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 2017-09-17.

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%
15965
27%
46866
21%
15925
67%
15925
42%
25629

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
57%
897
31%
2506
22%
895
64%
895
48%
1321
January16th to endNight
57%
834
33%
2562
26%
834
66%
834
42%
1374
February1st to 15thNight
50%
699
24%
2248
17%
698
59%
698
36%
1245
February16th to endNight
50%
632
30%
1894
19%
632
60%
632
38%
1073
March1st to 15thNight
58%
720
28%
2127
19%
720
65%
720
44%
1143
March16th to endNight
54%
672
25%
2016
18%
672
61%
672
39%
1143
April1st to 15thNight
48%
539
23%
1798
18%
539
58%
539
33%
990
April16th to endNight
47%
540
22%
1800
20%
540
54%
540
28%
1058
May1st to 15thNight
53%
540
20%
1580
17%
540
56%
540
29%
999
May16th to endNight
60%
562
19%
1498
14%
561
63%
561
37%
908
June1st to 15thNight
67%
540
19%
1440
15%
540
69%
540
47%
796
June16th to endNight
76%
540
27%
1440
22%
540
78%
540
56%
741
July1st to 15thNight
73%
510
18%
1360
16%
510
73%
510
41%
797
July16th to endNight
78%
564
27%
1416
23%
531
78%
531
46%
780
August1st to 15thNight
76%
539
22%
1664
23%
536
77%
536
41%
878
August16th to endNight
77%
573
29%
1910
34%
573
78%
573
41%
978
September1st to 15thNight
71%
540
28%
1800
30%
540
75%
540
40%
924
September16th to endNight
77%
498
36%
1796
38%
498
81%
498
48%
798
October1st to 15thNight
64%
643
28%
1963
22%
643
69%
643
40%
1067
October16th to endNight
66%
748
35%
2156
23%
748
72%
748
47%
1133
November1st to 15thNight
66%
875
33%
2275
21%
875
70%
875
51%
1236
November16th to endNight
62%
900
35%
2409
24%
900
68%
900
52%
1276
December1st to 15thNight
57%
900
25%
2520
17%
900
64%
900
42%
1417
December16th to endNight
54%
960
27%
2688
17%
960
62%
960
38%
1554

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%42342446%8%52%
47927
Night
5%5%2432335%7%55%
47038
Cloud CoverDay
5%4244245%6%8%51%
47925
Night
5%5%2442335%7%55%
47038
TransparencyDay
28%310%27%21%7%
47602
Night
27%311%28%21%7%
46866
SeeingDay
9%5%19%31%25%8%
5893
Night
7%318%48%19%1
15974

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
17%34322347%58%
1432
16th to endDay
25%25%323347%58%
1671
February1st to 15thDay
36%35%42445%8%50%
1612
16th to endDay
26%3432346%7%55%
1580
March1st to 15thDay
3424424348%55%
1830
16th to endDay
6%6%2442446%8%48%
2208
April1st to 15thDay
8%6%23324449%51%
2150
16th to endDay
12%7%235%3445%7%42%
2160
May1st to 15thDay
13%5%24435%5%7%7%40%
2369
16th to endDay
10%5%245%346%6%9%42%
2616
June1st to 15thDay
6%322325%6%6%10%49%
2520
16th to endDay
22122346%7%9%57%
2520
July1st to 15thDay
6%314425%6%8%8%48%
2520
16th to endDay
3213435%6%8%10%49%
2656
August1st to 15thDay
4314445%7%8%10%45%
2284
16th to endDay
4213335%5%7%8%53%
2292
September1st to 15thDay
7%31232345%7%57%
2160
16th to endDay
4313322335%65%
1869
October1st to 15thDay
7%5%23322447%56%
1667
16th to endDay
6%412311345%63%
1703
November1st to 15thDay
25%1431445%7%58%
1583
16th to endDay
25%2332235%8%59%
1549
December1st to 15thDay
36%25%42345%9%52%
1440
16th to endDay
5%5%34423347%52%
1536
January1st to 15thNight
16%24322347%60%
2506
16th to endNight
36%34313335%58%
2562
February1st to 15thNight
37%36%322347%52%
2238
16th to endNight
38%35%324335%55%
1894
March1st to 15thNight
35%2441335%7%57%
2127
16th to endNight
7%5%24423347%53%
2016
April1st to 15thNight
7%6%245%2445%7%50%
1798
16th to endNight
15%7%33413347%46%
1800
May1st to 15thNight
14%5%144335%6%5%44%
1579
16th to endNight
11%31442445%7%49%
1497
June1st to 15thNight
6%21231435%9%56%
1440
16th to endNight
221231346%9%62%
1440
July1st to 15thNight
6%21443447%9%51%
1440
16th to endNight
2313435%6%6%9%54%
1512
August1st to 15thNight
42244245%8%11%50%
1672
16th to endNight
431442445%8%56%
1910
September1st to 15thNight
7%21442345%8%55%
1800
16th to endNight
5%12323346%65%
1796
October1st to 15thNight
8%424223347%56%
1963
16th to endNight
7%412222236%62%
2156
November1st to 15thNight
4414213446%62%
2275
16th to endNight
45%23212346%63%
2409
December1st to 15thNight
47%24423348%54%
2520
16th to endNight
47%245%23448%51%
2688

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%2442335%7%58%
1432
16th to endDay
25%25%323447%58%
1671
February1st to 15thDay
36%3442445%8%50%
1612
16th to endDay
26%25%22445%7%55%
1580
March1st to 15thDay
3434433448%55%
1830
16th to endDay
6%6%2432346%8%48%
2206
April1st to 15thDay
7%6%2432445%9%50%
2150
16th to endDay
12%7%2442445%8%42%
2160
May1st to 15thDay
12%5%24435%5%7%8%40%
2369
16th to endDay
10%5%245%35%5%6%9%42%
2616
June1st to 15thDay
6%312425%5%7%9%49%
2520
16th to endDay
2112325%6%7%8%57%
2520
July1st to 15thDay
6%414335%6%8%9%47%
2520
16th to endDay
3214336%6%9%9%49%
2656
August1st to 15thDay
43235%35%7%7%11%43%
2284
16th to endDay
4213425%6%7%9%52%
2292
September1st to 15thDay
7%21332346%7%57%
2160
16th to endDay
4313413345%65%
1869
October1st to 15thDay
7%42331245%7%55%
1667
16th to endDay
6%312312345%63%
1703
November1st to 15thDay
26%233245%5%7%57%
1583
16th to endDay
343341245%8%58%
1549
December1st to 15thDay
36%345%2345%8%52%
1440
16th to endDay
5%5%35%42345%7%51%
1536
January1st to 15thNight
25%24323347%59%
2506
16th to endNight
36%34323345%58%
2562
February1st to 15thNight
47%37%322447%51%
2238
16th to endNight
38%35%424236%55%
1894
March1st to 15thNight
35%2442345%7%57%
2127
16th to endNight
6%5%2442335%6%53%
2016
April1st to 15thNight
7%5%245%2445%7%50%
1798
16th to endNight
15%7%24323346%46%
1800
May1st to 15thNight
14%5%244335%5%6%44%
1579
16th to endNight
11%41333445%7%49%
1497
June1st to 15thNight
7%212325%35%9%56%
1440
16th to endNight
22123135%6%8%62%
1440
July1st to 15thNight
6%22443446%10%50%
1440
16th to endNight
2213435%6%6%9%53%
1512
August1st to 15thNight
3214425%47%11%50%
1672
16th to endNight
4223434448%56%
1910
September1st to 15thNight
7%31442445%7%55%
1800
16th to endNight
4112323446%65%
1796
October1st to 15thNight
8%423313347%56%
1963
16th to endNight
7%5%13222336%62%
2156
November1st to 15thNight
4323313346%61%
2275
16th to endNight
4423312346%63%
2409
December1st to 15thNight
47%35%323348%54%
2520
16th to endNight
47%345%2335%8%51%
2688

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
24%211%36%20%3
1433
16th to endDay
25%28%34%22%6%
1671
February1st to 15thDay
30%413%35%12%4
1613
16th to endDay
26%28%33%24%4
1580
March1st to 15thDay
27%39%29%24%5%
1830
16th to endDay
31%412%27%19%5%
2208
April1st to 15thDay
31%310%28%18%7%
2150
16th to endDay
39%310%24%18%3
2160
May1st to 15thDay
38%413%25%14%2
2369
16th to endDay
36%5%16%23%13%5%
2620
June1st to 15thDay
26%6%15%21%20%8%
2520
16th to endDay
20%49%24%28%12%
2520
July1st to 15thDay
29%5%9%23%17%13%
2371
16th to endDay
26%5%10%28%20%9%
2489
August1st to 15thDay
30%5%13%22%16%11%
2269
16th to endDay
24%48%26%25%10%
2292
September1st to 15thDay
25%27%25%22%16%
2160
16th to endDay
21%2426%35%8%
1869
October1st to 15thDay
28%210%23%26%8%
1667
16th to endDay
21%27%30%28%9%
1703
November1st to 15thDay
24%29%26%25%10%
1583
16th to endDay
22%28%28%30%8%
1549
December1st to 15thDay
28%412%36%15%2
1440
16th to endDay
30%415%27%18%5%
1536
January1st to 15thNight
24%212%33%24%3
2506
16th to endNight
27%37%30%24%6%
2562
February1st to 15thNight
31%313%31%17%3
2248
16th to endNight
31%26%29%22%7%
1894
March1st to 15thNight
26%210%28%25%6%
2127
16th to endNight
30%212%26%22%5%
2016
April1st to 15thNight
31%410%28%18%6%
1798
16th to endNight
38%39%26%18%4
1800
May1st to 15thNight
39%413%23%15%2
1580
16th to endNight
32%5%20%23%11%6%
1498
June1st to 15thNight
24%419%27%14%10%
1440
16th to endNight
17%411%27%28%10%
1440
July1st to 15thNight
28%5%14%24%17%9%
1360
16th to endNight
23%5%13%29%18%8%
1416
August1st to 15thNight
24%6%16%26%17%9%
1664
16th to endNight
25%49%28%22%10%
1910
September1st to 15thNight
26%411%23%18%15%
1800
16th to endNight
18%37%28%32%9%
1796
October1st to 15thNight
28%312%19%26%9%
1963
16th to endNight
24%27%29%26%9%
2156
November1st to 15thNight
22%38%26%27%11%
2275
16th to endNight
22%27%30%28%8%
2409
December1st to 15thNight
28%313%32%18%4
2520
16th to endNight
30%313%30%18%2
2688

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
6%5%11%40%28%7%
90
16th to endDay
7%412%48%20%6%
96
February1st to 15thDay
27%32%45%12%
90
16th to endDay
4325%35%23%6%
81
March1st to 15thDay
5%11%22%35%20%3
120
16th to endDay
11%15%34%27%9%1
288
April1st to 15thDay
11%14%34%22%12%3
269
16th to endDay
22%12%30%21%8%3
270
May1st to 15thDay
15%5%18%36%18%4
444
16th to endDay
15%6%16%29%24%6%
517
June1st to 15thDay
7%417%31%29%9%
495
16th to endDay
2317%36%30%8%
495
July1st to 15thDay
9%213%29%32%12%
475
16th to endDay
6%111%25%40%13%
515
August1st to 15thDay
7%220%37%21%10%
315
16th to endDay
4318%32%30%10%
332
September1st to 15thDay
7%421%30%26%9%
315
16th to endDay
6%114%30%32%13%
134
October1st to 15thDay
8%214%25%31%17%
90
16th to endDay
6%6%12%26%35%13%
96
November1st to 15thDay
5%110%30%28%24%
90
16th to endDay
13%6%17%41%17%3
90
December1st to 15thDay
7%324%47%13%3
90
16th to endDay
1320%58%13%3
96
January1st to 15thNight
4325%48%14%3
900
16th to endNight
5%224%54%10%1
834
February1st to 15thNight
7%327%51%9%
704
16th to endNight
8%328%51%8%
632
March1st to 15thNight
5%325%52%12%
720
16th to endNight
8%424%51%11%
672
April1st to 15thNight
9%6%25%47%8%
539
16th to endNight
19%421%40%14%
540
May1st to 15thNight
15%5%15%43%17%1
540
16th to endNight
12%315%43%23%2
563
June1st to 15thNight
7%216%50%20%1
540
16th to endNight
3112%52%29%1
540
July1st to 15thNight
6%7%41%40%3
510
16th to endNight
36%39%47%2
564
August1st to 15thNight
5%6%41%42%2
539
16th to endNight
425%43%39%4
573
September1st to 15thNight
8%19%45%27%7%
540
16th to endNight
4110%48%31%3
498
October1st to 15thNight
11%115%46%21%2
643
16th to endNight
10%114%48%22%2
748
November1st to 15thNight
5%317%54%17%1
875
16th to endNight
6%320%52%15%1
900
December1st to 15thNight
7%321%54%11%
900
16th to endNight
7%421%52%11%1
960
Page generated at 2017-09-18 06:38:22. Version ac04

Copyright 2017 A. Danko


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