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 2005-11-05 to 2017-09-19.

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
76%
16258
31%
46995
29%
16214
78%
16214
47%
24802

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
71%
717
29%
2318
30%
716
74%
716
42%
1198
January16th to endNight
67%
768
32%
2304
30%
768
71%
768
38%
1286
February1st to 15thNight
74%
697
33%
2105
34%
697
77%
697
44%
1102
February16th to endNight
62%
632
26%
1895
30%
632
64%
632
31%
1170
March1st to 15thNight
73%
720
28%
2160
33%
720
74%
720
41%
1172
March16th to endNight
74%
768
26%
2029
24%
768
75%
768
44%
1165
April1st to 15thNight
66%
719
23%
1799
17%
719
67%
719
41%
1109
April16th to endNight
74%
720
29%
1800
19%
720
75%
720
50%
1033
May1st to 15thNight
72%
587
25%
1667
18%
587
72%
587
42%
960
May16th to endNight
69%
561
24%
1685
20%
561
69%
561
38%
976
June1st to 15thNight
76%
540
24%
1620
21%
540
76%
540
45%
877
June16th to endNight
92%
540
34%
1620
30%
540
92%
540
69%
693
July1st to 15thNight
88%
510
25%
1530
21%
510
88%
510
57%
735
July16th to endNight
85%
635
27%
1658
20%
596
85%
596
50%
878
August1st to 15thNight
86%
717
31%
1790
20%
713
86%
713
61%
922
August16th to endNight
90%
764
38%
1910
26%
764
90%
764
67%
945
September1st to 15thNight
85%
720
36%
1863
31%
720
85%
720
61%
940
September16th to endNight
88%
671
42%
1856
41%
671
89%
671
70%
820
October1st to 15thNight
80%
660
36%
1815
35%
660
81%
660
54%
938
October16th to endNight
77%
704
36%
2120
38%
704
79%
704
50%
1046
November1st to 15thNight
83%
700
33%
2275
38%
700
84%
700
51%
1054
November16th to endNight
76%
720
33%
2340
36%
720
78%
720
43%
1177
December1st to 15thNight
71%
720
32%
2340
34%
720
73%
720
39%
1236
December16th to endNight
64%
768
32%
2496
31%
768
69%
768
36%
1370

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
4312312336%66%
47802
Night
5%423323346%62%
47204
TransparencyDay
20%37%16%25%26%
47504
Night
24%38%16%22%25%
47003
SeeingDay
6%6%23%40%19%4
5936
Night
6%17%32%40%11%
16271

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
7%423323235%60%
1617
16th to endDay
10%413313446%57%
1920
February1st to 15thDay
7%313323446%59%
1751
16th to endDay
11%5%25%323447%49%
1579
March1st to 15thDay
5%21321445%9%59%
1800
16th to endDay
4223323448%60%
2190
April1st to 15thDay
5%42332335%6%57%
2149
16th to endDay
4312212236%69%
2160
May1st to 15thDay
35%22322346%63%
2280
16th to endDay
35%23322236%66%
2429
June1st to 15thDay
45%1322222468%
2340
16th to endDay
1121212382%
2340
July1st to 15thDay
2312222336%67%
2340
16th to endDay
2212222448%66%
2393
August1st to 15thDay
11121223477%
2160
16th to endDay
111211335%76%
2292
September1st to 15thDay
11131123477%
2097
16th to endDay
11122123379%
1849
October1st to 15thDay
4213322245%66%
1815
16th to endDay
441221223469%
1749
November1st to 15thDay
3212222345%69%
1584
16th to endDay
5%313213346%63%
1620
December1st to 15thDay
6%313423449%55%
1620
16th to endDay
11%413413336%55%
1728
January1st to 15thNight
6%323423336%60%
2318
16th to endNight
9%414423236%56%
2304
February1st to 15thNight
6%422312335%62%
2101
16th to endNight
11%6%34424335%49%
1895
March1st to 15thNight
6%423314248%57%
2160
16th to endNight
5%5%23314447%57%
2029
April1st to 15thNight
8%7%24323346%53%
1799
16th to endNight
5%5%23312335%63%
1800
May1st to 15thNight
47%24423348%54%
1667
16th to endNight
47%35%423336%55%
1684
June1st to 15thNight
25%35%423447%56%
1620
16th to endNight
11211223477%
1620
July1st to 15thNight
1313323446%64%
1620
16th to endNight
211343446%7%59%
1772
August1st to 15thNight
1412313347%66%
1800
16th to endNight
212212235%72%
1910
September1st to 15thNight
2313312335%69%
1863
16th to endNight
22121222380%
1856
October1st to 15thNight
3313313345%66%
1815
16th to endNight
5%423213245%65%
2120
November1st to 15thNight
221222343468%
2275
16th to endNight
4313323347%61%
2340
December1st to 15thNight
7%423423347%56%
2340
16th to endNight
10%42231244458%
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
27%36%12%25%25%
1618
16th to endDay
28%48%13%16%28%
1920
February1st to 15thDay
25%46%13%23%26%
1751
16th to endDay
34%5%8%14%25%11%
1579
March1st to 15thDay
22%49%19%21%21%
1800
16th to endDay
22%5%13%22%21%13%
2190
April1st to 15thDay
26%5%8%24%24%11%
2149
16th to endDay
17%410%22%27%17%
2160
May1st to 15thDay
22%48%21%25%18%
2280
16th to endDay
22%39%24%30%10%
2432
June1st to 15thDay
22%2418%30%21%
2340
16th to endDay
10%39%25%49%
2340
July1st to 15thDay
17%35%11%24%37%
2201
16th to endDay
16%49%22%26%19%
2244
August1st to 15thDay
11%1414%33%34%
2146
16th to endDay
11%2412%33%34%
2292
September1st to 15thDay
11%2411%34%35%
2097
16th to endDay
11%1411%34%36%
1849
October1st to 15thDay
20%35%18%25%26%
1815
16th to endDay
19%36%10%20%39%
1749
November1st to 15thDay
17%38%16%20%33%
1584
16th to endDay
22%36%13%20%34%
1620
December1st to 15thDay
26%5%10%15%17%25%
1620
16th to endDay
30%48%15%22%18%
1728
January1st to 15thNight
25%46%12%21%29%
2318
16th to endNight
31%39%11%15%30%
2304
February1st to 15thNight
24%38%16%20%26%
2112
16th to endNight
38%36%14%22%15%
1895
March1st to 15thNight
27%48%18%19%21%
2160
16th to endNight
27%412%20%20%15%
2029
April1st to 15thNight
31%410%21%19%12%
1799
16th to endNight
23%410%22%19%18%
1800
May1st to 15thNight
28%412%17%18%18%
1668
16th to endNight
30%410%22%20%11%
1685
June1st to 15thNight
27%210%18%24%16%
1620
16th to endNight
11%1416%24%41%
1620
July1st to 15thNight
18%27%14%26%30%
1530
16th to endNight
21%5%10%22%25%15%
1658
August1st to 15thNight
17%16%21%32%20%
1790
16th to endNight
13%2415%31%32%
1910
September1st to 15thNight
17%2412%30%32%
1863
16th to endNight
11%15%12%33%35%
1856
October1st to 15thNight
20%36%19%28%22%
1815
16th to endNight
22%25%12%19%38%
2120
November1st to 15thNight
19%37%15%18%36%
2275
16th to endNight
23%47%14%16%33%
2340
December1st to 15thNight
27%49%15%17%25%
2340
16th to endNight
29%5%8%13%22%20%
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
25%414%40%15%
96
16th to endDay
12%8%30%34%12%1
288
February1st to 15thDay
8%7%26%37%17%2
266
16th to endDay
12%13%31%28%11%1
238
March1st to 15thDay
6%11%27%32%16%4
270
16th to endDay
5%14%30%32%13%3
288
April1st to 15thDay
7%15%34%28%10%4
269
16th to endDay
217%36%32%7%4
270
May1st to 15thDay
8%11%32%34%10%2
288
16th to endDay
6%8%30%37%13%2
330
June1st to 15thDay
6%227%39%20%3
315
16th to endDay
115%45%27%9%
315
July1st to 15thDay
310%47%29%8%
305
16th to endDay
46%48%31%9%
327
August1st to 15thDay
212%54%25%5%
315
16th to endDay
37%51%27%9%
332
September1st to 15thDay
2121%52%18%3
315
16th to endDay
2325%47%14%5%
268
October1st to 15thDay
48%30%41%13%1
255
16th to endDay
7%227%35%20%5%
220
November1st to 15thDay
25%11%26%36%17%
90
16th to endDay
7%417%36%30%3
90
December1st to 15thDay
3216%40%32%5%
90
16th to endDay
14%322%33%26%
96
January1st to 15thNight
7%211%40%28%9%
720
16th to endNight
11%212%36%29%7%
768
February1st to 15thNight
7%111%38%32%8%
704
16th to endNight
14%212%39%24%7%
632
March1st to 15thNight
8%19%42%30%6%
720
16th to endNight
7%27%38%35%8%
768
April1st to 15thNight
9%212%40%29%5%
719
16th to endNight
7%29%37%34%8%
720
May1st to 15thNight
6%19%37%35%8%
588
16th to endNight
5%112%36%39%4
563
June1st to 15thNight
29%39%42%4
540
16th to endNight
1232%58%5%
540
July1st to 15thNight
120%66%10%
510
16th to endNight
2113%64%17%
635
August1st to 15thNight
3116%62%16%
717
16th to endNight
111%59%25%
764
September1st to 15thNight
3220%56%17%
720
16th to endNight
3328%48%16%
671
October1st to 15thNight
47%37%39%11%
660
16th to endNight
7%7%28%37%16%
704
November1st to 15thNight
317%37%36%14%
700
16th to endNight
5%19%33%34%15%
720
December1st to 15thNight
9%29%39%30%9%
720
16th to endNight
13%113%37%25%7%
768
Page generated at 2017-09-20 01:49:54. Version ac04

Copyright 2017 A. Danko


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