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 2018-03-11.

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%
16372
38%
49073
35%
16333
83%
16333
57%
22725

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%
778
33%
2522
36%
776
79%
776
47%
1218
January16th to endNight
72%
832
38%
2704
38%
832
78%
832
46%
1325
February1st to 15thNight
76%
759
37%
2351
37%
758
81%
758
55%
1090
February16th to endNight
71%
684
36%
2048
38%
684
75%
684
47%
1053
March1st to 15thNight
75%
764
40%
2101
33%
764
80%
764
60%
1009
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%
561
41%
1684
32%
561
85%
561
75%
673
June1st to 15thNight
88%
540
36%
1620
31%
540
90%
540
75%
644
June16th to endNight
91%
540
35%
1620
31%
540
91%
540
77%
636
July1st to 15thNight
85%
510
27%
1530
23%
510
85%
510
51%
758
July16th to endNight
84%
564
29%
1593
24%
531
85%
531
42%
868
August1st to 15thNight
85%
539
31%
1611
27%
536
86%
536
48%
821
August16th to endNight
83%
659
34%
1877
30%
659
83%
659
46%
1016
September1st to 15thNight
81%
720
34%
1980
29%
720
83%
720
55%
1018
September16th to endNight
87%
716
45%
1980
37%
716
90%
716
71%
879
October1st to 15thNight
85%
720
41%
2055
35%
720
88%
720
68%
899
October16th to endNight
86%
768
47%
2304
43%
768
90%
768
72%
945
November1st to 15thNight
84%
760
41%
2326
40%
760
87%
760
64%
1007
November16th to endNight
80%
780
42%
2535
44%
780
83%
780
56%
1108
December1st to 15thNight
76%
780
37%
2535
39%
780
78%
780
50%
1188
December16th to endNight
74%
832
38%
2704
41%
832
77%
832
46%
1335

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%
49553
Night
3212213346%69%
49272
TransparencyDay
16%2311%25%40%
49248
Night
17%1310%22%43%
49078
SeeingDay
4311%28%36%16%
6059
Night
49%42%38%4
16382

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
4313313246%65%
1746
16th to endDay
6%322312236%65%
1872
February1st to 15thDay
3313212337%67%
1836
16th to endDay
5%313212346%63%
1712
March1st to 15thDay
4213223336%67%
2095
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
1111121482%
2429
June1st to 15thDay
111111384%
2340
16th to endDay
111112384%
2340
July1st to 15thDay
121332446%10%59%
2340
16th to endDay
3325%5%246%8%11%46%
2467
August1st to 15thDay
3233235%6%10%57%
2340
16th to endDay
22232446%8%61%
2321
September1st to 15thDay
321332245%5%64%
1980
16th to endDay
11111122381%
1980
October1st to 15thDay
11111223477%
1905
16th to endDay
1121123479%
1920
November1st to 15thDay
1112212235%75%
1861
16th to endDay
421221236%72%
1755
December1st to 15thDay
5%313313445%62%
1755
16th to endDay
5%31332345%6%60%
1872
January1st to 15thNight
4214323336%64%
2522
16th to endNight
7%21421323464%
2704
February1st to 15thNight
3222212335%69%
2343
16th to endNight
6%213433336%62%
2048
March1st to 15thNight
3112213346%68%
2101
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%
1684
June1st to 15thNight
111122482%
1620
16th to endNight
111212482%
1620
July1st to 15thNight
11134245%6%9%59%
1620
16th to endNight
3213435%6%8%10%49%
1701
August1st to 15thNight
22123345%7%10%54%
1620
16th to endNight
1214436%5%6%7%55%
1877
September1st to 15thNight
221232346%7%62%
1980
16th to endNight
11211223477%
1980
October1st to 15thNight
211211225%78%
2055
16th to endNight
1121123480%
2304
November1st to 15thNight
1212212236%74%
2326
16th to endNight
421221222472%
2535
December1st to 15thNight
5%313312337%64%
2535
16th to endNight
6%313413335%61%
2704

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%2415%29%26%
1747
16th to endDay
22%1315%27%30%
1872
February1st to 15thDay
19%1416%28%29%
1836
16th to endDay
22%1315%31%25%
1712
March1st to 15thDay
18%118%31%37%
2095
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%23%58%
2432
June1st to 15thDay
9%315%71%
2340
16th to endDay
8%11310%75%
2340
July1st to 15thDay
19%47%14%19%34%
2201
16th to endDay
28%5%11%24%20%10%
2312
August1st to 15thDay
21%47%17%19%30%
2325
16th to endDay
19%35%17%28%25%
2321
September1st to 15thDay
20%3413%25%32%
1980
16th to endDay
10%2427%54%
1980
October1st to 15thDay
12%128%25%49%
1905
16th to endDay
10%137%28%49%
1920
November1st to 15thDay
13%1113%31%39%
1861
16th to endDay
16%119%28%41%
1755
December1st to 15thDay
24%2415%27%25%
1755
16th to endDay
25%25%20%29%16%
1872
January1st to 15thNight
23%2411%25%32%
2522
16th to endNight
25%1211%27%32%
2704
February1st to 15thNight
19%1413%25%36%
2354
16th to endNight
25%1211%25%32%
2048
March1st to 15thNight
17%118%24%46%
2101
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%
1685
June1st to 15thNight
8%1213%72%
1620
16th to endNight
7%1236%78%
1620
July1st to 15thNight
20%37%16%14%36%
1530
16th to endNight
25%5%10%20%21%15%
1593
August1st to 15thNight
21%47%17%17%30%
1611
16th to endNight
24%47%12%22%28%
1877
September1st to 15thNight
20%27%17%20%31%
1980
16th to endNight
11%115%20%59%
1980
October1st to 15thNight
12%118%21%54%
2055
16th to endNight
10%128%17%60%
2304
November1st to 15thNight
13%129%27%45%
2326
16th to endNight
17%128%24%46%
2535
December1st to 15thNight
21%1314%25%32%
2535
16th to endNight
24%15%15%29%22%
2704

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
12%8%36%32%9%
135
16th to endDay
5%29%34%33%15%
144
February1st to 15thDay
6%412%28%33%15%
261
16th to endDay
7%5%23%36%22%5%
290
March1st to 15thDay
6%6%16%32%22%15%
312
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
2217%35%33%10%
330
June1st to 15thDay
2310%37%31%15%
315
16th to endDay
115%27%42%20%
315
July1st to 15thDay
15%23%48%19%
305
16th to endDay
4115%46%32%
327
August1st to 15thDay
3218%51%24%
315
16th to endDay
1314%52%27%
332
September1st to 15thDay
6%16%26%42%15%
315
16th to endDay
4110%31%36%14%
315
October1st to 15thDay
3113%27%36%17%
240
16th to endDay
2216%52%25%
144
November1st to 15thDay
17%30%43%16%
135
16th to endDay
9%16%31%35%15%
135
December1st to 15thDay
5%8%30%45%11%
135
16th to endDay
9%17%25%31%15%
144
January1st to 15thNight
5%9%49%31%2
780
16th to endNight
10%10%46%29%2
832
February1st to 15thNight
5%110%48%29%3
764
16th to endNight
8%112%52%22%1
684
March1st to 15thNight
4115%49%26%3
764
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
563
June1st to 15thNight
17%50%38%1
540
16th to endNight
1437%52%3
540
July1st to 15thNight
25%30%55%6%
510
16th to endNight
6%218%61%11%
564
August1st to 15thNight
21219%62%11%
539
16th to endNight
3418%62%10%
659
September1st to 15thNight
46%27%53%7%
720
16th to endNight
26%40%43%6%
716
October1st to 15thNight
37%45%40%2
720
16th to endNight
16%39%45%6%
768
November1st to 15thNight
27%46%38%4
760
16th to endNight
5%7%43%38%3
780
December1st to 15thNight
7%7%48%33%1
780
16th to endNight
8%18%49%28%3
832
Page generated at 2018-03-12 10:28:06. Version ac04

Copyright 2018 A. Danko


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