Chandler
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chandler 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
80%
15514
37%
46533
34%
15477
83%
15477
57%
21598

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
77%
717
33%
2327
35%
716
80%
716
48%
1119
January16th to endNight
72%
768
37%
2496
37%
768
78%
768
44%
1240
February1st to 15thNight
75%
699
37%
2176
37%
699
81%
699
55%
993
February16th to endNight
70%
632
37%
1881
37%
632
74%
632
46%
968
March1st to 15thNight
74%
720
41%
1980
35%
720
80%
720
62%
947
March16th to endNight
77%
768
40%
2112
32%
768
84%
768
67%
967
April1st to 15thNight
74%
710
34%
1969
25%
710
80%
710
61%
939
April16th to endNight
75%
540
46%
1701
39%
540
84%
540
76%
640
May1st to 15thNight
77%
539
40%
1619
33%
539
82%
539
71%
659
May16th to endNight
83%
561
41%
1684
33%
561
87%
561
74%
678
June1st to 15thNight
88%
540
35%
1620
31%
540
89%
540
74%
646
June16th to endNight
92%
540
36%
1620
32%
540
92%
540
77%
638
July1st to 15thNight
85%
510
25%
1530
21%
510
85%
510
51%
757
July16th to endNight
83%
564
27%
1593
23%
531
84%
531
40%
895
August1st to 15thNight
85%
527
29%
1575
26%
524
86%
524
45%
818
August16th to endNight
84%
591
31%
1716
29%
591
84%
591
43%
948
September1st to 15thNight
81%
660
34%
1815
29%
660
83%
660
54%
939
September16th to endNight
85%
656
42%
1815
34%
656
88%
656
69%
826
October1st to 15thNight
83%
660
41%
1889
36%
660
86%
660
65%
850
October16th to endNight
87%
704
45%
2112
40%
704
90%
704
72%
870
November1st to 15thNight
88%
700
42%
2127
41%
700
89%
700
67%
896
November16th to endNight
79%
720
40%
2340
40%
720
83%
720
56%
1016
December1st to 15thNight
76%
720
38%
2340
40%
720
78%
720
50%
1079
December16th to endNight
72%
768
36%
2496
39%
768
75%
768
43%
1270

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
3212212346%69%
47431
Night
3212213346%69%
46731
TransparencyDay
16%25%11%24%39%
47126
Night
16%2410%22%42%
46537
SeeingDay
3211%26%37%18%
5316
Night
49%41%39%4
15525

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%313312236%66%
1611
16th to endDay
6%313212236%64%
1728
February1st to 15thDay
3213312236%68%
1682
16th to endDay
6%313313247%62%
1591
March1st to 15thDay
3212322345%68%
1980
16th to endDay
2212223245%70%
2112
April1st to 15thDay
212213337%71%
1977
16th to endDay
11111112481%
2256
May1st to 15thDay
11111225%80%
2331
16th to endDay
2111112482%
2429
June1st to 15thDay
11111112383%
2340
16th to endDay
111112383%
2340
July1st to 15thDay
22143245%7%8%59%
2340
16th to endDay
4313445%6%7%11%45%
2467
August1st to 15thDay
32133245%7%8%56%
2290
16th to endDay
31332347%10%57%
2129
September1st to 15thDay
331332345%6%62%
1815
16th to endDay
21121222479%
1815
October1st to 15thDay
111212335%75%
1738
16th to endDay
211123480%
1760
November1st to 15thDay
112112235%77%
1732
16th to endDay
421212235%72%
1620
December1st to 15thDay
6%313323335%63%
1620
16th to endDay
6%313313347%60%
1728
January1st to 15thNight
5%213323345%64%
2327
16th to endNight
8%212313325%63%
2496
February1st to 15thNight
3312212236%69%
2167
16th to endNight
6%312323336%62%
1881
March1st to 15thNight
4212212345%70%
1980
16th to endNight
311212235%75%
2112
April1st to 15thNight
3212212336%70%
1969
16th to endNight
1111112384%
1701
May1st to 15thNight
11112245%77%
1619
16th to endNight
11111211284%
1684
June1st to 15thNight
11111122481%
1620
16th to endNight
1112125%82%
1620
July1st to 15thNight
22133245%7%9%58%
1620
16th to endNight
4214426%6%7%12%47%
1701
August1st to 15thNight
21133245%8%10%54%
1584
16th to endNight
1214425%6%6%8%54%
1716
September1st to 15thNight
221342345%8%61%
1815
16th to endNight
11121233476%
1815
October1st to 15thNight
2112213235%75%
1889
16th to endNight
11111122479%
2112
November1st to 15thNight
211212225%76%
2127
16th to endNight
421221222473%
2340
December1st to 15thNight
7%212212346%65%
2340
16th to endNight
7%314323346%60%
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
21%25%15%28%27%
1612
16th to endDay
22%1415%26%29%
1728
February1st to 15thDay
18%25%16%27%28%
1682
16th to endDay
22%2315%31%24%
1591
March1st to 15thDay
17%137%29%39%
1980
16th to endDay
17%138%32%36%
2112
April1st to 15thDay
13%127%34%39%
1977
16th to endDay
9%126%23%56%
2256
May1st to 15thDay
8%138%22%56%
2331
16th to endDay
8%125%21%59%
2432
June1st to 15thDay
8%1314%70%
2340
16th to endDay
9%2310%73%
2340
July1st to 15thDay
19%6%9%14%17%32%
2201
16th to endDay
27%9%13%22%18%9%
2312
August1st to 15thDay
22%5%10%16%16%28%
2275
16th to endDay
19%6%8%17%26%21%
2129
September1st to 15thDay
21%38%13%23%29%
1815
16th to endDay
10%125%26%52%
1815
October1st to 15thDay
12%348%25%46%
1738
16th to endDay
9%148%26%49%
1760
November1st to 15thDay
11%1311%32%41%
1732
16th to endDay
16%139%27%42%
1620
December1st to 15thDay
23%35%15%29%23%
1620
16th to endDay
23%36%19%30%15%
1728
January1st to 15thNight
21%35%11%25%33%
2327
16th to endNight
24%2312%26%30%
2496
February1st to 15thNight
17%25%14%24%35%
2178
16th to endNight
25%2211%26%32%
1881
March1st to 15thNight
16%128%24%46%
1980
16th to endNight
13%138%30%42%
2112
April1st to 15thNight
15%136%28%43%
1969
16th to endNight
7%25%20%63%
1701
May1st to 15thNight
9%126%23%55%
1620
16th to endNight
9%115%16%66%
1685
June1st to 15thNight
8%12311%72%
1620
16th to endNight
8%337%76%
1620
July1st to 15thNight
19%411%17%13%33%
1530
16th to endNight
25%8%12%19%21%13%
1593
August1st to 15thNight
21%6%10%16%15%29%
1575
16th to endNight
25%5%7%13%24%22%
1716
September1st to 15thNight
19%49%17%20%29%
1815
16th to endNight
12%126%21%55%
1815
October1st to 15thNight
13%239%22%48%
1889
16th to endNight
10%48%17%57%
2112
November1st to 15thNight
12%138%26%48%
2127
16th to endNight
16%138%22%46%
2340
December1st to 15thNight
20%2414%27%30%
2340
16th to endNight
25%35%15%29%21%
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
17%111%34%31%4
90
16th to endDay
6%5%8%32%28%19%
96
February1st to 15thDay
5%114%29%41%7%
197
16th to endDay
7%321%34%26%6%
238
March1st to 15thDay
47%18%30%19%20%
270
16th to endDay
16%18%30%28%13%
288
April1st to 15thDay
45%20%30%26%12%
269
16th to endDay
28%26%30%24%6%
270
May1st to 15thDay
1423%29%29%12%
288
16th to endDay
2114%31%38%11%
330
June1st to 15thDay
328%33%35%16%
315
16th to endDay
2322%45%25%
315
July1st to 15thDay
3316%50%24%
305
16th to endDay
3312%43%38%
327
August1st to 15thDay
3215%45%34%
300
16th to endDay
117%51%29%
268
September1st to 15thDay
8%5%22%46%16%
255
16th to endDay
4111%29%38%14%
255
October1st to 15thDay
2315%28%33%16%
178
16th to endDay
2315%51%28%
96
November1st to 15thDay
113%27%41%16%
90
16th to endDay
4116%32%38%6%
90
December1st to 15thDay
31323%53%15%
90
16th to endDay
11%219%30%31%5%
96
January1st to 15thNight
6%9%52%28%2
720
16th to endNight
9%111%48%26%2
768
February1st to 15thNight
5%11%48%29%3
704
16th to endNight
8%113%51%24%1
632
March1st to 15thNight
5%115%47%26%4
720
16th to endNight
3113%43%33%4
768
April1st to 15thNight
3215%49%27%1
710
16th to endNight
1219%47%26%3
540
May1st to 15thNight
1116%46%31%2
540
16th to endNight
211%44%38%2
563
June1st to 15thNight
16%47%40%2
540
16th to endNight
1234%58%2
540
July1st to 15thNight
3328%55%7%
510
16th to endNight
4215%66%10%
564
August1st to 15thNight
2218%65%11%
527
16th to endNight
3219%62%12%
591
September1st to 15thNight
37%26%54%8%
660
16th to endNight
27%38%44%6%
656
October1st to 15thNight
28%45%40%1
660
16th to endNight
15%43%42%5%
704
November1st to 15thNight
26%47%39%3
700
16th to endNight
5%8%45%35%3
720
December1st to 15thNight
8%18%45%34%1
720
16th to endNight
8%19%49%27%2
768
Page generated at 2017-08-13 11:16:25. Version ac04

Copyright 2017 A. Danko


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