Rainwater Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rainwater Observatory clear sky chart from 2005-11-06 to 2024-01-11.

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
47%
23757
24%
74407
17%
23699
55%
23699
29%
44914

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 10thNight
24%
950
23%
2515
8%
946
36%
946
26%
1653
January11th to 20thNight
26%
905
23%
2353
8%
905
36%
905
22%
1655
January21st to endNight
21%
888
27%
2472
9%
888
35%
888
24%
1624
February1st to 10thNight
24%
720
23%
2160
9%
720
37%
720
22%
1428
February11th to 20thNight
24%
703
20%
2099
8%
700
34%
700
22%
1383
February21st to endNight
18%
592
22%
1776
6%
592
32%
592
19%
1217
March1st to 10thNight
31%
720
23%
2160
12%
720
40%
720
25%
1365
March11th to 20thNight
31%
576
19%
2016
11%
576
40%
576
20%
1283
March21st to endNight
32%
594
24%
2024
13%
594
45%
594
24%
1218
April1st to 10thNight
36%
540
26%
1800
17%
540
49%
540
26%
1061
April11th to 20thNight
39%
533
27%
1775
19%
533
53%
533
29%
1023
April21st to endNight
40%
540
28%
1800
19%
540
55%
540
32%
997
May1st to 10thNight
49%
540
24%
1800
17%
540
60%
540
35%
989
May11th to 20thNight
55%
531
21%
1684
17%
531
62%
531
31%
1003
May21st to endNight
65%
582
24%
1744
21%
582
69%
582
36%
1036
June1st to 10thNight
67%
540
21%
1505
19%
540
69%
540
34%
948
June11th to 20thNight
76%
540
25%
1440
22%
540
77%
540
48%
794
June21st to endNight
74%
540
23%
1440
20%
540
75%
540
42%
837
July1st to 10thNight
76%
525
18%
1400
17%
525
76%
525
36%
875
July11th to 20thNight
78%
522
18%
1551
17%
522
79%
522
35%
920
July21st to endNight
77%
591
17%
1792
20%
558
78%
558
33%
1050
August1st to 10thNight
81%
537
17%
1778
22%
534
82%
534
37%
975
August11th to 20thNight
75%
534
18%
1776
23%
534
76%
534
30%
1061
August21st to endNight
72%
594
22%
1980
26%
594
72%
594
28%
1204
September1st to 10thNight
68%
540
27%
1800
28%
540
71%
540
33%
1016
September11th to 20thNight
67%
609
26%
1869
24%
609
69%
609
32%
1127
September21st to endNight
68%
720
33%
1980
26%
720
71%
720
42%
1126
October1st to 10thNight
67%
720
34%
2011
26%
720
71%
720
49%
1061
October11th to 20thNight
52%
720
32%
2160
23%
720
61%
720
36%
1222
October21st to endNight
48%
792
32%
2376
24%
792
56%
792
34%
1383
November1st to 10thNight
52%
740
31%
2339
26%
740
61%
740
37%
1268
November11th to 20thNight
42%
760
29%
2470
20%
760
54%
760
33%
1367
November21st to endNight
40%
760
27%
2470
19%
760
51%
760
29%
1460
December1st to 10thNight
31%
760
24%
2470
15%
760
44%
760
23%
1572
December11th to 20thNight
32%
759
25%
2907
14%
758
44%
758
21%
1747
December21st to endNight
25%
1040
13%
4715
8%
1026
35%
1026
14%
2966

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
12%6%35%5%35%5%6%7%43%
74771
Night
12%6%25%43445%7%47%
74921
TransparencyDay
39%6%10%20%19%5%
74498
Night
36%5%10%20%21%7%
74715
SeeingDay
15%8%22%25%20%9%
13927
Night
15%8%24%29%20%4
23765

By Month

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 10thDay
19%7%25%5%23446%44%
1645
11th to 20thDay
19%9%35%5%2445%5%39%
1620
21st to endDay
15%7%245%34346%47%
1879
February1st to 10thDay
16%8%25%5%2445%7%40%
1800
11th to 20thDay
23%8%35%424445%38%
1748
21st to endDay
20%9%36%5%34345%39%
1480
March1st to 10thDay
15%7%37%6%24447%41%
1800
11th to 20thDay
15%7%36%5%35%5%5%7%37%
1958
21st to endDay
14%7%35%5%35%5%6%6%41%
2330
April1st to 10thDay
12%5%25%5%35%46%7%47%
2160
11th to 20thDay
14%6%25%5%3445%6%45%
2134
21st to endDay
10%5%35%5%3445%7%49%
2160
May1st to 10thDay
14%425%5%35%45%7%45%
2160
11th to 20thDay
9%6%26%6%45%6%7%9%42%
2207
21st to endDay
8%426%7%5%7%7%6%8%40%
2531
June1st to 10thDay
9%436%7%46%7%6%9%38%
2450
11th to 20thDay
5%435%6%46%7%7%9%44%
2520
21st to endDay
7%425%7%46%6%7%9%42%
2520
July1st to 10thDay
8%6%36%7%5%7%7%9%10%33%
2520
11th to 20thDay
10%436%7%5%8%8%9%9%32%
2350
21st to endDay
8%425%7%5%8%8%10%9%34%
2417
August1st to 10thDay
6%425%6%5%7%7%9%8%39%
2148
11th to 20thDay
8%5%38%7%6%7%7%6%8%35%
2125
21st to endDay
13%5%25%5%36%6%7%10%39%
2376
September1st to 10thDay
8%5%26%6%45%5%6%7%45%
2160
11th to 20thDay
12%5%36%6%35%447%45%
2071
21st to endDay
12%42342445%7%52%
1980
October1st to 10thDay
7%4135%3445%6%58%
1944
11th to 20thDay
11%4244245%47%54%
1800
21st to endDay
14%5%24433445%53%
1980
November1st to 10thDay
10%5%24423336%57%
1736
11th to 20thDay
13%6%24423345%53%
1710
21st to endDay
15%7%45%433446%45%
1710
December1st to 10thDay
18%8%35%435%35%7%39%
1710
11th to 20thDay
15%8%45%5%34345%43%
2149
21st to endDay
13%8%36%5%3446%6%42%
2783
January1st to 10thNight
19%7%24323346%45%
2515
11th to 20thNight
17%10%45%6%3334441%
2353
21st to endNight
18%7%35%434435%44%
2472
February1st to 10thNight
17%9%35%5%23446%41%
2160
11th to 20thNight
20%7%25%43343444%
2098
21st to endNight
21%8%26%5%34445%39%
1776
March1st to 10thNight
15%7%245%345%5%7%43%
2160
11th to 20thNight
15%6%36%5%45%5%47%40%
2016
21st to endNight
13%6%345%345%5%7%45%
2024
April1st to 10thNight
13%6%34425%45%6%49%
1800
11th to 20thNight
13%5%15%425%35%7%49%
1775
21st to endNight
9%425%43445%7%51%
1800
May1st to 10thNight
11%5%233235%5%8%52%
1800
11th to 20thNight
9%4245%45%5%7%9%45%
1684
21st to endNight
6%3245%35%6%7%12%47%
1744
June1st to 10thNight
5%435%6%47%6%5%10%45%
1505
11th to 20thNight
32235%245%7%11%56%
1440
21st to endNight
5%3245%345%6%11%51%
1440
July1st to 10thNight
4425%6%35%7%9%13%43%
1440
11th to 20thNight
5%4245%5%5%6%8%11%46%
1604
21st to endNight
4425%437%6%8%12%45%
1898
August1st to 10thNight
5%2235%35%6%9%11%49%
1790
11th to 20thNight
5%425%6%45%6%7%13%43%
1776
21st to endNight
8%426%5%45%6%7%8%46%
1980
September1st to 10thNight
8%5%25%43446%7%52%
1800
11th to 20thNight
8%6%25%5%345%6%8%48%
1869
21st to endNight
9%3234235%5%7%56%
1980
October1st to 10thNight
7%31342345%7%62%
2011
11th to 20thNight
12%5%2442435%7%53%
2160
21st to endNight
17%6%23323335%55%
2376
November1st to 10thNight
13%413324345%58%
2339
11th to 20thNight
12%5%2333335%6%54%
2470
21st to endNight
15%5%245%24446%49%
2470
December1st to 10thNight
17%8%35%43445%5%43%
2470
11th to 20thNight
15%6%36%5%34345%47%
3042
21st to endNight
16%10%36%6%345%6%6%35%
4884

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 10thDay
42%45%21%22%5%
1646
11th to 20thDay
48%36%18%20%5%
1620
21st to endDay
41%3420%26%6%
1879
February1st to 10thDay
43%49%19%18%7%
1800
11th to 20thDay
49%35%18%17%8%
1758
21st to endDay
50%45%14%20%8%
1480
March1st to 10thDay
45%47%16%18%11%
1800
11th to 20thDay
47%5%9%16%19%5%
1958
21st to endDay
43%5%8%24%18%3
2330
April1st to 10thDay
36%5%10%22%21%6%
2160
11th to 20thDay
40%36%19%26%6%
2134
21st to endDay
34%5%9%25%24%3
2160
May1st to 10thDay
39%5%9%23%20%4
2160
11th to 20thDay
38%7%14%24%16%1
2211
21st to endDay
40%7%12%24%15%2
2531
June1st to 10thDay
40%8%14%20%16%1
2450
11th to 20thDay
33%7%17%24%17%3
2520
21st to endDay
37%8%15%23%15%3
2520
July1st to 10thDay
41%10%17%20%8%3
2451
11th to 20thDay
42%10%21%18%7%2
2280
21st to endDay
40%12%18%20%8%1
2283
August1st to 10thDay
36%10%19%26%8%1
2136
11th to 20thDay
43%10%15%18%11%3
2125
21st to endDay
38%8%17%21%11%5%
2376
September1st to 10thDay
37%7%11%21%18%5%
2160
11th to 20thDay
39%6%11%16%21%6%
2071
21st to endDay
32%410%23%21%9%
1980
October1st to 10thDay
27%48%25%25%10%
1944
11th to 20thDay
32%36%20%30%9%
1800
21st to endDay
34%35%19%29%10%
1980
November1st to 10thDay
31%35%21%29%11%
1736
11th to 20thDay
34%35%19%26%13%
1710
21st to endDay
41%36%17%24%9%
1710
December1st to 10thDay
46%48%16%19%7%
1710
11th to 20thDay
44%36%18%23%6%
2146
21st to endDay
42%5%7%19%25%3
2783
January1st to 10thNight
42%36%18%26%5%
2515
11th to 20thNight
49%35%17%20%7%
2353
21st to endNight
44%3418%25%6%
2472
February1st to 10thNight
45%46%18%19%8%
2160
11th to 20thNight
45%45%19%19%9%
2099
21st to endNight
49%46%13%18%10%
1776
March1st to 10thNight
40%47%16%20%12%
2160
11th to 20thNight
44%5%9%17%18%7%
2016
21st to endNight
39%48%23%20%6%
2024
April1st to 10thNight
36%5%9%22%19%9%
1800
11th to 20thNight
36%38%20%25%8%
1775
21st to endNight
32%410%25%24%5%
1800
May1st to 10thNight
30%5%10%27%23%5%
1800
11th to 20thNight
34%6%15%24%18%2
1685
21st to endNight
29%9%14%27%18%3
1745
June1st to 10thNight
34%7%15%23%19%2
1505
11th to 20thNight
22%7%18%31%16%6%
1440
21st to endNight
27%7%19%24%20%4
1440
July1st to 10thNight
28%11%22%24%11%3
1400
11th to 20thNight
27%11%25%25%9%2
1551
21st to endNight
27%12%24%27%9%2
1792
August1st to 10thNight
25%10%25%30%11%1
1778
11th to 20thNight
32%10%22%22%11%4
1776
21st to endNight
34%9%17%23%12%4
1980
September1st to 10thNight
31%6%13%23%22%5%
1800
11th to 20thNight
33%7%12%17%22%8%
1869
21st to endNight
28%48%26%23%10%
1980
October1st to 10thNight
23%410%23%26%14%
2011
11th to 20thNight
32%46%19%29%11%
2160
21st to endNight
35%35%16%28%13%
2376
November1st to 10thNight
30%37%18%28%13%
2339
11th to 20thNight
31%47%18%26%13%
2470
21st to endNight
37%36%21%21%11%
2470
December1st to 10thNight
43%49%17%21%6%
2470
11th to 20thNight
41%37%16%27%6%
3044
21st to endNight
46%5%8%15%24%3
4884

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 10thDay
24%20%36%16%3
270
11th to 20thDay
30%17%34%12%5%2
240
21st to endDay
25%24%35%13%21
264
February1st to 10thDay
24%20%38%13%5%
240
11th to 20thDay
38%15%33%11%2
240
21st to endDay
36%14%39%9%2
198
March1st to 10thDay
24%20%35%18%3
240
11th to 20thDay
28%18%38%13%3
240
21st to endDay
22%17%35%17%8%
416
April1st to 10thDay
19%16%31%23%9%1
420
11th to 20thDay
23%13%33%20%10%2
412
21st to endDay
15%12%30%30%12%1
420
May1st to 10thDay
19%7%25%34%12%3
423
11th to 20thDay
11%6%24%34%17%8%
447
21st to endDay
9%225%30%21%13%
485
June1st to 10thDay
13%317%28%29%11%
560
11th to 20thDay
6%217%32%32%11%
630
21st to endDay
8%313%34%27%15%
630
July1st to 10thDay
9%29%32%33%15%
621
11th to 20thDay
10%26%26%35%22%
618
21st to endDay
7%28%25%39%19%
555
August1st to 10thDay
7%29%26%32%24%
446
11th to 20thDay
10%17%27%34%21%
439
21st to endDay
15%26%24%31%22%
495
September1st to 10thDay
9%28%31%38%12%
450
11th to 20thDay
11%310%26%34%15%
450
21st to endDay
12%212%32%29%12%
450
October1st to 10thDay
10%421%31%24%10%
414
11th to 20thDay
11%9%32%33%11%3
270
21st to endDay
21%10%28%26%12%3
297
November1st to 10thDay
16%7%27%32%13%4
270
11th to 20thDay
15%14%40%24%7%
270
21st to endDay
18%16%37%18%10%2
270
December1st to 10thDay
27%16%36%17%31
270
11th to 20thDay
24%16%35%16%9%
270
21st to endDay
30%12%38%15%31
297
January1st to 10thNight
24%15%35%22%4
950
11th to 20thNight
22%15%31%25%7%
905
21st to endNight
24%14%38%21%3
888
February1st to 10thNight
23%14%35%23%6%
720
11th to 20thNight
26%16%32%23%4
703
21st to endNight
26%16%35%21%2
592
March1st to 10thNight
20%15%32%27%7%
720
11th to 20thNight
19%11%35%27%7%1
576
21st to endNight
16%14%33%27%10%1
594
April1st to 10thNight
16%12%33%27%11%1
540
11th to 20thNight
16%12%29%29%12%2
533
21st to endNight
11%10%35%33%10%1
540
May1st to 10thNight
12%5%29%37%15%2
540
11th to 20thNight
11%225%37%21%4
531
21st to endNight
6%217%38%31%6%
584
June1st to 10thNight
6%112%38%34%8%
540
11th to 20thNight
4110%34%40%11%
540
21st to endNight
6%111%33%37%13%
540
July1st to 10thNight
5%17%29%42%16%
525
11th to 20thNight
6%16%30%39%19%
522
21st to endNight
5%16%28%46%15%
591
August1st to 10thNight
5%425%48%18%
537
11th to 20thNight
6%1430%46%13%
534
21st to endNight
10%15%26%43%14%
594
September1st to 10thNight
10%29%33%40%7%
540
11th to 20thNight
11%211%29%40%7%
609
21st to endNight
11%112%34%36%6%
720
October1st to 10thNight
8%218%34%32%6%
720
11th to 20thNight
14%6%21%37%19%2
720
21st to endNight
20%6%23%30%20%2
792
November1st to 10thNight
14%6%23%33%20%4
740
11th to 20thNight
15%8%31%34%12%1
760
21st to endNight
19%8%29%29%13%2
760
December1st to 10thNight
23%10%31%28%8%
760
11th to 20thNight
21%11%33%27%8%
760
21st to endNight
25%13%32%25%5%
1045
Page generated at 2024-01-08 10:14:16. Version ac07

Copyright 2024 Attilla Danko


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