Rocky Mountain Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rocky Mountain Sky Observatory clear sky chart from 2005-11-05 to 2018-08-29.

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
62%
17246
28%
50605
22%
17206
67%
17206
42%
27646

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
56%
972
30%
2716
22%
970
63%
970
47%
1445
January16th to endNight
58%
903
34%
2775
28%
903
67%
903
43%
1472
February1st to 15thNight
50%
759
25%
2439
18%
758
60%
758
37%
1343
February16th to endNight
50%
684
30%
2050
19%
684
60%
684
38%
1165
March1st to 15thNight
59%
780
29%
2304
19%
780
67%
780
46%
1215
March16th to endNight
54%
728
26%
2184
18%
728
61%
728
39%
1235
April1st to 15thNight
48%
584
23%
1948
18%
584
57%
584
31%
1092
April16th to endNight
47%
579
22%
1929
20%
579
55%
579
28%
1130
May1st to 15thNight
54%
585
20%
1712
17%
585
57%
585
28%
1091
May16th to endNight
60%
610
18%
1626
14%
609
62%
609
37%
987
June1st to 15thNight
67%
585
22%
1560
16%
585
69%
585
48%
849
June16th to endNight
75%
585
26%
1560
21%
585
76%
585
54%
815
July1st to 15thNight
73%
555
21%
1480
18%
555
74%
555
43%
855
July16th to endNight
78%
612
27%
1544
24%
579
78%
579
47%
839
August1st to 15thNight
76%
575
23%
1774
23%
572
76%
572
42%
930
August16th to endNight
77%
615
29%
2050
34%
615
78%
615
41%
1043
September1st to 15thNight
71%
540
28%
1800
30%
540
75%
540
40%
924
September16th to endNight
75%
537
36%
1938
38%
537
80%
537
46%
879
October1st to 15thNight
65%
702
28%
2142
21%
702
70%
702
41%
1164
October16th to endNight
66%
816
37%
2352
25%
816
72%
816
48%
1228
November1st to 15thNight
64%
950
33%
2470
20%
950
69%
950
51%
1339
November16th to endNight
63%
975
35%
2610
24%
975
69%
975
51%
1388
December1st to 15thNight
57%
975
26%
2730
18%
975
63%
975
43%
1520
December16th to endNight
54%
1040
28%
2912
18%
1040
62%
1040
38%
1698

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
6%42342446%8%52%
51665
Night
5%5%2432335%7%55%
50777
Cloud CoverDay
5%4244245%6%8%51%
51663
Night
5%42442335%7%55%
50777
TransparencyDay
28%410%27%21%8%
51340
Night
27%311%28%21%7%
50605
SeeingDay
9%5%19%32%24%7%
7163
Night
7%318%49%19%1
17255

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
27%34322348%57%
1552
16th to endDay
25%25%423348%57%
1811
February1st to 15thDay
36%35%42445%8%50%
1751
16th to endDay
26%25%32335%7%56%
1710
March1st to 15thDay
3424333348%57%
1982
16th to endDay
7%6%2442446%8%48%
2392
April1st to 15thDay
8%6%23324449%51%
2330
16th to endDay
13%7%235%3445%7%43%
2306
May1st to 15thDay
13%5%24425%5%8%7%39%
2567
16th to endDay
10%5%145%35%6%6%9%42%
2840
June1st to 15thDay
6%312325%6%6%10%50%
2730
16th to endDay
32123346%7%8%56%
2730
July1st to 15thDay
6%314325%6%7%8%49%
2730
16th to endDay
3214435%6%8%10%48%
2880
August1st to 15thDay
4314446%7%8%10%44%
2427
16th to endDay
4213335%5%7%8%53%
2449
September1st to 15thDay
7%31232345%7%57%
2160
16th to endDay
5%313323335%63%
2022
October1st to 15thDay
7%413322447%56%
1818
16th to endDay
6%412211345%64%
1858
November1st to 15thDay
25%1441345%8%57%
1718
16th to endDay
242332235%8%59%
1678
December1st to 15thDay
36%2442345%8%53%
1560
16th to endDay
5%5%24423348%53%
1664
January1st to 15thNight
16%24423347%59%
2716
16th to endNight
36%34313346%59%
2775
February1st to 15thNight
37%36%32235%7%52%
2429
16th to endNight
38%35%324335%55%
2050
March1st to 15thNight
35%2341335%7%58%
2304
16th to endNight
7%6%24423347%53%
2184
April1st to 15thNight
8%6%2442445%7%49%
1948
16th to endNight
15%6%23413347%46%
1929
May1st to 15thNight
15%5%144345%6%5%43%
1711
16th to endNight
11%41442445%7%49%
1625
June1st to 15thNight
6%21231435%9%58%
1560
16th to endNight
321331346%9%61%
1560
July1st to 15thNight
6%21442446%9%52%
1560
16th to endNight
2313435%5%6%9%54%
1640
August1st to 15thNight
32243245%8%11%51%
1782
16th to endNight
431442445%8%55%
2050
September1st to 15thNight
7%21442345%8%55%
1800
16th to endNight
6%12323346%64%
1938
October1st to 15thNight
8%424223346%56%
2142
16th to endNight
7%413222236%62%
2352
November1st to 15thNight
4314313446%62%
2470
16th to endNight
442322235%7%62%
2610
December1st to 15thNight
47%24423347%56%
2730
16th to endNight
47%245%23448%51%
2912

Percentage Cloud Cover SE (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
27%2442345%7%57%
1552
16th to endDay
25%25%32345%7%57%
1811
February1st to 15thDay
36%3442445%8%50%
1751
16th to endDay
26%25%22445%7%55%
1710
March1st to 15thDay
3424434348%56%
1982
16th to endDay
6%6%2443346%8%48%
2390
April1st to 15thDay
8%6%2432445%9%50%
2330
16th to endDay
12%7%2442445%8%42%
2306
May1st to 15thDay
13%5%24436%5%7%8%39%
2567
16th to endDay
10%5%245%35%5%6%9%42%
2840
June1st to 15thDay
6%312425%5%7%9%50%
2730
16th to endDay
3212325%6%7%8%55%
2730
July1st to 15thDay
5%314335%5%7%9%49%
2730
16th to endDay
3214335%6%9%10%48%
2880
August1st to 15thDay
43235%35%7%8%11%43%
2427
16th to endDay
4213425%6%7%9%52%
2449
September1st to 15thDay
7%21332346%7%57%
2160
16th to endDay
5%313413345%63%
2022
October1st to 15thDay
7%42331245%7%56%
1818
16th to endDay
6%31231235%5%64%
1858
November1st to 15thDay
26%2332445%8%57%
1718
16th to endDay
242331235%9%59%
1678
December1st to 15thDay
36%2442345%8%54%
1560
16th to endDay
5%5%35%42345%7%52%
1664
January1st to 15thNight
15%24423347%59%
2716
16th to endNight
35%34323345%58%
2775
February1st to 15thNight
46%36%422448%52%
2429
16th to endNight
38%35%424235%55%
2050
March1st to 15thNight
35%2442335%7%58%
2304
16th to endNight
7%5%2442335%6%53%
2184
April1st to 15thNight
7%6%25%5%2435%7%48%
1948
16th to endNight
15%7%24323346%46%
1929
May1st to 15thNight
15%5%244345%5%6%43%
1711
16th to endNight
11%41333446%7%49%
1625
June1st to 15thNight
6%21231435%9%58%
1560
16th to endNight
32133135%6%9%60%
1560
July1st to 15thNight
5%21443446%10%52%
1560
16th to endNight
2213435%6%6%9%54%
1640
August1st to 15thNight
3214425%47%11%51%
1782
16th to endNight
422343445%9%55%
2050
September1st to 15thNight
7%31442445%7%55%
1800
16th to endNight
5%212323446%64%
1938
October1st to 15thNight
8%423313346%56%
2142
16th to endNight
7%5%13222336%62%
2352
November1st to 15thNight
431332335%6%61%
2470
16th to endNight
442331335%6%62%
2610
December1st to 15thNight
36%24323348%55%
2730
16th to endNight
47%345%2345%8%50%
2912

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
25%211%35%20%4
1553
16th to endDay
26%28%34%21%6%
1811
February1st to 15thDay
29%414%35%12%3
1752
16th to endDay
26%28%32%25%4
1710
March1st to 15thDay
26%39%28%25%7%
1982
16th to endDay
31%412%28%18%4
2392
April1st to 15thDay
31%310%28%18%7%
2330
16th to endDay
39%39%25%18%3
2306
May1st to 15thDay
39%414%25%14%2
2567
16th to endDay
35%5%16%23%14%4
2844
June1st to 15thDay
25%6%14%21%20%10%
2730
16th to endDay
22%49%23%27%12%
2730
July1st to 15thDay
28%5%9%23%19%14%
2581
16th to endDay
26%5%11%28%20%8%
2713
August1st to 15thDay
30%5%13%22%16%11%
2412
16th to endDay
25%48%26%25%10%
2449
September1st to 15thDay
25%27%25%22%16%
2160
16th to endDay
23%2425%34%8%
2022
October1st to 15thDay
27%39%22%27%8%
1818
16th to endDay
21%27%29%28%10%
1858
November1st to 15thDay
24%29%27%26%9%
1718
16th to endDay
22%28%28%31%7%
1678
December1st to 15thDay
27%411%35%17%3
1560
16th to endDay
29%414%28%18%4
1664
January1st to 15thNight
24%211%33%23%4
2716
16th to endNight
26%37%30%26%6%
2775
February1st to 15thNight
30%313%31%17%3
2439
16th to endNight
32%26%28%23%7%
2050
March1st to 15thNight
25%29%27%27%7%
2304
16th to endNight
30%212%27%21%4
2184
April1st to 15thNight
33%49%28%17%6%
1948
16th to endNight
37%39%26%19%4
1929
May1st to 15thNight
40%413%23%15%2
1712
16th to endNight
32%420%23%12%6%
1626
June1st to 15thNight
23%418%26%16%10%
1560
16th to endNight
18%411%27%27%9%
1560
July1st to 15thNight
27%5%14%24%19%9%
1480
16th to endNight
23%5%15%29%18%7%
1544
August1st to 15thNight
23%6%16%27%16%9%
1774
16th to endNight
24%49%29%21%9%
2050
September1st to 15thNight
26%411%23%18%15%
1800
16th to endNight
20%37%28%30%9%
1938
October1st to 15thNight
28%311%20%25%10%
2142
16th to endNight
24%26%28%26%10%
2352
November1st to 15thNight
22%38%27%26%11%
2470
16th to endNight
22%28%30%28%8%
2610
December1st to 15thNight
27%312%31%19%5%
2730
16th to endNight
31%313%30%18%1
2912

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%38%45%28%5%
135
16th to endDay
6%213%47%23%5%
144
February1st to 15thDay
37%33%45%10%
135
16th to endDay
3229%43%17%4
120
March1st to 15thDay
5%8%24%37%20%2
167
16th to endDay
11%13%33%28%10%1
352
April1st to 15thDay
11%14%34%24%11%3
329
16th to endDay
21%11%30%21%10%4
318
May1st to 15thDay
16%5%18%34%21%4
517
16th to endDay
15%6%16%29%25%7%
597
June1st to 15thDay
6%418%32%29%9%
570
16th to endDay
4317%36%29%8%
570
July1st to 15thDay
8%213%28%34%12%
550
16th to endDay
5%111%26%40%13%
595
August1st to 15thDay
6%121%37%22%9%
359
16th to endDay
5%320%31%28%10%
385
September1st to 15thDay
7%421%30%26%9%
315
16th to endDay
10%118%27%30%11%
177
October1st to 15thDay
10%314%31%26%13%
135
16th to endDay
6%6%16%29%27%12%
144
November1st to 15thDay
4212%40%23%16%
135
16th to endDay
8%7%15%46%19%2
135
December1st to 15thDay
6%5%23%47%11%5%
135
16th to endDay
2225%52%15%2
144
January1st to 15thNight
4325%50%13%3
975
16th to endNight
5%223%55%10%1
903
February1st to 15thNight
7%328%51%9%
764
16th to endNight
8%328%51%7%
684
March1st to 15thNight
5%325%53%12%
780
16th to endNight
8%324%50%11%
728
April1st to 15thNight
10%7%26%47%8%
584
16th to endNight
19%421%39%15%
579
May1st to 15thNight
16%415%42%18%1
585
16th to endNight
12%215%42%24%2
611
June1st to 15thNight
6%217%49%21%1
585
16th to endNight
4112%51%28%1
585
July1st to 15thNight
6%17%41%40%3
555
16th to endNight
36%41%45%2
612
August1st to 15thNight
5%7%42%41%2
575
16th to endNight
426%44%38%4
615
September1st to 15thNight
8%19%45%27%7%
540
16th to endNight
5%111%47%30%3
537
October1st to 15thNight
12%115%47%20%2
702
16th to endNight
10%114%49%21%2
816
November1st to 15thNight
5%318%54%16%1
950
16th to endNight
5%420%53%14%1
975
December1st to 15thNight
7%321%55%10%
975
16th to endNight
7%422%53%11%1
1040
Page generated at 2018-08-30 03:34:22. Version ac04

Copyright 2018 A. Danko


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