29%15%3
540
May1st to 15thNight
5%11%31%32%15%3
540
16th to endNight
415%28%26%22%3
563
June1st to 15thNight
39%31%35%17%2
540
16th to endNight
25%24%38%25%4
540
July1st to 15thNight
5%113%38%33%6%
510
16th to endNight
6%17%36%39%9%
564
August1st to 15thNight
6%37%33%41%8%
527
16th to endNight
4110%30%41%11%
563
September1st to 15thNight
5%310%30%41%9%
660
16th to endNight
35%16%28%35%10%
656
October1st to 15thNight
5%7%21%35%21%7%
660
16th to endNight
47%18%30%29%9%
704
November1st to 15thNight
37%25%30%26%6%
700
16th to endNight
6%10%20%33%22%5%
720
December1st to 15thNight
9%8%21%35%21%2
720
16th to endNight
13%9%22%30%21%2
768
Page generated at 2017-08-13 11:16:24. Version ac04

Copyright 2017 A. Danko


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