Zion Gateway to the Stars
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Zion Gateway to the Stars clear sky chart from 2005-11-05 to 2017-10-06.

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
67%
15697
32%
47130
26%
15658
73%
15658
49%
23339

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
65%
717
30%
2327
29%
716
71%
716
45%
1143
January16th to endNight
62%
768
32%
2496
29%
768
69%
768
41%
1303
February1st to 15thNight
64%
697
28%
2217
26%
697
71%
697
43%
1140
February16th to endNight
54%
632
30%
1895
26%
632
61%
632
39%
1045
March1st to 15thNight
59%
720
33%
2022
25%
720
68%
720
49%
1050
March16th to endNight
61%
768
31%
2112
20%
768
70%
768
48%
1113
April1st to 15thNight
49%
701
26%
1927
13%
701
59%
701
45%
1028
April16th to endNight
51%
540
37%
1620
21%
540
64%
540
48%
766
May1st to 15thNight
60%
540
32%
1619
23%
539
66%
539
53%
770
May16th to endNight
62%
562
29%
1685
21%
561
69%
561
50%
807
June1st to 15thNight
68%
540
30%
1620
25%
540
72%
540
64%
688
June16th to endNight
77%
540
32%
1620
31%
540
79%
540
73%
650
July1st to 15thNight
81%
510
22%
1530
21%
510
82%
510
48%
773
July16th to endNight
79%
564
23%
1593
20%
531
79%
531
35%
911
August1st to 15thNight
81%
539
30%
1611
25%
536
82%
536
51%
773
August16th to endNight
83%
627
38%
1788
32%
627
83%
627
53%
895
September1st to 15thNight
80%
720
31%
1980
26%
720
82%
720
51%
1027
September16th to endNight
80%
716
44%
1980
32%
716
87%
716
68%
888
October1st to 15thNight
70%
684
35%
1950
27%
684
76%
684
55%
961
October16th to endNight
69%
704
38%
2112
29%
704
79%
704
56%
975
November1st to 15thNight
72%
700
33%
2250
30%
700
79%
700
53%
1030
November16th to endNight
68%
720
37%
2340
34%
720
76%
720
52%
1066
December1st to 15thNight
67%
720
30%
2340
27%
720
73%
720
45%
1153
December16th to endNight
57%
768
28%
2496
24%
768
65%
768
34%
1384

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
4413323446%61%
48065
Night
4312323346%63%
47325
TransparencyDay
22%48%19%26%19%
47760
Night
20%49%20%28%17%
47131
SeeingDay
7%12%28%32%14%4
5505
Night
5%317%36%29%6%
15708

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
5%6%23312145%63%
1611
16th to endDay
6%6%1332235%6%59%
1728
February1st to 15thDay
36%1222445%7%57%
1643
16th to endDay
7%8%23324436%53%
1579
March1st to 15thDay
3413323445%62%
1936
16th to endDay
5%5%2232346%8%55%
2112
April1st to 15thDay
5%5%2332335%7%57%
2017
16th to endDay
4313322346%64%
2340
May1st to 15thDay
332332445%8%57%
2331
16th to endDay
331332345%6%61%
2429
June1st to 15thDay
111221234373%
2340
16th to endDay
11111233477%
2340
July1st to 15thDay
4314425%6%5%7%55%
2340
16th to endDay
5%425%6%47%5%7%9%41%
2467
August1st to 15thDay
43145%35%5%6%6%54%
2340
16th to endDay
321332445%7%59%
2413
September1st to 15thDay
43145%345%5%6%56%
1980
16th to endDay
321232333471%
1980
October1st to 15thDay
5%31231234466%
1805
16th to endDay
412213245%70%
1760
November1st to 15thDay
3212212345%69%
1606
16th to endDay
4412212346%66%
1620
December1st to 15thDay
37%13323347%57%
1620
16th to endDay
9%8%13312337%54%
1728
January1st to 15thNight
6%5%2212335%63%
2327
16th to endNight
6%5%13313446%58%
2496
February1st to 15thNight
35%12323437%61%
2206
16th to endNight
6%8%13323446%54%
1895
March1st to 15thNight
441221345%7%60%
2022
16th to endNight
321232445%8%62%
2112
April1st to 15thNight
5%313413345%62%
1927
16th to endNight
3312223347%64%
1620
May1st to 15thNight
332222346%66%
1619
16th to endNight
2212323345%67%
1684
June1st to 15thNight
1111211246%74%
1620
16th to endNight
1211223480%
1620
July1st to 15thNight
111343446%9%59%
1620
16th to endNight
3313445%8%8%8%47%
1701
August1st to 15thNight
1213324448%62%
1620
16th to endNight
221242345%7%63%
1788
September1st to 15thNight
5%21231335%6%63%
1980
16th to endNight
21111223378%
1980
October1st to 15thNight
4212222346%68%
1950
16th to endNight
321222224470%
2112
November1st to 15thNight
1212222446%67%
2250
16th to endNight
4312212236%69%
2340
December1st to 15thNight
5%5%1221335%7%60%
2340
16th to endNight
8%6%2331335%8%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%311%30%27%3
1612
16th to endDay
25%411%28%22%7%
1728
February1st to 15thDay
24%5%13%25%22%9%
1643
16th to endDay
31%39%19%29%6%
1579
March1st to 15thDay
21%47%27%31%7%
1936
16th to endDay
25%48%25%27%8%
2112
April1st to 15thDay
25%37%21%27%14%
2017
16th to endDay
21%36%22%32%13%
2340
May1st to 15thDay
23%49%16%32%13%
2331
16th to endDay
21%48%16%31%17%
2432
June1st to 15thDay
13%25%7%29%41%
2340
16th to endDay
9%235%20%57%
2340
July1st to 15thDay
27%6%7%11%14%32%
2201
16th to endDay
34%7%10%17%14%16%
2312
August1st to 15thDay
25%6%8%14%18%26%
2325
16th to endDay
21%5%7%16%25%23%
2413
September1st to 15thDay
25%5%10%13%16%30%
1980
16th to endDay
16%25%15%28%30%
1980
October1st to 15thDay
19%36%17%32%20%
1805
16th to endDay
16%36%19%36%17%
1760
November1st to 15thDay
16%38%23%33%15%
1606
16th to endDay
18%37%26%31%12%
1620
December1st to 15thDay
25%415%26%25%2
1620
16th to endDay
31%5%16%22%20%3
1728
January1st to 15thNight
22%312%28%27%4
2327
16th to endNight
26%410%25%23%9%
2496
February1st to 15thNight
23%411%25%23%11%
2217
16th to endNight
28%49%18%32%6%
1895
March1st to 15thNight
21%38%27%32%6%
2022
16th to endNight
18%6%9%28%27%10%
2112
April1st to 15thNight
23%47%22%29%13%
1927
16th to endNight
18%36%22%36%12%
1620
May1st to 15thNight
17%38%19%36%14%
1620
16th to endNight
18%47%17%34%19%
1685
June1st to 15thNight
11%249%29%41%
1620
16th to endNight
9%135%19%60%
1620
July1st to 15thNight
19%6%10%13%16%33%
1530
16th to endNight
28%8%10%19%13%19%
1593
August1st to 15thNight
20%211%14%22%28%
1611
16th to endNight
18%48%16%26%26%
1788
September1st to 15thNight
19%5%8%14%21%30%
1980
16th to endNight
11%25%16%29%34%
1980
October1st to 15thNight
18%36%17%32%21%
1950
16th to endNight
15%37%15%40%17%
2112
November1st to 15thNight
16%410%21%32%14%
2250
16th to endNight
18%26%21%36%14%
2340
December1st to 15thNight
22%314%28%25%4
2340
16th to endNight
30%5%14%24%20%4
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
31%8%17%26%15%
90
16th to endDay
11%7%16%30%31%3
96
February1st to 15thDay
10%6%23%29%24%5%
158
16th to endDay
14%22%33%19%8%1
238
March1st to 15thDay
8%19%32%27%10%2
270
16th to endDay
8%22%37%24%6%
288
April1st to 15thDay
9%28%30%19%7%3
269
16th to endDay
12%29%25%21%9%1
270
May1st to 15thDay
7%20%35%28%7%1
288
16th to endDay
8%19%29%26%13%3
330
June1st to 15thDay
5%13%35%31%11%3
315
16th to endDay
429%39%20%5%
315
July1st to 15thDay
4324%45%16%5%
305
16th to endDay
7%219%43%21%6%
327
August1st to 15thDay
7%325%41%15%6%
315
16th to endDay
4126%38%20%8%
332
September1st to 15thDay
5%434%33%15%7%
315
16th to endDay
5%10%25%35%19%5%
315
October1st to 15thDay
5%15%35%26%13%3
207
16th to endDay
11%8%32%38%8%1
96
November1st to 15thDay
310%18%33%30%4
90
16th to endDay
11%8%38%32%8%
90
December1st to 15thDay
12%23%45%17%1
90
16th to endDay
17%8%17%32%19%4
96
January1st to 15thNight
9%317%37%23%9%
720
16th to endNight
9%218%37%23%7%
768
February1st to 15thNight
6%119%42%23%5%
704
16th to endNight
9%5%25%38%17%3
632
March1st to 15thNight
7%7%22%37%21%4
720
16th to endNight
38%22%36%24%3
768
April1st to 15thNight
5%9%29%32%18%4
701
16th to endNight
6%11%26%33%17%3
540
May1st to 15thNight
5%425%40%19%4
540
16th to endNight
37%23%35%26%4
563
June1st to 15thNight
2321%42%28%1
540
16th to endNight
2115%42%36%2
540
July1st to 15thNight
27%35%47%7%
510
16th to endNight
5%5%31%48%9%
564
August1st to 15thNight
25%33%50%7%
539
16th to endNight
36%29%47%12%
627
September1st to 15thNight
6%5%29%45%11%
720
16th to endNight
3111%31%39%12%
716
October1st to 15thNight
4317%40%25%8%
684
16th to endNight
4318%34%27%11%
704
November1st to 15thNight
2117%42%28%8%
700
16th to endNight
5%416%36%28%8%
720
December1st to 15thNight
9%216%43%21%5%
720
16th to endNight
12%5%19%38%21%3
768
Page generated at 2017-10-07 12:07:52. Version ac04

Copyright 2017 A. Danko


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