Sky Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sky Ranch Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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
56%
24376
31%
79709
21%
24276
67%
24276
43%
39220

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 10thNight
52%
792
31%
4081
25%
775
67%
775
34%
1741
January11th to 20thNight
51%
758
40%
3925
25%
740
66%
740
39%
1384
January21st to endNight
52%
825
23%
4271
24%
814
67%
814
30%
1955
February1st to 10thNight
46%
760
32%
2443
21%
760
62%
760
47%
1149
February11th to 20thNight
41%
742
31%
2218
17%
740
55%
740
45%
1120
February21st to endNight
35%
628
37%
1884
15%
628
56%
628
49%
904
March1st to 10thNight
42%
742
35%
2128
17%
742
58%
742
48%
1079
March11th to 20thNight
48%
720
33%
1980
17%
720
57%
720
46%
1063
March21st to endNight
44%
720
34%
2106
15%
720
61%
720
45%
1070
April1st to 10thNight
39%
540
36%
1800
17%
540
63%
540
47%
803
April11th to 20thNight
43%
533
33%
1777
19%
533
63%
533
41%
842
April21st to endNight
39%
540
35%
1800
18%
540
64%
540
45%
815
May1st to 10thNight
47%
540
29%
1800
21%
540
62%
540
47%
828
May11th to 20thNight
50%
531
24%
1688
18%
531
59%
531
36%
927
May21st to endNight
51%
584
33%
1552
16%
582
67%
582
52%
799
June1st to 10thNight
63%
540
26%
1440
19%
540
68%
540
46%
797
June11th to 20thNight
63%
540
33%
1440
22%
540
70%
540
59%
704
June21st to endNight
67%
540
24%
1440
18%
540
70%
540
42%
832
July1st to 10thNight
71%
525
18%
1434
16%
525
72%
525
33%
904
July11th to 20thNight
77%
522
17%
1566
15%
522
78%
522
34%
919
July21st to endNight
71%
591
14%
1674
14%
558
71%
558
26%
1087
August1st to 10thNight
75%
537
15%
1661
15%
534
75%
534
30%
1002
August11th to 20thNight
73%
534
18%
1778
20%
534
74%
534
27%
1085
August21st to endNight
79%
594
24%
1980
27%
594
82%
594
37%
1081
September1st to 10thNight
74%
540
26%
1800
27%
540
77%
540
34%
1000
September11th to 20thNight
75%
540
36%
1800
36%
540
79%
540
40%
930
September21st to endNight
67%
580
34%
1997
28%
580
75%
580
47%
920
October1st to 10thNight
63%
720
32%
2160
23%
720
69%
720
45%
1130
October11th to 20thNight
63%
720
41%
2160
24%
720
75%
720
61%
955
October21st to endNight
60%
792
40%
2376
24%
792
71%
792
56%
1093
November1st to 10thNight
65%
768
42%
2248
26%
768
76%
768
66%
972
November11th to 20thNight
61%
950
39%
2470
23%
950
69%
950
64%
1182
November21st to endNight
54%
950
37%
2470
21%
950
63%
950
50%
1341
December1st to 10thNight
53%
950
36%
2615
20%
950
64%
950
52%
1311
December11th to 20thNight
49%
949
33%
3107
19%
948
60%
948
43%
1544
December21st to endNight
43%
1039
21%
4640
18%
1026
55%
1026
36%
1952

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
23134245%6%8%62%
78736
Night
332343445%8%61%
80826
TransparencyDay
20%6%10%22%27%15%
78459
Night
21%6%10%22%27%15%
80624
SeeingDay
5%12%27%30%20%6%
14116
Night
47%28%41%18%1
24405

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 10thDay
143432346%9%60%
2808
11th to 20thDay
242221335%7%70%
2860
21st to endDay
35%245%345%6%9%54%
3146
February1st to 10thDay
2415%43345%7%62%
1734
11th to 20thDay
232442445%8%62%
1849
21st to endDay
1323333448%66%
1570
March1st to 10thDay
23133345%7%8%62%
1946
11th to 20thDay
25%34434347%61%
1980
21st to endDay
23133245%5%9%62%
2248
April1st to 10thDay
221232345%8%68%
2160
11th to 20thDay
232442345%7%64%
2131
21st to endDay
331322335%7%68%
2160
May1st to 10thDay
221332345%9%68%
2160
11th to 20thDay
33234345%6%7%60%
2201
21st to endDay
221232345%8%67%
2724
June1st to 10thDay
2132235%7%10%65%
2520
11th to 20thDay
2112313447%72%
2520
21st to endDay
43124245%6%8%60%
2520
July1st to 10thDay
33236%36%7%8%10%48%
2478
11th to 20thDay
23135%35%7%8%12%50%
2340
21st to endDay
33246%47%9%9%11%40%
2545
August1st to 10thDay
33245%45%7%9%11%48%
2267
11th to 20thDay
23245%36%7%8%11%49%
2123
21st to endDay
33235%45%6%7%11%52%
2376
September1st to 10thDay
5%423435%5%7%9%53%
2160
11th to 20thDay
4313425%5%6%7%61%
2160
21st to endDay
2212324347%70%
1959
October1st to 10thDay
6%32433445%6%61%
1800
11th to 20thDay
321222224477%
1800
21st to endDay
331332223474%
1980
November1st to 10thDay
211121335%7%74%
1809
11th to 20thDay
1212213447%72%
1710
21st to endDay
232343335%7%66%
1710
December1st to 10thDay
241332445%7%66%
1562
11th to 20thDay
2325%43446%7%60%
1926
21st to endDay
2413423447%65%
2794
January1st to 10thNight
1435%6%3445%7%57%
4162
11th to 20thNight
2313424446%69%
4110
21st to endNight
37%244345%6%10%53%
4521
February1st to 10thNight
15%24324446%64%
2443
11th to 20thNight
35%2342345%8%61%
2218
21st to endNight
2423424346%66%
1884
March1st to 10thNight
35%2332445%7%62%
2128
11th to 20thNight
4424425%45%6%61%
1980
21st to endNight
3324324446%64%
2106
April1st to 10thNight
322332436%7%65%
1800
11th to 20thNight
342343445%6%63%
1777
21st to endNight
321332345%6%68%
1800
May1st to 10thNight
331342346%7%64%
1800
11th to 20thNight
5%4245%15%5%5%7%56%
1688
21st to endNight
3213324448%67%
1552
June1st to 10thNight
12134347%7%11%55%
1440
11th to 20thNight
211332445%7%69%
1440
21st to endNight
43235%35%6%8%8%53%
1440
July1st to 10thNight
3315%6%36%8%9%11%44%
1476
11th to 20thNight
33235%37%9%9%14%43%
1620
21st to endNight
4426%7%5%6%7%9%16%35%
1773
August1st to 10thNight
2325%6%37%9%10%11%42%
1670
11th to 20thNight
35%25%6%5%6%7%8%13%39%
1778
21st to endNight
32245%46%6%9%12%47%
1980
September1st to 10thNight
43146%45%6%9%11%47%
1800
11th to 20thNight
43244345%7%8%58%
1800
21st to endNight
3313324446%67%
1997
October1st to 10thNight
6%32442435%6%62%
2160
11th to 20thNight
3212212345%76%
2160
21st to endNight
4212312336%72%
2376
November1st to 10thNight
1211212345%78%
2248
11th to 20thNight
121232235%6%74%
2470
21st to endNight
4323423346%65%
2470
December1st to 10thNight
341231345%7%67%
2615
11th to 20thNight
331343445%9%60%
3271
21st to endNight
35%24433346%63%
4873

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 10thDay
19%410%32%30%4
2809
11th to 20thDay
14%5%12%38%27%4
2860
21st to endDay
24%7%10%24%29%7%
3146
February1st to 10thDay
21%412%25%28%11%
1734
11th to 20thDay
21%5%7%26%29%13%
1859
21st to endDay
18%46%21%33%19%
1570
March1st to 10thDay
18%6%6%23%31%17%
1946
11th to 20thDay
23%38%19%32%15%
1980
21st to endDay
18%5%9%22%32%14%
2248
April1st to 10thDay
15%47%20%34%20%
2160
11th to 20thDay
20%46%19%30%21%
2134
21st to endDay
16%48%22%34%17%
2160
May1st to 10thDay
15%48%18%32%23%
2160
11th to 20thDay
23%6%10%18%25%17%
2204
21st to endDay
16%6%9%18%24%28%
2724
June1st to 10thDay
14%5%10%22%25%23%
2520
11th to 20thDay
13%36%13%23%42%
2520
21st to endDay
21%6%9%19%22%24%
2520
July1st to 10thDay
27%11%14%16%17%15%
2411
11th to 20thDay
23%9%18%25%15%9%
2271
21st to endDay
31%12%21%24%9%2
2404
August1st to 10thDay
26%12%18%21%14%9%
2252
11th to 20thDay
26%10%15%23%18%8%
2123
21st to endDay
24%9%14%25%22%5%
2376
September1st to 10thDay
25%7%12%22%22%11%
2160
11th to 20thDay
23%6%9%18%25%19%
2160
21st to endDay
15%5%6%23%33%19%
1959
October1st to 10thDay
24%6%7%19%25%19%
1800
11th to 20thDay
14%3414%34%32%
1800
21st to endDay
16%36%21%36%18%
1980
November1st to 10thDay
11%27%22%39%18%
1809
11th to 20thDay
13%38%25%39%12%
1710
21st to endDay
18%46%23%33%15%
1710
December1st to 10thDay
17%411%33%26%8%
1562
11th to 20thDay
23%413%23%29%8%
1924
21st to endDay
19%39%21%32%16%
2794
January1st to 10thNight
23%313%27%26%7%
4162
11th to 20thNight
15%5%10%37%27%7%
4110
21st to endNight
24%6%12%24%29%6%
4521
February1st to 10thNight
19%411%26%27%13%
2443
11th to 20thNight
22%49%24%27%14%
2218
21st to endNight
18%46%16%34%21%
1884
March1st to 10thNight
20%46%24%31%16%
2128
11th to 20thNight
22%5%8%19%31%15%
1980
21st to endNight
20%5%7%19%34%15%
2106
April1st to 10thNight
17%47%20%32%21%
1800
11th to 20thNight
21%36%20%27%23%
1777
21st to endNight
18%48%19%35%16%
1800
May1st to 10thNight
18%410%14%31%22%
1800
11th to 20thNight
27%7%10%18%20%17%
1689
21st to endNight
17%5%10%17%23%28%
1552
June1st to 10thNight
21%8%14%17%19%22%
1440
11th to 20thNight
15%46%14%20%40%
1440
21st to endNight
24%9%12%15%17%24%
1440
July1st to 10thNight
31%11%14%19%12%13%
1434
11th to 20thNight
25%13%21%19%13%8%
1566
21st to endNight
34%14%24%20%7%1
1674
August1st to 10thNight
28%14%20%19%11%8%
1661
11th to 20thNight
31%13%19%17%12%7%
1778
21st to endNight
24%10%17%27%14%7%
1980
September1st to 10thNight
26%10%16%19%19%10%
1800
11th to 20thNight
22%8%12%17%21%20%
1800
21st to endNight
19%5%8%18%29%21%
1997
October1st to 10thNight
23%5%9%20%20%23%
2160
11th to 20thNight
12%45%14%34%31%
2160
21st to endNight
15%36%19%38%19%
2376
November1st to 10thNight
10%36%22%41%18%
2248
11th to 20thNight
12%36%23%40%15%
2470
21st to endNight
21%46%20%32%17%
2470
December1st to 10thNight
17%410%31%29%8%
2615
11th to 20thNight
21%411%26%30%9%
3272
21st to endNight
21%310%22%32%12%
4873

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 10thDay
5%15%38%30%11%
270
11th to 20thDay
9%16%36%27%12%
270
21st to endDay
39%35%37%13%2
297
February1st to 10thDay
421%37%27%11%
270
11th to 20thDay
7%20%41%24%7%
270
21st to endDay
12%24%40%21%4
225
March1st to 10thDay
6%24%34%27%10%
351
11th to 20thDay
10%26%30%23%10%1
420
21st to endDay
10%34%30%18%8%
462
April1st to 10thDay
8%22%37%23%8%2
420
11th to 20thDay
10%28%36%16%8%1
412
21st to endDay
9%24%38%24%6%1
420
May1st to 10thDay
420%42%25%8%1
423
11th to 20thDay
5%14%33%30%15%3
469
21st to endDay
413%31%37%14%1
679
June1st to 10thDay
26%22%39%27%4
630
11th to 20thDay
26%24%37%28%3
630
21st to endDay
6%420%34%29%6%
630
July1st to 10thDay
4214%35%34%12%
581
11th to 20thDay
37%29%41%20%
444
21st to endDay
217%23%42%25%
487
August1st to 10thDay
3311%29%36%18%
447
11th to 20thDay
3117%33%34%12%
437
21st to endDay
5%111%33%35%15%
495
September1st to 10thDay
5%316%33%29%14%
450
11th to 20thDay
4224%36%26%8%
450
21st to endDay
36%24%31%27%9%
293
October1st to 10thDay
6%10%27%24%26%6%
270
11th to 20thDay
6%12%26%28%22%6%
270
21st to endDay
10%11%26%27%20%5%
297
November1st to 10thDay
416%33%32%14%1
270
11th to 20thDay
48%29%36%21%1
270
21st to endDay
9%16%34%27%14%1
270
December1st to 10thDay
416%32%34%13%1
270
11th to 20thDay
8%12%36%34%10%1
270
21st to endDay
9%20%35%32%4
297
January1st to 10thNight
5%6%33%41%15%1
799
11th to 20thNight
46%34%41%14%1
760
21st to endNight
5%8%31%41%13%2
836
February1st to 10thNight
49%38%40%9%1
760
11th to 20thNight
6%10%40%36%8%
744
21st to endNight
6%10%48%33%3
628
March1st to 10thNight
5%10%40%35%8%
742
11th to 20thNight
6%12%32%39%12%
720
21st to endNight
413%36%39%8%
720
April1st to 10thNight
413%41%37%41
540
11th to 20thNight
416%35%37%8%
533
21st to endNight
5%13%41%34%7%1
540
May1st to 10thNight
48%37%40%11%
540
11th to 20thNight
6%8%30%40%15%1
531
21st to endNight
48%35%41%13%
584
June1st to 10thNight
26%25%46%20%1
540
11th to 20thNight
2329%49%17%1
540
21st to endNight
3319%48%26%1
540
July1st to 10thNight
4113%45%33%3
525
11th to 20thNight
419%35%48%4
522
21st to endNight
6%18%30%49%7%
591
August1st to 10thNight
319%31%48%8%
537
11th to 20thNight
3211%45%36%3
534
21st to endNight
318%43%40%5%
594
September1st to 10thNight
4312%49%31%2
540
11th to 20thNight
5%314%47%31%1
540
21st to endNight
4421%45%24%2
580
October1st to 10thNight
6%423%46%20%1
720
11th to 20thNight
3427%47%17%2
720
21st to endNight
5%6%26%39%21%3
792
November1st to 10thNight
25%26%46%20%1
768
11th to 20thNight
26%28%45%18%2
950
21st to endNight
5%9%28%39%17%2
950
December1st to 10thNight
5%10%30%43%12%
950
11th to 20thNight
6%10%32%41%11%
950
21st to endNight
6%9%37%41%7%
1045
Page generated at 2024-03-03 04:28:56. Version ac07

Copyright © 2024 Attilla Danko.


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