Sierrita Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sierrita Mountain Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
75%
15701
37%
47122
32%
15663
80%
15663
56%
22065

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
34%
2327
36%
716
80%
716
53%
1049
January16th to endNight
67%
768
35%
2496
34%
768
74%
768
43%
1261
February1st to 15thNight
73%
699
38%
2179
37%
699
80%
699
54%
1002
February16th to endNight
65%
632
39%
1847
34%
632
73%
632
51%
917
March1st to 15thNight
67%
720
41%
1980
33%
720
76%
720
61%
945
March16th to endNight
73%
768
39%
2112
30%
768
81%
768
61%
1001
April1st to 15thNight
67%
701
36%
1960
24%
701
75%
701
58%
935
April16th to endNight
70%
540
46%
1767
39%
540
82%
540
73%
649
May1st to 15thNight
70%
539
40%
1619
29%
539
80%
539
71%
649
May16th to endNight
75%
561
43%
1684
32%
561
83%
561
73%
670
June1st to 15thNight
82%
540
35%
1620
30%
540
84%
540
70%
671
June16th to endNight
86%
540
33%
1620
28%
540
86%
540
66%
695
July1st to 15thNight
81%
510
20%
1530
17%
510
81%
510
40%
843
July16th to endNight
82%
564
20%
1593
17%
531
81%
531
32%
958
August1st to 15thNight
87%
539
27%
1611
24%
536
87%
536
48%
818
August16th to endNight
83%
630
32%
1896
31%
630
83%
630
44%
1010
September1st to 15thNight
77%
720
30%
1980
26%
720
78%
720
44%
1128
September16th to endNight
83%
716
46%
1980
38%
716
87%
716
71%
890
October1st to 15thNight
79%
684
41%
1969
32%
684
85%
684
68%
857
October16th to endNight
85%
704
45%
2112
40%
704
90%
704
70%
878
November1st to 15thNight
81%
700
44%
2100
40%
700
85%
700
69%
885
November16th to endNight
72%
720
39%
2304
37%
720
77%
720
52%
1067
December1st to 15thNight
72%
720
39%
2340
38%
720
77%
720
52%
1047
December16th to endNight
66%
768
36%
2496
36%
768
71%
768
44%
1240

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
3212323346%65%
48072
Night
3212213346%68%
47318
TransparencyDay
19%35%11%24%36%
47767
Night
17%25%13%26%34%
47124
SeeingDay
5%6%19%32%24%11%
5527
Night
3212%37%36%7%
15711

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
2213324346%65%
1611
16th to endDay
5%412413346%62%
1728
February1st to 15thDay
5%312212227%67%
1682
16th to endDay
5%413312346%62%
1625
March1st to 15thDay
3212213347%67%
1980
16th to endDay
22221223474%
2112
April1st to 15thDay
2111222246%71%
1986
16th to endDay
11111111482%
2190
May1st to 15thDay
1111222479%
2331
16th to endDay
1111122383%
2429
June1st to 15thDay
211111135%80%
2340
16th to endDay
211221334473%
2340
July1st to 15thDay
5%3246%36%6%7%10%42%
2340
16th to endDay
7%437%8%5%7%6%8%10%28%
2467
August1st to 15thDay
6%4245%47%6%7%8%41%
2340
16th to endDay
43245%35%6%6%7%48%
2303
September1st to 15thDay
6%4234345%6%8%50%
1980
16th to endDay
321221234472%
1980
October1st to 15thDay
11211233476%
1788
16th to endDay
111212135%78%
1760
November1st to 15thDay
111112235%77%
1759
16th to endDay
222313335%70%
1653
December1st to 15thDay
6%21232335%6%63%
1620
16th to endDay
5%21331336%6%62%
1728
January1st to 15thNight
5%211222346%68%
2327
16th to endNight
5%313424446%60%
2496
February1st to 15thNight
3212313246%68%
2168
16th to endNight
3312323447%63%
1847
March1st to 15thNight
3212213345%71%
1980
16th to endNight
21121333473%
2112
April1st to 15thNight
2112213335%71%
1960
16th to endNight
21111385%
1767
May1st to 15thNight
1111335%78%
1619
16th to endNight
1111112383%
1684
June1st to 15thNight
211222480%
1620
16th to endNight
2112111235%75%
1620
July1st to 15thNight
22235%35%6%6%10%50%
1620
16th to endNight
33145%37%9%10%16%34%
1701
August1st to 15thNight
222325%6%7%9%55%
1620
16th to endNight
33144245%7%10%52%
1896
September1st to 15thNight
43144245%5%7%55%
1980
16th to endNight
112211335%77%
1980
October1st to 15thNight
1121232479%
1969
16th to endNight
11121112480%
2112
November1st to 15thNight
112212235%76%
2100
16th to endNight
4213322235%67%
2304
December1st to 15thNight
5%312112337%67%
2340
16th to endNight
5%313423346%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
20%2413%26%32%
1612
16th to endDay
23%2315%25%29%
1728
February1st to 15thDay
19%2312%27%35%
1682
16th to endDay
22%2313%29%28%
1625
March1st to 15thDay
17%127%30%39%
1980
16th to endDay
15%118%31%40%
2112
April1st to 15thDay
14%115%38%38%
1986
16th to endDay
9%126%25%55%
2190
May1st to 15thDay
9%117%21%58%
2331
16th to endDay
8%115%25%58%
2432
June1st to 15thDay
9%11419%64%
2340
16th to endDay
15%225%17%56%
2340
July1st to 15thDay
31%8%12%15%14%17%
2201
16th to endDay
45%10%16%18%6%2
2312
August1st to 15thDay
35%8%11%14%16%13%
2325
16th to endDay
30%7%11%17%17%14%
2303
September1st to 15thDay
29%5%8%17%19%19%
1980
16th to endDay
15%229%33%36%
1980
October1st to 15thDay
12%2410%28%41%
1788
16th to endDay
10%138%26%49%
1760
November1st to 15thDay
11%1110%34%40%
1759
16th to endDay
17%138%28%39%
1653
December1st to 15thDay
22%2315%31%25%
1620
16th to endDay
21%27%17%31%19%
1728
January1st to 15thNight
18%26%13%27%31%
2327
16th to endNight
25%3413%29%23%
2496
February1st to 15thNight
17%2415%25%34%
2179
16th to endNight
20%2313%33%26%
1847
March1st to 15thNight
15%1211%28%40%
1980
16th to endNight
14%2210%32%37%
2112
April1st to 15thNight
16%129%33%36%
1960
16th to endNight
8%7%26%55%
1767
May1st to 15thNight
8%137%25%53%
1620
16th to endNight
8%115%23%59%
1685
June1st to 15thNight
10%11320%62%
1620
16th to endNight
13%3319%59%
1620
July1st to 15thNight
25%7%15%15%15%20%
1530
16th to endNight
29%10%22%23%10%2
1593
August1st to 15thNight
20%5%16%23%18%15%
1611
16th to endNight
23%5%15%18%20%15%
1896
September1st to 15thNight
26%49%20%20%17%
1980
16th to endNight
10%2212%36%35%
1980
October1st to 15thNight
10%2414%27%40%
1969
16th to endNight
10%1311%24%48%
2112
November1st to 15thNight
11%1213%32%38%
2100
16th to endNight
19%239%24%39%
2304
December1st to 15thNight
18%1416%30%27%
2340
16th to endNight
24%25%19%28%19%
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
8%421%40%24%1
90
16th to endDay
6%8%16%33%22%12%
96
February1st to 15thDay
5%11%21%36%20%5%
197
16th to endDay
9%14%32%28%13%2
238
March1st to 15thDay
6%14%27%29%15%8%
270
16th to endDay
214%29%31%14%7%
288
April1st to 15thDay
413%34%24%15%8%
269
16th to endDay
116%34%27%12%6%
270
May1st to 15thDay
413%30%30%13%7%
288
16th to endDay
27%28%37%20%4
330
June1st to 15thDay
3324%43%19%6%
315
16th to endDay
5%11%42%27%11%
315
July1st to 15thDay
7%9%35%28%18%
305
16th to endDay
9%5%25%31%28%
327
August1st to 15thDay
6%425%40%21%
315
16th to endDay
5%15%26%38%22%
332
September1st to 15thDay
9%19%38%28%12%
315
16th to endDay
6%318%33%28%9%
315
October1st to 15thDay
28%18%34%26%10%
190
16th to endDay
48%22%45%18%
96
November1st to 15thDay
38%18%27%28%12%
90
16th to endDay
5%5%18%40%24%5%
90
December1st to 15thDay
5%212%28%37%13%
90
16th to endDay
8%6%30%26%26%3
96
January1st to 15thNight
6%210%46%30%4
720
16th to endNight
6%414%43%26%5%
768
February1st to 15thNight
4312%41%31%5%
704
16th to endNight
45%20%46%19%3
632
March1st to 15thNight
3420%39%26%5%
720
16th to endNight
2315%42%30%5%
768
April1st to 15thNight
3420%45%22%2
701
16th to endNight
2321%44%23%4
540
May1st to 15thNight
322%41%29%2
540
16th to endNight
1218%40%33%3
563
June1st to 15thNight
2110%47%34%3
540
16th to endNight
25%34%53%3
540
July1st to 15thNight
3424%58%8%
510
16th to endNight
4317%58%16%
564
August1st to 15thNight
3118%60%15%
539
16th to endNight
4319%57%15%
630
September1st to 15thNight
5%5%24%50%14%
720
16th to endNight
110%34%43%10%
716
October1st to 15thNight
1113%41%34%7%
684
16th to endNight
17%36%40%12%
704
November1st to 15thNight
1113%39%35%8%
700
16th to endNight
4114%36%32%9%
720
December1st to 15thNight
7%312%38%30%7%
720
16th to endNight
6%314%43%24%6%
768
Page generated at 2017-10-07 11:07:53. Version ac04

Copyright 2017 A. Danko


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