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Phoenix
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Phoenix clear sky chart from 2005-11-05 to 2017-05-24.

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%
15306
38%
45847
35%
15267
83%
15267
58%
21209

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
76%
718
33%
2327
36%
716
79%
716
48%
1113
January16th to endNight
71%
768
37%
2496
37%
768
77%
768
44%
1244
February1st to 15thNight
76%
699
38%
2166
38%
698
81%
698
55%
998
February16th to endNight
71%
632
37%
1892
38%
632
75%
632
47%
972
March1st to 15thNight
74%
720
41%
1980
35%
720
80%
720
61%
944
March16th to endNight
78%
768
41%
2112
33%
768
84%
768
66%
972
April1st to 15thNight
73%
719
34%
1978
24%
719
80%
719
61%
947
April16th to endNight
73%
540
47%
1684
38%
540
82%
540
75%
640
May1st to 15thNight
78%
539
40%
1619
33%
539
83%
539
68%
676
May16th to endNight
80%
540
40%
1621
31%
540
85%
540
74%
650
June1st to 15thNight
89%
495
38%
1485
33%
495
90%
495
75%
592
June16th to endNight
91%
495
33%
1485
29%
495
91%
495
76%
586
July1st to 15thNight
84%
465
28%
1395
24%
465
84%
465
50%
697
July16th to endNight
86%
522
30%
1467
25%
489
87%
489
46%
772
August1st to 15thNight
86%
494
33%
1476
29%
491
87%
491
49%
745
August16th to endNight
82%
604
33%
1720
29%
604
82%
604
46%
931
September1st to 15thNight
81%
660
35%
1815
30%
660
83%
660
54%
935
September16th to endNight
87%
656
42%
1815
35%
656
90%
656
70%
813
October1st to 15thNight
83%
660
42%
1884
36%
660
87%
660
66%
839
October16th to endNight
86%
704
45%
2112
41%
704
89%
704
71%
874
November1st to 15thNight
86%
700
43%
2142
42%
700
88%
700
67%
897
November16th to endNight
80%
720
41%
2340
42%
720
83%
720
56%
1024
December1st to 15thNight
76%
720
38%
2340
40%
720
78%
720
50%
1094
December16th to endNight
73%
768
37%
2496
40%
768
75%
768
44%
1254

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
2212212346%70%
46425
Night
3212213335%69%
46046
TransparencyDay
16%2311%25%40%
46120
Night
17%1310%23%43%
45852
SeeingDay
4312%29%35%14%
5023
Night
419%42%38%4
15316

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
4312313245%66%
1611
16th to endDay
6%322312337%64%
1728
February1st to 15thDay
2314212237%67%
1691
16th to endDay
5%323312346%62%
1582
March1st to 15thDay
4212223336%68%
1980
16th to endDay
2212212345%70%
2112
April1st to 15thDay
212213347%71%
1970
16th to endDay
111112125%80%
2274
May1st to 15thDay
11111226%80%
2331
16th to endDay
1111111482%
2335
June1st to 15thDay
111111383%
2145
16th to endDay
111112383%
2145
July1st to 15thDay
22133245%6%10%57%
2145
16th to endDay
3325%5%246%8%11%46%
2285
August1st to 15thDay
3233235%7%9%57%
2145
16th to endDay
22232446%9%60%
2127
September1st to 15thDay
321332245%5%63%
1815
16th to endDay
21111122480%
1815
October1st to 15thDay
211213335%75%
1746
16th to endDay
1121223479%
1760
November1st to 15thDay
112112235%77%
1715
16th to endDay
421221235%73%
1620
December1st to 15thDay
5%412313345%63%
1620
16th to endDay
6%31332335%6%59%
1728
January1st to 15thNight
4214223335%65%
2327
16th to endNight
8%214223235%63%
2496
February1st to 15thNight
3322212335%69%
2158
16th to endNight
6%212433336%62%
1892
March1st to 15thNight
3112212346%69%
1980
16th to endNight
211122236%74%
2112
April1st to 15thNight
2212213346%69%
1978
16th to endNight
11111111384%
1684
May1st to 15thNight
121233478%
1619
16th to endNight
11111112284%
1621
June1st to 15thNight
111122482%
1485
16th to endNight
1111212383%
1485
July1st to 15thNight
11134245%6%9%58%
1485
16th to endNight
3213335%7%8%10%50%
1575
August1st to 15thNight
12123346%7%10%55%
1485
16th to endNight
1214435%5%6%7%55%
1720
September1st to 15thNight
22124235%6%7%62%
1815
16th to endNight
112112235%76%
1815
October1st to 15thNight
211212235%76%
1884
16th to endNight
111121123479%
2112
November1st to 15thNight
111212335%76%
2142
16th to endNight
421221222473%
2340
December1st to 15thNight
6%313312336%64%
2340
16th to endNight
7%323423335%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%2416%28%27%
1612
16th to endDay
22%1315%26%30%
1728
February1st to 15thDay
18%1418%28%29%
1691
16th to endDay
22%1315%31%25%
1582
March1st to 15thDay
18%118%31%38%
1980
16th to endDay
17%128%33%35%
2112
April1st to 15thDay
14%128%34%39%
1970
16th to endDay
10%16%25%55%
2274
May1st to 15thDay
8%117%23%57%
2331
16th to endDay
9%16%24%58%
2338
June1st to 15thDay
9%314%71%
2145
16th to endDay
8%11310%74%
2145
July1st to 15thDay
21%48%14%18%33%
2006
16th to endDay
28%5%10%23%21%11%
2130
August1st to 15thDay
21%47%18%19%29%
2130
16th to endDay
19%45%18%29%22%
2127
September1st to 15thDay
22%3412%24%32%
1815
16th to endDay
10%25%26%53%
1815
October1st to 15thDay
13%128%26%46%
1746
16th to endDay
10%137%28%48%
1760
November1st to 15thDay
11%1112%32%41%
1715
16th to endDay
16%1110%28%41%
1620
December1st to 15thDay
23%2415%29%23%
1620
16th to endDay
26%25%21%29%15%
1728
January1st to 15thNight
22%2411%24%34%
2327
16th to endNight
26%1212%27%30%
2496
February1st to 15thNight
18%1414%25%35%
2169
16th to endNight
25%1212%26%32%
1892
March1st to 15thNight
16%118%23%47%
1980
16th to endNight
13%128%30%43%
2112
April1st to 15thNight
16%117%28%44%
1978
16th to endNight
8%15%20%64%
1684
May1st to 15thNight
11%2424%56%
1620
16th to endNight
9%16%15%66%
1622
June1st to 15thNight
9%1212%73%
1485
16th to endNight
8%1236%78%
1485
July1st to 15thNight
21%37%16%14%36%
1395
16th to endNight
23%5%10%20%23%17%
1467
August1st to 15thNight
21%47%18%17%29%
1476
16th to endNight
24%47%13%24%25%
1720
September1st to 15thNight
20%27%17%20%31%
1815
16th to endNight
11%115%21%57%
1815
October1st to 15thNight
13%119%23%50%
1884
16th to endNight
10%128%17%58%
2112
November1st to 15thNight
11%118%27%48%
2142
16th to endNight
17%128%23%46%
2340
December1st to 15thNight
21%1314%27%31%
2340
16th to endNight
26%15%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%18%43%27%1
90
16th to endDay
6%39%36%26%18%
96
February1st to 15thDay
4413%31%35%9%
206
16th to endDay
7%5%23%32%23%6%
238
March1st to 15thDay
5%7%18%31%20%17%
270
16th to endDay
37%20%28%27%13%
288
April1st to 15thDay
5%8%20%28%26%11%
269
16th to endDay
210%24%34%19%8%
270
May1st to 15thDay
16%23%31%25%11%
288
16th to endDay
2216%36%33%8%
301
June1st to 15thDay
2311%40%30%11%
255
16th to endDay
216%30%43%16%
255
July1st to 15thDay
117%25%49%15%
245
16th to endDay
4116%49%28%
271
August1st to 15thDay
3219%51%22%
255
16th to endDay
1216%55%22%
268
September1st to 15thDay
7%27%27%40%14%
255
16th to endDay
5%210%32%38%11%
255
October1st to 15thDay
4215%27%33%16%
186
16th to endDay
2217%56%21%
96
November1st to 15thDay
117%30%42%17%
90
16th to endDay
11%27%36%35%6%
90
December1st to 15thDay
35%25%50%15%
90
16th to endDay
12%123%29%28%5%
96
January1st to 15thNight
5%9%50%30%2
720
16th to endNight
10%10%47%28%2
768
February1st to 15thNight
5%111%49%28%3
704
16th to endNight
9%112%52%22%2
632
March1st to 15thNight
4115%48%26%3
720
16th to endNight
3211%45%32%5%
768
April1st to 15thNight
4115%49%26%2
719
16th to endNight
2220%46%26%2
540
May1st to 15thNight
1215%46%31%3
540
16th to endNight
213%40%39%2
542
June1st to 15thNight
16%51%38%1
495
16th to endNight
2437%52%3
495
July1st to 15thNight
25%30%54%7%
465
16th to endNight
5%219%62%10%
522
August1st to 15thNight
21220%63%10%
494
16th to endNight
3419%62%10%
604
September1st to 15thNight
46%26%54%7%
660
16th to endNight
216%39%43%7%
656
October1st to 15thNight
38%45%39%2
660
16th to endNight
16%41%43%6%
704
November1st to 15thNight
27%44%39%4
700
16th to endNight
5%7%45%37%3
720
December1st to 15thNight
7%7%47%34%1
720
16th to endNight
9%18%50%26%3
768
Page generated at 2017-05-25 10:27:30. Version ac04

Copyright 2017 A. Danko


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