Roadrunner Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roadrunner Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
77%
15628
36%
46966
33%
15589
81%
15589
54%
22393

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
69%
719
31%
2327
31%
716
75%
716
45%
1141
January16th to endNight
66%
768
36%
2496
33%
768
74%
768
42%
1274
February1st to 15thNight
70%
700
35%
2199
33%
700
78%
700
50%
1051
February16th to endNight
68%
632
37%
1868
36%
632
72%
632
45%
978
March1st to 15thNight
71%
720
40%
1980
33%
720
77%
720
58%
966
March16th to endNight
77%
768
39%
2112
31%
768
83%
768
62%
996
April1st to 15thNight
74%
695
33%
1954
26%
695
79%
695
57%
953
April16th to endNight
77%
540
44%
1723
39%
540
84%
540
70%
670
May1st to 15thNight
79%
539
40%
1619
33%
539
84%
539
68%
676
May16th to endNight
83%
561
41%
1684
34%
561
86%
561
73%
677
June1st to 15thNight
89%
540
34%
1620
31%
540
89%
540
70%
665
June16th to endNight
91%
540
34%
1620
31%
540
91%
540
74%
654
July1st to 15thNight
83%
510
23%
1530
20%
510
84%
510
46%
798
July16th to endNight
82%
564
25%
1593
22%
531
82%
531
38%
914
August1st to 15thNight
83%
539
29%
1611
26%
536
83%
536
44%
851
August16th to endNight
84%
618
31%
1860
30%
618
85%
618
42%
1026
September1st to 15thNight
80%
720
32%
1980
29%
720
81%
720
51%
1042
September16th to endNight
84%
683
43%
1890
34%
683
87%
683
64%
877
October1st to 15thNight
78%
660
41%
1903
34%
660
82%
660
63%
861
October16th to endNight
86%
704
44%
2112
40%
704
89%
704
67%
910
November1st to 15thNight
80%
700
42%
2109
37%
700
85%
700
64%
920
November16th to endNight
75%
720
40%
2340
39%
720
80%
720
54%
1052
December1st to 15thNight
71%
720
37%
2340
38%
720
75%
720
47%
1126
December16th to endNight
68%
768
35%
2496
36%
768
73%
768
40%
1315

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
4212213346%67%
47915
Night
4212213346%67%
47162
TransparencyDay
17%2412%24%37%
47610
Night
18%2411%23%38%
46968
SeeingDay
5%417%36%28%7%
5448
Night
5%110%40%37%4
15636

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%222213345%64%
1611
16th to endDay
9%313213236%63%
1728
February1st to 15thDay
431422246%65%
1661
16th to endDay
9%312323245%60%
1606
March1st to 15thDay
5%213213345%65%
1980
16th to endDay
3213312345%69%
2112
April1st to 15thDay
322223347%68%
1993
16th to endDay
21112125%79%
2234
May1st to 15thDay
111112236%77%
2331
16th to endDay
21111121381%
2429
June1st to 15thDay
1111212481%
2340
16th to endDay
11111122481%
2340
July1st to 15thDay
221342447%9%56%
2340
16th to endDay
5%225%5%36%7%7%13%42%
2467
August1st to 15thDay
3214425%5%6%10%53%
2340
16th to endDay
3213435%5%5%8%57%
2339
September1st to 15thDay
421232345%6%63%
1980
16th to endDay
31112235%77%
1882
October1st to 15thDay
21221334473%
1727
16th to endDay
11221122478%
1760
November1st to 15thDay
221212246%74%
1747
16th to endDay
5%21321222471%
1620
December1st to 15thDay
8%313313336%61%
1620
16th to endDay
9%323323346%58%
1728
January1st to 15thNight
7%212314345%63%
2327
16th to endNight
10%31321333461%
2496
February1st to 15thNight
5%313213346%65%
2188
16th to endNight
8%224313446%59%
1868
March1st to 15thNight
5%212212245%69%
1980
16th to endNight
3111213235%72%
2112
April1st to 15thNight
4212214335%68%
1954
16th to endNight
211222382%
1723
May1st to 15thNight
111112346%74%
1619
16th to endNight
2111112382%
1684
June1st to 15thNight
11111222479%
1620
16th to endNight
1111123480%
1620
July1st to 15thNight
11135%345%7%10%54%
1620
16th to endNight
22245%35%6%9%14%42%
1701
August1st to 15thNight
23135%345%7%9%52%
1620
16th to endNight
2223435%6%7%8%51%
1860
September1st to 15thNight
321342346%8%60%
1980
16th to endNight
21222223475%
1890
October1st to 15thNight
311221224473%
1903
16th to endNight
12111222478%
2112
November1st to 15thNight
31222245%74%
2109
16th to endNight
42321232471%
2340
December1st to 15thNight
9%22313345%63%
2340
16th to endNight
10%323223345%58%
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
23%25%13%26%28%
1612
16th to endDay
24%2316%24%29%
1728
February1st to 15thDay
20%25%16%26%29%
1661
16th to endDay
25%2315%29%24%
1606
March1st to 15thDay
20%127%30%37%
1980
16th to endDay
18%138%32%34%
2112
April1st to 15thDay
15%129%34%35%
1993
16th to endDay
10%118%24%52%
2234
May1st to 15thDay
9%128%25%52%
2331
16th to endDay
10%116%24%56%
2432
June1st to 15thDay
9%11316%67%
2340
16th to endDay
8%125%11%70%
2340
July1st to 15thDay
21%5%9%15%18%29%
2201
16th to endDay
30%7%15%23%16%7%
2312
August1st to 15thDay
23%5%9%18%16%25%
2325
16th to endDay
22%5%7%18%24%22%
2339
September1st to 15thDay
19%47%15%25%27%
1980
16th to endDay
10%127%28%50%
1882
October1st to 15thDay
13%2310%24%44%
1727
16th to endDay
11%148%26%48%
1760
November1st to 15thDay
12%1210%34%38%
1747
16th to endDay
18%2211%23%42%
1620
December1st to 15thDay
25%25%15%28%23%
1620
16th to endDay
26%35%19%28%16%
1728
January1st to 15thNight
23%2410%25%31%
2327
16th to endNight
26%2312%26%28%
2496
February1st to 15thNight
20%2414%24%32%
2199
16th to endNight
26%2213%27%27%
1868
March1st to 15thNight
18%129%26%42%
1980
16th to endNight
15%129%32%37%
2112
April1st to 15thNight
18%127%30%39%
1954
16th to endNight
8%126%23%57%
1723
May1st to 15thNight
10%127%27%49%
1620
16th to endNight
9%17%18%61%
1685
June1st to 15thNight
10%11412%69%
1620
16th to endNight
8%13410%71%
1620
July1st to 15thNight
21%6%11%15%14%30%
1530
16th to endNight
26%9%14%20%20%9%
1593
August1st to 15thNight
24%410%18%15%26%
1611
16th to endNight
25%6%8%15%22%21%
1860
September1st to 15thNight
20%48%19%21%24%
1980
16th to endNight
13%225%26%49%
1890
October1st to 15thNight
13%239%24%46%
1903
16th to endNight
11%228%20%53%
2112
November1st to 15thNight
13%1210%29%42%
2109
16th to endNight
18%2210%22%43%
2340
December1st to 15thNight
22%2414%28%27%
2340
16th to endNight
28%25%16%28%19%
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
27%317%34%16%
90
16th to endDay
9%5%16%39%19%9%
96
February1st to 15thDay
5%320%43%26%
176
16th to endDay
10%8%28%35%16%
238
March1st to 15thDay
6%8%27%33%20%4
270
16th to endDay
311%30%32%19%3
288
April1st to 15thDay
5%11%27%34%15%5%
269
16th to endDay
215%34%31%13%2
270
May1st to 15thDay
312%26%36%17%3
288
16th to endDay
25%26%40%23%2
330
June1st to 15thDay
5%223%38%25%5%
315
16th to endDay
28%44%32%11%
315
July1st to 15thDay
29%37%39%9%
305
16th to endDay
4330%37%23%
327
August1st to 15thDay
5%129%46%17%
315
16th to endDay
1329%46%18%
332
September1st to 15thDay
6%18%36%38%8%
315
16th to endDay
6%115%44%28%3
280
October1st to 15thDay
5%416%35%30%7%
167
16th to endDay
5%343%39%8%
96
November1st to 15thDay
5%413%41%24%11%
90
16th to endDay
12%115%48%22%
90
December1st to 15thDay
8%6%43%36%4
90
16th to endDay
20%5%19%37%16%
96
January1st to 15thNight
8%214%50%22%2
720
16th to endNight
11%214%43%23%3
768
February1st to 15thNight
6%213%50%24%2
704
16th to endNight
9%114%50%22%1
632
March1st to 15thNight
6%116%44%26%4
720
16th to endNight
3310%44%34%4
768
April1st to 15thNight
4312%50%26%2
695
16th to endNight
2215%47%28%3
540
May1st to 15thNight
2213%45%32%4
540
16th to endNight
2110%41%39%4
563
June1st to 15thNight
115%45%44%2
540
16th to endNight
1330%58%5%
540
July1st to 15thNight
25%24%59%7%
510
16th to endNight
3214%66%12%
564
August1st to 15thNight
3116%64%13%
539
16th to endNight
3119%65%9%
618
September1st to 15thNight
36%30%50%8%
720
16th to endNight
217%39%42%6%
683
October1st to 15thNight
3111%43%37%3
660
16th to endNight
27%43%39%7%
704
November1st to 15thNight
419%45%33%5%
700
16th to endNight
5%12%47%30%3
720
December1st to 15thNight
10%110%45%30%1
720
16th to endNight
11%111%48%24%2
768
Page generated at 2017-09-23 03:43:39. Version ac04

Copyright 2017 A. Danko


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