Grand Canyon Caverns
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Canyon Caverns clear sky chart from 2005-11-05 to 2017-09-22.

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
69%
15745
34%
46982
28%
15709
75%
15709
52%
22630

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
66%
716
32%
2327
31%
716
73%
716
46%
1132
January16th to endNight
62%
768
34%
2496
31%
768
71%
768
41%
1258
February1st to 15thNight
66%
700
34%
2157
31%
700
74%
700
50%
1043
February16th to endNight
55%
632
34%
1895
32%
632
63%
632
43%
1004
March1st to 15thNight
62%
720
35%
2034
29%
720
72%
720
53%
1021
March16th to endNight
64%
768
34%
2112
25%
768
72%
768
54%
1060
April1st to 15thNight
53%
719
30%
1937
16%
719
62%
719
50%
1007
April16th to endNight
61%
561
41%
1641
25%
561
73%
561
63%
710
May1st to 15thNight
64%
539
35%
1619
24%
539
71%
539
61%
709
May16th to endNight
64%
561
35%
1685
25%
561
71%
561
63%
723
June1st to 15thNight
73%
540
31%
1620
26%
540
76%
540
67%
680
June16th to endNight
82%
540
34%
1620
32%
540
83%
540
73%
654
July1st to 15thNight
82%
510
24%
1530
21%
510
82%
510
49%
758
July16th to endNight
80%
564
23%
1593
20%
531
81%
531
40%
877
August1st to 15thNight
84%
539
34%
1611
29%
536
85%
536
53%
779
August16th to endNight
82%
693
38%
1848
29%
693
83%
693
54%
965
September1st to 15thNight
78%
720
29%
1980
24%
720
80%
720
48%
1080
September16th to endNight
78%
683
45%
1890
33%
683
87%
683
73%
820
October1st to 15thNight
72%
660
39%
1856
31%
660
78%
660
62%
861
October16th to endNight
73%
704
41%
2112
33%
704
81%
704
63%
941
November1st to 15thNight
71%
700
37%
2243
32%
700
79%
700
55%
1008
November16th to endNight
69%
720
39%
2340
35%
720
78%
720
54%
1030
December1st to 15thNight
68%
720
33%
2340
31%
720
75%
720
44%
1166
December16th to endNight
60%
768
31%
2496
29%
768
66%
768
36%
1344

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
4313323346%63%
47899
Night
3312213346%67%
47177
TransparencyDay
22%36%15%27%24%
47594
Night
18%36%17%29%23%
46983
SeeingDay
7%10%25%32%17%6%
5536
Night
4317%34%32%7%
15756

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
35%14222335%65%
1611
16th to endDay
7%5%13313245%61%
1728
February1st to 15thDay
45%23212347%60%
1703
16th to endDay
8%6%23423336%55%
1579
March1st to 15thDay
3422313346%65%
1926
16th to endDay
3422223346%64%
2112
April1st to 15thDay
3314324345%63%
2009
16th to endDay
221221223472%
2318
May1st to 15thDay
2213313346%67%
2331
16th to endDay
2313213235%70%
2429
June1st to 15thDay
111211122480%
2340
16th to endDay
21221222379%
2340
July1st to 15thDay
3315%436%5%5%8%52%
2340
16th to endDay
6%426%7%47%6%7%8%37%
2467
August1st to 15thDay
4425%5%35%46%5%51%
2340
16th to endDay
44245%35%5%5%6%53%
2349
September1st to 15thDay
4225%4345%5%6%55%
1980
16th to endDay
221221223474%
1882
October1st to 15thDay
231331333468%
1773
16th to endDay
2112222235%73%
1760
November1st to 15thDay
2212212236%72%
1614
16th to endDay
331222224470%
1620
December1st to 15thDay
5%7%14322349%57%
1620
16th to endDay
8%6%1421335%6%56%
1728
January1st to 15thNight
4422213235%64%
2327
16th to endNight
5%6%13313335%61%
2496
February1st to 15thNight
25%23212235%67%
2146
16th to endNight
5%5%2442225%6%59%
1895
March1st to 15thNight
231222345%6%64%
2034
16th to endNight
221231335%6%66%
2112
April1st to 15thNight
3212323335%67%
1937
16th to endNight
111212235%76%
1641
May1st to 15thNight
2212212126%74%
1619
16th to endNight
112312245%73%
1684
June1st to 15thNight
11212235%77%
1620
16th to endNight
1211222381%
1620
July1st to 15thNight
211331346%9%60%
1620
16th to endNight
2214435%6%8%11%48%
1701
August1st to 15thNight
211331335%8%65%
1620
16th to endNight
2312313447%63%
1848
September1st to 15thNight
3213425%447%60%
1980
16th to endNight
1111123381%
1890
October1st to 15thNight
2112212245%73%
1856
16th to endNight
1112121246%74%
2112
November1st to 15thNight
121331333471%
2243
16th to endNight
2212312235%71%
2340
December1st to 15thNight
5%31222345%7%59%
2340
16th to endNight
7%5%23324445%56%
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
22%25%19%37%12%
1612
16th to endDay
26%28%19%30%13%
1728
February1st to 15thDay
23%38%20%24%20%
1703
16th to endDay
30%36%16%29%14%
1579
March1st to 15thDay
20%3418%37%15%
1926
16th to endDay
20%36%22%30%16%
2112
April1st to 15thDay
21%36%18%29%20%
2009
16th to endDay
15%2418%33%24%
2318
May1st to 15thDay
17%26%16%34%22%
2331
16th to endDay
17%35%13%33%26%
2432
June1st to 15thDay
10%129%24%52%
2340
16th to endDay
11%125%18%59%
2340
July1st to 15thDay
28%5%7%10%14%32%
2201
16th to endDay
38%8%12%14%14%10%
2312
August1st to 15thDay
31%6%8%11%20%21%
2325
16th to endDay
29%6%6%14%25%17%
2349
September1st to 15thDay
27%5%9%13%19%24%
1980
16th to endDay
15%2412%29%35%
1882
October1st to 15thDay
20%2314%29%29%
1773
16th to endDay
14%25%14%34%28%
1760
November1st to 15thDay
15%2422%31%24%
1614
16th to endDay
18%25%19%30%24%
1620
December1st to 15thDay
26%49%23%25%10%
1620
16th to endDay
29%410%21%24%9%
1728
January1st to 15thNight
22%35%24%33%12%
2327
16th to endNight
25%37%20%28%15%
2496
February1st to 15thNight
20%38%20%26%21%
2157
16th to endNight
25%35%19%30%15%
1895
March1st to 15thNight
18%36%19%37%14%
2034
16th to endNight
17%48%21%32%16%
2112
April1st to 15thNight
20%3417%34%18%
1937
16th to endNight
11%25%19%33%27%
1641
May1st to 15thNight
14%15%17%33%28%
1620
16th to endNight
12%26%14%37%26%
1685
June1st to 15thNight
10%236%26%50%
1620
16th to endNight
9%126%17%62%
1620
July1st to 15thNight
19%5%9%13%15%36%
1530
16th to endNight
24%8%15%18%20%12%
1593
August1st to 15thNight
16%5%7%18%26%25%
1611
16th to endNight
19%47%19%29%20%
1848
September1st to 15thNight
22%5%9%16%22%22%
1980
16th to endNight
9%1312%33%39%
1890
October1st to 15thNight
14%26%17%30%29%
1856
16th to endNight
12%36%12%32%32%
2112
November1st to 15thNight
16%3418%36%20%
2243
16th to endNight
16%25%17%30%26%
2340
December1st to 15thNight
22%48%23%28%12%
2340
16th to endNight
29%49%22%25%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
24%11%25%27%7%3
90
16th to endDay
11%5%23%29%19%10%
96
February1st to 15thDay
10%10%32%27%16%3
218
16th to endDay
16%18%30%21%10%2
238
March1st to 15thDay
9%17%25%30%14%3
270
16th to endDay
5%22%27%27%14%3
288
April1st to 15thDay
10%19%33%21%9%5%
269
16th to endDay
5%28%33%21%7%3
270
May1st to 15thDay
6%15%33%30%11%2
288
16th to endDay
7%14%29%30%13%3
330
June1st to 15thDay
38%32%35%13%6%
315
16th to endDay
3121%45%18%9%
315
July1st to 15thDay
4122%43%21%5%
305
16th to endDay
6%114%38%29%9%
327
August1st to 15thDay
7%217%38%24%9%
315
16th to endDay
6%113%39%26%12%
332
September1st to 15thDay
4424%37%22%6%
315
16th to endDay
5%10%22%31%21%8%
280
October1st to 15thDay
5%10%31%31%15%5%
213
16th to endDay
6%9%18%38%21%5%
96
November1st to 15thDay
210%17%23%33%13%
90
16th to endDay
12%11%30%31%14%1
90
December1st to 15thDay
35%21%42%25%2
90
16th to endDay
13%8%25%40%11%1
96
January1st to 15thNight
6%419%38%22%9%
720
16th to endNight
10%417%34%26%5%
768
February1st to 15thNight
5%320%40%25%5%
704
16th to endNight
8%427%36%18%3
632
March1st to 15thNight
45%23%37%25%3
720
16th to endNight
35%22%37%25%5%
768
April1st to 15thNight
48%28%31%20%5%
719
16th to endNight
18%25%37%22%4
561
May1st to 15thNight
4323%39%25%3
540
16th to endNight
15%23%36%27%5%
563
June1st to 15thNight
1219%38%32%4
540
16th to endNight
112%36%43%6%
540
July1st to 15thNight
36%30%50%8%
510
16th to endNight
4324%55%12%
564
August1st to 15thNight
3426%55%9%
539
16th to endNight
35%23%47%19%
693
September1st to 15thNight
37%27%45%15%
720
16th to endNight
2214%28%37%14%
683
October1st to 15thNight
3316%40%30%6%
660
16th to endNight
2118%33%31%12%
704
November1st to 15thNight
3218%35%32%8%
700
16th to endNight
3417%36%27%9%
720
December1st to 15thNight
8%217%38%27%5%
720
16th to endNight
11%419%35%23%5%
768
Page generated at 2017-09-23 03:43:40. Version ac04

Copyright 2017 A. Danko


Grand Canyon Caverns Clear Sky Chart | Charts Home