Rainwater Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rainwater Observatory clear sky chart from 2005-11-05 to 2018-03-21.

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
48%
16196
25%
49159
18%
16152
56%
16152
31%
29497

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
29%
975
24%
2560
9%
970
40%
970
27%
1666
January16th to endNight
22%
967
25%
2631
8%
967
35%
967
24%
1749
February1st to 15thNight
25%
764
23%
2292
9%
761
38%
761
23%
1486
February16th to endNight
24%
683
25%
2049
9%
683
36%
683
23%
1324
March1st to 15thNight
30%
741
21%
2301
12%
741
39%
741
24%
1467
March16th to endNight
36%
594
24%
2074
15%
594
48%
594
26%
1211
April1st to 15thNight
39%
539
25%
1797
16%
539
52%
539
30%
1024
April16th to endNight
45%
540
27%
1800
20%
540
58%
540
33%
980
May1st to 15thNight
50%
540
21%
1800
14%
540
60%
540
30%
1050
May16th to endNight
64%
561
24%
1683
21%
561
68%
561
36%
987
June1st to 15thNight
73%
540
20%
1482
19%
540
75%
540
40%
892
June16th to endNight
75%
540
25%
1440
21%
540
76%
540
44%
822
July1st to 15thNight
79%
510
19%
1406
18%
510
79%
510
40%
830
July16th to endNight
79%
564
17%
1671
20%
531
80%
531
34%
980
August1st to 15thNight
80%
539
18%
1788
22%
536
81%
536
34%
1022
August16th to endNight
74%
573
23%
1910
28%
573
74%
573
27%
1177
September1st to 15thNight
66%
540
24%
1800
25%
540
69%
540
31%
1052
September16th to endNight
71%
703
33%
1966
28%
703
73%
703
42%
1114
October1st to 15thNight
64%
720
33%
2061
26%
720
68%
720
44%
1122
October16th to endNight
52%
768
35%
2304
27%
768
60%
768
38%
1267
November1st to 15thNight
49%
760
30%
2427
24%
760
59%
760
36%
1322
November16th to endNight
43%
780
30%
2535
21%
780
56%
780
32%
1421
December1st to 15thNight
33%
780
24%
2535
14%
780
46%
780
25%
1571
December16th to endNight
27%
975
19%
2847
10%
975
37%
975
20%
1961

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%5%25%5%35%5%5%7%41%
49662
Night
11%5%2442445%7%48%
49360
TransparencyDay
40%5%10%19%18%5%
49366
Night
35%410%21%20%7%
49161
SeeingDay
13%6%20%24%23%11%
6088
Night
14%7%23%28%21%4
16198

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 15thDay
18%6%25%5%13445%41%
1705
16th to endDay
16%5%2442333447%
1942
February1st to 15thDay
16%7%25%5%23446%40%
1900
16th to endDay
18%7%26%424445%39%
1710
March1st to 15thDay
15%7%36%6%24336%40%
1999
16th to endDay
13%7%25%5%35%5%5%5%41%
2273
April1st to 15thDay
12%5%245%3445%7%45%
2151
16th to endDay
10%5%25%5%34347%48%
2160
May1st to 15thDay
14%5%35%6%35%446%39%
2151
16th to endDay
8%425%7%47%6%6%7%38%
2429
June1st to 15thDay
5%426%7%47%6%6%10%37%
2474
16th to endDay
6%325%7%46%7%6%8%41%
2520
July1st to 15thDay
9%5%35%6%49%7%8%8%31%
2466
16th to endDay
9%426%7%48%8%8%9%29%
2379
August1st to 15thDay
7%5%25%7%5%7%7%7%8%35%
2160
16th to endDay
11%5%26%6%46%6%6%9%33%
2292
September1st to 15thDay
10%427%6%36%5%6%7%39%
2160
16th to endDay
12%4145%24446%48%
1980
October1st to 15thDay
8%42342445%6%53%
1896
16th to endDay
11%313312325%59%
1920
November1st to 15thDay
10%414424335%55%
1759
16th to endDay
14%6%33322246%50%
1755
December1st to 15thDay
17%8%44423346%38%
1755
16th to endDay
18%8%35%423346%38%
1726
January1st to 15thNight
15%6%24323245%47%
2560
16th to endNight
17%6%35%42333444%
2631
February1st to 15thNight
16%7%25%423346%43%
2283
16th to endNight
17%7%25%422335%44%
2049
March1st to 15thNight
15%6%1442445%7%42%
2301
16th to endNight
12%434424447%47%
2074
April1st to 15thNight
11%42342435%6%51%
1797
16th to endNight
8%314425%35%8%52%
1800
May1st to 15thNight
10%4134345%5%8%47%
1799
16th to endNight
6%3244245%7%10%47%
1683
June1st to 15thNight
33245%36%5%6%10%48%
1482
16th to endNight
32235%2447%13%50%
1440
July1st to 15thNight
33245%35%5%8%11%46%
1490
16th to endNight
4314336%6%8%12%44%
1786
August1st to 15thNight
5%213445%6%8%11%45%
1800
16th to endNight
7%315%5%35%6%7%10%42%
1910
September1st to 15thNight
9%41443445%6%49%
1800
16th to endNight
6%4234235%5%8%53%
1966
October1st to 15thNight
8%31331335%8%57%
2061
16th to endNight
14%313312225%58%
2304
November1st to 15thNight
11%41332335%6%55%
2427
16th to endNight
13%413313345%53%
2535
December1st to 15thNight
14%7%35%323445%45%
2535
16th to endNight
17%8%37%5%2344437%
2847

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
44%36%17%22%5%
1706
16th to endDay
41%3420%23%7%
1942
February1st to 15thDay
43%38%21%17%5%
1902
16th to endDay
46%45%17%20%6%
1710
March1st to 15thDay
46%37%17%17%7%
1999
16th to endDay
43%48%21%20%1
2275
April1st to 15thDay
37%49%20%21%6%
2151
16th to endDay
36%49%22%24%2
2160
May1st to 15thDay
44%5%9%17%18%4
2151
16th to endDay
41%6%14%21%13%1
2433
June1st to 15thDay
39%7%15%21%15%
2474
16th to endDay
36%7%15%19%17%3
2520
July1st to 15thDay
42%9%16%20%6%3
2321
16th to endDay
44%10%17%18%8%
2231
August1st to 15thDay
40%9%16%19%10%3
2148
16th to endDay
43%9%14%19%9%3
2292
September1st to 15thDay
41%8%12%19%12%5%
2160
16th to endDay
35%410%22%18%8%
1980
October1st to 15thDay
31%48%22%23%11%
1896
16th to endDay
29%2318%34%11%
1920
November1st to 15thDay
31%35%20%29%9%
1759
16th to endDay
36%26%18%25%10%
1755
December1st to 15thDay
46%38%18%16%7%
1755
16th to endDay
47%39%19%15%4
1726
January1st to 15thNight
40%35%18%26%5%
2560
16th to endNight
44%3417%22%8%
2631
February1st to 15thNight
43%35%19%20%7%
2292
16th to endNight
42%35%19%19%8%
2049
March1st to 15thNight
41%48%17%18%9%
2301
16th to endNight
37%48%22%22%4
2074
April1st to 15thNight
34%39%22%21%8%
1797
16th to endNight
30%410%23%25%6%
1800
May1st to 15thNight
34%5%11%22%20%5%
1800
16th to endNight
29%7%15%25%18%3
1685
June1st to 15thNight
30%5%17%25%19%1
1482
16th to endNight
25%6%18%25%20%4
1440
July1st to 15thNight
26%8%22%26%11%4
1406
16th to endNight
27%11%22%27%10%1
1671
August1st to 15thNight
28%8%22%23%12%3
1788
16th to endNight
34%9%16%23%12%3
1910
September1st to 15thNight
33%6%13%23%16%6%
1800
16th to endNight
28%410%23%24%8%
1966
October1st to 15thNight
26%39%22%24%13%
2061
16th to endNight
30%2314%32%16%
2304
November1st to 15thNight
29%37%19%26%12%
2427
16th to endNight
33%35%18%24%13%
2535
December1st to 15thNight
41%39%19%20%6%
2535
16th to endNight
49%38%15%17%5%
2847

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
18%17%37%19%5%1
135
16th to endDay
23%22%38%9%23
144
February1st to 15thDay
25%19%38%12%3
135
16th to endDay
25%12%47%13%1
120
March1st to 15thDay
23%21%45%8%
135
16th to endDay
20%11%34%23%10%
215
April1st to 15thDay
19%11%27%25%12%2
270
16th to endDay
14%7%28%30%15%2
270
May1st to 15thDay
17%7%22%34%12%5%
288
16th to endDay
11%226%25%19%13%
331
June1st to 15thDay
8%114%28%32%14%
449
16th to endDay
6%213%31%31%15%
495
July1st to 15thDay
7%19%32%33%16%
475
16th to endDay
9%1420%37%26%
428
August1st to 15thDay
9%17%21%32%26%
313
16th to endDay
16%5%25%27%25%
332
September1st to 15thDay
9%311%20%38%17%
315
16th to endDay
10%17%29%35%14%
314
October1st to 15thDay
10%420%30%25%8%
231
16th to endDay
14%9%29%24%16%5%
144
November1st to 15thDay
17%5%35%28%11%1
135
16th to endDay
9%14%38%17%17%2
135
December1st to 15thDay
28%14%33%16%6%1
135
16th to endDay
27%14%38%16%3
144
January1st to 15thNight
21%15%31%24%7%
975
16th to endNight
21%13%38%22%3
967
February1st to 15thNight
20%14%35%24%5%
764
16th to endNight
21%15%35%24%3
683
March1st to 15thNight
19%13%33%27%6%
741
16th to endNight
14%11%31%28%12%1
594
April1st to 15thNight
12%11%34%26%13%1
539
16th to endNight
10%9%31%34%12%2
540
May1st to 15thNight
12%426%37%16%2
540
16th to endNight
6%119%37%30%4
563
June1st to 15thNight
48%40%36%9%
540
16th to endNight
3110%26%44%13%
540
July1st to 15thNight
36%32%40%16%
510
16th to endNight
4425%46%18%
564
August1st to 15thNight
6%224%46%19%
539
16th to endNight
8%327%46%13%
573
September1st to 15thNight
10%210%27%39%8%
540
16th to endNight
8%19%34%39%6%
703
October1st to 15thNight
10%316%33%30%5%
720
16th to endNight
16%7%20%29%24%2
768
November1st to 15thNight
12%6%28%29%20%3
760
16th to endNight
16%8%27%28%16%2
780
December1st to 15thNight
20%10%31%28%10%
780
16th to endNight
23%13%31%24%6%
975
Page generated at 2018-03-22 10:34:27. Version ac04

Copyright 2018 A. Danko


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