Tucson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tucson 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
77%
15447
36%
46528
32%
15409
81%
15409
55%
21958

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
72%
718
32%
2327
32%
716
76%
716
51%
1069
January16th to endNight
67%
768
35%
2496
34%
768
75%
768
43%
1268
February1st to 15thNight
74%
700
36%
2204
37%
700
80%
700
53%
1013
February16th to endNight
67%
632
38%
1834
35%
632
74%
632
52%
917
March1st to 15thNight
68%
720
40%
1980
32%
720
76%
720
60%
954
March16th to endNight
76%
768
39%
2112
29%
768
83%
768
63%
994
April1st to 15thNight
70%
685
35%
1944
27%
685
77%
685
58%
919
April16th to endNight
75%
540
45%
1788
41%
540
84%
540
71%
656
May1st to 15thNight
75%
539
41%
1619
32%
539
82%
539
75%
633
May16th to endNight
79%
561
42%
1684
35%
561
83%
561
75%
656
June1st to 15thNight
85%
540
35%
1620
31%
540
86%
540
71%
662
June16th to endNight
86%
540
32%
1620
28%
540
87%
540
65%
698
July1st to 15thNight
84%
510
20%
1530
18%
510
84%
510
41%
829
July16th to endNight
83%
564
18%
1593
16%
531
82%
531
31%
973
August1st to 15thNight
88%
527
25%
1575
24%
524
88%
524
44%
845
August16th to endNight
85%
547
28%
1718
29%
547
85%
547
39%
933
September1st to 15thNight
80%
660
30%
1815
26%
660
81%
660
43%
1038
September16th to endNight
82%
656
42%
1815
32%
656
86%
656
66%
840
October1st to 15thNight
82%
660
41%
1917
34%
660
86%
660
65%
858
October16th to endNight
88%
704
44%
2112
40%
704
90%
704
69%
901
November1st to 15thNight
81%
700
43%
2100
39%
700
85%
700
69%
883
November16th to endNight
73%
720
39%
2289
36%
720
79%
720
52%
1057
December1st to 15thNight
72%
720
38%
2340
39%
720
77%
720
51%
1077
December16th to endNight
69%
768
34%
2496
35%
768
73%
768
42%
1285

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
3112323346%66%
47441
Night
3112213346%68%
46724
TransparencyDay
18%46%11%24%35%
47136
Night
17%36%12%25%34%
46530
SeeingDay
5%8%22%34%22%6%
5267
Night
4112%40%35%5%
15456

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
4212313336%66%
1611
16th to endDay
7%312322336%62%
1728
February1st to 15thDay
5%312212335%69%
1658
16th to endDay
7%212323335%64%
1639
March1st to 15thDay
412313346%68%
1980
16th to endDay
3111112335%75%
2112
April1st to 15thDay
31122246%72%
2003
16th to endDay
1111112382%
2169
May1st to 15thDay
1121213480%
2331
16th to endDay
1111122384%
2429
June1st to 15thDay
211112135%79%
2340
16th to endDay
112112346%73%
2340
July1st to 15thDay
42145%36%8%8%8%46%
2340
16th to endDay
6%425%7%47%8%8%11%32%
2467
August1st to 15thDay
5%325%5%35%6%7%8%45%
2290
16th to endDay
32145%46%6%7%8%49%
2126
September1st to 15thDay
6%2235%45%5%6%6%52%
1815
16th to endDay
3112212335%71%
1815
October1st to 15thDay
22212235%75%
1713
16th to endDay
1111213479%
1760
November1st to 15thDay
1111246%78%
1759
16th to endDay
322212335%71%
1668
December1st to 15thDay
7%12223247%64%
1620
16th to endDay
6%21222325%6%63%
1728
January1st to 15thNight
5%212212345%67%
2327
16th to endNight
7%21332435%6%60%
2496
February1st to 15thNight
412213346%69%
2193
16th to endNight
6%211213446%64%
1834
March1st to 15thNight
5%112213236%70%
1980
16th to endNight
31221223474%
2112
April1st to 15thNight
222213345%71%
1944
16th to endNight
21111385%
1788
May1st to 15thNight
111236%79%
1619
16th to endNight
111112385%
1684
June1st to 15thNight
111122481%
1620
16th to endNight
1111212235%75%
1620
July1st to 15thNight
1214425%7%6%11%52%
1620
16th to endNight
32145%35%8%9%15%40%
1701
August1st to 15thNight
1212315%5%7%10%57%
1584
16th to endNight
21135%35%5%8%10%52%
1718
September1st to 15thNight
42144245%5%7%57%
1815
16th to endNight
212212235%75%
1815
October1st to 15thNight
21111233476%
1917
16th to endNight
11111222479%
2112
November1st to 15thNight
112211235%77%
2100
16th to endNight
5%212212335%69%
2289
December1st to 15thNight
6%22212336%68%
2340
16th to endNight
8%213423335%61%
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
19%35%13%26%31%
1612
16th to endDay
23%3414%25%28%
1728
February1st to 15thDay
19%1413%26%34%
1658
16th to endDay
22%2413%29%27%
1639
March1st to 15thDay
17%237%30%39%
1980
16th to endDay
13%248%30%40%
2112
April1st to 15thDay
13%136%36%38%
2003
16th to endDay
9%127%23%56%
2169
May1st to 15thDay
9%237%20%57%
2331
16th to endDay
7%136%23%57%
2432
June1st to 15thDay
9%12319%63%
2340
16th to endDay
12%35%6%16%56%
2340
July1st to 15thDay
28%10%13%14%14%18%
2201
16th to endDay
40%13%17%18%8%2
2312
August1st to 15thDay
33%9%12%14%16%13%
2275
16th to endDay
29%8%13%18%17%12%
2126
September1st to 15thDay
29%6%10%17%15%19%
1815
16th to endDay
15%249%32%34%
1815
October1st to 15thDay
12%35%10%26%41%
1713
16th to endDay
10%148%27%47%
1760
November1st to 15thDay
8%2410%34%40%
1759
16th to endDay
16%249%28%38%
1668
December1st to 15thDay
20%25%15%31%23%
1620
16th to endDay
21%38%18%31%17%
1728
January1st to 15thNight
19%26%12%27%31%
2327
16th to endNight
24%45%13%29%22%
2496
February1st to 15thNight
17%25%15%24%33%
2204
16th to endNight
20%25%12%32%26%
1834
March1st to 15thNight
16%2410%26%39%
1980
16th to endNight
14%2310%32%36%
2112
April1st to 15thNight
16%238%34%35%
1944
16th to endNight
7%117%25%55%
1788
May1st to 15thNight
7%15%8%26%51%
1620
16th to endNight
7%126%24%57%
1685
June1st to 15thNight
9%12418%62%
1620
16th to endNight
12%145%17%58%
1620
July1st to 15thNight
21%10%16%17%15%18%
1530
16th to endNight
27%14%22%23%9%2
1593
August1st to 15thNight
19%10%16%19%19%15%
1575
16th to endNight
25%7%15%19%17%14%
1718
September1st to 15thNight
24%7%10%21%18%17%
1815
16th to endNight
12%3412%33%34%
1815
October1st to 15thNight
11%35%13%25%40%
1917
16th to endNight
10%2311%23%48%
2112
November1st to 15thNight
11%1412%33%37%
2100
16th to endNight
18%2410%23%39%
2289
December1st to 15thNight
19%25%15%30%25%
2340
16th to endNight
26%27%15%29%18%
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
10%6%21%48%13%
90
16th to endDay
6%320%39%21%8%
96
February1st to 15thDay
6%10%20%39%19%2
173
16th to endDay
11%13%36%25%10%2
238
March1st to 15thDay
5%17%30%26%12%7%
270
16th to endDay
120%33%23%15%5%
288
April1st to 15thDay
5%17%34%24%15%3
269
16th to endDay
225%31%26%12%1
270
May1st to 15thDay
218%34%28%12%4
288
16th to endDay
39%32%37%14%3
330
June1st to 15thDay
4329%41%14%6%
315
16th to endDay
2114%47%25%7%
315
July1st to 15thDay
6%9%40%34%8%
305
16th to endDay
7%6%34%30%19%
327
August1st to 15thDay
6%6%37%34%14%
300
16th to endDay
5%15%37%37%11%
268
September1st to 15thDay
10%116%38%26%6%
255
16th to endDay
8%5%23%29%27%5%
255
October1st to 15thDay
36%22%38%19%9%
153
16th to endDay
216%33%47%9%
96
November1st to 15thDay
38%22%40%18%6%
90
16th to endDay
6%5%33%32%21%1
90
December1st to 15thDay
3314%35%42%1
90
16th to endDay
16%7%29%33%13%
96
January1st to 15thNight
6%116%49%23%3
720
16th to endNight
8%216%43%25%3
768
February1st to 15thNight
4213%46%29%3
704
16th to endNight
7%218%49%20%1
632
March1st to 15thNight
4419%40%27%3
720
16th to endNight
3314%45%29%4
768
April1st to 15thNight
3416%50%22%1
685
16th to endNight
1417%49%23%2
540
May1st to 15thNight
318%43%30%2
540
16th to endNight
1115%45%33%1
563
June1st to 15thNight
119%47%37%2
540
16th to endNight
16%37%51%2
540
July1st to 15thNight
15%21%65%6%
510
16th to endNight
4117%60%16%
564
August1st to 15thNight
2215%63%15%
527
16th to endNight
2219%61%13%
547
September1st to 15thNight
36%27%49%11%
660
16th to endNight
210%35%41%9%
656
October1st to 15thNight
211%41%37%5%
660
16th to endNight
26%43%37%8%
704
November1st to 15thNight
1112%42%37%5%
700
16th to endNight
6%115%41%31%4
720
December1st to 15thNight
7%213%44%27%3
720
16th to endNight
10%213%48%20%4
768
Page generated at 2017-08-13 11:16:42. Version ac04

Copyright 2017 A. Danko


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