Sky Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sky Mountain Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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
40%
24573
28%
79710
12%
24463
55%
24463
35%
40496

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
32%
944
32%
4337
10%
926
53%
926
26%
1935
January11th to 20thNight
27%
822
38%
4074
14%
802
51%
802
30%
1469
January21st to endNight
30%
832
22%
4317
13%
814
53%
814
26%
1921
February1st to 10thNight
18%
760
30%
2466
8%
760
44%
760
34%
1216
February11th to 20thNight
19%
720
30%
2152
8%
718
42%
718
33%
1126
February21st to endNight
18%
592
37%
1776
6%
592
49%
592
37%
887
March1st to 10thNight
24%
720
28%
2152
7%
720
44%
720
35%
1082
March11th to 20thNight
35%
720
27%
1980
12%
720
47%
720
39%
1117
March21st to endNight
26%
676
32%
2062
7%
676
51%
676
36%
1052
April1st to 10thNight
25%
540
27%
1800
8%
540
48%
540
34%
855
April11th to 20thNight
28%
533
25%
1777
12%
533
46%
533
28%
940
April21st to endNight
33%
540
25%
1800
10%
540
53%
540
28%
980
May1st to 10thNight
34%
540
23%
1762
13%
540
49%
540
28%
978
May11th to 20thNight
42%
531
16%
1474
8%
531
49%
531
27%
944
May21st to endNight
39%
584
22%
1552
8%
582
51%
582
34%
912
June1st to 10thNight
54%
540
25%
1440
15%
540
62%
540
40%
799
June11th to 20thNight
53%
540
27%
1440
16%
540
62%
540
48%
756
June21st to endNight
58%
540
21%
1440
15%
540
64%
540
39%
848
July1st to 10thNight
67%
525
17%
1400
14%
525
69%
525
29%
916
July11th to 20thNight
75%
522
20%
1392
16%
522
76%
522
38%
824
July21st to endNight
71%
591
11%
1632
11%
558
71%
558
22%
1130
August1st to 10thNight
68%
537
13%
1628
12%
534
69%
534
26%
1024
August11th to 20thNight
70%
534
20%
1778
21%
534
73%
534
31%
1021
August21st to endNight
68%
594
21%
1980
21%
594
71%
594
30%
1137
September1st to 10thNight
65%
540
26%
1800
23%
540
72%
540
35%
970
September11th to 20thNight
59%
540
35%
1808
25%
540
72%
540
42%
888
September21st to endNight
55%
540
31%
1980
24%
540
68%
540
40%
924
October1st to 10thNight
48%
710
29%
2150
15%
710
59%
710
42%
1108
October11th to 20thNight
46%
720
38%
2160
16%
720
63%
720
54%
948
October21st to endNight
43%
792
37%
2376
15%
792
59%
792
43%
1181
November1st to 10thNight
39%
915
36%
2395
12%
915
55%
915
52%
1167
November11th to 20thNight
34%
950
39%
2470
13%
950
52%
950
50%
1223
November21st to endNight
35%
950
34%
2503
12%
950
51%
950
46%
1297
December1st to 10thNight
30%
950
31%
2660
9%
950
48%
950
41%
1318
December11th to 20thNight
25%
950
30%
3119
8%
949
45%
949
34%
1549
December21st to endNight
21%
1039
20%
4678
6%
1026
43%
1026
24%
2054

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
3425%5%35%5%6%8%53%
78451
Night
24244245%6%8%60%
80684
TransparencyDay
26%7%13%22%23%9%
78164
Night
21%7%13%25%24%9%
80493
SeeingDay
9%19%32%25%12%3
14378
Night
5%15%35%29%14%2
24591

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
1325%5%2446%9%59%
2538
11th to 20thDay
22442346%8%64%
2773
21st to endDay
6%46%43445%8%56%
3146
February1st to 10thDay
5%36%42445%8%59%
1713
11th to 20thDay
1225%32445%9%63%
1789
21st to endDay
15%37%5%2445%8%56%
1480
March1st to 10thDay
1425%4245%5%9%58%
1804
11th to 20thDay
27%35%5%345%7%7%52%
1980
21st to endDay
16%35%5%36%45%10%51%
2294
April1st to 10thDay
25%245%245%6%9%54%
2160
11th to 20thDay
38%47%7%25%46%8%48%
2131
21st to endDay
47%36%6%36%6%7%9%44%
2160
May1st to 10thDay
47%46%5%45%6%7%7%45%
2196
11th to 20thDay
6%7%36%7%45%6%6%9%40%
2417
21st to endDay
45%245%45%6%8%9%50%
2724
June1st to 10thDay
2424436%7%8%11%48%
2520
11th to 20thDay
2224435%7%7%9%56%
2520
21st to endDay
23245%37%7%8%9%48%
2520
July1st to 10thDay
5%425%5%46%7%8%10%43%
2520
11th to 20thDay
4425%7%5%8%7%8%10%41%
2520
21st to endDay
5%5%37%8%5%8%10%10%10%29%
2586
August1st to 10thDay
5%5%26%7%5%8%8%7%9%37%
2299
11th to 20thDay
5%435%5%46%7%7%9%45%
2123
21st to endDay
45%26%6%36%5%7%9%45%
2376
September1st to 10thDay
45%25%5%36%8%6%9%49%
2160
11th to 20thDay
43133345%6%8%60%
2150
21st to endDay
431343345%5%65%
1980
October1st to 10thDay
44145%45%5%5%5%57%
1805
11th to 20thDay
2213222346%73%
1800
21st to endDay
35%23323346%66%
1972
November1st to 10thDay
122331335%7%70%
1673
11th to 20thDay
21332245%7%69%
1710
21st to endDay
1325%424348%65%
1672
December1st to 10thDay
32432346%7%66%
1520
11th to 20thDay
131442347%10%62%
1926
21st to endDay
1336%5%3446%7%60%
2794
January1st to 10thNight
237%6%2445%8%59%
4417
11th to 20thNight
21342345%7%68%
4224
21st to endNight
425%5%345%6%8%59%
4521
February1st to 10thNight
436%5%23337%64%
2466
11th to 20thNight
1425%5%25%447%62%
2152
21st to endNight
426%42345%6%64%
1776
March1st to 10thNight
14232245%6%7%64%
2152
11th to 20thNight
25%2442446%9%59%
1980
21st to endNight
15%234235%6%8%61%
2062
April1st to 10thNight
141432436%8%64%
1800
11th to 20thNight
37%25%425%45%8%56%
1777
21st to endNight
36%25%425%46%8%54%
1800
May1st to 10thNight
35%45%5%3446%7%55%
1762
11th to 20thNight
5%9%25%5%35%6%7%8%46%
1474
21st to endNight
7%4144244410%55%
1552
June1st to 10thNight
3314335%5%6%10%58%
1440
11th to 20thNight
12233235%5%9%65%
1440
21st to endNight
23245%45%5%7%11%52%
1440
July1st to 10thNight
5%425%6%5%7%9%7%10%41%
1440
11th to 20thNight
4424436%7%9%10%50%
1440
21st to endNight
4436%6%5%7%8%9%14%34%
1728
August1st to 10thNight
4426%5%5%6%7%8%10%43%
1637
11th to 20thNight
4425%6%35%6%9%11%46%
1778
21st to endNight
4325%5%46%6%8%9%48%
1980
September1st to 10thNight
44245%3448%9%51%
1800
11th to 20thNight
5%41332445%8%61%
1808
21st to endNight
3314423446%64%
1980
October1st to 10thNight
43133235%5%6%64%
2150
11th to 20thNight
111221235%5%78%
2160
21st to endNight
35%23313446%67%
2376
November1st to 10thNight
121221335%7%72%
2395
11th to 20thNight
1113213346%74%
2470
21st to endNight
142331335%7%67%
2503
December1st to 10thNight
122333335%9%67%
2660
11th to 20thNight
1325%32346%9%61%
3271
21st to endNight
325%4345%6%8%59%
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
18%5%17%29%26%5%
2539
11th to 20thDay
15%7%16%33%24%5%
2773
21st to endDay
25%7%12%29%22%6%
3146
February1st to 10thDay
24%413%28%21%9%
1713
11th to 20thDay
20%5%11%26%29%9%
1799
21st to endDay
26%5%9%22%25%13%
1480
March1st to 10thDay
22%5%11%23%28%10%
1804
11th to 20thDay
29%6%12%24%23%6%
1980
21st to endDay
30%6%10%26%22%5%
2294
April1st to 10thDay
28%6%12%21%21%12%
2160
11th to 20thDay
34%6%9%25%18%9%
2134
21st to endDay
35%7%12%21%20%6%
2160
May1st to 10thDay
36%8%12%19%19%6%
2196
11th to 20thDay
39%10%14%19%14%4
2421
21st to endDay
28%9%12%19%21%11%
2724
June1st to 10thDay
25%11%14%20%19%10%
2520
11th to 20thDay
22%8%11%16%23%20%
2520
21st to endDay
28%10%13%19%19%11%
2520
July1st to 10thDay
32%11%14%16%17%10%
2451
11th to 20thDay
32%10%16%24%13%5%
2445
21st to endDay
39%15%20%17%7%1
2442
August1st to 10thDay
39%12%17%13%13%6%
2284
11th to 20thDay
33%8%14%20%17%7%
2123
21st to endDay
32%9%14%20%21%4
2376
September1st to 10thDay
29%7%13%20%20%11%
2160
11th to 20thDay
22%7%12%17%28%15%
2150
21st to endDay
21%5%8%24%32%10%
1980
October1st to 10thDay
26%8%10%18%27%10%
1805
11th to 20thDay
15%48%19%39%15%
1800
21st to endDay
20%48%26%31%10%
1972
November1st to 10thDay
14%410%21%36%13%
1673
11th to 20thDay
15%5%9%31%31%8%
1710
21st to endDay
21%48%21%31%14%
1672
December1st to 10thDay
18%5%14%30%24%8%
1520
11th to 20thDay
16%7%15%26%29%8%
1924
21st to endDay
20%7%14%24%22%14%
2794
January1st to 10thNight
20%7%13%26%28%5%
4417
11th to 20thNight
14%5%13%37%25%5%
4224
21st to endNight
20%9%16%29%22%5%
4521
February1st to 10thNight
22%411%31%22%9%
2466
11th to 20thNight
23%412%27%27%7%
2152
21st to endNight
19%5%10%25%30%11%
1776
March1st to 10thNight
19%6%12%26%28%9%
2152
11th to 20thNight
23%8%12%28%24%5%
1980
21st to endNight
20%7%13%28%29%4
2062
April1st to 10thNight
19%6%14%26%26%9%
1800
11th to 20thNight
27%6%11%26%24%6%
1777
21st to endNight
28%7%12%28%20%5%
1800
May1st to 10thNight
30%6%13%25%19%7%
1762
11th to 20thNight
35%9%18%18%15%5%
1475
21st to endNight
27%8%14%20%21%11%
1552
June1st to 10thNight
22%8%18%20%18%13%
1440
11th to 20thNight
16%8%11%21%24%20%
1440
21st to endNight
25%9%13%19%20%13%
1440
July1st to 10thNight
34%12%13%17%16%9%
1400
11th to 20thNight
25%11%21%25%13%6%
1392
21st to endNight
37%17%22%17%7%
1632
August1st to 10thNight
32%15%18%17%12%7%
1628
11th to 20thNight
30%9%19%22%14%6%
1778
21st to endNight
29%11%17%22%17%4
1980
September1st to 10thNight
27%7%15%22%21%7%
1800
11th to 20thNight
21%6%12%21%25%14%
1808
21st to endNight
20%6%10%23%32%8%
1980
October1st to 10thNight
20%7%14%20%27%12%
2150
11th to 20thNight
11%5%10%20%39%16%
2160
21st to endNight
20%5%8%27%29%12%
2376
November1st to 10thNight
13%410%26%32%14%
2395
11th to 20thNight
13%5%8%33%30%11%
2470
21st to endNight
18%5%10%22%33%13%
2503
December1st to 10thNight
16%6%16%30%24%9%
2660
11th to 20thNight
17%8%13%25%30%7%
3272
21st to endNight
19%8%15%23%23%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
16%22%32%19%9%1
270
11th to 20thDay
17%24%38%17%3
270
21st to endDay
425%41%22%7%1
297
February1st to 10thDay
11%37%37%12%11
270
11th to 20thDay
12%38%34%12%4
252
21st to endDay
18%32%35%14%1
198
March1st to 10thDay
14%30%35%18%3
244
11th to 20thDay
12%33%33%16%5%1
420
21st to endDay
17%38%35%7%2
462
April1st to 10thDay
14%34%34%14%21
420
11th to 20thDay
18%35%32%13%2
412
21st to endDay
16%35%33%13%3
420
May1st to 10thDay
12%28%38%16%41
459
11th to 20thDay
9%18%35%25%11%2
625
21st to endDay
7%19%32%29%12%2
679
June1st to 10thDay
414%32%30%17%3
630
11th to 20thDay
5%14%36%27%14%3
630
21st to endDay
311%34%29%20%4
630
July1st to 10thDay
7%425%37%22%6%
621
11th to 20thDay
4219%40%27%7%
618
21st to endDay
5%317%41%27%7%
528
August1st to 10thDay
8%423%39%21%5%
447
11th to 20thDay
6%430%39%17%4
437
21st to endDay
8%5%26%40%18%3
495
September1st to 10thDay
6%8%29%36%16%5%
450
11th to 20thDay
5%11%38%29%15%2
440
21st to endDay
6%12%27%30%21%4
270
October1st to 10thDay
9%17%27%27%16%4
270
11th to 20thDay
9%25%27%25%11%3
270
21st to endDay
11%21%34%22%11%1
297
November1st to 10thDay
8%28%32%22%9%1
270
11th to 20thDay
6%25%37%20%9%2
270
21st to endDay
7%20%41%26%6%1
270
December1st to 10thDay
14%26%35%17%7%1
270
11th to 20thDay
8%34%36%16%7%
270
21st to endDay
11%36%35%13%4
297
January1st to 10thNight
5%25%35%25%9%2
950
11th to 20thNight
5%25%40%23%6%1
822
21st to endNight
217%47%26%7%1
836
February1st to 10thNight
421%54%17%4
760
11th to 20thNight
5%23%49%18%6%
722
21st to endNight
421%54%19%2
592
March1st to 10thNight
426%44%21%5%1
720
11th to 20thNight
6%14%42%27%10%1
720
21st to endNight
6%21%45%23%4
676
April1st to 10thNight
8%20%45%24%4
540
11th to 20thNight
10%19%39%26%6%
533
21st to endNight
7%19%36%29%9%
540
May1st to 10thNight
6%14%39%31%8%1
540
11th to 20thNight
10%10%33%32%14%1
531
21st to endNight
7%15%34%29%14%2
584
June1st to 10thNight
49%26%37%22%1
540
11th to 20thNight
210%32%41%14%1
540
21st to endNight
35%26%39%25%2
540
July1st to 10thNight
7%214%40%33%3
525
11th to 20thNight
5%111%38%39%7%
522
21st to endNight
5%19%35%43%6%
591
August1st to 10thNight
5%312%39%36%5%
537
11th to 20thNight
5%412%44%31%4
534
21st to endNight
5%215%41%31%5%
594
September1st to 10thNight
4419%41%26%6%
540
11th to 20thNight
5%8%24%37%22%5%
540
21st to endNight
48%28%40%17%3
540
October1st to 10thNight
5%11%33%34%15%2
710
11th to 20thNight
213%37%32%14%3
720
21st to endNight
6%14%34%29%15%3
792
November1st to 10thNight
317%38%29%12%1
915
11th to 20thNight
418%40%26%9%2
950
21st to endNight
6%16%39%29%9%1
950
December1st to 10thNight
5%21%42%25%7%
950
11th to 20thNight
422%45%21%7%1
950
21st to endNight
6%26%43%20%41
1045
Page generated at 2024-02-12 04:35:35. Version ac07

Copyright 2024 Attilla Danko


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