Sierra Vista
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sierra Vista 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%
15378
35%
46511
31%
15341
81%
15341
53%
22072

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
78%
716
34%
2327
35%
716
82%
716
55%
1037
January16th to endNight
67%
768
36%
2496
34%
768
76%
768
45%
1221
February1st to 15thNight
74%
697
37%
2222
35%
696
83%
696
57%
981
February16th to endNight
65%
632
42%
1793
34%
632
75%
632
55%
884
March1st to 15thNight
70%
720
42%
1980
33%
720
78%
720
62%
943
March16th to endNight
73%
768
39%
2112
28%
768
81%
768
62%
995
April1st to 15thNight
71%
662
37%
1921
28%
662
79%
662
59%
881
April16th to endNight
70%
540
44%
1800
37%
540
83%
540
68%
679
May1st to 15thNight
74%
539
38%
1676
32%
539
82%
539
71%
665
May16th to endNight
80%
561
43%
1684
37%
561
85%
561
74%
663
June1st to 15thNight
85%
540
35%
1620
30%
540
87%
540
68%
677
June16th to endNight
87%
540
31%
1620
28%
540
87%
540
54%
767
July1st to 15thNight
81%
510
15%
1530
13%
510
81%
510
34%
890
July16th to endNight
77%
564
12%
1593
11%
531
77%
531
25%
1041
August1st to 15thNight
82%
527
19%
1575
18%
524
82%
524
33%
931
August16th to endNight
81%
525
23%
1735
25%
525
81%
525
34%
963
September1st to 15thNight
78%
641
25%
1796
22%
641
78%
641
37%
1093
September16th to endNight
87%
656
39%
1815
32%
656
89%
656
62%
867
October1st to 15thNight
84%
660
40%
1939
33%
660
87%
660
66%
857
October16th to endNight
88%
704
43%
2112
38%
704
91%
704
70%
888
November1st to 15thNight
83%
700
44%
2100
39%
700
87%
700
71%
865
November16th to endNight
72%
720
41%
2229
36%
720
77%
720
53%
1045
December1st to 15thNight
73%
720
39%
2340
39%
720
78%
720
53%
1047
December16th to endNight
68%
768
36%
2496
36%
768
74%
768
47%
1192

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
2213324446%63%
47453
Night
2212323346%67%
46714
TransparencyDay
21%36%12%27%28%
47148
Night
18%37%15%29%26%
46520
SeeingDay
46%17%27%27%15%
5218
Night
3111%39%36%6%
15392

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
1212333445%65%
1611
16th to endDay
432431335%6%61%
1728
February1st to 15thDay
231321232471%
1631
16th to endDay
2313413335%66%
1681
March1st to 15thDay
122224346%69%
1980
16th to endDay
121221233473%
2112
April1st to 15thDay
112212345%73%
2027
16th to endDay
1111112382%
2160
May1st to 15thDay
221221480%
2271
16th to endDay
1111222481%
2429
June1st to 15thDay
111112235%77%
2340
16th to endDay
2223325%45%6%62%
2340
July1st to 15thDay
6%325%7%49%8%8%10%35%
2340
16th to endDay
7%6%38%9%5%8%6%8%10%24%
2467
August1st to 15thDay
6%426%7%5%8%7%7%8%34%
2290
16th to endDay
33146%47%7%8%10%41%
2113
September1st to 15thDay
6%5%26%6%46%5%6%7%42%
1832
16th to endDay
3213322446%65%
1815
October1st to 15thDay
1112323335%72%
1691
16th to endDay
11111223477%
1760
November1st to 15thDay
111112336%77%
1759
16th to endDay
2213112235%71%
1728
December1st to 15thDay
2112324346%66%
1620
16th to endDay
2313313248%64%
1728
January1st to 15thNight
2113213346%68%
2327
16th to endNight
3224423446%61%
2496
February1st to 15thNight
1112312347%69%
2218
16th to endNight
1113324345%68%
1793
March1st to 15thNight
1112213246%71%
1980
16th to endNight
111231324473%
2112
April1st to 15thNight
111222324473%
1921
16th to endNight
1111122481%
1800
May1st to 15thNight
1112226%79%
1676
16th to endNight
11112384%
1684
June1st to 15thNight
31111223477%
1620
16th to endNight
1213245%5%6%66%
1620
July1st to 15thNight
23245%37%6%9%13%42%
1620
16th to endNight
4415%5%48%8%11%14%30%
1701
August1st to 15thNight
3314435%7%9%11%45%
1584
16th to endNight
4314425%6%7%11%46%
1735
September1st to 15thNight
6%3145%35%6%6%9%48%
1796
16th to endNight
312212445%71%
1815
October1st to 15thNight
2212245%75%
1939
16th to endNight
1111123379%
2112
November1st to 15thNight
111112225%79%
2100
16th to endNight
331231223470%
2229
December1st to 15thNight
3212212337%68%
2340
16th to endNight
2214323445%65%
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%25%14%33%24%
1612
16th to endDay
23%2218%31%22%
1728
February1st to 15thDay
17%2212%32%32%
1631
16th to endDay
20%2213%33%27%
1681
March1st to 15thDay
16%137%38%32%
1980
16th to endDay
15%128%36%35%
2112
April1st to 15thDay
13%218%40%34%
2027
16th to endDay
9%115%31%50%
2160
May1st to 15thDay
10%126%26%52%
2271
16th to endDay
9%125%31%50%
2432
June1st to 15thDay
12%115%23%55%
2340
16th to endDay
21%348%23%38%
2340
July1st to 15thDay
36%10%15%15%12%8%
2201
16th to endDay
49%10%20%13%4
2312
August1st to 15thDay
42%9%14%16%14%3
2275
16th to endDay
33%9%16%19%11%8%
2113
September1st to 15thDay
37%6%9%17%20%8%
1832
16th to endDay
20%25%15%34%21%
1815
October1st to 15thDay
16%15%16%27%32%
1691
16th to endDay
11%2214%31%38%
1760
November1st to 15thDay
10%1313%37%32%
1759
16th to endDay
17%1214%31%32%
1728
December1st to 15thDay
19%2418%36%18%
1620
16th to endDay
21%17%20%33%15%
1728
January1st to 15thNight
17%25%14%33%25%
2327
16th to endNight
23%2417%32%18%
2496
February1st to 15thNight
16%1415%30%31%
2229
16th to endNight
18%2215%35%25%
1793
March1st to 15thNight
15%1211%34%33%
1980
16th to endNight
14%239%36%33%
2112
April1st to 15thNight
16%1210%39%29%
1921
16th to endNight
10%128%30%47%
1800
May1st to 15thNight
9%227%33%44%
1677
16th to endNight
7%2210%34%43%
1685
June1st to 15thNight
11%12427%51%
1620
16th to endNight
17%4210%25%39%
1620
July1st to 15thNight
27%10%23%18%11%8%
1530
16th to endNight
36%12%30%15%41
1593
August1st to 15thNight
29%10%20%20%17%3
1575
16th to endNight
28%7%21%19%14%8%
1735
September1st to 15thNight
29%8%14%21%18%7%
1796
16th to endNight
15%27%17%38%19%
1815
October1st to 15thNight
13%18%19%29%28%
1939
16th to endNight
10%1315%29%39%
2112
November1st to 15thNight
10%1418%35%30%
2100
16th to endNight
20%1213%31%31%
2229
December1st to 15thNight
18%2421%34%19%
2340
16th to endNight
22%26%20%32%15%
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
5%226%36%28%
90
16th to endDay
8%5%16%32%27%10%
96
February1st to 15thDay
46%15%28%32%12%
146
16th to endDay
7%15%32%22%18%3
238
March1st to 15thDay
414%26%25%19%10%
270
16th to endDay
414%27%26%15%11%
288
April1st to 15thDay
414%28%27%19%5%
269
16th to endDay
217%30%27%15%7%
270
May1st to 15thDay
213%32%26%13%10%
288
16th to endDay
25%25%39%20%7%
330
June1st to 15thDay
4119%35%22%14%
315
16th to endDay
38%35%31%20%
315
July1st to 15thDay
7%1329%35%22%
305
16th to endDay
10%1222%33%30%
327
August1st to 15thDay
6%2116%41%33%
300
16th to endDay
2219%45%29%
268
September1st to 15thDay
9%17%25%42%13%
255
16th to endDay
5%213%25%35%17%
255
October1st to 15thDay
116%25%34%21%
131
16th to endDay
39%19%30%37%
96
November1st to 15thDay
15%22%26%33%11%
90
16th to endDay
16%32%28%26%4
90
December1st to 15thDay
3215%27%34%16%
90
16th to endDay
11%6%21%31%26%3
96
January1st to 15thNight
3111%50%29%3
720
16th to endNight
4217%46%26%2
768
February1st to 15thNight
2314%45%28%4
704
16th to endNight
2324%46%21%1
632
March1st to 15thNight
2320%45%25%3
720
16th to endNight
2316%45%28%4
768
April1st to 15thNight
2319%52%21%1
662
16th to endNight
1222%50%20%2
540
May1st to 15thNight
1120%46%29%2
540
16th to endNight
1113%46%34%2
563
June1st to 15thNight
36%48%39%1
540
16th to endNight
11236%54%3
540
July1st to 15thNight
3123%59%10%
510
16th to endNight
7%13%60%17%
564
August1st to 15thNight
4112%61%19%
527
16th to endNight
6%14%60%18%
525
September1st to 15thNight
7%1315%57%15%
641
16th to endNight
4332%51%8%
656
October1st to 15thNight
110%43%35%8%
660
16th to endNight
16%38%44%8%
704
November1st to 15thNight
2110%40%37%7%
700
16th to endNight
5%114%42%30%6%
720
December1st to 15thNight
5%213%44%28%5%
720
16th to endNight
4317%47%22%5%
768
Page generated at 2017-08-13 11:16:33. Version ac04

Copyright 2017 A. Danko


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