RTMC
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RTMC 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
64%
16161
36%
46990
26%
16122
73%
16122
54%
22057

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
54%
716
30%
2327
22%
716
65%
716
40%
1159
January16th to endNight
49%
768
35%
2343
24%
768
63%
768
38%
1234
February1st to 15thNight
52%
700
34%
2108
27%
699
64%
699
44%
1062
February16th to endNight
47%
632
33%
1895
25%
632
61%
632
36%
1033
March1st to 15thNight
52%
720
32%
2154
23%
720
66%
720
43%
1087
March16th to endNight
52%
768
34%
2047
21%
768
64%
768
47%
1086
April1st to 15thNight
42%
719
35%
1799
13%
719
56%
719
49%
937
April16th to endNight
50%
720
39%
1800
14%
720
64%
720
60%
859
May1st to 15thNight
57%
548
39%
1627
22%
547
67%
547
64%
658
May16th to endNight
56%
561
37%
1685
20%
561
68%
561
64%
692
June1st to 15thNight
69%
540
34%
1620
25%
540
75%
540
71%
645
June16th to endNight
73%
540
37%
1620
29%
540
79%
540
82%
613
July1st to 15thNight
87%
510
29%
1530
25%
510
87%
510
64%
658
July16th to endNight
85%
575
33%
1604
28%
542
85%
542
57%
753
August1st to 15thNight
90%
717
37%
1790
24%
713
90%
713
74%
841
August16th to endNight
88%
764
43%
1910
29%
764
89%
764
73%
902
September1st to 15thNight
88%
720
40%
1875
31%
720
90%
720
72%
865
September16th to endNight
82%
671
48%
1856
40%
671
90%
671
82%
741
October1st to 15thNight
66%
660
42%
1815
31%
660
76%
660
63%
836
October16th to endNight
73%
704
43%
2134
37%
704
83%
704
63%
897
November1st to 15thNight
67%
700
36%
2275
32%
700
78%
700
56%
979
November16th to endNight
65%
720
39%
2340
36%
720
75%
720
50%
1064
December1st to 15thNight
54%
720
33%
2340
26%
720
66%
720
40%
1174
December16th to endNight
47%
768
34%
2496
26%
768
61%
768
35%
1282

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
2212323346%66%
47819
Night
1212213346%69%
47190
TransparencyDay
16%45%14%27%31%
47516
Night
14%45%14%29%31%
46995
SeeingDay
414%31%34%11%2
5858
Night
28%20%30%29%8%
16171

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
131332446%9%59%
1611
16th to endDay
25%15%423447%57%
1878
February1st to 15thDay
1413434447%60%
1751
16th to endDay
1415%43346%9%54%
1579
March1st to 15thDay
221321346%9%61%
1806
16th to endDay
1213325%5%5%9%59%
2174
April1st to 15thDay
2313324345%65%
2149
16th to endDay
211113348%70%
2160
May1st to 15thDay
2211213246%71%
2322
16th to endDay
112213335%73%
2429
June1st to 15thDay
1212236%77%
2340
16th to endDay
11111112383%
2340
July1st to 15thDay
321232345%6%63%
2340
16th to endDay
33234245%6%8%55%
2453
August1st to 15thDay
21232345%5%68%
2160
16th to endDay
1112323446%66%
2292
September1st to 15thDay
2112323445%67%
2084
16th to endDay
12221222478%
1849
October1st to 15thDay
2112312235%72%
1815
16th to endDay
121212235%76%
1735
November1st to 15thDay
1212223336%70%
1584
16th to endDay
2212323348%63%
1620
December1st to 15thDay
14143345%6%9%54%
1620
16th to endDay
2424435%46%7%55%
1728
January1st to 15thNight
13243235%6%8%57%
2327
16th to endNight
33245%2345%8%57%
2343
February1st to 15thNight
231341246%9%59%
2101
16th to endNight
1324445%5%5%9%54%
1895
March1st to 15thNight
13133245%5%8%60%
2154
16th to endNight
2133235%7%8%60%
2047
April1st to 15thNight
21321245%6%67%
1799
16th to endNight
111212346%75%
1800
May1st to 15thNight
1113346%76%
1627
16th to endNight
121213480%
1684
June1st to 15thNight
111122482%
1620
16th to endNight
111111386%
1620
July1st to 15thNight
222213235%73%
1620
16th to endNight
2213213336%68%
1712
August1st to 15thNight
11111233479%
1800
16th to endNight
1111222480%
1910
September1st to 15thNight
1221123478%
1875
16th to endNight
112388%
1856
October1st to 15thNight
111222245%74%
1815
16th to endNight
111221223476%
2134
November1st to 15thNight
13313346%71%
2275
16th to endNight
22231335%7%67%
2340
December1st to 15thNight
231332445%9%57%
2340
16th to endNight
342332446%9%55%
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
20%5%7%16%29%20%
1612
16th to endDay
25%5%6%17%24%19%
1878
February1st to 15thDay
22%5%5%19%25%22%
1751
16th to endDay
24%8%6%17%31%12%
1579
March1st to 15thDay
17%5%6%19%30%20%
1806
16th to endDay
19%6%6%23%26%17%
2174
April1st to 15thDay
20%45%17%34%17%
2149
16th to endDay
11%36%20%34%23%
2160
May1st to 15thDay
13%35%15%35%26%
2322
16th to endDay
13%25%15%37%25%
2432
June1st to 15thDay
10%2310%23%50%
2340
16th to endDay
8%11415%68%
2340
July1st to 15thDay
17%25%9%19%45%
2201
16th to endDay
22%47%15%22%28%
2299
August1st to 15thDay
15%3410%18%47%
2146
16th to endDay
15%3411%28%37%
2292
September1st to 15thDay
16%349%26%38%
2084
16th to endDay
11%127%31%46%
1849
October1st to 15thDay
14%3312%32%33%
1815
16th to endDay
11%25%10%31%37%
1735
November1st to 15thDay
15%35%16%32%27%
1584
16th to endDay
18%45%16%29%25%
1620
December1st to 15thDay
21%8%10%18%22%19%
1620
16th to endDay
25%8%6%21%21%16%
1728
January1st to 15thNight
20%6%7%15%27%22%
2327
16th to endNight
24%5%6%15%23%23%
2343
February1st to 15thNight
19%6%6%16%27%23%
2112
16th to endNight
23%8%5%16%28%17%
1895
March1st to 15thNight
19%6%5%17%26%23%
2154
16th to endNight
17%6%6%21%30%17%
2047
April1st to 15thNight
16%47%18%33%20%
1799
16th to endNight
9%35%17%42%22%
1800
May1st to 15thNight
8%25%16%39%27%
1628
16th to endNight
8%2416%40%27%
1685
June1st to 15thNight
8%1212%22%53%
1620
16th to endNight
5%16%16%69%
1620
July1st to 15thNight
13%25%6%20%52%
1530
16th to endNight
17%26%18%25%30%
1604
August1st to 15thNight
8%2313%22%48%
1790
16th to endNight
10%1211%31%42%
1910
September1st to 15thNight
10%1410%26%45%
1875
16th to endNight
5%118%35%47%
1856
October1st to 15thNight
11%3313%33%34%
1815
16th to endNight
11%25%7%32%40%
2134
November1st to 15thNight
13%4412%35%29%
2275
16th to endNight
15%5%417%28%28%
2340
December1st to 15thNight
20%6%8%15%25%21%
2340
16th to endNight
23%6%7%20%23%18%
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
5%24%35%30%31
90
16th to endDay
7%26%32%26%5%2
246
February1st to 15thDay
5%23%30%30%8%1
266
16th to endDay
7%30%31%23%5%
238
March1st to 15thDay
6%22%37%23%8%1
270
16th to endDay
5%26%35%25%6%
288
April1st to 15thDay
9%28%36%15%7%1
269
16th to endDay
433%35%20%4
270
May1st to 15thDay
6%19%37%28%43
288
16th to endDay
316%39%30%7%2
330
June1st to 15thDay
212%37%39%6%2
315
16th to endDay
3436%39%11%5%
315
July1st to 15thDay
419%50%20%5%
305
16th to endDay
418%50%16%9%
327
August1st to 15thDay
3322%48%14%7%
315
16th to endDay
3122%46%20%5%
332
September1st to 15thDay
26%31%45%13%
315
16th to endDay
48%28%41%15%1
268
October1st to 15thDay
316%38%32%9%
255
16th to endDay
38%34%33%19%
190
November1st to 15thDay
213%24%25%27%6%
90
16th to endDay
420%33%27%14%
90
December1st to 15thDay
417%26%38%10%2
90
16th to endDay
7%21%28%34%8%
96
January1st to 15thNight
39%25%33%18%9%
720
16th to endNight
412%26%26%24%5%
768
February1st to 15thNight
49%27%31%21%5%
704
16th to endNight
215%31%26%18%5%
632
March1st to 15thNight
213%26%31%20%5%
720
16th to endNight
114%26%30%20%5%
768
April1st to 15thNight
119%31%23%17%5%
719
16th to endNight
16%30%24%21%6%
720
May1st to 15thNight
11%27%36%19%4
548
16th to endNight
10%29%30%26%3
563
June1st to 15thNight
423%45%24%2
540
16th to endNight
123%45%27%1
540
July1st to 15thNight
25%38%45%7%
510
16th to endNight
3332%52%7%
575
August1st to 15thNight
2428%50%14%
717
16th to endNight
25%22%52%17%
764
September1st to 15thNight
15%28%49%14%
720
16th to endNight
1212%27%43%13%
671
October1st to 15thNight
15%22%30%32%7%
660
16th to endNight
15%15%29%31%15%
704
November1st to 15thNight
1420%32%31%10%
700
16th to endNight
37%19%30%27%12%
720
December1st to 15thNight
310%26%30%22%6%
720
16th to endNight
5%16%25%29%17%5%
768
Page generated at 2017-09-20 01:49:50. Version ac04

Copyright 2017 A. Danko


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