Rock Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
73%
24980
30%
74544
28%
24927
75%
24927
44%
40185

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
65%
757
29%
2457
29%
756
68%
756
38%
1309
January11th to 20thNight
68%
728
34%
2262
33%
728
73%
728
40%
1215
January21st to endNight
63%
792
35%
2376
29%
792
71%
792
40%
1292
February1st to 10thNight
70%
720
34%
2160
34%
720
74%
720
44%
1125
February11th to 20thNight
64%
700
30%
2098
29%
700
69%
700
37%
1183
February21st to endNight
60%
592
28%
1776
29%
592
64%
592
35%
1054
March1st to 10thNight
63%
720
23%
2160
26%
720
66%
720
33%
1296
March11th to 20thNight
68%
720
26%
2086
27%
720
70%
720
39%
1196
March21st to endNight
67%
792
26%
2039
20%
792
70%
792
42%
1238
April1st to 10thNight
65%
720
25%
1800
19%
720
66%
720
39%
1133
April11th to 20thNight
63%
711
27%
1779
18%
711
64%
711
44%
1071
April21st to endNight
69%
720
27%
1800
17%
720
70%
720
44%
1087
May1st to 10thNight
66%
612
23%
1692
17%
612
67%
612
39%
1023
May11th to 20thNight
65%
531
22%
1595
17%
531
65%
531
36%
960
May21st to endNight
65%
582
23%
1746
19%
582
65%
582
37%
1036
June1st to 10thNight
72%
540
23%
1620
19%
540
72%
540
42%
917
June11th to 20thNight
79%
540
30%
1620
27%
540
79%
540
53%
803
June21st to endNight
82%
540
29%
1620
26%
540
83%
540
55%
781
July1st to 10thNight
87%
525
28%
1575
23%
525
87%
525
60%
726
July11th to 20thNight
89%
522
28%
1566
24%
522
89%
522
56%
752
July21st to endNight
85%
699
27%
1776
20%
660
85%
660
52%
948
August1st to 10thNight
86%
716
31%
1780
20%
712
86%
712
61%
919
August11th to 20thNight
88%
712
36%
1780
22%
712
88%
712
69%
883
August21st to endNight
86%
792
37%
1980
26%
792
86%
792
65%
997
September1st to 10thNight
81%
720
38%
1803
31%
720
81%
720
57%
969
September11th to 20thNight
83%
720
39%
1980
38%
720
83%
720
64%
924
September21st to endNight
84%
720
41%
1980
40%
720
85%
720
65%
919
October1st to 10thNight
79%
720
34%
1980
33%
720
80%
720
53%
1031
October11th to 20thNight
77%
720
39%
1998
38%
720
78%
720
53%
1016
October21st to endNight
75%
792
37%
2460
39%
792
78%
792
51%
1168
November1st to 10thNight
80%
740
34%
2405
38%
740
82%
740
52%
1102
November11th to 20thNight
79%
760
36%
2470
39%
760
81%
760
50%
1154
November21st to endNight
68%
760
31%
2470
32%
760
72%
760
38%
1321
December1st to 10thNight
68%
760
31%
2470
31%
760
72%
760
40%
1282
December11th to 20thNight
61%
760
28%
2955
31%
759
66%
759
26%
1757
December21st to endNight
60%
825
19%
4430
30%
817
66%
817
20%
2598

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
5%423323346%65%
74830
Night
6%6%24423346%59%
74934
TransparencyDay
21%47%17%25%26%
74564
Night
25%5%8%17%21%24%
74722
SeeingDay
6%6%22%38%21%7%
14581
Night
7%210%35%37%9%
25000

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
8%5%23333347%58%
1708
11th to 20thDay
8%5%233245%47%59%
1737
21st to endDay
9%5%24423345%59%
1980
February1st to 10thDay
8%4244235%45%61%
1800
11th to 20thDay
9%423323448%58%
1750
21st to endDay
9%6%15%4245%5%7%52%
1480
March1st to 10thDay
7%425%425%6%6%8%51%
1800
11th to 20thDay
7%42442445%8%57%
1872
21st to endDay
5%3233345%5%8%60%
2312
April1st to 10thDay
7%5%2433446%7%56%
2160
11th to 20thDay
3424323446%64%
2129
21st to endDay
5%423323337%67%
2160
May1st to 10thDay
46%24433447%59%
2263
11th to 20thDay
35%24423247%64%
2301
21st to endDay
46%34422346%61%
2530
June1st to 10thDay
46%24322245%66%
2340
11th to 20thDay
25%13322225%74%
2340
21st to endDay
231332323376%
2340
July1st to 10thDay
2313323335%72%
2340
11th to 20thDay
1213223448%70%
2340
21st to endDay
221242345%9%65%
2433
August1st to 10thDay
1212222345%77%
2149
11th to 20thDay
1112212235%79%
2122
21st to endDay
121232234476%
2376
September1st to 10thDay
2212322345%75%
2156
11th to 20thDay
221221122481%
1980
21st to endDay
131331123478%
1980
October1st to 10thDay
4313323346%68%
1980
11th to 20thDay
4413222235%71%
1958
21st to endDay
3312323235%72%
1895
November1st to 10thDay
3322213346%70%
1674
11th to 20thDay
4213323346%69%
1710
21st to endDay
6%41432445%8%60%
1710
December1st to 10thDay
6%42342445%9%57%
1710
11th to 20thDay
12%6%25%6%335%5%7%45%
2169
21st to endDay
11%6%25%5%45%6%5%7%43%
3146
January1st to 10thNight
9%424424447%56%
2457
11th to 20thNight
7%6%24433346%59%
2262
21st to endNight
9%5%24322347%58%
2376
February1st to 10thNight
7%5%23323345%62%
2160
11th to 20thNight
9%6%34423435%57%
2098
21st to endNight
11%7%34434346%52%
1776
March1st to 10thNight
8%6%45%425%45%8%49%
2160
11th to 20thNight
9%6%33424348%54%
2086
21st to endNight
7%7%25%42445%6%54%
2039
April1st to 10thNight
8%8%35%5%2336%7%50%
1800
11th to 20thNight
7%9%33422346%57%
1779
21st to endNight
6%7%35%423345%56%
1800
May1st to 10thNight
410%36%6%2335%8%50%
1692
11th to 20thNight
48%5%8%5%34347%49%
1594
21st to endNight
7%10%46%5%22346%52%
1746
June1st to 10thNight
36%48%5%3345%7%52%
1620
11th to 20thNight
26%35%423446%61%
1620
21st to endNight
2434333345%67%
1620
July1st to 10thNight
15%24323346%67%
1620
11th to 20thNight
12144345%5%6%65%
1620
21st to endNight
22145%345%6%7%60%
1881
August1st to 10thNight
25%22323346%69%
1790
11th to 20thNight
1313324437%70%
1780
21st to endNight
1325%324345%69%
1980
September1st to 10thNight
35%24313346%67%
1803
11th to 20thNight
342331223375%
1980
21st to endNight
231322333475%
1980
October1st to 10thNight
35%23423346%64%
1980
11th to 20thNight
5%5%2332234468%
1998
21st to endNight
45%23323245%68%
2460
November1st to 10thNight
4322324445%68%
2405
11th to 20thNight
3413323345%68%
2470
21st to endNight
6%425%43445%9%54%
2470
December1st to 10thNight
7%5%2442335%8%56%
2470
11th to 20thNight
13%7%35%5%235%5%7%46%
3041
21st to endNight
9%8%36%6%35%5%5%7%43%
4521

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
27%47%18%24%20%
1709
11th to 20thDay
26%47%13%23%26%
1737
21st to endDay
29%48%14%18%27%
1980
February1st to 10thDay
26%46%12%23%29%
1800
11th to 20thDay
26%5%6%15%27%22%
1760
21st to endDay
30%6%9%13%23%19%
1480
March1st to 10thDay
29%6%8%18%19%20%
1800
11th to 20thDay
25%6%10%19%24%16%
1872
21st to endDay
22%7%13%23%21%14%
2312
April1st to 10thDay
27%5%10%24%22%12%
2160
11th to 20thDay
21%5%8%19%28%18%
2132
21st to endDay
19%5%9%24%31%12%
2160
May1st to 10thDay
25%5%10%19%25%16%
2263
11th to 20thDay
20%5%8%24%30%13%
2304
21st to endDay
25%49%25%28%9%
2530
June1st to 10thDay
21%46%22%30%16%
2340
11th to 20thDay
15%35%14%29%34%
2340
21st to endDay
15%1410%24%46%
2340
July1st to 10thDay
14%35%13%24%42%
2276
11th to 20thDay
13%49%21%26%27%
2271
21st to endDay
15%6%10%24%28%16%
2298
August1st to 10thDay
11%2415%29%38%
2135
11th to 20thDay
8%35%18%29%37%
2122
21st to endDay
11%3413%33%36%
2376
September1st to 10thDay
13%35%9%33%37%
2156
11th to 20thDay
9%2410%36%39%
1980
21st to endDay
13%2414%31%35%
1980
October1st to 10thDay
18%46%19%22%32%
1980
11th to 20thDay
17%35%13%26%36%
1958
21st to endDay
16%45%11%21%43%
1895
November1st to 10thDay
16%36%18%22%34%
1674
11th to 20thDay
18%37%13%21%39%
1710
21st to endDay
23%5%8%12%20%32%
1710
December1st to 10thDay
25%410%17%17%28%
1710
11th to 20thDay
36%8%8%12%19%17%
2168
21st to endDay
38%8%8%19%16%12%
3146
January1st to 10thNight
28%5%7%14%24%23%
2457
11th to 20thNight
27%5%6%13%21%28%
2262
21st to endNight
28%410%12%16%30%
2376
February1st to 10thNight
25%48%15%21%28%
2160
11th to 20thNight
31%46%14%20%26%
2099
21st to endNight
34%46%14%22%20%
1776
March1st to 10thNight
34%6%9%17%16%19%
2160
11th to 20thNight
29%5%9%18%21%18%
2086
21st to endNight
29%6%11%21%20%13%
2039
April1st to 10thNight
33%5%11%21%17%13%
1800
11th to 20thNight
27%6%10%18%21%18%
1779
21st to endNight
28%5%10%23%20%13%
1800
May1st to 10thNight
30%7%12%18%17%16%
1692
11th to 20thNight
32%6%10%21%18%12%
1595
21st to endNight
32%6%11%24%19%9%
1746
June1st to 10thNight
28%414%19%21%14%
1620
11th to 20thNight
21%26%19%25%27%
1620
21st to endNight
19%26%16%22%35%
1620
July1st to 10thNight
17%16%19%23%35%
1575
11th to 20thNight
16%411%22%25%21%
1566
21st to endNight
20%6%12%25%26%12%
1776
August1st to 10thNight
17%36%19%29%26%
1780
11th to 20thNight
12%36%25%26%27%
1780
21st to endNight
15%26%17%28%32%
1980
September1st to 10thNight
19%3413%26%34%
1803
11th to 20thNight
14%25%10%30%38%
1980
21st to endNight
13%36%16%33%30%
1980
October1st to 10thNight
21%46%20%21%29%
1980
11th to 20thNight
20%36%16%22%33%
1998
21st to endNight
19%45%11%21%41%
2460
November1st to 10thNight
18%48%17%19%35%
2405
11th to 20thNight
20%36%12%20%39%
2470
21st to endNight
28%5%7%15%14%31%
2470
December1st to 10thNight
26%49%16%15%28%
2470
11th to 20thNight
35%7%8%13%20%17%
3041
21st to endNight
35%11%10%17%15%12%
4521

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
15%419%41%17%3
270
11th to 20thDay
13%6%22%34%21%3
345
21st to endDay
10%10%29%33%15%3
462
February1st to 10thDay
9%9%26%33%17%6%
420
11th to 20thDay
9%13%30%32%14%2
415
21st to endDay
11%14%32%29%13%1
346
March1st to 10thDay
12%14%32%28%12%3
420
11th to 20thDay
12%10%30%30%15%3
420
21st to endDay
7%16%32%32%11%3
462
April1st to 10thDay
11%9%32%28%15%5%
420
11th to 20thDay
416%33%33%11%4
412
21st to endDay
5%12%30%30%15%7%
420
May1st to 10thDay
9%9%34%29%14%4
423
11th to 20thDay
7%8%26%38%17%4
448
21st to endDay
6%9%29%34%17%4
485
June1st to 10thDay
4322%38%25%7%
450
11th to 20thDay
4322%39%24%9%
450
21st to endDay
4214%45%25%10%
450
July1st to 10thDay
217%48%29%12%
446
11th to 20thDay
16%45%32%16%
444
21st to endDay
215%46%31%15%
487
August1st to 10thDay
2111%47%28%12%
447
11th to 20thDay
217%47%29%14%
437
21st to endDay
27%45%32%13%
495
September1st to 10thDay
3117%48%20%11%
450
11th to 20thDay
3219%46%21%8%
450
21st to endDay
3422%38%24%10%
450
October1st to 10thDay
37%24%37%24%5%
450
11th to 20thDay
46%23%40%21%7%
450
21st to endDay
5%5%21%34%25%10%
410
November1st to 10thDay
4417%36%30%9%
270
11th to 20thDay
3417%40%27%9%
270
21st to endDay
6%8%19%40%20%8%
270
December1st to 10thDay
9%5%18%38%26%5%
270
11th to 20thDay
6%320%38%24%9%
270
21st to endDay
18%8%24%31%16%4
297
January1st to 10thNight
9%216%41%24%7%
760
11th to 20thNight
9%312%40%28%8%
728
21st to endNight
13%215%41%25%4
792
February1st to 10thNight
9%212%40%28%8%
720
11th to 20thNight
11%414%39%25%7%
704
21st to endNight
14%415%41%22%5%
592
March1st to 10thNight
10%414%45%23%4
720
11th to 20thNight
12%311%37%29%8%
720
21st to endNight
10%312%42%29%5%
792
April1st to 10thNight
12%311%43%28%4
720
11th to 20thNight
9%315%38%29%6%
711
21st to endNight
8%410%37%34%7%
720
May1st to 10thNight
7%412%37%34%5%
612
11th to 20thNight
7%114%35%36%8%
531
21st to endNight
8%312%40%33%4
584
June1st to 10thNight
4210%43%35%6%
540
11th to 20thNight
317%38%46%4
540
21st to endNight
316%36%50%5%
540
July1st to 10thNight
2227%58%11%
525
11th to 20thNight
2120%63%14%
522
21st to endNight
3217%58%20%
699
August1st to 10thNight
32124%55%15%
716
11th to 20thNight
2218%57%21%
712
21st to endNight
2215%60%21%
792
September1st to 10thNight
415%20%54%16%
720
11th to 20thNight
41327%54%11%
720
21st to endNight
46%32%46%12%
720
October1st to 10thNight
5%15%40%41%8%
720
11th to 20thNight
6%18%37%38%10%
720
21st to endNight
5%211%32%35%14%
792
November1st to 10thNight
428%42%33%11%
740
11th to 20thNight
419%41%33%12%
760
21st to endNight
8%214%39%30%8%
760
December1st to 10thNight
10%213%42%26%7%
760
11th to 20thNight
14%214%41%23%5%
760
21st to endNight
11%418%38%22%7%
836
Page generated at 2024-01-09 22:25:00. Version ac07

Copyright 2024 Attilla Danko


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